PROGRAMME AND ABSTRACT VOLUME · Monday, 6th January 0930–1730 1800 Tuesday, 7th January: Welcome...

MINERAL DEPOSITS

STUDIES GROUP

43rd Annual Meeting, 6–8 January 2020

Natural History Museum, London @MDSG_UK

‘METALS FOR A GREEN FUTURE’

PROGRAMME AND

ABSTRACT VOLUME

The organizers thank all the generous sponsors of MDSG 2020.

TABLE OF CONTENTS

Oral Programme 3

Posters list 5

Abstracts of oral presentations 7

Abstracts of Poster Presentations 39

Author index 81

Delegate list 83

Monday, 6th January

0930–1730

1800

Tuesday, 7th January: Welcome at 0850 page

0900-0930Thompson, J

KEYNOTEGreen metals – opportunities and challenges 7

0930–0950 Goodenough et al. Lithium pegmatites in Africa 8

0950–1010 Beard et al. Geomodels for HiTech materials in alkali-silicate & carbonatite systems 9

1010-1030 Palmer and Marlow The REE-enriched Twyfelskupje Carbonatite Complex, Southern Namibia 10

1030-1100

1100-1120 Herrington et al. The minerals supply challenge of a net zero carbon pledge 11

1120-1140 Putzolu et al.Influence of the petrology of parent rock on the Co deportment in Ni laterite deposits: the Santa Fé

(Brazil) and Wingellina (Western Australia) case studies 12

1140-1200 Price et al.So predictable; a remarkably uniform episode of lode-gold mineralisation along the Mougooderra Shear

Zone, Western Australia13

1200-1220 Clarke et al. Tectono-magmatic constraints on gold-tellurium fertility, Fiji 14

1220-1240 Harbidge et al. Hydrothermal alteration patterns surrounding the Yalea Au deposit as reflected by mica chemistry 15

1240-1340

1340-1410Dilles J

KEYNOTEStructural geology of porphyry copper deposits from regional tectonic setting to vein-formation 16

1410-1430 Strachan et al.Geochronology and structural controls of propylitic alteration in the Quellaveco Cu-Mo porphyry district,

Peru17

1430-1450 Nathwani et al.The magmatic evolution of the Yarabamba batholith, Southern Peru: protracted magmatism culminating

in multi-centred giant porphyry Cu-Mo mineralisation18

1450-1510 Carter et al. Yerington District, Nevada: New porphyry system petrogeochronology 19

1510-1540

1540-1600 PlotinskayaMolybdenite from porphyry deposits of the Urals: trace elements geochemistry and 3R-2H polytypes

distribution20

1600-1620 Tuffield et al. Zircon-hosted apatite inclusions: A powerful tool for reconstruction of Cl contents in melts. 21

1620-1640 Berry et al.Post-subduction magmatism and gold mineralisation in the Colorado Mineral Belt: insights from

accessory minerals22

1640-1700 Loader et al.Accessory Mineral Chemistry Reveals the Petrogenesis of an Evolving Porphyry Magma System:

Chuquicamata and the Fortuna Complex23

1700-1830 POSTER SESSION, sponsored by Rio Tinto

1900 CONFERENCE BANQUET, sponsored by BHP, First Quantum Minerals, Olympus, Zeiss and TESCAN

and the MDSG Project Prize, sponsored by Addison Mining Services

Porphyry Workshop - Dick Sillitoe

ORAL PROGRAMME

REGISTRATION

AND ICE-BREAKER sponsored by SRK

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Wedesday, 8th January

0900-0920 Hollings and CundariNi-Cu-PGE mineralization of the 1.1 Ga Midcontinent Rift of N. America: rethinking models for the rift and

the implications for mineralization24

0920-0940 Ward et al.Neoproterozoic rift magmatism along the Congo-Kalahari craton margins: new temporal and geochemical

constraints for Ni-Cu-(PGE) fertility in the Zambezi belt25

0940-1000 Blanks and Holwell The Ni-rich Munali magmatic sulfide deposit: where is the Cu? 26

1000-1020 Hughes et al.A major swarm of ‘lamprophyric’ dykes exposed in platinum mines of the Bushveld Complex, South

Africa: Geochronology, petrology and mineral chemistry27

1020-1040 Key et al.An update on exploration for nickel in the Molopo Farms Complex’ feeder zone; results of airborne and

ground high-resolution geophysics28

1040-1110

1110-1140Gleeson

KEYNOTE

Early diagenetic controls on the size of Paleozoic mudstone-hosted zinc deposits

Sponsored by the Applied Mineralogy Group29

1140-1200 Chirico et al. Mineralogical characterization of non-sulfide Zn (Pb) ores in the Florida Canyon Project (Northern Peru) 30

1200-1220 Currie et al.(U+Th)/Ne dating of hematite from Leadhills-Wanlockhead Pb-Zn ore deposit: new insight into Triassic-

Jurassic basin-to-basement ore-forming processes31

1220-1340

1340-1400 Keith et al.Boiling-induced trace element fractionation and precipitation in submarine back-arc hydrothermal

systems, New Hebrides, SW Pacific32

1400-1420 Pring Olympic Dam in a Test Tube: hydrothermal experiments on the formation of a giant IOGC Deposit 33

1420-1440 Lindsay et al.A machine learning approach to investigating regional geochemical data sets: An example of PGE

geochemistry from the North Atlantic Igneous Province and its shifting geodynamic environment34

1440-1500 Ferguson et al.A Detailed Investigation into the Reconciliation of Hyperspectral Core Data and Platinum-Group Element

Grade35

1500-1530

1530-1550 HollisGeochemical and hyperspectral halos to high-grade Ag-Zn-(Au) mineralization in the Eastern Goldfields,

Western Australia36

1550-1610 MenziesNon-destructive Micro-XRF exploration techniques for understanding ore deposit petrogenesis and

predicting micro-metallurgy37

1610-1630 Thompson, A Exploration needs innovation - examples from Canada 38

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1 Borst et al. Looking for hi-tech metals in Angola: the Nejoio alkaline complex 40

2 Deady et al. Fertility of post-collisional settings for rare earth element mineralisation 41

3 Dolgopolova et al. Lithium in late-orogenic and intraplate granites and pegmatites of Eurasia 42

4 Lindsay, D.H.M. et al. Mineral paragenesis of element vein deposits in the Cobalt Embayment, Ontario 43

5 Marquis et al. From magma reservoir to regolith: controls on the distribution of Ion Adsorption Rare Earth Element Ores 44

6Villanova-de-Benavent

and Smith

REE adsorption experiments onto kaolinite with different ligands: Implications on ion-adsorption REE deposits

formation45

7 Wall et al. HiTech AlkCarb -New Geomodels for rare earths and other economic deposits in carbonatites and alkaline rocks 46

8 Eskdale et al. Genesis of Cobalt-bearing Mineralisation in the English Lake District 47

9 Lyell et al. Sulphur and lead isotope systematics of the Cononish Au-Ag-Te deposit, Scotland 48

10 Tonks et al. Pyrophyllite Chemistry as a Vectoring and Fertility Indicator for High-Sulphidation Epithermal Deposits 49

11 Andrews et al.A Petro-chronological Framework for the Ordubad Region, Azerbaijan, Lesser Caucasus -Implications for Regional

Metallogeny50

12 Blanks and Holwell Oxidised fluids as a key control on the source and availability of metals for porphyry-epithermal Cu-Au-Te deposits 51

13 Brugge et al. Apatite inclusions in Zircon: records of porphyry melt evolution 52

14 Carter et al.Exsolution and migration of mineralising fluids in porphyry magmatic systems - Evidence from the Yerington District,

Nevada53

15Hart-Madigan and

Wilkinson

Chlorite and epidote chemistry distinguish between propylitic alteration formed in porphyry versus epithermal

environments54

16 Hovakimyan et al.Favorable tectonic setting and fracture network environment for the formation of the giant Kadjaran porphyry Cu-

Mo deposit in Armenia, Lesser Caucasus55

17 Large et al. Magmatic Arc evolution culminating in porphyry copper formation at Rio Blanco-Los Bronces 56

18 Stonadge et al. Porphyry Copper Fertility in the West Luzon Arc, Philippines: an Integrated Accessory Mineral Approach 57

19 Zhang et al. Discriminating porphyry and endoskarn-forming magmatic-hydrothermal systems in the Daye district, China 58

20 Deng et al. Asthenosphere upwelling as a mechanism of remobilizing the Cu-enriched cumulate 59

21 Matthews et al. Titanite as a recorder of magmatic and hydrothermal evolution in the Los Picos-Fortuna Igneous Complex, Chile 60

22 Smith et al.Origin and significance of volatile saturation features in the San Francisco batholith, Rio Blanco-Los Bronces porphyry

district, Chile61

23 Schaarschmidt et al. Processes of metal enrichment displayed by epithermal Pb-Zn±Ag±Au veins in Milos, Greece 62

24 Compton-Jones et al.Precious metal geochemistry of ‘lamprophyric’ dykes intersecting the Bushveld Complex: Initial observations and

thoughts on the sub-Bushveld lithospheric mantle63

25 Miron et al. Alteration in the Platreef of the Bushveld Complex: A hyperspectral, mineralogical and mass balance study 64

26 Tapster et al. Protracted timescales of magmatism documented in the Platreef, Bushveld Complex 65

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27 Brookes et al.Variations in White mica compositions in the quartz-sericite-pyrite alteration associated with the Perkoa VHMS,

Burkina Faso66

28 Croft et al.Understanding New VMS Prospects in Tigray, Ethiopia: The Ophiolite-Related Teklil Cu Prospect Compared to

Potential Au-Rich VMS Prospects of the Zager Licence Area67

29 Ito et al. Ni enrichment associated with Fe isotope fractionation in Ni laterite deposits, Sulawesi Island, Indonesia 68

30 Jenkins et al.Extending the Irish Carboniferous lead-zinc play into northern England? Evidence from basin analysis and seismic

interpretation69

31 Platten and Dominy The recognition of depositional bed-forms on fine sediments in some hydrothermal veins in central Wales 70

32 Seltmann et al. The Syrymbet tin deposit,Northern Kazakhstan 71

33 Dixon et al. Magnetic fabrics:measuring the orientation of differenthydrothermal fluid events? 72

34 Fiedrich et al.The fluid and melt inclusion record of the magmatic-hydrothermal transition in magma chambers and its bearing to

ore formation73

35 Hughes et al.A pyroxenite xenolith record of subduction-related metal and metalloid mobilisation in the upper mantle and lower

crust74

36 Kunz et al. Micas, Melting and Mineralisation 75

37 Banks et al. High-precision geochemical analysis on low amounts of sample by low-volume solution ICP-MS 76

38 Kocher The Natural History Museum’s ore collection: A unique sample repository for ore deposits research 77

39 Marquis et al. Portable XRF analysis for porphyry fertility indicators 78

40 Mottram et al.Direct dating of hydrothermal copper-gold systems using calcite U-Pb geochronology from the central Yukon

Territory, Canada79

41 Santoro et al.Advantages and challenges of integrated automated mineralogy (TIMA X-analyser, TESCAN) for the characterization

of Ni-Co laterite ores: the example of the Wingellina deposit (Western Australia)80

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Mineral Deposits Studies Group Annual Meeting 2020 Oral Session, 7th January 2020

CRITICAL METALS

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Green metals – opportunities and challenges

Thompson, J.F.H.1

1PetraScience Consultants Inc., Vancouver, Canada jfhthompson@gmail,com

___________________________________________________________________________ Renewable energy, particularly wind and solar, and transportation involving electric cars are developing rapidly driven in part by climate change mitigation. These technologies require a broad suite of metals and dramatic growth in the markets for these metals is anticipated (e.g., World Bank, 2017). Given their importance to the green economy, these commodities have been termed green metals. The major base metals, copper, nickel and zinc, are expected to benefit to varying degrees from the emerging green markets, and while demand growth may occur, ongoing increases in supply may largely satisfy demand over time without major disruption. Copper is likely to see the largest growth to meet the increased use of electric cars. Expansion of major porphyry mines and new sediment-hosted discoveries may satisfy demand but if not addressed, sustainability challenges – lower grades, increased energy consumption per unit of production, and environment, social and governance (ESG) issues – may detract from green credentials. The metals that have grabbed most attention are lithium and cobalt due to their critical importance in lithium ion batteries, the current incumbent battery for electric cars. The increase in electric car production, and plans by several countries to move away from internal combustion engines in the coming decade, fuelled growth and significant speculation. Prices for both commodities escalated dramatically from 2017-18, but have since fallen equally dramatically in 2019 as production increased, electric car growth failed to meet the most bullish expectations, and the reality of supply and demand sank in. Regardless, significant growth is still anticipated probably accompanied by more volatile fluctuations in prices. Sources of lithium and cobalt are significantly different in terms of deposit styles, their distribution in specific countries, processing, access to markets, and ESG concerns. Geological environments are very different and include pegmatites and salt-lake brines for lithium, and sediment-hosted Cu, magmatic Ni-Cu, and As-rich veins for cobalt. Critical geological controls for these metals in most of these settings are poorly understood, with the resulting development challenges and opportunities potentially exacerbated by processing problems and new methods respectively. Complexity associated with the supply of these metals may cause short to mid-term disruption. Other critical metals, with criticality defined by their specific end-use and restricted supply, are also important for green technologies, especially solar PV. The size of most of the associated markets are small and many are by-products of the mining and processing of other metals. As a result, prices will be volatile, inhibiting long term investment in exploration and development without government intervention. The geological understanding, particularly their distribution at all scales, are in most cases poorly understood. Finally, changing technologies, substitution and recycling will all play a role in the use, availability and cost of these metals. Companies interested in pursuing these commodities will need to monitor developments with care and those that also participate in downstream markets may be better placed to make strategic investments. References: La Porta et al. (2017) World Bank Group. http://documents.worldbank.org/curated/en/207371500386458722/The-

Growing-Role-of-Minerals-and-Metals-for-a-Low-Carbon-Future

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Lithium pegmatites in Africa

Goodenough, K.M.1*, Shaw, R.A.2, and Nex, P.3

1British Geological Survey, the Lyell Centre, Research Avenue South, Edinburgh EH14 4AP, UK. *Corresponding author: [email protected] 2British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK 3Paul Nex, University of the Witwatersrand

___________________________________________________________________________ Global commitments to a switch to electric vehicles have led to forecasts of growing demand for a range of ‘battery raw materials’ of which lithium (Li) is one of the most important. Lithium is currently sourced from two main sources: lithium brines in the salars of South America; and rare-metal pegmatites, a subset of which are enriched in Li. Rare-metal pegmatites occur worldwide, in orogenic belts of all ages, although with a prevalence in the Precambrian. Our current focus is on lithium pegmatites in Africa and this talk will give a brief overview. The African continent was affected by orogenic events throughout the Precambrian, most of which are associated with rare-metal pegmatites. Late-Archaean deformation and magmatism is recorded in several of the cratons that make up the ‘building blocks’ of Africa, and rare-metal pegmatites occur in greenstone belts within the cratons. Palaeoproterozoic to Mesoproterozoic orogenic belts wrap around most of the cratons, indicating zones of accretion and reworking, and many of these also contain rare-metal pegmatites. The late Neoproterozoic – Cambrian ‘Pan-African’ orogeny, associated with the assembly of Gondwana, represents the last major orogenic event in Africa and also the last significant pulse of rare-metal pegmatite magmatism. Late-Archaean Li pegmatites occur in Zimbabwe, where the pegmatite at Bikita represents the only current Li production on the African continent. We have also recently recognised the presence of Li pegmatites in the West African Craton in Sierra Leone, which are likely of Archaean age. Within the Palaeoproterozoic Birimian belts in West Africa, Li pegmatites are being explored in Mali and Ghana. Mesoproterozoic pegmatites occur in the Kibaran and Karagwe-Ankole orogenic belts, and pegmatites of this age include some major Li resources such as the Manono-Kitolo pegmatites in the DR Congo, and the Kamativi pegmatite in Zimbabwe. Pan-African Li pegmatites are known in Mozambique and Namibia, and many other rare-metal pegmatites of this age may also contain Li. The key lithium mineral in many of these pegmatites is spodumene. In the Birimian pegmatites in Ghana, spodumene crystals are up to 50 cm long. However, in many pegmatites, late overprints by alkaline fluids have led to albitisation and greisenisation, which may be associated with spodumene breakdown. This late alteration is commonly associated with the introduction of tin and tantalum, which have been the main commodities mined at places like Kamativi and Uis. It is notable that Li pegmatites virtually never occur within the TTG orthogneiss terranes that cover large parts of the African continents. Instead, such pegmatites occur in metasedimentary belts within or surrounding the Archaean cratons. This supports a hypothesis in which these metasedimentary belts represent the source for the pegmatite magmas, which are formed by low-degree partial melting that creates a flux-rich, low-viscosity magma that can migrate through the crust and coalesce into larger magma bodies. The presence of fluxing elements allows undercooling, creating the large crystals seen in pegmatites. However, much research needs to be done to prove these hypothesis; to understand what are the most fertile source rocks for Li pegmatites; and to understand the late-stage metasomatic processes that have a significant effect on the ore mineralogy. Furthermore, the extensive weathering across much of the African continent obscures evidence for pegmatites, meaning that many of the continent’s Li pegmatites almost certainly remain to be discovered, and clear exploration indicators need to be developed.

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Geomodels for HiTech materials in alkali-silicate & carbonatite systems

Beard, C.D.1, Wall, F.2, Finch, A.A.3, Hutchison, W.3, Siegfried P.R.2,4, Borst., A.M.3, Broom-Fendley, S.2 and Goodenough K.M.1

1British Geological Survey, The Lyell Centre, Edinburgh, EH14 4AP; [email protected]

2Camborne School of Mines, University of Exeter, Penryn Campus, Cornwall, TR10 9FE.

3School of Earth and Environmental Sciences, University of St Andrews, St Andrews, KY16 9AL, UK

4GeoAfrica Prospecting Services, P.O. Box 24218, Windhoek, Namibia

__________________________________________________________________________

Development of renewable energy infrastructure requires critical raw materials, such as REE and Nb, and is driving expansion and diversification in their supply chains. Although alternative sources are being explored, the majority of the world's resources are found in alkaline silicate rocks and carbonatites (hereafter 'alkaline'). These unusual magmatic systems also represent major sources of F, Sc and P. Exploration models for critical raw materials are comparatively less well developed than those for major- and precious metals, such as iron, copper and gold, where the mineral exploration industry has traditionally focussed. The diversity of lithologic relationships and local names for many alkaline rock types represent further barriers for economic geologists wishing to join the alkaline community and facilitate the green revolution.

As part of the EU H2020 HiTech AlkCarb project, a global review of maps, cross-sections and geophysical observations from alkaline systems was used to generate two interactive 3D geomodels at district-scale (ca. 15 km lateral). These place the various classes of mineralisation within a depth and horizontal reference frame and are intended as a first-pass conceptual guide for exploration. The first model is representative of silicate-dominated examples with little or no carbonatite emplaced in failed continental rift or intraplate settings at a depth of ca. 3–5 km (e.g., Gardar Province, Greenland and Kola Province, Russia). Silicate systems can contain orthomagmatic REE-HFSE or Sc mineralisation in igneous cumulates, roof-zone REE-Nb-Ta mineralisation where residual melts and fluids react with country rock, or granite pegmatite REE-HFSE mineralisation that is focussed in the upper portions of silica-saturated

intrusive bodies. The second model represents systems with higher fractions of carbonatite that are found in continental rifts, intraplate settings and additionally orogenic belts, emplaced within ~75 Ma of peak orogenesis (e.g., Mianning Dechang belt, China [1, 2]). Contrary to the silicate-dominated case, mineralisation type in carbonatites appears to be at least partially controlled by confining pressure, with almost all examples of economic interest at palaeodepths <5 km. The potential exception is phoscorites (representing immiscible Fe-P-rich melts) where some evidence suggests deeper, even >10 km depths of crystallisation. Much like silicate systems, orthomagmatic REE-Nb-P mineralisation occurs in igneous cumulates (of apatite, pyrochlore) and roof-type REE-F mineralisation in complex polyphase assemblages (of fluorite, REE-F carbonates) near the upper margins of magmatic bodies. Furthermore, weathering has played an important role in some carbonatites, upgrading and redistributing the commodities of interest. The geological models are presented alongside recommended geophysical, structural, and geochemical approaches for exploration targeting, as well as metallurgical and environmental factors pertinent for the development of resources hosted by carbonatite and alkaline-silicate magmatic systems.

[1] Goodenough et al. (2019) SGA meeting, Glasgow

[2] Deady et al. (2020) MDSG meeting, London

This research is funded through the EU Horizon 2020 research and innovation programme (#689909).

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The REE Enriched Twyfelskupje Carbonatite Complex, Southern Namibia

Palmer, M.R.1 and Marlow A.G.2 1School of Ocean and Earth Science, University of Southampton, Southampton SO14 3ZH, UK. [email protected] 2Consultant Geologist, Avanti Resources, 11 Mills Beach Close, Mornington, Victoria 3931, Australia

___________________________________________________________________________ The Twyfelskupje carbonatite complex (Sperrgebiet, Southern Namibia) exhibits most of the typical igneous emplacement structures of carbonatites; including, plugs, cone sheets and dyke stockworks. The excellent exposure and preservation has allowed a combination of field evidence and geochemical study of the link between rare earth element (REE) mineralization, igneous structures and geochemical evolution during igneous fractionation and subsolidus hydrothermal-metasomatic alteration. Overall, this reveals a geochemical pathway from the more primitive central calcio-carbonatite plugs to the more evolved peripheral magnesio-carbonatite cone sheets, characterized by a reduction in CaO/MgO, CO2 and REE, and an increase in SiO2. This decrease in CaO/MgO ratios from the central zone to the cone sheets likely reflects evolution by fractionation from a single magma, whereas the intermediate CaO/MgO ratios of the younger central zone dykes suggests they originated from a separate magma source. While all structural components of the complex show some silica enrichment, it is most pronounced in the cone sheets. This observation, together with the negative correlation between SiO2 and LOI, reflects decreasing CO2 during both fractionation, and hydrothermal alteration. The dominant REE minerals comprise fluorocarbonates and monazite. They are characterized by variable Ca, high F, and light REE in the order Ce>La>Nd+Pr; including parisite-(Ce), synchysite-(Ce), (possibly cordylite-(Ce)), and the phosphate monazite-(Ce). Chondrite-normalized REE profiles of these minerals show a similar degree of light REE enrichment as the whole rocks, confirming that they collectively define the REE abundance of the TCC. Overall, the early calcio-carbonatite plugs are REE enriched (mean 4.47 wt % REO (REE oxide)) relative to the magnesio-carbonatite cone sheets (mean 2.51 wt % REO). While hydrothermal processes during late-magmatic and post-magmatic stages play the most important role in the formation of REE minerals in most carbonatites, the emplacement fabric and structures defined by the Twyfelskupje REE fluorocarbonates in the calcio-carbonatites of the central zone suggest they represent original orthomagmatic mineral assemblages. In comparison, the more varied replacement textures and alteration assemblages displayed by the evolved magnesio-carbonatites of the peripheral cone sheets reflect multiple stages of alteration and re-crystallization that reduced the REE contents relative to the central zone.

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The minerals supply challenge of a net zero carbon pledge Herrington, R. J.1 and the SoS MinErals team 1LODE Group, Natural History Museum, London SW75BD

___________________________________________________________________________ The UK’s Committee on Climate Change stated in their May 2019 report [1] ‘that [carbon] net-zero is necessary, feasible and cost-effective’. A key component of that net zero attainment is that ‘all cars and vans to be electric by 2050’. This further requires that ‘all sales to be pure battery electric by 2035 at the latest’. On the 27th June, the UK government was the first major economy to enshrine this net zero pledge in national law. This presentation is a response to this report based on recent outputs from the Security of Supply Mineral Resources Programme supported by UKRI and other partners (see: https://www.bgs.ac.uk/SoSMinErals/?src=topNav)

There are 31.5 million cars on the UK roads but fewer than 0.2% of them are electric (EV). Replacing just the cars with EVs (not including LGV and HGV fleets), assuming they use resource-frugal NMC 811 batteries, would take 207,900 tonnes cobalt, 264,600 tonnes of lithium carbonate (LCE), at least 7,200 tonnes of neodymium and dysprosium and 2,362,500 tonnes copper (representing 2 x Co, 1 x Nd, 0.75 x Li and 0.5 x Cu production worldwide in 2018). Extrapolating this to the currently projected estimate of 2 billion cars worldwide annual production of these metals would have to increase by 70% for Nd & Dy, 100% for Cu and 350% for Co for the entire period until 2050. Energy costs for the target 31.5 million cars in the UK requires 6% of the UK’s current annual electrical usage7. Extrapolated to 2 billion cars worldwide, the energy demand for extracting and processing the metals is almost 4 times the total annual UK electrical output.

There are serious implications for the electrical power generation in the UK since driving the current 252.5 billion miles in an EV uses at least 63 TWh of power, 20% of current generation capacity in the UK. For that an extra 18GW of new installed capacity and related infrastructure is needed, which if from wind turbines will demand a further 84,600t of copper, 3600t of neodymium and 234t of dysprosium. For the world’s projected 2 billion cars a further years’ worth of total global copper supply and 10 years’ worth of global neodymium and dysprosium production would be needed to build those windfarms. The solar alternative to wind is also resource hungry; the UK would require ~72GW of photovoltaic input to fuel the EV fleet; over five times the current installed capacity. If CdTe-type photovoltaic power is used, that would consume over thirty years of current annual tellurium supply. All these wind turbine and solar generation options for the added electrical power generation capacity have substantial demands for steel, aluminium, cement and glass which has also been highlighted by previous authors [2] but not discussed in detail here.

Moves to a net zero society has a significant resource footprint, such that the availability (and price) of raw materials will likely be a major limiting factor. The UK’s industrial and environmental strategies will depend not just on novel technologies for energy generation, but on the discovery of new mineral resources, and more efficient extraction of a greater diversity and range of elements and minerals from our mines. Over the next few decades, global supply of raw materials must drastically change to accommodate the world’s transformation to a low carbon economy. It is essential to have timely and sustainable supplies of many raw materials in quantities greatly exceeding current global mining and processing capacity.

References: [1] Net Zero – The UK’s contribution to stopping global warming, 2019, report, UK Parliamentary Committee on

Climate Change, London, May 2019, 275pp

[2] Vidal et al. (2013) Nat Geosci 6:894-896

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Influence of the petrology of parent rock on the Co deportment in Ni laterite

deposits: the Santa Fé (Brazil) and Wingellina (Western Australia) case studies

Putzolu, F.1*, Mondillo, N.1,2, Boni, M. 1,2, Santoro, L.2, Porto3, C. Herrington, R.2

1Dipartimento Scienze della Terra Università di Napoli “Federico II” Complesso Universitario di Monte S. Angelo, Via Cintia 26 80126-Napoli, Italy 2Earth Sciences Department, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK 3Instituto de Geociências da Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 274 - Cidade Universitária - Ilha do Fundão, Rio de Janeiro, Brazil *Corresponding author: [email protected]

___________________________________________________________________________ In the last few years the rising demand for Co, combined with the high socio-political instability of the world leading producer, the Democratic Republic of Congo, has triggered an increase in research for unconventional Co sources able to support the future growth in the global market of this high-tech metal. Although Ni laterite deposits account for a significant portion of current Co production (ca. 40%), Co exploitation from these ores is often challenging due to: (1) the complexity arising from their mineralogy, (2) Co spatial distribution within the ores and (3) metallurgical processing routes. Factors controlling the effective Co endowment in Ni laterites and either favouring or restricting the effective Co enrichment during lateritic weathering can be related to both pre-lateritic and post-lateritic processes. Pre-lateritic processes, determining the Co-deportment in the parent rock, directly influence the availability of Co during lateritization, particularly because they can favour the formation of primary Co-bearing minerals either suitable or resistant to weathering. Among the post-lateritic processes, the most important factors controlling Co endowment are the variation of element availability and the changes of pH of the system. In this work, we have investigated the Co deportment in the Santa Fé and Wingellina Ni-laterite deposits by means of Multivariate Statistical Analyses (MSA), such as Principal Component Analysis and the Factor Analysis, which have been interpreted on the basis of the major mineralogical and petrological characteristics of the two deposits. The aim of the study was to assess if and how the pre-lateritic history of a Ni-Co laterite parent rock could have an impact on the supergene enrichment process. The Santa Fé laterite develops from the alteration of the Santa Fé ultramafic alkaline pluton, while the Wingellina deposit develops from the weathering of a mafic to ultramafic subalkaline intrusion (i.e. Giles Complex). At Santa Fé a significant portion of the Co variance can be explained by Co association with Cr and Mn in the oxy-hydroxides-dominated zones of the deposit (i.e. limonite ore). The association of Co with Cr is related to the presence of minor amounts of Co and other transition metals (mostly Mn, Ni and Zn) in chromite and ferritchromite. The MSA conducted at Wingellina gave completely different results, with Co variance totally explained by Co association with Mn in the limonite ore, in agreement with other studies showing the special affinity between Co and Mn-oxy-hydroxides [1,2]. The contrasting Co deportments observed in the two case studies are related to the very different pre-lateritic Co behaviour during the formation and the hydrothermal alteration of the Santa Fé and Wingellina parent rocks. Regarding the Santa Fé deposit, the Co association with Cr has been likely promoted either by the high Co affinity with chromite during the orthomagmatic stage in basaltic alkaline melts [3], and by the hydrothermal chromite-to-ferritchromite transformation [4]. Contrariwise, at Wingellina, the tholeiitic affinity of the parent rock together with the absence of hydrothermally-related element redistribution in magmatic spinels, enhanced the Co concentration in olivine, whose complete dissolution during weathering led to a higher availability of Co during the supergene mineralising process. This study shows that the petrology of the magmatic parent rock strongly influences Co-deportment in the secondary minerals of a Ni-laterite. This might be kept in mind for improving the exploration strategies as well as the efficiency of metal recovery. References: [1] Putzolu et al. (2018) Ore Geol Rev 97:21–34. [2] Putzolu et al. (2019) J Geochem Expl 196:282-296. [3] Horn et al. (1994) Chem Geol 117:193-218. [4] Gahlan and Arai (2007) Petrol Sci Journal 102:69-85

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So predictable; a remarkably uniform episode of lode-gold mineralisation along the Mougooderra Shear Zone, Western Australia

Price, J.P.1, Blenkinsop, T.G.1, Goodenough, K.M.2, Boyce, A.J.3, Kerr, A.C.1 and Kuehnapfel C.4 1School of Earth & Ocean Sciences, Cardiff University, CF10 3AT, UK, [email protected] 2British Geological Survey, The Lyell Centre, Edinburgh, EH14 4AP, UK. 3Scottish Universities Environmental Research Centre, Glasgow, G75 OQF, UK. 4Minjar Gold Pty., Golden Dragon Project, 70km south of Yalgoo, Western Australia.

________________________________________________________________________ Mineral exploration in the Murchison Domain in the Archaean Yilgarn Craton, Western Australia, is particularly difficult. A combination of minimal (< 5 %) outcrop, thick transported cover (up to 30 m) and a high degree of weathering provide further challenges for those exploring for lode-gold mineralisation in a highly prospective, albeit obscured, terrane [1]. The 2.95-2.8 Ga Yalgoo-Singleton Greenstone Belt comprises a typical Archaean supracrustal succession of metavolcanic and metasedimentary rocks, intruded by thick mafic-ultramafic sills [1][2]. The belt is dissected by a number of structures including the unexposed ~60 km Mougooderra Shear Zone (MSZ), host to most of the belts current 1 Moz gold resource. Despite its endowment, the geometry and kinematics of this structure and its contained lode-gold mineralisation have long been poorly understood. Recent structural analysis has revealed that mineralisation along the length of the MSZ is structurally-controlled and conforms to the fault-valve model of Sibson [3], whereby high pore fluid pressures have facilitated reverse movement along a steeply-oriented structure. The current study builds upon this work to elucidate the paragenesis of lode-gold mineralisation along the MSZ, employing SEM analysis, quartz δ18O and sulphide δ34S stable isotope analysis on a suite of ore samples from six deposits along the shear.

Our paragenetic study reveals the sulphide assemblage at the 400 koz Silverstone deposit consists of pyrite, pyrrhotite and arsenopyrite, with minor chalcopyrite and Sb-sulphides, primarily ullmannite (NiSbS) and stibnite (Sb2S3). The ore zone has experienced intense carbonate alteration, with a chlorite-sericite-albite-calcite alteration assemblage in mafic protoliths and talc-magnesite-fuchsite assemblage in ultramafic protoliths. At least two discrete gold-bearing phases are identified, comprising an earlier phase of arsenopyrite and a later phase of gold-bearing antimony sulphides. Gold occurs both as inclusions and as free gold. These assemblages and textures are very consistent at deposits over a strike length of over 30 km. All δ34S sulphide analyses along the length of the MSZ fall in the range -1.5 to +5.0 ‰. The δ34S signature of gold-bearing arsenopyrite is consistently heavier (+4.0 to +5.0 ‰) than overprinting pyrite (+1.0 to +3.0 ‰) at all deposits, and unmineralised pyrite distal to the ore zone is markedly lighter (-1.5 to +0.5 ‰). Preliminary quartz δ18O data from Silverstone indicate that whilst all generations of quartz fall in the range +10.5 and +16.0 ‰, δ18O values of mineralised quartz in the ore zone are very well constrained at +13.9 to +14.8 ‰, to depths of 300 m and more than 5 km along strike.

The uniformity of mineral assemblages, ore textures and δ34S sulphide data at deposits along the length of the MSZ supports structural analysis and demonstrate that mineralisation across the belt formed as part of the same episode of crustal shortening. The disparity in δ34S of arsenopyrite and pyrite plausibly results from fractionation of S isotopes due to variations in pH/fO2, as modelled and tested by Ohmoto [4], rather than the tapping of multiple reservoirs. Additionally, δ18O analysis of quartz and δ34S analysis of sulphides show great potential for use as vectors towards mineralisation in a particularly challenging exploration environment.

References:

[1] Van Kranendonk, MJ et al. (2013) Precam Res 229: 49-92.

[2] Watkins, KP & Hickman, AH. (1990) Geol Surv West Aus Bulletin 137:267 pp.

[3] Sibson RH et al. (1988) Geology 16(6): 551-555.

[4] Ohmoto, H. (1972) Econ Geol, 67(5): 551-578.

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Tectono-magmatic constraints on gold-tellurium fertility, Fiji

Clarke, R.H.1, Smith, D.1, Holwell, D.A.1, Naden, J2, Mann, S.3, and Siddle, R.4

1School of Geography, Geology and the Environment, University of Leicester, LE1, 7RH 2British Geological Survey, Environmental Science Centre, Keyworth, Nottingham, NG12 5GG 3Lion One Metals Limited, Waimalika, Nadi, Republic of Fiji 4Addison Mining Services Ltd, High Beech Road, Loughton, Essex, England, IG10 4BN

___________________________________________________________________________ Alkaline-associated gold-telluride deposits form some of the world’s largest and most important sources of gold [1], and as such have well-studied and documented characteristics [2,3,4], including high Au:Ag ratios, high gold tonnages which can exceed 3 Moz (e.g. Cripple Creek, Porgera, Vatukoula), and enrichments in critical metals, such as tellurium. The common thread between these deposits is the tectonic regime they are found in, and not a specific geochemical signature (other than the alkali-enrichment of associated magmas).

Fiji is often considered an archetype for the post-subduction extensional deposits, with its relatively young age and simple oceanic-arc geology providing an exceptional case study to support their understanding. This study focuses primarily on Tuvatu, one of the multiple deposits and prospects along Fiji’s >250 km mineralised gold belt. Tuvatu lies in the Navilawa Caldera along the west coast of Viti Levu, and is the second largest Au-Ag-telluride deposit in Fiji [5]. Within the caldera, volcaniclastics are intruded by monzonites, the latter of which host the majority of the mineralisation. Broadly speaking, mineralisation occurs either as thin but laterally extensive individual veins of calcite-feldspar-quartz-pyrite ± biotite and other sulphides, with gold as native gold, electrum or tellurides; or thicker quartz-pyrite-magnetite veins with coarse biotites (<3 cm) and more abundant sulphide phases in the ‘H-T corridor’. Resource extension has prompted identification and re-interpretation of lodes as such: the NW-SE trending H-T corridor lodes dip variably and are less laterally extensive, whilst other lodes may be split into several groups including N-S lodes dipping steeply to the east (UR, URW), E-W lodes dipping steeply south (Murau, Snake), and flatter lodes dipping easterly (SKL). Only 50 km from Tuvatu is the world-class Vatukoula (or ‘Emperor’) Gold Mine, prominent in industry due to its long history of gold production. Approximately 7 Moz of gold has so far been mined from Vatukoula, with another 4 Moz in combined resources/reserves [1] – and in the 1970s/80s it was the only direct tellurium producer in the world. Comparisons are often drawn between Tuvatu and Vatukoula, as both are epithermal, low-sulphidation gold-telluride deposits hosted within calderas of near identical age (5.4–4.6 Ma [6]). Alkaline magmatism in both calderas has similar chemical characteristics: both deposits are associated with potassic lavas and shallow intrusions synchronous with extension and post-subduction at the Vitiaz (Fiji) Arc. As such, magmatism has long been considered the source of enrichment. With this in mind, we hope to establish a common magmatic framework that can be utilised for exploration. In this presentation we cover a preliminary 3D model of Tuvatu in conjunction with geochemical and petrographic studies of the regional magmatic evolution, aiding understanding of Fiji’s melt sources, in turn aiding the understanding of gold and tellurium sources for Tuvatu and the rest of Fiji. This will better constrain whether enrichment is due to a source control, or tapping a zone of fertility. References:

[1] Pals D and Spry P (2003) Min & Pet 79: 285-307

[2] Jenson E and Barton M (2000) SEG Rev. 13: 279-314

[3] Kelley K and Spry P (2016) Rev. in Econ Geol 18: 195-216

[4] Holwell D et al. (2019) Nat. Comms. 10: 3511-10

[5] Scherbarth N and Spry P (2006) Econ Geol 101: 135-158

[6] Forsythe N, Spry P and Thompson M (2019) Geosciences 9: 42

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Hydrothermal alteration patterns surrounding the Yalea Au deposit as

reflected by mica chemistry.

Harbidge R.C.1, Lambert-Smith J.1, Blenkinsop T.1, Allibone A.2, Holliday J.3

1Cardiff University, Cardiff CF10 3AT, United Kingdom, [email protected] 2Rodinian, PO Box 758, Wanaka 9343, New Zealand 3Barrick, 1st Floor, 2 Savoy Court, Strand, London, WC2R 0EZ, United Kingdom

___________________________________________________________________________ Patterns in muscovite, paragonite, and phengite Al-Si chemistry, and biotite Mg-Fe chemistry were examined for the Lower Proterozoic Yalea gold deposit in the Kédougou-Kéniéba Inlier, Western Mali. The structurally controlled deposit forms part of the ~25 km long Loulo-Gounkoto gold district, a >17 Million ounce gold camp and is hosted in greenschist-facies quartz wackes, argillites and marbles. Superimposed metasomatic hydrothermal alteration halos extend for up to ~15 km from the economic zone. This includes an envelope of plagioclase-biotite-sericite alteration extending ~1060 m into the hangingwall, overprinting regional pre-mineralisation albitisation and tourmalinisation [1]. The mineralogy of this envelope was investigated to better constrain the development of the hydrothermal system at Yalea. Alteration around gold mineralisation at Yalea is characterised by an outer zone of increasingly Mg-rich biotite followed by a ~200 m zone of more phengitic white mica proximal to the mineralised carbonate-rich ore body. This change can be identified by a colour change from brown to green biotite, and a volumetric increase in white mica and dolomite-ankerite alteration. The Fe/(Fe+Mg) in biotite subtly decreases toward the ore body (from 0.38 to 0.35 apfu), and in muscovite increases subtly from 0.43 to 0.47 apfu. Where green biotite is present in the immediate hanging-wall and footwall of the ore body, magnetite, hematite and minor anhydrite, allanite, epidote, apatite and scheelite are present. This skarn assemblage, together with green biotite is most abundant in the footwall of the deposit. The systematic increase of Fe-Mg ratios in biotite may reflect the increasing abundance of sulphide mineralisation toward the ore. High Fe/(Fe+Mg) in phengitic micas is potentially indicative of relatively oxidized conditions [2]. The zonation of mica composition around the Yalea orebody opens up the opportunity for further investigation into the viability of ore deposit targeting with the use of hyperspectral SWIR data which can detect these changes in the VNIR range (300 – 2500 µm).

References: [1] Lawrence et al. (2015) Econ Geol 108: 199-227 [2] Deer Howie and Zussman (2003) Geol Soc Vol 3A: 87-238

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Structural geology of porphyry copper deposits from regional tectonic setting to vein- and permeability-formation Dilles, J.H.1*

*Corresponding author: [email protected] 1College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR USA

___________________________________________________________________________

Porphyry Cu±Mo±Au deposits underpin much of the mining industry and global economy. The deposits form in the upper crust, as the result of crustal-scale hydrous intermediate-silicic magmatism, generally associated with convergent margin arcs. Structure and tectonics play key roles in both porphyry copper formation and preservation1. Several deposits and districts have been affected by post-ore strike-slip faulting that has offset orebodies laterally, and elsewhere by normal faulting that has offset orebodies and tilted crustal blocks to allow geologists to observe up to 6km crustal sections in cross-section. Ore-forming environments are commonly characterized by regional shortening contemporaneous with magmatism. The ore-forming environment is characterized by both a lithostatically pressured deep zone at >400°C characterized by plastic/ductile deformation in the carapace of the pluton that is the source of ore fluids, and an overlying brittle zone characterized by hydrostatically pressured and advecting local groundwaters. Ascending magmatic-hydrothermal fluids periodically hydrofracture and breach the deep ductile zone, allow porphyry dikes to be emplaced upward, and heat the crust. The position of the brittle-ductile interface therefore is dynamic, and changes with time. Ultimately, as the deep magma cools and solidifies, the overlying crust also cools and high temperature early veins are cut by lower temperature veins as observed in all deposits. In a few districts characterized by compressive tectonics and shortening, extreme topography and hydrothermally weakened rock may be related to several km of exhumation where there are magmatic timescales of >1 m.y. These conditions result in telescoped systems such as in the central Andes and Butte, Montana2. In these localities, deeply formed porphyry Cu±Mo±Au deposits are cut by shallow Cordilleran base metal lodes to form large deposits. References [1] Tosdal R and Dilles J (in press) Rev in Econ Geol: Structural Geology of Mineral Deposits [2] Houston R and Dilles J (2013) Econ Geol, 108:1397-1424.

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Geochronology and structural controls of propylitic alteration in the

Quellaveco Cu-Mo porphyry district, Peru

Strachan, R.1,2, Vermeesch, P.1, Wilkinson, J.J.2, Buret, Y.2, Mitchell, T.1, Ihlenfeld, C.3. and Valdivia. V.3

1University College London, Gower Street, London, WC1E 6BT 2Natural History Museum, Cromwell Road, London, SW7 5BD 320 Carlton House Terrace, St. James's, London SW1Y 5AN

Porphyry deposits are known for their distinctive alteration footprint, which is often key to their

successful discovery. Over recent years, several studies have highlighted the importance of a better

understanding of the most extensive part of this footprint, the propylitic halo [1]. This study focuses

on the district-wide propylitic alteration associated with the Quellaveco Cu-Mo deposit, located in

the northern segment of the Paleocene-Eocene metallogenic belt, southern Peru [2]. The aim of the

study was to detect changes in U-Pb age of 81 samples containing propylitic vein-hosted and wallrock

replacement titanite, apatite, epidote and zircon across the district, and potentially relate them to

the sequence of intrusive events and fluid migration pathways developed in the period leading up to

porphyry mineralisation.

As magma and fluid movement through the upper crust is predominantly focused by areas of

increased permeability, such as the damage zone surrounding fault systems [3], it is expected that

the often complex and multiphase emplacement of porphyry-related magmas and fluids will be

channelled by certain fault structures. At Quellaveco, there are two major fault sets: WNW-ESE

trending, which are associated with the regional Incapuquio Fault System; and NE-SW trending faults.

The locations of the known mineralised centres in the area appear to coincide with the intersection

points of these faults. If, therefore, particular structures have acted as magma and fluid conduits,

potentially during multiple events, it would be expected that these pathways have preserved a

detectable geochronological and geochemical trace.

Preliminary LA-ICP-MS U-Pb dating, combined with SEM textural classifications of the samples, has

highlighted several phases of alteration with ages spanning the range ~75 – 60 Ma. With a porphyry

system emplacement age of ~56 – 54 Ma at Quellaveco [4,5], this suggests the development of

alteration which is significantly older than the deposit, and implies a long history of propylitic

alteration in the district. With this novel application of propylitic U-Pb geochronology we hope to

temporally constrain particular phases of the propylitic alteration and link these to specific structural

conduits, thereby developing a district-wide understanding of fluid flow during the build up to

mineralisation at Quellaveco.

References: [1] Wilkinson, J. J., Chang, Z., Cooke, D. R., Baker, M. J., Wilkinson, C. C., Inglis, S., Chen, H., and Bruce Gemmell, J., (2015) The chlorite proximitor: A new tool for detecting porphyry ore deposits: Journal of Geochemical Exploration 152: 10-26 [2 Tosdal, R., Simmons, A., and Clark, A. (2017) Overview of the Geologic Setting and Porphyry Cu-Mo Deposits of Southern Peru, in Proceedings X International Congress of Prospectors and Explorers, Peru, 10-14 May 2017. [3] Sibson, R., Francois, R., and Poulsen, K. (1988) High-angle reverse faults, fluid-pressure cycling, and mesothermal golf-quartz deposits: Geology 16: 551-555 [4] Sillitoe, R., and Mortensen, J. (2010) Longevity of Porphyry Copper Formation at Quellaveco, Peru: Economic Geology 105: 1157-1162 [5] Simmons, A., Tosdal, R., Wooden, J., Mattos, R., Concha, O., McCracken, S., and Beale, T. (2013) Punctuated Magmatism Associated with Porphyry Cu-Mo Formation in the Paleocene to Eocene of Southern Peru: Economic Geology 108: 625-639

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The magmatic evolution of the Yarabamba batholith, Southern Peru: protracted magmatism culminating in multi-centred giant porphyry Cu-Mo mineralisation

Nathwani, C.1,2, Buret, Y.1, Wilkinson, J.J.1,2 and Ihlenfeld, C.3

1London Centre for Ore Deposits and Exploration (LODE), Department of Earth Sciences, Natural History Museum, Cromwell Road, South Kensington, London, SW7 5BD, UK. [email protected]

2Department of Earth Science and Engineering, Imperial College London, Exhibition Road, South Kensington Campus, London, SW7 2AZ, UK.

3Anglo American plc, 20 Carlton House Terrace, London, SW1Y 5AN, UK.

__________________________________________________________________________ Porphyry Cu ore deposits are the rare product of a larger underlying long-lived upper crustal magma system that exsolves metalliferous fluids during the emplacement of porphyritic stocks and dykes. However, the exact magmatic processes that govern the transition of typical magma systems towards metallogenically fertile magmatism remain poorly understood. The Yarabamba batholith, Southern Peru, is a composite batholith that was assembled over a protracted period (69-57 Ma) that culminated in the generation of three giant porphyry Cu-Mo deposits between ~58-53 Ma: Quellaveco, Cuajone and Toquepala [1] [2]. In this study we track the magmatic evolution of the Yarabamba batholith and the Quellaveco porphyry Cu-Mo deposit using whole-rock and zircon chemistry. The Quellaveco deposit consists of several generations of porphyry stocks and dykes that were each accompanied by hydrothermal alteration and mineralisation. We show that the magmas building the Yarabamba batholith became increasingly evolved and hydrous during the Palaeocene, culminating in the emplacement of compositionally distinct, high Sr/Y porphyry intrusions associated with mineralisation. We show using Eu/Eu*, Hf and Ti that zircon also records this evolution path, in part inheriting the chemistry of the bulk magma but also tracking in-situ melt chemistry during crystallisation. We demonstrate using modelling and core-rim analyses that the zircon Eu anomaly is related to fractional crystallisation processes and does not require elevated melt oxidation state as previously suggested.

References: [1] Sillitoe R H and Mortensen J K (2010) Econ Geol 105: 1157-1162 [2] Simmons A T, Tosdal R M, Wooden J L, Mattos R, Concha O, Mccracken S, and Beale T (2013) Punctuated magmatism associated with porphyry Cu-Mo formation in the Paleocene to Eocene of southern Peru: Econ Geol: 108: 625-639

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Yerington District, Nevada: New porphyry system petrogeochronology Carter, L.C.1, Williamson, B.J.1, Tapster, S.R.2, Armstrong, R.N.3 and Buret, Y.3 1Camborne School of Mines, University of Exeter, Cornwall, UK. [email protected] 2BGS, Keyworth, UK 3Natural History Museum, London, UK

___________________________________________________________________________ The Yerington District, Nevada, provides a first-order control on porphyry copper deposit (PCD) models [1][2][3] and the magmatic-hydrothermal transition [4] as, due to tectonic tilting, it exposes a ca. 8 km deep section from volcanic to plutonic environments through no less than 4 PCDs. The general sequence of pluton emplacement, from McLeod to Bear to Luhr Hill granite, that culminated in PCD formation, has long been established [5] and provides the basis for more recent numerical models for batholith construction and mineralisation [6]. Based on macro- to micro-scale field-based and textural observations, and new high precision CA-ID-TIMS zircon U-Pb age determinations, we have revised this petrogeochronological framework. The cupolas (upper parts) of the underlying Luhr Hill granite were previously suggested to have been the source (directly, or indirectly via dykes) of the mineralising fluids [3][6]. From our field investigations, however, we could find no evidence (e.g. miarolitic cavities and veins) in the cupolas or large porphyry dykes for volatile exsolution, rather the presence of graphic textures in (rare) quartz-feldspar orbicules in the Luhr Hill granite suggests that the magmas were fluid undersaturated [4]. The only substantive evidence for fluid exsolution, in the form of miarolitic cavities and veins, was found in aplite dykes, which are volumetrically minor yet occur pervasively from below to within the PCDs. The aplites are penecontemporaneous with, yet distinct from porphyritic dyke intrusions and cross-cut the upper portions of the Luhr Hill granite and its cupolas [4]. From new whole rock and zircon LA-ICP-MS trace element data, they are also distinct from the other intrusive phases. Importantly, of all the magmatic units in the Yerington district, the aplites were found to be the most closely associated with mineralisation below and within the PCDs, containing A-type veins and mineralised miarolitic cavities. From our new high-precision CA-ID-TIMS zircon U-Pb ages for magmatic units of the Yerington District, plutonic phases and generations of porphyry dykes related to the Ann Mason and Yerington PCDs are at least 2 Ma younger than previously reported [5][7]. In addition, volcanic rocks (Fulstone Volcanics), which were previously thought to be linked to the Luhr Hill granite [8], and to post-date PCD mineralisation [5], predate the plutonic units (in both age determination and geochemical characteristics). Importantly, with respect to the timing of mineralisation, the aplite dykes, which appear to have provided the pathways for mineralising fluids [4], are younger than previously described mineralised phases of the Ann Mason and Yerington PCDs [8]. It is hoped that our new petrogeochronological data will provide an improved framework for future numerical models for batholith construction and mineralisation. References: [1] Seedorff E et al. (2005) Econ Geol 100: 251-298 [2] Sillitoe R H (2010) Econ Geol 105: 3-41

[3] Dilles J H (1987) Econ Geol 82: 1750-1789

[4] Carter L C et al. (2019) Proceedings of the 15th SGA Biennial: 973-976

[5] Dilles J H and Wright J E (1988) Geol Soc Am Bull 100: 644-652

[6] Schopa A et al. (2017) Econ Geol 112: 1653-1672

[7] Banik T J et al. (2017) Geosphere 13: 1113-1132

[8] Proffett J M (2009) Geology 37: 675-678

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Molybdenite from porphyry deposits of the Urals: trace elements

geochemistry and 3R-2H polytypes distribution

Plotinskaya, O.Y.1, Abramova, V.D.1, Najorka, J.2 Seltmann R.2, and Shilovskikh, V.V.3

1Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of

Sciences, 119017, 35, Staromonetny per., Moscow, Russia, [email protected] 2Natural History Museum, Department of Earth Sciences, CERCAMS, London, UK 3Centre for Geo-Environmental Research and Modelling, Saint-Petersburg State University

_________________________________________________________________________________

Molybdenite from four porphyry deposits of the South and Middle Urals (Tomino, Mikheevskoe and

Benkala porphyry Cu and Talitsa porphyry Mo deposits [1]) were studied with EMPA, LA-ICPMS,

EBSD, and micro-XRD techniques. Most trace elements analyzed (Si, Ti, Ca, V, Fe, Co, Ni, Cu, Zn, As,

Se, Ag, Sb, Te, Au, Pb, and Bi) form mineral inclusions within molybdenite in all the deposits studied;

only Re and W are most likely to be incorporated into the molybdenite lattice.

Silurian Tomino porphyry Cu deposit was formed within oceanic arc setting is featured by high

contents of Re (8.7 to 5800 ppm, geom. mean 938 ppm) and low contents of W (up to 5.8 ppm) in

molybdenite. The latter is represented by a mixture of 3R and 2H polytypes.

The Late Devonian to Early Carboniferous Mikheevskoe porphyry Cu deposit is linked to an intra-

oceanic arc. Tevelev et al. [3] however supposed subduction under the accretion prism on the

eastern margin of the East-Uralian continent. Molybdenite here is also enriched in Re (83 to 3440

ppm, geom. mean 967 ppm) and depleted in W (1.0 to 4.9 ppm) and is represented by 3R and 2H

polytypes [2]. At that elevated contents of Re (several thousand ppm) were identified in both pure 3R

and pure 2H molybdenites.

The Early Carboniferous Benkala porphyry Cu deposit from an Andean-type geotectonic environment

is featured by lower content Re (364 to 744 ppm, geom. mean 574 ppm) and higher contents of W

(29.2 to 76.8 ppm, geom. mean 46.9 ppm).

The Late Carboniferous Talitsa Mo porphyry deposit is linked to collisional setting. Molybdenite here

has low content of Re (40.8 to 388 ppm, geom. mean 109 ppm) and elevated W contents (6.0 to 232

ppm, geom. mean 17.4 ppm) and is represented by 2H polytype only.

Thus, trace element geochemistry of molybdenite can be useful tool to discriminate the geotectonic

environment for porphyry Cu(Mo) deposits. Elevated contents of Re are usually confined to 3R

polytype of molybdenite but occasionally occur within 2H-molybdenite.

References:

[1] Plotinskaya OY et al. (2017) Ore Geol Rev 85: 153-173

[2] Plotinskaya OY et al. (2019) Mineral Mag 83: 639-644

[3] Tevelev AV et al. (2006) Paleozoides of the Juncture Zone between the Eastern Urals and Transural Region

(in Russian).

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Zircon-hosted apatite inclusions: A powerful tool for reconstruction of Cl contents in melts

Tuffield, L.1, Buret, Y.T.1, Large, S.J.E.2, Spratt, J.1, Brugge, E.3 and Wilkinson, J.J.2,3

1Core Research Laboratories, Natural History Museum, Cromwell Road, London, SW7 5BD, UK [email protected] 2LODE, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK 3Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ __________________________________________________________________________________________

Chlorine in the exsolved volatile phase plays an important role in complexing with metals in the extraction and concentration of metals in magmatic-hydrothermal ore deposits. Therefore, tracking the concentration and evolution of Cl in the parent melt is of particular importance in understanding porphyry copper deposits. The incorporation of Cl into apatite can be used to track the volatile content of melts; however, low closure temperatures and the rapid diffusion of halogens in apatite make it susceptible to sub-solidus re-equilibration by later thermal events and hydrothermal fluids. This susceptibility compromises the ability of apatite to retain the primary halogen signature. The common occurrence of apatite as an inclusion phase in zircon crystals, together with the refractory nature of zircon, open up the possibility that such inclusions may preserve the primary Clmelt compositions [1]. The Rio-Blanco-Los Bronces porphyry copper district is located in central Chile, which hosts several world class porphyry copper deposits and barren intrusions [2]. This makes it an excellent area for the investigation of the role of Clmelt in the formation of porphyry copper deposits, as well as the effect of sub-solidus re-equilibration of Cl in apatite. For this study we analysed apatite crystals that occur both in the groundmass and as inclusions in zircons. This geochemical analysis was carried out using EPMA for halogen and major elements, and LA-ICP-MS for trace elements, on four samples from the Los Bronces porphyry copper district. These samples include a barren intrusion unrelated to mineralisation that precedes mineralisation by around 10 Ma, and pre-, syn- and post-mineralisation porphyries. Apatite inclusions hosted in zircon crystals typically exhibit a large range in Cl concentrations (<0.5-2.5 wt.% Cl), with all inclusion data exhibiting polymodal distributions of Cl concentrations. In contrast, groundmass apatites from all samples are characterised by uniformly low Cl concentrations (<0.5 wt.% Cl). These results are consistent with the apatite crystals in the groundmass having experienced sub-solidus re-equilibration, related to the pervasive hydrothermal alteration in the district. The large range in Cl concentrations recorded by the apatite inclusions is interpreted to reflect the changing Clmelt for the duration of apatite and zircon crystallisation. Additionally, the apatites hosted in zircon crystals show significant inter-sample variations, evolving from low Cl concentration (<0.5 wt.% Cl) in the barren intrusion, to higher Cl concentrations (0.5-2.5 wt.% Cl) in the samples associated with porphyry Cu mineralisation. These data can be used to show that the Clmelt was significantly higher (0.05-0.40 wt.% Clmelt) in the melts associated with porphyry copper mineralisation, compared with barren magmatism (0.04 wt.% Clmelt) [3]. We demonstrate that due to the rapid diffusion of halogens in apatite in the presence of melt or hydrothermal fluid, the study of apatite inclusions hosted in zircon crystals is required to reconstruct primary melt compositions, and to record and track the evolution of Cl concentrations in porphyry forming magmas. This study reveals high Clmelt concentrations in the magmas related to mineralisation in the Los Bronces district, facilitating the efficient extraction and concentration of metals. Further work examining zircon-hosted apatite inclusions from mineralised and unmineralised intrusions could provide more insight into Cl contents in porphyry forming magmas. References: [1] Brugge, E. et al. (2019). Proc. 15th SGA Biennial Meeting, Vol. 2, 983-986. [2] Toro, J.C. et al, (2012). SEG, Special Publication, 16:105-126. [3] Li, H. and Hermann, J. (2017) Am. Mineral. 102:580-594.

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Post-subduction magmatism and gold mineralisation in the Colorado Mineral Belt: insights from accessory minerals Berry, J.1, Miles, A.J.1, Smith, D.J.1, and Holwell, D.A.1. 1School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH

___________________________________________________________________________ Magmatism that occurs following subduction (post-subduction) is commonly associated with gold (Au) and tellurium (Te) mineralisation [1]. These post-subduction magmas tend to be low volume, hydrous melts that are variably alkali-enriched, and often associated with porphyry-epithermal deposits. The processes controlling post-subduction enrichments in gold and tellurium are thought to begin during active subduction. Arc magmas have a ‘cryptic’ amphibole signature, whereby La/Yb and Dy/Yb ratios suggest the presence of amphibole during magma differentiation, but arc magmas lack a phenocrystic amphibole phase [2]. Therefore, it is plausible that amphibole remains as a residue in the lower crust. These cumulates act as a ‘sponge’ and can filter water throughout the subduction to post-subduction system. Sulphide minerals in cumulate residues could be important hosts for a significant portion of chalcophile elements, such as Au and Te [3]. These sulphides can be remelted during post-subduction magmatism [1]. Low-degree partial melting of a metasomatised mantle source may also explain the relative enrichment and affinity for post-subduction alkali magmas to be associated with Au-Te porphyry-epithermal systems [4]. Whole-rock data can be a useful tool in investigating magmatic processes, as it provides an integrated record of numerous magmatic events. However, this homogenisation restricts its ability to isolate precise and distinct magmatic events in different parts of the crust, and in regions where mineralisation is common, it may be influenced by the effects of alteration. Accessory minerals can provide robust and abundant data for many stages throughout a magmatic history. Zircon, apatite, and titanite have proven their use in porphyry-epithermal systems [e.g. 5, 6]. Accessory minerals can form at any depth in the crust provided the right conditions exist – including the lower crust [7]. If we can determine the location of their formation, accessory minerals may record deep crustal processes that are otherwise lost. Zircon is an incredibly robust mineral that can host other, less-robust minerals, such as sulphide [8] or apatite [9]. Zircon can also be inherited from deeper regions of the system, where antecrystic cores can record a different, lower crustal signal from younger rims [10]. The textural context of these minerals combined with U-Pb dating of zircons from samples can provide insight into transcrustal processes that occur to form porphyry-epithermal deposits. The Cenozoic intrusions of the Colorado Mineral Belt (CMB) are an ideal field site for this study, as the CMB hosts numerous subduction and post-subduction magmas that are variably enriched in Au-Te. Off-axis from the CMB is the world class Cripple Creek gold deposit, which offers a broad comparison from intrusions with varying potential for gold mineralisation.

References:

[1] Richards (2009) Geol. Soc. America. 37(3):247-250

[2] Davidson et al. (2007) Geol. Soc. America. 35(9):787-790

[3] Richards (2011) Econ. Geol. 106(7):1075-1081

[4] Holwell et al. (2019) Nature Comm. 10:3511

[5] Chelle-Michou et al. (2014) Lithos. 198-199:129-140

[6] Mao et al. (2016) Econ. Geol. 111:1187-1222

[7] Liu et al. (2014) Geology. 42(1):43-46

[8] Simpson (2014) BSc Thesis. Univ. of Wollongong.

[9] Miles et al. (2013) Contrib. Min. Petrol. 166:1-19

[10] Miles and Woodcock (2018) Lithos. 304-307:245-257

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Accessory Mineral Chemistry Reveals the Petrogenesis of an Evolving Porphyry Magma System: Chuquicamata and the Fortuna Complex Loader, M.A.1, Wilkinson, J.J.1 and Buret, Y.T.1 1Natural History Museum, Cromwell Road, London SW7 5BD

___________________________________________________________________________ Magma systems associated with porphyry deposits show a chemical evolution which diverges from

typical magma differentiation trends [1, 2]. These different trends suggest some divergence in the

processes by which porphyry magmas chemically differentiate, such as the fractional crystallisation

of different proportions of minerals in the lower crust. Understanding the processes by which

porphyry magmas form is a fundamental step in understanding the discontinuous spatial and

temporal distribution of porphyry deposits, and their relative scarcity in the global arc magmatic

record. Of special importance are localities where there exists a preserved volcanic or intrusive

record over several million years prior to mineralization.

The bulk rock chemistry of porphyry intrusions within the deposits a) records only the final

composition of the protracted evolution of the magma system, and b) are often hydrothermally

altered, obscuring the original igneous chemistry and complicating an assessment of their

petrogenesis. However, accessory minerals within these rocks, such as zircon and apatite, may

provide a more useful tracer of magmatic evolution because they may record a protracted magmatic

evolution and may be less susceptible to alteration. Here, we report zircon and apatite trace element

chemistry for representative porphyritic intrusions of the Chuquicamata porphyry Cu-Mo deposit,

and the nearby plutonic rocks of the Fortuna Complex [3]. The Fortuna Complex is a part of the

broader Late Eocene magmatic system which precedes mineralisation at Chuquicamata and El Abra

deposits. Textural and chemical comparison with zircon and apatite from unaltered rocks suggests

that accessory phases from the porphyry intrusions record primary magmatic signatures.

We show that the chemistry of zircon and apatite (especially rare earth element concentrations)

show a systematic variability both between successive intrusions, and a core to rim and inter-grain

variability within a particular rock sample. We suggest that the inter-sample variability is in part

controlled by deep crustal fractionation processes (which control the bulk magma chemistry),

whereas the intra-sample variability is controlled by in situ shallow crustal crystallisation of other

trace element-bearing phases (which influences the residual melt chemistry). We further speculate

on the influence of oxidation state, melt chemistry, competition for trace elements in residual melts,

and temperature in controlling these chemical differences.

References:

[1] Richards J (2012) Econ Geol 106(7), 1075-1081

[2] Loucks RR (2014) Aust J Earth Sci 61(1), 5-16

[3] Dilles et al. (2011) SGA abst. 1, 398–400

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Mineral Deposits Studies Group Annual Meeting 2020 Oral Session, 8th January 2020 Ni-Cu-PGE DEPOSITS

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Ni-Cu-PGE mineralization of the 1.1 Ga Midcontinent Rift of N. America:

rethinking models for the rift and the implications for mineralization

Hollings, P.1 and Cundari, R.2

1Department of Geology, Lakehead University, 955 Oliver Road Thunder Bay, ON P7B 5E1 Canada. [email protected] 2Ontario Geological Survey, Ministry of Energy, Northern Development and Mines, ON P7E 6S7 Canada

___________________________________________________________________________

The ~1.1 Ga Midcontinent Rift (MCR) of North America comprises ∼1,500,000 km3 of basaltic sheets, flows and intrusive rocks emplaced in the Lake Superior region during the Mesoproterozoic [1]. Recent discoveries of high-grade Ni-Cu-PGE deposits within mafic intrusions associated of the MCR has resulted in a significant increase in exploration activity in the Lake Superior region. Many of these deposits, particularly Thunder North in Ontario, Tamarack in Minnesota, and Eagle in Michigan, are associated with ultramafic intrusions emplaced during an early phase of rift activity and are often spatially linked with long-lived crustal structures [2]. The Thunder Bay – Lake Nipigon region is emerging as the most prospective PGM-rich magmatic sulfide district in Canada and, arguably, the world. It has delivered the highest number of new platinum group metal discoveries over the past 15 years.

The current paradigm for the MCR invokes an upwelling mantle plume as the cause of magmatism and mineralization but recent geochronological, geochemical and mineralogical data are not fully consistent with this model. Arguments against an active plume include: 1) geochronological data which shows that magmatism lasted for at least 20 and perhaps 60 million years [3] unlike the majority of plume-related Large Igneous Provinces (LIPs) which typically last less than 1–5 m.y. 2) the absence of a giant radiating dike swarm typical of plume-related LIPS, 3) the ultramafic rocks in the MCR have been used to suggest a plume but maximum olivine forsterite compositions from the ultramafic intrusions suggest a parental magma with 8-10 wt% MgO rather than an ultramafic mantle source and 4) ongoing studies of an extensive database of ~3000 whole rock analyses from the MCR has identified four distinct trends which, combined with isotopic data [4,5] suggest a complex and heterogeneous mantle source for the MCR that underwent a progressive depletion in incompatible elements as MCR development progressed.

The long duration of MCR magmatism, absence of primary ultramafic magmas, lack of a radiating dike swarm and heterogeneous mantle source characteristics all suggest that an alternative model involving passive rifting may be a better fit for the MCR. Upwelling of underplated magma left by an earlier plume event (e.g. the Marathon LIP) could account for the OIB-like geochemistry of the MCR. The long-lived nature of the MCR, problems with the current model and the fact that prospective intrusions may have been emplaced throughout the span of MCR-related magmatism make it increasingly important to fingerprint prospective intrusions. Identifying the unique characteristics of fertile magma sources will aid in vectoring toward new discoveries.

References:

[1] Klewin K and Shirey S (1992) Tectonophysics 213: 33–40.

[2] Hollings P et al. (2007) Can. Jour. of Earth Sci. 44: 1087-1110.

[3] Heaman L et al. (2007) Can. Jour. of Earth Sci. 44: 1055-1086.

[4] Hollings P et al. (2007) Can. Jour. of Earth Sci. 44: 1111-1129.

[5] Hollings P et al. (2012) Precam.Res. 214– 215: 269– 279.

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Neoproterozoic rift magmatism along the Congo-Kalahari craton margins: new temporal and geochemical constraints for Ni-Cu-(PGE) fertility in the Zambezi belt Ward, L.A.1, Holwell, D.1, Tapster, S.2, Barry, T.1, and Walker, R.1 1Department of Geology, Geography and the Environment, University of Leicester, [email protected] 2 NERC Isotope Geosciences Laboratory, British Geological Survey

___________________________________________________________________________ Magmatic Ni-Cu-(PGE) sulphide deposits represent some of the world’s most valuable metal accumulations, accounting globally for ~56% of annual Ni and ~96% of PGE production. There is a widely recognised spatial association between many of the world’s largest, and most lucrative, Ni-Cu-(PGE) sulphide deposits and craton, or palaeocraton, margins (e.g. Voisey’s Bay, Noril’sk, Jinchuan). This association is thought to represent the surface manifestation of magma emplacement into zones of thinned continental lithosphere [1]. Large and sustained magma volumes are able to ascend through trans-crustal fault networks in these regions, becoming channelised in the upper crust into high-flux magma conduits, creating prime conditions for ore genesis [2, 3]. Craton margins are therefore frequently targeted as regions of possible enhanced metal prospectivity. Although many aspects of the magmatic ore system are well-constrained, a substantial research and exploration challenge lies in understanding why unmineralised intrusions occur in an otherwise prospective geological setting. Within a number of well-explored terrains, mineralisation is often unevenly distributed amongst superficially similar intrusions. For example, in the Voisey’s Bay district in northern Canada, the Voisey’s Bay intrusion hosts a significant economic ore-body, whilst the apparently similar surrounding intrusions (e.g. Pants Lake) are sub- to un-economic [2]. Similarly, within the Yunnan and Sichuan Provinces of south-west China, a number of mineralised intrusions are surrounded by superficially similar intrusions, containing sub-economic to uneconomic accumulations of low tenor sulphide [3]. Understanding why unmineralised intrusions form within otherwise prospective terrains is key to successful exploration. This study investigates the differences between mineralised and barren intrusions by assessing the temporal and isotopic characteristics of a suite of mineralised and unmineralised intrusions from the Zambezi belt, southern Zambia. The Zambezi belt represents an example of an intra-continental rift system with abundant mafic-ultramafic rift magmatism and sulphide mineralisation, including the economic Munali Ni deposit. Using high precision dating techniques (CA-ID-TIMS) and a range of isotopic tracers (Lu-Hf, Sm-Nd, Rb-Sr), we investigate the provincial/regional geodynamic controls on magma fertility prior to shallow upper-crustal emplacement. Preliminary investigations identify a temporal distinction between the apparently fertile and barren intrusions (distinguished based on geochemical fertility indicators e.g. Cu/Pd). We observe that it is during discrete magmatic episodes, during the initiation of Zambezi rifting (ca. 880 to 820 Ma) that magmatism was particularly capable of segregating economic accumulations of sulphide. Intrusions emplaced after ca. 820 Ma show no evidence of sulphide segregation from their parental magmas. We continue to investigate whether the geodynamic evolution of the Zambezi Belt exerted a fundamental control over magma fertility and frame findings in the context of basin evolution and potential magma sources. References:

[1] Begg et al. (2010) Econ Geol 6: 1057-1070

[2] Barnes et al. (2015) Ore Geol Reviews 76: 296-316

[3] Lightfoot and Lamswood (2015) Ore Geol Reviews 64: 354-386

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The Ni-rich Munali magmatic sulfide deposit: where is the Cu? Blanks, D.E.1 and Holwell, D.A.1 1School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester, LE1 7RH, UK [email protected]

___________________________________________________________________________ The Munali magmatic sulfide deposit is a highly complex Neoproterozoic Ni-Cu-Co-PGE mafic-ultramafic breccia deposit located within the Zambezi Belt in southern Zambia. The deposit represents a multi-phase dynamic system comprised of an early unmineralised gabbroic core, surrounded by a later marginal mafic-ultramafic breccia unit that is host to the sulfide ore [1]. This marginal mafic-ultramafic unit comprises dolerite, weakly mineralised poikilitic gabbro and a suite of atypical ultramafic rocks that include Cr-poor, apatite-bearing dunite and rare wehrlite and clinopyroxenite. The deposit is mined principally for its Ni resource, with Cu, PGE and Co as supplementary by-products and at present, is open at depth. Sulfide mineralisation is comprised of pyrrhotite >> pentlandite > chalcopyrite ± pyrite associated with abundant carbonate-apatite-magnetite. The sulfide is hosted predominantly within three main sulfide sheets (between 1 to 30 m in thickness) within the mafic-ultramafic breccia unit, where it displays variable sulfide breccia textures and mineralisation styles. The bulk sulfide at Munali displays high Ni/Cu ratios (~ 7.5 to 10) and moderate to high Pd/Ir ratios (~ 150 to 3500) and an extreme negative Au anomaly, which is atypical for a mafic-ultramafic complex. Bulk PGE profiles of the sulfide mineralisation styles highlight a key trend that suggests a highly fractionated magmatic system with respect to PGE that is unusually depleted in Cu and Au in comparison to magmatic sulfide deposit worldwide, representing a distinct fractionated Cu-Au-poor sulfide system. The sulfide geochemistry may indicate that the Cu-poor nature of the orebody may reflect an inherent characteristic of the initial sulfide liquid composition, or the orebody currently discovered represents primarily the mss portion of a larger scale sulfide system whereby the Cu-rich sulfide may have migrated during emplacement. There is textural evidence for Cu-rich sulfide liquid migration within the deposit on a cm scale, whereby chalcopyrite is present within cracks and fractures in the brecciated host rocks. As such, Munali may represent a magmatic system where the primary sulfide melt that crystallised was unusually low in Cu and Au or one that on a larger scale, has a thusfar undiscovered Cu-rich portion, which may be additionally enriched in Au and PGE. This Cu-rich sulfide may have migrated via pre-existing structures or as a result of syn- to post-tectonic processes. Thus there remains the possibility of discovering a Cu-rich portion of the orebody a depth. However it is possible that the Cu and Au depletion may be due to secondary processes such as fluid mobilisation. Hydrothermal fluids may have interacted with the sulfides and stripped them of their most mobile metals (such as Cu and Au) via, for example, Cl-rich fluids [2,3] resulting in the depletion in both Au and Cu within the orebody. These fluids may have been magmatic-metamorphic in origin, or derived from Cl-rich evaporitic sediments, for which there is evidence in the immediate host rocks. Therefore Munali may alternatively represent a sulfide system where syn-to-post magmatic processes may have altered or displaced the Cu(-Au)-rich component of the orebody and that these may now reside outside of the magmatic system. References:

[1] Holwell D et al. (2017) Ore Geol Rev 90:553-575

[2] Arid H and Bourdreau A (2013) Contrib Mineral Petrol 166:1143-1160

[3] Hanley J et al. (2005) Mineralium Deposita 40:237-256

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A major swarm of ‘lamprophyric’ dykes exposed in platinum mines of the Bushveld Complex, South Africa: Geochronology, petrology and mineral chemistry

Hughes, H.S.R.1*, Kinnaird, J.A.2, Kramers, J.D.3, McDonald, I.4, Daya, P.2, Compton-Jones, C.J.1, Nex, P.A.M.2, Bybee, G.M.2 1Camborne School of Mines, College of Engineering, Mathematics & Physical Sciences, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK (*[email protected]) 2School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg South Africa 3Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa

4School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff CF10 3AT, UK

___________________________________________________________________________ Here we document a major swarm of ‘lamprophyric’ dykes cross-cutting portions of the 2.06 Ga

Bushveld Complex. The dykes are mostly blind at surface but exposed by underground platinum

mining operations in the Rustenburg Layered Suite of the Bushveld Complex, providing a unique

subsurface insight into the magnitude of the swarm. The dykes predominantly strike WNW-ESE and

fall along subparallel anastomosing sets in plan view. Most dykes range from 0.5 to 2 m in true width,

sometimes with millimetre-scale veinlets as off-shooting networks. The dykes bifurcate and

anastomose at various scales in plan view. All dykes are vertical/subvertical and the margins may be

chilled, often foliated, with lineations defined by alignment of mica crystals. Abrupt changes in

mineral abundance are often recognisable as bands across a single dyke, demonstrating their

compound nature. Dykes can appear ‘stepped’ in cross-section, sometimes with accumulations of

olivine macrocrysts and/or crustal xenoliths located within these steps (typically of Transvaal

Supergroup sediments and Bushveld lithologies).

We present the mineralogy, petrology, mineral chemistry and 40Ar-39Ar geochronology (of micas) of

the dykes. Mica geochronology place the dykes being between 177.2 and 131.8 Ma. The dykes are

mineralogically diverse, but most consist olivine macrocrysts (variably serpentinised) and tabular

euhedral phlogopite with a groundmass of phlogopite, Cr-diopside and augite, serpentinite, calcite,

baryte, apatite, Mn-ilmenite and Mg-chromite, sometimes with perovskite, sodalite, rutile, Ca-Na-

carbonate, and schorlomite. We also use the chemistry of phlogopites to classify their lithology.

Together, the mineralogy, phlogopite chemistry and age of the dykes (alongside bulk geochemistry –

Compton-Jones et al., this conference) classify the majority of these as orangeites. We demonstrate

that these are similar to diamondiferous orangeite dykes outcropping at Swartruggens (Helam),

Klipspringer and Star. However, unlike these other orangeite dyke clusters that can each be traced

along strike for < 10 km, the Bushveld dykes can be traced for at least 50 km along strike due to their

exposure in underground mines. The similarity in ages between Swartruggens and Klipspringer has

previously been suggested as signalling a widespread orangeite emplacement event at c. 150 Ma [1].

Based on our results from the Bushveld dykes, we support this statement and suggest that such an

event was not only widespread, but volumetrically more significant than previously realised. This

provides a tantalising opportunity to progress research into the lithospheric mantle below the

Bushveld Complex and, together with mantle xenolith studies, assess how the geochemistry of this

has changed through time, particularly for precious metals.

[1] Westerlund, K., 2000. Doctoral dissertation, University of Cape Town.

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An update on exploration for nickel in the Molopo Farms Complex’ feeder zone; results of airborne and ground high-resolution geophysics Key, R.M.1, Moore, A.E.1, Ovadia, D.C.1, Schaffalitzky, C.1 and Ramokate, V.L.1 1Kalahari Key Mineral Exploration Company (Pty) Ltd. P O Box 405239, Broadhurst, Gaborone, Botswana

___________________________________________________________________________ Over the last three years, Kalahari Key Mineral Exploration Company (Pty) Ltd’s (‘KKME’) exploration for nickel-PGMs-bearing massive sulphides in the ENE-WSW Jwaneng-Makopong Shear/Feeder zone through the centre of the Molopo Farms Complex (MFC) has progressed from a desk-study and re-interpretation of existing geological, geophysical and geochemical data to high-resolution geophysical fieldwork. This has pinpointed drilling sites over 8 targets, with a further 9 targets also worthy of further study. The MFC is part of the Palaeoproterozoic Bushveld Large Igneous Province of southern Africa. Our re-logging of core from previous exploration projects helped confirm that the MFC was a syn-tectonic intrusion emplaced during deformation of the western part of the Kaapvaal Craton. During this c.2050 Ma deformation event, lateral movement along the regional Jwaneng-Makopong Shear Zone produced a series of elongate ENE-WSW lenticular bodies in the feeder zone to the MFC (shown by 3D re-interpretation of 1990s airborne magnetic data). Away from the shear/feeder zone, the MFC is severely deformed by brittle and ductile structures that disrupted layering and associated mineralization. NRGTM were commissioned to fly an XCITETM high-resolution, time-domain electromagnetic and magnetic survey between the 1st and 9th October 2018 along the Jwaneng-Makopong Feeder Zone in KKME’s licence areas. 2,531 line-km were flown with a traverse line spacing of 300m; the EM sensor was 30m above ground and the magnetic sensor was 45m above ground [1]. Their data was interpreted by Cas Lötter of Spectral Geophysics. Seventeen conducting targets were identified along the length of the feeder zone. Phase 1 of the follow-up ground geophysics over 12 of the conducting targets took place during June to August 2019 using SQUID TDEM (Time Domain B Field electromagnetic survey). The conductor targets were investigated by surveying along 200m spaced lines at reading intervals of either 50m or 100m, through 1km by 1km fixed transmitter loops (Figure 1). The nominal parameters employed for the full duration of the survey were: transmitter loop size = 1km by 1km; transmitter current = 100Amp; transmitter turn-off time = 1.8msec; transmitter frequency = 0.5Hz (1 sec off-time); stacking = 64 cycles.

Figure 1. The location of the ten transmitter loops on XCITETM 2ND vertical derivative of RTP TMI. References:

[1] NRGTM (2018) Confidential Report. Kalahari Key Mineral Exploration Company (Pty) Ltd.

[2] Spectral Geophysics (2019). Confidential Report. Kalahari Key Mineral Exploration Company (Pty) Ltd.

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Mineral Deposits Studies Group Annual Meeting 2020 Oral Session, 8th January 2020 Pb-Zn DEPOSITS

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Early diagenetic controls on the size of Palaeozoic mudstone-hosted Zn deposits Gleeson, S.A.1,2, Magnall, J.M.1 and Reynolds, M.A,3 1GFZ German Research Centre for Geosciences, Potsdam, 14473, Germany 2Institute for Geological Sciences, Freie Universität, Berlin, 74-100 Malterstrasse, 12249 Berlin 3Dept. of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Canada

___________________________________________________________________________ The North American Cordillera contains a number of large Zn deposits hosted in Palaeozoic

biosiliceous, carbonaceous, radiolarian-rich mudstones. Stratabound barite units are associated with

the ore deposits, but are also found regionally in barren, correlative sequences. Recent studies have

shown that stratabound barite, pyrite and authigenic carbonate formed in the sediment at the

sulphate methane transition zone (SMTZ) and are a product of pre-ore diagenesis. Stratabound

diagenetic pyrite, preserves positive δ34S values which suggest that the anaerobic oxidation of

methane coupled with sulphate reduction (AOM-SR), which was an important source of reduced

sulphur during diagenesis.

The hydrothermal systems are superimposed on this diagenetic environment, do not exhale onto the

seafloor and developed in non-euxinic conditions. The δ34S values in ore-stage pyrites suggest

reduced S is derived from a number of sources, including recycling of sulphate from the dissolution of

diagenetic barite. The radiolarian-rich host rocks, likely dominated by Opal A in the top 100s of

metres of the sediment, had high porosities and permabilities that allowed the ore deposits to form

in the sub-surface and prevented significant exhalation of the hydrothermal system into the water

column. Therefore, the biosiliceous nature of host rock, together with the ability of the hydrothermal

fluids to dissolve authigenic barite and carbonate, are major controls on the genesis and size of these

important deposits.

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Mineralogical characterization of Nonsulfide Zn (Pb) ores in the Florida Canyon Project (Northern Peru)

Chirico, R.1, Mondillo N.1, 2, Boni M.1, 2 and Mota e Silva J.3

1 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Via Cintia 26, 80126 Napoli, Italy, [email protected] 2 Natural History Museum, Cromwell Rd, Kensington, London SW7 5BD, United Kingdom 3 Nexa Resources, Distrito de San Borja, Departamento de Lima, Peru

___________________________________________________________________________ The Florida Canyon Project is located in the sub-Andean fold-and-thrust belt of Northern Peru, in the upper Amazon River Basin. The mineralization is hosted by the dolomitized carbonate rocks of the Chambará Formation (Pucará Group, Upper Triassic to Lower Jurassic), and consists of both Zn-Pb sulfide and nonsulfide ores. In the Florida Canyon project area, there is a cluster of several orebodies: e.g. San Jorge, Central, Karen Milagros and Sam Fault. The resources of the Project have been calculated so far at 12.1 million tons with a grade of 10.7% zinc and 1.2% lead [4]. The present economic value of the deposit mostly resides in the sulfides (especially occurring in the Karen-Milagros area). However, recent explorative drilling has also found abundant nonsulfide intersections up to 500 m in depth [3]. The primary mineralization, considered a classical Mississippi Valley-Type (MVT) deposit, consists of stratabound mantos with mixed sulfides, or of disseminated patches of sphalerite and/or galena in fractures [1]. The sulfides are usually confined to porous rocks, such as grainstones, packstones or rudstones, and are associated with pervasive dolomitization and carbonate dissolution. Nonsulfides are not uniformly distributed in the project area. They are quite abundant in the San Jorge orebody, which is characterized by abundant karst-related features, and in the Central orebody. On the contrary, in the Karen-Milagros area, the secondary mineralization occurs in form of a limited supergene alteration controlled by fractures. The mineralogical-petrographic study at the macro- and microscale revealed that almost all the analyzed nonsulfide samples are characterized by an association consisting essentially of several generations of smithsonite and hemimorphite, either as earthy aggregates replacing former sulfides, or as colloform agglomerates filling porosity. Replacive smithsonite and hemimorphite directly substitute both sphalerite and dolomite crystals, and commonly show inherited pseudomorphic textures, often associated with relicts of the primary sulfides. Less abundant cerussite and anglesite can be generally found as alteration rims of galena grains, which rarely also contain small inclusions of Ag-minerals. The colloform nonsulfide aggregates are mainly characterized by smithsonite occurring either as white to grey coarse-grained crystals, or as brownish to yellowish concretions (“rice-shaped” smithsonite). The white to grey coarse-grained crystals show a well-developed zonation with variable concentrations of CaO (0.7 to 2.0 wt.%) and traces of Fe. They are associated with F-apatite, quartz, less abundant Zn-bearing micas and clays and are generally coated by late microcrystalline hemimorphite. Brownish to yellowish smithsonite concretions, mostly characterized by stoichiometric composition, are intimately associated with hemimorphite, together with Pb-Zn phosphates and V-bearing minerals. Pb-Zn-Si-bearing Fe-(hydr)oxides are ubiquitous in almost all the nonsulfide-bearing samples. The mineralogical assemblage provided by this characterization confirms in part those described in previous studies, the biggest difference is on part of the nonsulfide mineralization. The genesis of the nonsulfide ore is considered to be likely associated to supergene alteration of the primary MVT ore, developed through groundwater circulation in faults and intricate fault-related karst systems. However, the presence of the peculiar grey smithsonite texture identified with the present study can partly modify this simple genetic model. More specific analyses are required to confirm these genetic aspects. References: [1] Basuki NI et al. (2008) Econ Geol 103:783-799

[2] Basuki NI and Spooner ETC (2009) Explor Min Geol 18:25-39

[3] de Oliveira SB et al. (2019) Trans Inst Min Metall B 128: 27-36

[4] SRK Consulting (2017)

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(U+Th)/Ne dating of hematite from Leadhills-Wanlockhead Pb-Zn ore deposit:

new insight into Triassic-Jurassic basin-to-basement ore-forming processes

Currie D.1, Stuart, F.M.1, Boyce A.1, Essien B.1, Faithfull J.2 1SUERC, Rankine Avenue, East Kilbride, G75 0QF, [email protected] 2Hunterian Museum, Glasgow, G3 8AW

___________________________________________________________________________ Epigenetic hydrothermal Pb-Zn ore deposits are widespread across W. Europe [1]. Many share

common characteristics: extensional fault-controlled vein mineralisation; hosted by Palaeozoic-

Mesozoic basins and/or adjacent basement; S and metals predominantly sourced from the

basement; low temperature (<120-200°C) moderate to high salinity (10 to 30 wt. % NaCl+CaCl2)

mineralising fluids of meteoric origin; deep convective basin-to-basement hydrothermal fluid

circulation model for ore-forming processes [2-6]. However, the timing of ore precipitation is largely

unknown and has hindered our understanding the key ore-forming processes and means we have no

strong tectonic framework.

The Leadhills-Wanlockhead (L-W) Pb-Zn deposit, S. Scotland, was mined from the 12th to mid-

20th C, producing 500 kt Pb, 10 kt Zn, 1 m oz Ag and minor Cu from 70 NW-SE tending fault-controlled

veins within Ordo-Silurian metasedimentary basement [7]. A revised paragenetic study demonstrates

that a phase of hematite mineralisation predates the Pb-Zn sulphides. By applying the new

(U+Th)/21Ne dating technique to hematite, we show that the Pb-Zn mineralisation cannot predate

190-200 Ma. This is significantly later than the Carboniferous age (265-320 Ma [8]) derived from K-Ar

dating of fault gouge clay. Mean δ34S values of vein galena (-9.7 ± 0.8 ‰, n=40) and sphalerite (-6.3 ±

0.5 ‰, n=16) are remarkably homogeneous across >40 veins and consistent with the derivation of S

in fluids that have equilibrated with the basement [9]. The homogeneity suggests that the S source,

ore fluid temperature (190 ± 20°C), and oxidation state remained stable during the Pb-Zn

mineralisation.

Based on the late Triassic-early Jurassic hematite precipitation age, a revised model for ore

generation must now consider the role of regional extension in the late Triassic onwards and the

availability and importance of large volumes of brines from the nearby Upper Palaeozoic-Mesozoic

clastic Thornhill Basin. Fluid penetrated to at least 5 km depth in the basement along new and

reactivated fracture systems is required to increase salinity causing thermohaline circulation and

scavenging of metals and S from the basement, producing physio-chemical conditions necessary to

allow transition from an oxidized to a reduced mineralising fluid and for the precipitation of metals

from both. The extent to which Upper Palaeozoic-Mesozoic clastic basins contributed fluids and

metals to several Pb-Zn deposits across W. Europe remains to be tested, but this study demonstrates

that the (U+Th)/21Ne chronometer holds great potential for resolving key issues in such enigmatic ore

deposits.

References:

[1] Gleeson and Yardley (2002) in Water-Rock Interactions: 189-205, Kluwer Academic Publishers, Netherlands

[2] Samson and Banks (1988) Min Dep 23: 1-8

[3] Halliday A.N and Mitchell J.G (1984) EPSL 68:229-239

[4] Cann J.R and Banks D.A (2001) Proc Yorks Geol Soc. 53:187-196

[5] Gleeson S.A et al (2001) Geochim Cosmochim Acta 13:2067-2079

[6] Munoz M. et al (1994) App Geochem 9:609-626

[7] Wilson and Flett (1921) Geol S of Sco S Mem 17:1-152

[8] Ineson and Mitchell (1974) Inst Min Metall Trans 83: 13-18

[9] Anderson I.K et al. (1989) J Geol Soc 146:715-720

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Mineral Deposits Studies Group Annual Meeting 2020 Oral Session, 8th January 2020 ORE-FORMING HYDROTHERMAL PROCESSES

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Boiling-induced trace element fractionation and precipitation in submarine

back-arc hydrothermal systems, New Hebrides, SW Pacific

Keith M.1, Haase K. M.1, Schwarz-Schampera U.2, Klemd R.1, Hannington M.3,4, Strauss H.5, McConachy T.6 and Anderson M.7 1GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany ([email protected]) 2Bundesanstalt für Geowissenschaften und Rohstoffe, 30655 Hannover, Germany 3Geomar, Helmholtz Centre for Ocean Research Kiel, 24148 Kiel, Germany 4Department of Earth Sciences, University of Ottawa, Ottawa, ON, K1N 6N6, Canada 5Institut für Geologie und Paläontologie, Universität Münster, 48419 Münster, Germany 6Neptune Minerals Inc., Waverton, NSW 2060, Australia 7University of Toronto, Department of Earth Sciences, Toronto, ON, M5S 3B1, Canada

___________________________________________________________________________ Hydrothermal activity is known from subduction zone systems [1, 2], including many back-arc regions that are associated with young volcanism along extensional structures. Hydrothermal processes in these environments are distinct compared to mid-ocean ridge-related vent fields, and dramatic variations in fluid boiling temperatures associated with changes in water depth are key processes for metal and metalloid fractionation and precipitation in submarine arc/back-arc systems. Here we present data on the mineralogy and chemistry of sulphide chimneys from two recently discovered hydrothermal vent sites in the submarine caldera of Nifonea volcano, Vate back-arc trough, New Hebrides subduction zone. The lack of hydrothermal host rock alteration and only minor amounts of hydrothermal debris suggest a young age of the hydrothermal system (<5 yrs). The focused discharge of hydrothermal fluids with temperatures (up to 368°C) near the seawater boiling curve (at ~1860 m water depth) together with “jets of steam” emitted from the chimney structures provide evidence for fluid boiling. Black smoke and clear fluids emitted at different vent sites indicate that fluid processes, as well as metal and metalloid deposition vary on a small-scale (<0.5 km2) and between the seafloor and sub-seafloor environment. This coincides with changes in sulphide mineralogy and texture between different chimneys, with sulphide dendrites and zoning reflecting temperature gradients, fluid evolution and boiling. Differences in the chemistry of the seafloor sulphides between the main and northern vent site likely reflect compositional variations in their associated hydrothermal fluids. Trace element-As ratios of sulphides from the main vent field correlate with the discharging fluid [3], whereas the ratios of the northern vent site sulphides are distinct and rather resemble brine-dominated fluids similar to those of the Reykjanes geothermal system, Iceland [4]. High concentrations of elements with a magmatic volatile affinity such as As and

Se, together with high Se/S ratios (up to 5650106) [5], may further imply a magmatic volatile influx

to the Nifonea hydrothermal system. In contrast, 34S investigations on sulphide separates likely reflect variable degrees of mixing between hydrothermal fluid and at least 15 % of seawater. Thus, we conclude that the sulphide mineralogy and chemistry at Nifonea is controlled by a three-stage metal and metalloid fractionation and precipitation process: (1) deep (> 1 km) element partitioning between the magma and exsolving aqueous volatiles contributed to the overlying hydrothermal system, (2) subsequent fluid boiling and local brine upwelling in the hydrothermal environment (<1 km), and (3) fluid-seawater mixing (~15 %) near or at the seafloor causing the diverse mineralogy and chemistry of the Nifonea seafloor sulphides. References:

[1] Keith M et al. (2016) Ore Geol Rev 72: 728-745

[2] Keith et al. (2018) Contrib Min Pet 173: 1-16

[3] Schmidt et al. (2017) Geochim Cosmochim Acta 207: 185-209

[4] Hannington et al. (2016) Nat Geosci 9: 299-302

[5] Martin et al. (2019) Ore Geol Rev 106: 205-225

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Mineral Deposits Studies Group Annual Meeting 2020 Oral Session, 8th January 2020 ORE-FORMING HYDROTHERMAL PROCESSES

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Olympic Dam in a Test Tube: hydrothermal experiments on the formation of a

giant IOGC Deposit

Pring A.1

1College of Science and Engineering, Flinders University, South Australia Currently on leave at Magdalene College, University of Cambridge CB3 0AG

___________________________________________________________________________ The giant Olympic Dam deposit in South Australia is the archetypal Iron Oxide Copper Gold (IOCG) deposit. Discovered in 1975 and in production since 1988, it is considered the largest U and the fifth largest Cu deposit in the world. After over 30 years of production the ore reserves have only just been touched. Despite every extensive drilling program and geological and geometallurgical research many aspects of the geology and origins of the deposit remain unclear. The deposit is hosted in a hematite-brecciated granite with the copper mineralogy showing distinct zoning, while the uranium mineralogy is not zoned. The relationship between the brecciation event and the emplacement of copper sulphide mineralogy is unclear.

I will present an overview of our recent hydrothermal experimental work on the formation of the copper and uranium mineralization which highlight the role of the generation of porosity and fluid

flow during mineral formation.

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Mineral Deposits Studies Group Annual Meeting 2020 Oral Session, 8th January 2020 NEW ANALYTICAL METHODS

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A machine learning approach to investigating regional geochemical data sets: An example of PGE geochemistry from the North Atlantic Igneous Province and its shifting geodynamic environment

Lindsay, J. J.1, Hughes, H. S. R.1, Yeomans, C. M.1, Andersen, J. C. Ø.1

1Camborne School of Mines, University of Exeter, Penryn, Cornwall, UK

__________________________________________________________________________________

The Icelandic hotspot, the surface expression of the underlying Icelandic mantle plume, first erupted lava ca. 62 Ma heralding the opening of the North Atlantic Ocean. Greenland and the British Isles began to rift apart while plume-derived volcanism persisted into the newly opened ocean basin. Collectively, the igneous rocks produced from this event are referred to as the North Atlantic Igneous Province (NAIP). Today, intraplate and rift volcanism are active simultaneously on Iceland, and the plume has transitioned through different geodynamic environments. Hughes et al. [1] demonstrated a systematic shift in the relative platinum-group element (PGE) abundances of NAIP lavas from oldest to youngest (e.g. continental to oceanic). This change is suggested to represent the progressive decreasing role of contamination of plume-derived magmas with subcontinental lithospheric mantle material in the melting regime. This indicates that the metal basket of large igneous provinces may change with geodynamic environment and throughout the lifetime of a mantle plume. Given the large multi-element geochemical dataset available for the region, machine learning is employed to explore the controls on shifting concentrations in more detail. Machine learning is a powerful data science tool, able to analyse high-dimensional data, like the inter-element relationships in a full suite of major, minor and trace element concentrations for a large sample set. The key advantage to using machine learning in analysis is ability to cluster samples across multi-dimensional space. While traditional approaches to geochemistry provide invaluable insights into magmatic processes such as melting and fractionation, by considering the entire dataset on an objective basis using machine learning, we can highlight new facets within the broader data structure and update previous geochemical groupings accordingly. For this study, the NAIP dataset is manipulated using Principle Component Analysis (PCA) and t-Distributed Stochastic Neighbour Embedding (t-SNE) to increase separability in the data prior to classification via the k-Means Clustering technique. PCA and t-SNE are, respectively, linear and non-linear transformations that help explore relationships that may not be obvious through standard analysis. The new multi-element classifications will be compared to the original age-based classifications [1], to assess the performance of both approaches. Early results show that by adjusting the included variables, clustering shifts significantly from the original definitions with respect to PGE concentrations, supporting further metallogenic controls beyond the time-progressive model. Ultimately, the study explores the use of machine learning in a geochemical context and, more specifically, aims to contribute to the current understanding of mantle controls on PGE in NAIP lavas. This technique serves as a test-of-purpose for a larger project, looking at the controls on PGE concentrations in global plume magmas, and perhaps beyond this in wider geochemical applications. Successful clustering techniques used in the NAIP dataset can be utilised for larger, more diverse datasets to maximise the information output of a geochemical study in conjunction with more traditional methods. References: [1] Hughes H. S. R et al. (2015) Lithos 233:89-110.

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A Detailed Investigation into the Reconciliation of Hyperspectral Core Data and Platinum-Group Element Grade

Ferguson, J.J.1* Hughes, H.S.R.1, McDonald, I.2, Andersen, J.C.Ø.1, Lloyd, A.4, Stevens, F.4, Acheampong, K.4, Rollinson, G.K.1

1 Camborne School of Mines, CEMPS, University of Exeter, Penryn Campus, Cornwall, UK (*[email protected]) 2 School of Earth and Ocean Sciences, Main Building, Park Place, Cardiff University, Cardiff, UK 3 AngloAmerican South Africa, 44 Main Street, Johannesburg, 2001, South Africa

___________________________________________________________________________ The Northern Limb of the Bushveld Complex represents an exciting frontier for mining development and mineral exploration. The Ni-Cu-platinum-group element (PGE) orebody of the Platreef (and ‘Flatreef’) allow for large-scale, relatively low-cost mining amenable to mechanization. Alongside bulk-geochemical data and ‘traditional’ core logging, hyperspectral imaging has been identified as a potentially powerful exploration tool in the hydrothermally overprinted rocks of the Platreef. Hyperspectral imaging of Anglo American’s modern and legacy drill core aims to introduce a new approach that increases productivity of existing projects in the region and identify new targets. This study investigates the fine-scale variability of high-grade interval (12.26 g/t 3PGE+Au) of Platreef that appears relatively unaltered. We use a 1m core length (i.e., typical assay interval) to pilot an integrated approach of detailed analytical techniques and traditional petrographic study at a very fine resolution (i.e., 5-10cm intervals). Replacement of pyroxenes and BMS is ubiquitous throughout the core, even when not initially visible in hand specimen. The relative abundance and pervasiveness of micas, amphiboles, serpentinite, and clays vary significantly throughout the metre section. Whilst hyperspectral imaging is limited by the pixel size and resolution of scans, it shows promise in identifying complex mineral assemblages in these mafic-ultramafic lithologies. An investigation into the PGE grade by detailed documentation of platinum-group minerals (PGM) using SEM-EDS and QEMSCAN® has shown over the 1m intersection a plethora of PGM species aligned with previous studies (e.g. [1]). However, very fine scale changes in PGM are seen throughout the 1m interval through different mineral associations and changes in PGM size – these appear to be linked to (i) the grain-size of the host lithology and this is negatively correlated with (ii) the degree of alteration of that host. An LA-ICP-MS study into the trace element concentration of the base metal sulphides (BMS) shows a linear relationship between BMS abundance and grade. Time-resolved analysis (TRA) and trace element concentrations have identified PGE-rich pyrites (up to 600 ppm total PGE) as well as more commonly reported PGM within the BMS. Our petrographic investigations compliment previous studies [2] which show that the replacement of primary sulphide assemblages by late stage relatively low-temperature fluids can mobilise and cannibalise PGE from primary BMS hosts. These changes ultimately incur geometallurgical complexities, however evidence shows of a potentially quantifiable link between silicate alteration assemblages and thus there may be scope to use alteration mapping as a proxy for geometallurgy. The size of silicate minerals identified in the hyperspectral longwave infrared (LWIR) correlate with grain size throughout the metre section by the identification of interstitial plagioclase in pyroxenite. Using this as a proxy, relationships can be found within the metre section that have metallurgical implications for the extent and quantity of alteration products, quantity of deleterious elements that negatively affect processing, PGE grade in solid solution in BMS, PGM species and size. In order to effectively perform an accurate resource estimation and geometallurgical characterisation, the deposit needs effective domaining. Representativity remains a key issue in this orebody as the variability depicted within a metre section exceeds initial expectations. [1] Hutchinson D, Kinnaird J A (2005) App Earth Sci, 114:208-224 [2] Hollwell D A, Adeyimi Z, Ward L, Smith D J, Graham S D, McDonald I, Smith J W (2017) Ore Geo

Rev, 91:718-740

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Geochemical and hyperspectral halos to high-grade Ag-Zn-(Au) mineralization in the Eastern Goldfields, Western Australia Hollis, S.P.1, Foury S.2, Caruso S.3, Barrote V.4 and Pumphrey A.5 1iCRAG & School of Earth Sciences, University College Dublin, Ireland; [email protected] 2Institut Polytechnique UniLaSalle, France 3Centre for Exploration Targeting, University of Western Australia, Perth, Australia 4Curtin University, Perth, Western Australia, Australia 5MacPhersons Resources, Kalgoorlie, Western Australia, Australia

___________________________________________________________________________ With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle geochemical halos surrounding orebodies at minimal expense. The high-grade Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity and tectonic setting, it is interpreted to represent a shallow-water and low temperature VHMS deposit with ‘epithermal characteristics’ (i.e. a hybrid bimodal felsic VHMS deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic base metals that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb±Pb±As±(Cu) bearing sulfosalts, minor pyrrhotite, arsenopyrite and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite and bournonite. Zones of sulfide mineralization are marked by significant enrichments in Fe, Zn, Pb, Ag, Au, As, Sb, Cu, Cd, Ni, Co, Sn, Bi and Tl (in order of decreasing abundance) reflecting the diverse mineral suite present. Basaltic rocks show reduced mass gains in most elements, with zones of intense hydrothermal alteration restricted to thick sequences of hyaloclastite and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, marked by high Alteration Index and CCPI values, strong Na-Ca depletion, an absence of feldspar (albite) in thermal infrared (TIR) hyperspectral data, and increases in quartz and white mica contents. White mica compositions range from muscovite in distal positions, with increasingly paragonitic compositions associated with zones of high-grade polymetallic sulfide mineralization. Mg-chlorite in dacite often occurs adjacent to zones of polymetallic sulfide mineralization and is restricted to narrow intervals. Both chlorite and carbonate are abundant in mafic rocks. Shifts to more Mg-rich chlorite and Mg-rich carbonate in basaltic rocks occur in hyaloclastite and near felsic contacts.

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In-situ non-destructive Micro-XRF analysis: Implications for ore mineralogy, petrogenesis and micro-metallurgy assessment Menzies, A.H.1; Tagle, R.1; Butcher, A.R.2; Dehaine, Q.2; Cook, N.3; Sayab, M.2; Sorjonen-Ward, P.2; and Molnar, F.2 1Bruker Nano GmbH, Berlin; Germany, email: [email protected] 2Geological Survey of Finland/Geologian tutkimuskeskus, Espoo, Finland 3Mawson Oy, Rovaniemi, Finland

___________________________________________________________________________ The microanalysis of samples is common practice and provides valuable information on a variety of levels. This is particularly true for mineral exploration and process mineralogy. The exploration process and metallurgical understanding occurs on scales that vary by numerous orders of magnitude. An important link in this chain is the transition from samples collected in the field to analysis in the laboratory. The Micro-XRF is an analytical tool that preserves these relationships allowing micro-analytical interpretations to be easily related to field samples (i.e. visually) as well as enabling the ability to select the appropriate samples for more detailed microanalysis, which is often costlier and time consuming. Here we report on a detailed characterisation of cobalt-rich samples from the Rompas - Rajapalot Au-Co project (Mawson Oy) using a geometallurgical approach that employs geoanalytical techniques to achieve multi-scale, multi-modal, and multi-dimensional information (involving the integration of 2D, 3D and 4D imaging and analysis of rock samples). The focus of this study is on the analysis of drill core sections and their interpretation, from both an up-scaling and down-scaling viewpoint using Micro-XRF as a key component of the overall workflow. This includes characterization of: • Cobalt mineralogy and distribution of cobalt and associated metals/elements,

• Key mineralogical/geometallurgical ore properties,

• Mineral associations

• Microstructural relationships

The end result is a new perspective on the commercial process mineralogy at Rompas - Rajapalot,

incorporating details about liberation of both ore and gangue minerals.

Figure 1. Centimetre-scale elemental mapping of cobalt mineralisation in drill hole PAL0163 by micro-XRF

(directly onto a cut surface of a drill core), to reveal the spatial distribution of mineral species and their

relationship to the micro-structural fabric.

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Exploration needs innovation - examples from Canada Thompson, A.J.B. 1, Killeen, J. 2 and Das, S. 2 1PetraScience Consultants Inc., 3995 24th Avenue West, Vancouver, BC V6S 1M1 Canada 2Prospectors & Developers Association of Canada (PDAC), 800-170 University Ave Toronto, ON M5H 3B3

Canada

___________________________________________________________________________ The increased demand for the metals needed by society in the future is creating challenges for discovery. Exploration programs are adapting to new commodities and to a more difficult environment for operating. A variety of innovative approaches are being implemented to aid in the search for resources. Innovation allows for more efficient targeting as well as delivering environmentally low impact programs. In combination these new approaches are an important part of developing resources responsibly. Innovation is inherent in exploration which is driven by the need to find new deposits at depth or in under explored regions. Historically, introduction of new geochemical or geophysical techniques have typically been at the forefront of new practices. Development of better geologic models and step changes in our understanding of processes are harder to measure, but clearly also influenced discovery rates in recent decades. More recently the type and quantity of data available has exploded. Our ability to image rocks, downhole, in core boxes or from above with drones has created a wealth of new data. Tied to imaging are vast amounts of additional data that can be collected in real time including geochemical, geophysical and geotechnical information. Analysis at the drill and on-site core scanning are routine in many projects. Concurrent with introduction of rapid data collection are the significant changes in computing and digital access on a global scale that facilitates analysis. Tasks which were daunting only a few years ago are now executed with ease. As a consequence, groups are tackling machine-learning and artificial intelligence for a range of problem solving and tasks. Examples from Canada provide insight into the variety of innovations being implemented currently in mineral exploration. Greenfields exploration examples include water efficient closed-loop diamond drilling, collection of IP/resistivity data for three-dimensional modelling and an intriguing use of genomics and biogeochemistry. In mine and district exploration, down hole data collection includes new techniques for collecting borehole electromagnetic data as well as comprehensive approaches to geology and mineralogy. Meanwhile, several groups are applying machine learning to a variety of tasks and are being successful in outlining targets in Finland, the Yukon and Chile. The examples from Canada demonstrate that innovation typically results from sustained and intentional efforts, with small consulting groups, service companies and academic teams dominating. Larger organizations within the mining industry can struggle to maintain the organizational culture and structure that allows innovation to flourish. Funding is a critical component; both high profile contests with interest from venture capitalists and government grants play important roles in supporting successful outcomes. Exploration for green metals and the commodities of the future will benefit from the significant changes occurring through new data collection and analysis as well as more efficient and lower impact programs. Communicating to local communities, and the public in general, about how we search for metals in the modern world is also an important aspect of delivering the discoveries of the future.

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POSTER

SESSION

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session CRITICAL METALS

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Looking for hi-tech metals in Angola: the Nejoio alkaline complex

Borst A.M., Finch A.A.1, Siegfried P.R.2, Bambi A.3, Tchimbali G.1, Dos Santos A.1, Lopes E.3,

Eugenio A.3, Jeremias E.3 and Azevedo S.3

1School of Earth and Environmental Sciences, University of St Andrews, North Street, KY16 9AL, Scotland *[email protected] 2GeoAfrica Prospecting Services, P.O. Box 24218, Windhoek, Namibia 3Departamento de Geologia, Universidade Agostinho Neto, Avenida 4 de Fevereiro 71, Luanda, Angola

____________________________________________________________________

Angola is home to some 35 carbonatite and alkaline silicate complexes [1], many of which are part of the same tectono-magmatic events that formed economically relevant deposits of hi-tech metals such as rare earth elements (REE) and niobium, in Namibia and Brazil. Past work in Angola has focussed mostly on the carbonatites, which include Tchivira, Bonga, Bailundo, Virulundo and Longonjo (currently explored by Pensana Metals), hosting enrichments in fluorite, Nb and light REE. In contrast, limited data is available on the alkaline silicate complexes. Here we present new findings of a recent field expedition to the Nejoio alkaline complex, Namibe Province, southern Angola.

Nejoio is an oval-shaped syenitic intrusion (104 ± 0.8 Ma [4]) measuring 2 by 1.5 km and emplaced within a Paleoproterozoic basement. It lies approximately 25 km to the SE of the much larger, 40 by 17 km Lutala syenite complex, which forms a 1.5 km high mountain range known as Serra de Neve. Nejoio and Lutala are both reported to host agpaitic mineral assemblages such as eudialyte, wöhlerite and låvenite [1,2,3]. Nejoio’s topographic expression forms two horse-shoe shaped ridges that are truncated towards the west. The outer ridge is dominantly in mildly fenitised granites and gneisses. The intrusive units are split into a central zone and an outer ring, both made up of feldspathoidal syenites [3]. The central zone comprises laminated nepheline-sodalite syenites, in some places showing spectacular circular igneous layering with stark contrasts in feldspar lamination and complex magma mingling textures between mafic and felsic members. These features indicate turbulent magma chamber conditions and possibly repeated injection of magmas. Mingling textures and brecciation are seen to intensify towards the outer margins of the central zone. The external zone comprises cancrinite-sodalite-nepheline syenites, where cancrinite forms yellow-green transparent crystals. All units contain photochromic blue sodalite (hackmanite), some of which luminesce orange under UV and have hexagonal prismatic forms enclosed in larger feldspars, suggesting they are secondary after nepheline. Na-pyroxene (aegirine) is the dominant mafic phase, while Na-amphibole (arfvedsonite) is dominant in some minor units within the central zone [2]. Pyrite and fluorite are abundant in all rocks, including in late-stage veins. Further petrographic work will identify which Zr-Ti-Nb bearing assemblages are present, and establish whether the units are dominantly agpaitic (containing complex Na-HFSE minerals such as eudialyte and wöhlerite), miaskitic (containing zircon, titanite and Fe-Ti oxides) or transitional. XRD confirms the presence of orange titanite in the inner ring sodalite syenites, hinting at a miaskitic or transitional character. The overall abundance of cancrinite, sodalite, fluorite and pyrite furthermore suggests the system was enriched in CO2, H2O, Cl, F and S, respectively. Although this may be conducive to metal enrichment, relatively oxidized conditions may have hindered evolution towards a dominantly agpaitic mineral assemblage and enrichment style.

References: [1] Woolley, A. (2001). GeolSoc, NHM London, 1-372 [2] Rodrigues, B. (1872) Revista da Faculdade de Ciências. Universidade de Lisboa, 17. 89-108 [3] Rodrigues, B. (1978). Bol Museo e Lab Min e Geol, Faculdade de Ciências, Universidade de Lisboa, 15 : 1-174 [4] Allsopp, H. & Hargraves, R. (1985). Trans Geol Soc South Africa 88, 295-29

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Fertility of post-collisional settings for rare earth element mineralisation. Deady, E.1, Goodenough K.M.1 and Beard C.1 1British Geological Survey, The Lyell Centre, Edinburgh, EH14 4AP [email protected]

__________________________________________________________________________

The rare earth elements (REE) and other critical elements, such as Nb, play a key role in the move towards a net-zero carbon world as they are required for manufacture of green technology such as electric vehicles and wind turbines. Typically the REE and Nb are extracted from carbonatite, with China and Brazil respectively dominating current production [1]. Mineralised carbonatites are known from failed continental rift and small-scale extensional regimes, and also from emplacement into convergent continental settings within c. 75 Ma of peak collisional activity, here called post-collisional [2]. Many major REE resources were formed in post collisional tectonic settings (Mianning-Dechang REE belt [3], China, and Mountain Pass, USA [4]). However, the geology of post-collisional carbonatites has been widely overlooked in the modern academic literature. This poster will illustrate the mineralogy and petrology of a series of REE-mineralised but uneconomic occurrences that are interpreted to represent a variety of depths of <5km within a post-collisional magmatic system. Observations from the F-Ba-bastnäsite deposit at Kizilcaören, Turkey represent the shallowest part of the system. Here the mineralisation is represented by lobes and sheets of fluorite-bastnäsite-barite rock hosted in folded metasedimentary rocks. This suggests a separation of a fluorite phase from the carbonatite [5]. Similar features are recorded in the Mianning-Dechange REE belt. At Mushghai Khudag, Mongolia [6], peralkaline silicate dykes and carbonatite intrusions are also associated with fluorite rich zones. Together these localities can be used to understand the shallower levels of the system. At Cnoc nan Cuilean, Scotland [7], deeper levels of the system are exposed. Here, a complex igneous history includes the formation of moderately REE-enriched syenitic lithologies and later carbo-hydrothermal alteration that has led to the enrichment of REE into veins [8]. If the upper parts of the system record immiscible carbonate, fluorite, and alkaline silicate phases, these deeper intrusions may provide evidence for that immiscibility within the magma chamber. Features from these examples are combined to build a genetic model for post-collisional carbonatite systems, demonstrating some of the key processes that can facilitate REE mineralisation. These are 1. Mantle metasomatism, the introduction of metals and elements through initial subduction and arc magmatism is important for the metal budget of the SCLM in post-collisional settings. 2. Melting of the SCLM produces enriched magmas that evolve in a series of magma chambers, eventually leading immiscibility of carbonate- and fluorite-rich phases. These factors are key to our understanding of critical metal enrichment and the expected structure of a post-collisional carbonatite complex. These features can be combined to understand and hence demonstrate the importance of these setting in exploration for REE deposits.

References:

[1] Brown et al. (2019) World Mineral Production 2013-2017

[2] Beard, C. et al. (2020) MDSG 2020, London

[3] Xie et al. (2015) OGR 70: 595-612

[4] Castor, S. B. (2008) The Can Min 46(4): 779-806

[5] Öztürk et al. (2019) OGR 105: 423-444

[6] Kynicky et al. (2019) Geosci Fron 10: 527-537

[7] Walters et al. (2013) Cont Min and Pet 166: 1177-1202

[8] Hughes et al. (2013) Geol Mag 150(5): 783-800

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Lithium in late-orogenic and intraplate granites and pegmatites of Eurasia Dolgopolova A.1, Seltmann R.1, and Baisalova, A.2 1Natural History Museum, Earth Sciences Dept., CERCAMS, London, U.K.; [email protected] 2Satbayev University Almaty, Kazakhstan

___________________________________________________________________________ Lithium enrichments are well known from Palaeozoic and Mesozoic rare metal granites and pegmatites across Transeurasian orogenic belts. In this pilot study we set the framework for a compilation of the current knowledge, classify the Li-bearing granite-related mineral systems of Eurasia in their geotectonic setting, geodynamic-metallogenic framework, spatial and temporal distribution, and re-assess the data inventory using modern geochemical, mineralogical, petrological, geochronological, and isotope geochemical data. The study aims to aid a modern understanding of lithium cycles during construction and destruction of the continental crust, leading to either Li enrichments in granites and pegmatites, or lithium enrichment in sediments and mineral waters. Lithium among other rare metals (F, Rb, Cs, Be, Zr, Hf, Nb, Ta, Sn, Mo, W) is found genetically and spatially related to magmatic activities of accretionary (collisional) and late- to post-collisional formations that are especially widespread in the Variscan orogenic belt and in the Central Asian Orogenic Belt (CAOB). In the Variscan (Hercynian) belt of Europe, extending from the Iberian Peninsula over Pyrenees, French Massif Central, Cornwall and Ireland to Erzgebirge / Krusne hory, geochemically diverse late- and post-collisional Li-enriched granites formed by anatectic melting of Palaeozoic sedimentary successions and associated mafic to felsic volcanic rocks [1,2]. The compositional diversity of the least evolved of these granites is largely inherited from the protoliths [1]. The rare metal granites and ongonites (topaz rhyolites, Li-F granites) of the CAOB were dominantly formed during late Palaeozoic, and early, mid to late Mesozoic epochs of intraplate magmatism (often referred to plume processes forming Large Igneous Provinces, LIPS) [3,4]. Lithium occurs, jointly with other rare metals (Nb, Ta, Rb, Cs, Be, Sn), most often in Li-Cs-Ta pegmatites (LCT group), derived from granitoids of different compositions. Metal enrichments in the parent magma may be within average values for the upper continental crust or elevated due to fractionation processes. Li-bearing pegmatites often form relatively independent swarms of veins or dikes which may be tens of millions of years younger than the enclosing granites. Evolution of granitic magmas and origin of ore-forming fluids leading to rare-metal mineralization may be driven by different mechanisms, including thermal effects and material supply from crust – mantle interaction, deep crustal or mantle plume sources, as in the case of Li-Cs-Ta pegmatites and coexisting Li-F granites in Central Asia [3]. The compositions and ages of coexisting rare-metal pegmatites and granites have important petrogenetic implications for the formation mechanisms of mineralization. References:

[1] Romer RL et al. (2014). Geochimica et Cosmochimica Acta 131: 98-114.

[2] Gourcerol B et al. (2019). Ore Geology Reviews 109: 494-519.

[3] Ernst R. et al. (2015) Large Igneous Provinces. Cambridge Univ Press, 666pp.

[4] Kremenetsky et al. (2000) Ore-bearing granites of Russia. IMGRE Moscow, Russia, 372pp.

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Mineral paragenesis of 5-element vein deposits in the Cobalt Embayment, Ontario Lindsay, D.H.M1,2*, Kocher, S.2, Herrington, R.J.1,2, Doyle, P.3 1Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK *Corresponding author: [email protected] 2Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK 3Battery Mineral Resources Ltd., Suite 5600, 100 King Street West, Toronto, M5X 1C9, ON, Canada

___________________________________________________________________________ The five-element vein (Ag-Co-Ni-Bi-As) deposits of Cobalt, Ontario are among the most famous

examples of this type of mineralisation in the world and have produced over 500 million ounces of

silver to date with nickel and cobalt recovered as a by-product. With increasing demand for cobalt as

a component of high-performance Li batteries, these deposits have become the focus of new

exploration. Despite numerous studies of these deposits and other global examples, models for ore

genesis remain poorly understood, limiting exploration success and accuracy of resource models.

By combining a detailed petrographic and mineral chemistry study of Co-Ni-Fe arsenides and

sulpharsenides with fluid inclusion microthermometry data and field observations we try to build a

refined genetic model for the Silverfields, Kilpatrick and McAra vein systems in the Cobalt

Embayment

Optical and electron microscopy observations reveal significant local variation in ore mineralogy and

chemical composition, notably in sulphur, iron and native metal enrichment. This may reflect the

partial control of different host rock environments on local ore-fluid composition. Zoning textures in

arborescent growths of Co-Ni mono/di-arsenides and sulpharsenides evidence fluctuations in sulphur

and arsenic fugacity in the mineralising fluid. This is in agreement with genetic models based on

mixing of fluids of different redox states. Fluid inclusion microthermometry will be undertaken on

quartz- and carbonate-hosted inclusions to further characterise the fluids associated with the vein

systems and better constrain the conditions for ore deposition.

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From magma reservoir to regolith: controls on the distribution of ion adsorption rare earth element ores

Marquis, E.1, Estrade, G.2, Villanova-de-Benavent, C.3, Goodenough, K.4 and Smith, M.3 1School of Geography, Geology and the Environment, University of Leicester, United Kingdom, [email protected] 2 Géosciences Environnement Toulouse, Université Toulouse 3 Paul Sabatier, France 3School of Environment and Technology, University of Brighton, United Kingdom 4British Geological Survey, the Lyell Centre, Research Avenue South, Edinburgh, United Kingdom

___________________________________________________________________________ High field strength magnets and rechargeable batteries, which are extensively used in low carbon technologies, require a secure and sustainable supply of the rare earth elements (REE), particularly Nd, Dy and Pr [1]. Ion adsorption deposits are the main source of heavy REE (REE: Gd-Lu), which include Dy, to global markets [2]. Although low grade, these regolith-hosted REE deposits host over 50% of their REE in an ion exchangeable form [3], and so the REE can be liberated using in-situ or heap leaching techniques with weak electrolyte solutions [4]. The Ambohimirahavavy Alkaline Complex (AAC), part of the Cenozoic Ampasindava Alkaline Province (northern Madagascar), is an alkaline to peralkaline igneous complex that has undergone extensive tropical weathering leading to the development of thick regolith profiles hosting ion adsorption ores [5]. The southern portion of the AAC is comprised of a caldera complex, eroded to expose a sub-volcanic nepheline and alkali feldspar syenite ring dyke and marginal concentric dyke swarm of peralkaline granite and microsyenite, which are variably REE-enriched. These units intrude limestone, marl and sandstone of the Jurassic Isalo Group [5]. Estrade [6] proposed that the quantity of ion exchangeable REE in the regolith is principally controlled by the nature of the protolith, thus the evolution of the various intrusive units is key to developing a model for ion adsorption ore formation. Whole rock geochemical data show that the ring dyke syenites and marginal dyke swarm rocks have a similar or common parental magma. Progressive decreases in whole rock K/Rb indicate that differentiation progressed as follows: (least) alkali feldspar syenite to nepheline syenite to microsyenite dykes to peralkaline granitic dykes (most). However, the exponential enrichment in REE in the peralkaline granitic dykes (up to 14,800 ppm REE) relative to other intrusive rocks (100 to 800 ppm REE) cannot be accounted for by simple fractional crystallisation alone. Based on LA-ICP-MS trace element analyses of amphibole and pyroxene, coupled with petrographic observations, we propose that the residual melts that differentiated from the syenite crystal mushes were volatile-rich and sequestered REE. Quartz from the peralkaline granitic dykes yields δ¹⁸O of +9.9 to +10.4‰, indicative of minimal crustal assimilation during parental melt evolution. Therefore, we suggest that silica-saturation was triggered by accumulation of these volatile-rich melts in the upper portions of the magma reservoir underlying the AAC caldera, which resulted in (re-)melting of previously crystallised cumulates and/or minor assimilation of crustal material. Extraction of these silica-saturated melts during doming, associated with magma reservoir inflation, would account for the concentric outcrop expression of the marginal dyke swarm. Thus, the most REE-enriched protoliths are concentrated on the outer flanks of the AAC’s southern caldera, which correspond with higher-grade ion adsorption ores in the regolith [6].

References:

[1] Goodenough et al. (2016) Nat Resour Res 27:201-216

[2] European Commission (2017) Study on the review of the list of critical raw materials. European Commission,

Brussels.

[3] Sanematsu and Watanabe (2016) Rev Econ Geol 18:55-79

[4] Moldoveanu and Papangelakis (2012) Hydrometallurgy 117:71-78

[5] Papini and Benvenuti (2008) J Afr Earth Sci 51:21-38

[6] Estrade et al. (2019) Ore Geol Rev 122:103027

This work was funded by NERC grant NE/M011429/1 “SoS Rare”

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REE adsorption experiments onto kaolinite with different ligands: Implications on ion-adsorption REE deposits formation

Villanova-de-Benavent C.1 and Smith M.1

1School of Environment and Technology, University of Brighton, Cockroft Building, Lewes Road, BN7 1GJ Brighton, United Kingdom.

___________________________________________________________________________ Ion adsorption rare earth element (REE, La-Lu, Y) ores are the main source of heavy REE (HREE, Tb-Lu) and Y in the world [1]. In an increasing demand on REE worldwide, especially towards the HREE, these deposits have gained interest because of the easy extraction of the ore, and the low radioactivity, which are usually characteristic of other REE deposits [1, 2]. These deposits form after weathering of granitic bedrocks that contain magmatic and/or hydrothermal REE-bearing minerals (e.g., phosphates, silicates and fluorocarbonates [1]). These minerals are altered and/or dissolved by acidic soil water (pH~4-6), releasing REE that can be incorporated into the solution as REE3+ ions, organic or inorganic aqueous complexes [1]. The concentration of REE in the aqueous solution is controlled by the presence of anionic and/or complexing ligands, the redox conditions, the dissolution of primary and secondary REE-minerals, and the REE scavenging by minerals [3]. Further down, if the solution pH increases (~4.5-6.5), REE can be adsorbed onto clays [1]. These clays (mostly kaolinite and halloysite) are the main REE ores in ion adsorption deposits [1; and references therein]. Clay minerals are important adsorption agents because they occur in small grain sizes, and they have high specific surface areas [4]. The aim of this study is to determine the influence of the solution composition on the REE adsorption onto kaolinite, and hence to shed light into the formation of ion adsorption REE deposits. The experiments involved introducing kaolinite powder (provided by Imerys®, with 2 µm average particle size, LOI 11.16 wt.%, and ζ-potential of -36.6 mV) into REE-containing solutions, following a solid/solution ratio of 2.5 g/L [3], which was kept in suspension with a shaker. The solutions consisted of: i) deionised water; and low and high ionic strength solutions (0.025 and 0.5 M, respectively) containing ii) NaCl, iii) Na2SO4 and iv) NaHCO3 (using reagent grade electrolytes). The solutions were prepared at different pH: a) ~2 (NaCl); b) ~4 (water, NaCl, Na2SO4); and c) 6-8 (water, NaCl, NaHCO3); buffered using 0.5 M NaOH. The solutions contained 100 ppb REE (La-Lu + Y) + Sc + Th (multi-element calibration standard 8500-6944 from Agilent technologies®; 10 μg/L Ce, Dy, Er, Eu, Gd, Ho, la, Lu, Nd, Pr, Sc, Sm, Tb, Th, Tm, Y, Yb; 5% HNO3 matrix). The experiment included a set of REE-free blanks with the same saline solution, 5% HNO3 and similar pH; and a kaolinite-free blank. The experiments ran for one day, with sampling after 2, 6 and 24 hours. The samples were centrifuged, and the supernatant was diluted with 4% HNO3 for ICP-MS analysis (inductively couple plasma mass spectrometry). The results indicated that the adsorption reaction is quick (already stated by [3]), detected after a few hours, and that it is more favourable in 0.025M solutions, whereas 0.5M solutions may induce desorption (as discussed by [5]). The optimum adsorption was observed in the solution consisting of water at pH4, and the least adsorption was in NaHCO3 solution at pH6-8 (both 0.025 and 0.5M). According to the sorption coefficient (calculated with the formula proposed by [3]), a slight fractionation of HREE towards the solid phase was detected in the solutions containing NaCl, Na2SO4 and NaHCO3, especially at 0.5M. In conclusion, after examining all the results obtained, the most influencing factor is the ionic strength, followed by the type of ligand and pH. Hence, in the weathering profile, adsorption onto kaolinite is more likely if the REE aqueous solutions are highly diluted and have a pH closer to 4, and REE would remain in solution at high concentrations of NaCl or Na2SO4, or with the presence of NaHCO3. References:

[1] Sanematsu K and Watanabe Y (2016) Econ Geol 18:55-79

[2] Goodenough KM et al. (2017) Nat Res Research DOI: 10.1007/s11053-017-9336-5

[3] Coppin F et al. (2002) Chem Geol 182:57-68

[4] Awwiller DN and Mack LE (1991) Tex Gulf Stream Geol 19:311-314.

[5] Moldoveanu GA and Papangelakis VG (2012) Hydrometallurgy 117-118:71-78

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HiTech AlkCarb - New Geomodels for rare earths and other economic deposits in carbonatites and alkaline rocks Wall, F.1, Smith, K.,1 and colleagues from HiTech AlkCarb. 1 Camborne School of Mines, University of Exeter, Penryn Campus, Cornwall, TR10 9FE, [email protected]

___________________________________________________________________________

The HiTech AlkCarb project has been developing new geomodels and sustainable exploration methods for alkaline igneous rocks and carbonatites. It has four main objectives.

Develop new geomodels to explore for 'hi-tech' raw materials (such as the rare earth elements, scandium, niobium, tantalum, zirconium, hafnium and fluorspar) associated with alkaline rocks and carbonatites.

Improve and develop interpretation of geophysical and downhole data in order to understand alkaline rock and carbonatite systems down to depths of approximately one kilometre.

Build exploration expertise in hi-tech raw materials, and to ensure knowledge exchange between Europe and Africa.

Assess environmental and socio-economic impacts of mining for these raw materials, and develop best practice.

The team includes five universities (Tuebingen, St Andrews, G d’Annunzio, Mendel, Exeter), four SMEs (terratec Geophysical Services, Lancaster, GeoAfrica, ASEC), the Natural History Museum, London, the British Geological Survey and Geological Survey of Denmark and Greenland.

The outputs are deliverables to the European Union; most of them are being made available publically and also published as peer reviewed papers. Outputs are listed on the project website: www.carbonatites.eu and include:

1. A database of alkaline rock and carbonatites. This website provides an interactive, digitised version of the Alkaline Rocks and Carbonatites of the World volumes, by Alan Woolley. Information can be accessed by using a map feature, search or occurrence information.

2. A series of publications investigating key geological questions that help define geomodels and exploration indicators. These include a review of the fenite metasomatic aureoles around carbonatites, sulphur isotope evidence for crustal recycling in alkaline rocks, a model for Italian carbonatites and pyrochlore as a monitor for magmatic and hydrothermal processes.

3. A mineral systems approach to exploration models, using a risk assessment approach used previously in the oil industry.

4. A new geomodel for the Kaiserstuhl natural laboratory, Germany, combining geophysics and geology.

5. Two new conceptual models for alkaline complexes and carbonatites, in 3D PDFs including information on process mineralogy, environment and social factors

Acknowledgement:

This project has received funding from the European Union's Horizon 2020 research and innovation programme (grant agreement no. 689909).

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Genesis of Cobalt-bearing Mineralisation in the English Lake District Eskdale, A.E.1 and Solferino, G.F.D.1 1Department of Earth Sciences, Royal Holloway University of London, [email protected]

___________________________________________________________________________ Energy Critical Elements (ECE) such as Bi, Ga, Ge, In, REE, Sb, Te, Se and Co are all essential to the development and advancement of our society, from lithium batteries to ceramics and renewable technologies [1]. With the supply of these materials monopolised by the USA, Russia and China (Soleille et al, 2018), and heavy UK reliance on importation of ECE, it has never been more important a time to establish new prospects for ECE. The English Lake District is a particularly useful locality to study ECE mineralisation for two reasons. First, the ease of access for fieldwork with extensive literature covering the geological history. Second, the presence of vein-type mineralisation of ECE-bearing assemblages hosted in a variety of different lithologies within proximity to a regional intrusive body. This combination forms the perfect ground to investigate how these ECE ores formed and how the interaction of different host rock influences the process. Key literature from Ixer [3] and Stanley [4] from the 1980’s highlight Co-As-Bi bearing minerals at the localities of Scar Crags and Dale Head North (DHN) within the Lake District. Recent investigation into these two areas confirmed the presence of As and Co minerals at both areas, with DHN also hosting LREE-bearing minerals (allanite, carbo-fluoride) and Y-HREE bearing phosphate [5]. It was determined that ECE mineralisation at Scar Crag was derived from a single, S-bearing fluid whilst DHN mineralisation was precipitated from a mixture of magmatic and re-circulating, formation fluids in two stages. This difference was most likely controlled by the permeability of the local host rocks to each area [5]. At DHN, presence of chlorite-only micro-veins and veins with chlorite growing inward from the walls surrounding late sulphides (chalcopyrite – arsenopyrite -pyrrhotite) as the centre-line confirms the two stages of fluid pulses. A third locality has been chosen for further investigation into ECE-bearing assemblages across the Lake District. Ulpha is the new locality with three key areas of interest (Holehouse Gill, Long Garth and the Ulpha Mine) selected for detailed mapping, collection of structural data and to sample both mineralisation and host rock. Literature indicates the area used to be historically mined for Cu with surveys from the British Geological Survey (BGS) also highlighting prospect for Bi and Co-bearing minerals (erythrite) associated to various Cu-As sulphides [4, 6]. Samples from the fieldwork campaign will be analysed to identify ECE-bearing assemblages, asses their abundance and the varying mineral phases. A detailed fluid inclusion analysis to assess the type and abundance of ECE minerals. Following this we will develop a regional model for the emplacement and source of ECE mineralisation across the varying environments.

References:

[1] Atwater H and Fromer N (2011) Resnick Institute Report:1-40

[2] Soleille S et al. (2017) European Commission Report: 5-92

[3] Ixer R et al. (1979) Mineral Magazine 43: 389-395

[4] Stanley C and Vaughan D (1982) J Geol Soc 139: 569-579

[5] Westwood N (2018) Unpublished MRes Thesis: 3-168

[6] Cameron D et al. (1993) British Geological Survey Exploration Report: 14-16

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session GOLD DEPOSITS

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Sulphur and lead isotope systematics of the Cononish Au-Ag-Te deposit, Scotland Lyell, C.M.1, Boyce, A.J.1, Mark, D.F.1, Pashley, V.2, McCarthy, W.3, Cloutier, J.4, Sangster, C.J.5 1Scottish Universities Environmental Research Centre [email protected] 2British Geological Survey 3University of St Andrews 4CODES, University of Tasmania 5Scotgold Resources Limited

______________________________________________________________________ The genesis of ‘orogenic’, vein-hosted gold mineralisation in metamorphic belts is controversial. The Cononish Au-Ag-Te deposit is no exception. Situated in the mining district of Tyndrum, it has become Scotland’s first ever commercial gold mine with a current resource of 266koz Au and 1096koz Ag. Ore consists of a series of hydrothermal quartz ± carbonate veins that occupy an anastomosing, transtensional fault zone striking NE-SW - sub-parallel to the nearby Tyndrum Fault [1]. Mineralisation crosscuts deformed (D1-D4) stratigraphy of the Dalradian Supergroup; metamorphosed to epidote-amphibolite facies ~470Ma [2]. Whilst Cononish displays broad commonalities with the orogenic group of ore deposit [3], K-feldspar alteration in an auriferous breccia yield Ar/Ar ages of 408 ± 2Ma and 407 ± 1Ma [4]. This links mineralisation to the main episode of shear-modulated, post Caledonian magmatism in the Grampian belt [5]. It has been suggested that orogenic gold systems derive their metals from redox reactions and subsequent remobilization of locally enriched, mineralised horizons [6]. New sulphur and lead isotope analyses were conducted on a suite of early auriferous and later, non-auriferous vein sulphides in order to resolve the source(s) of S and Pb, and by inference the source(s) of gold, to the Cononish system. S-isotope analyses of sulphides display a broad range of δ34S from -3.8 to 11‰. Previous models [7] strongly imply mixed magmatic and metasedimentary sulphur sources, however, the full range of δ34S observed at Cononish could theoretically be derived solely from underlying, mineralised SEDEX horizons. A comparison of lead isotopes from Cononish sulphides with SEDEX, Dalradian and magmatic endmembers [8,9] supports this hypothesis and suggests that mixing between SEDEX and Dalradian strata was the main source of lead to both auriferous and non-auriferous sulphides. These data imply that, given the homogeneity of Pb-sources, these strata were not a major gold source. Thus, via the law of parsimony, we suggest post Caledonian magmatism was the most plausible genetic contributor to economic gold enrichment at Cononish. References:

[1] Treagus J E et al. (1999) Journal Geol Soc London 156:591-604

[2] Stephenson D et al. (2013) Proc Geol As 124:3-82

[3] Goldfarb R J et al. (2005) Econ Geol 100th Anniv 407-450

[4] Rice C M et al. (2013) MDSG proceedings

[5] Miles A J et al. (2016) Gondwana Research 39:250-260

[6] Groves G J and Vearncombe J R (1990) Geologishe Rundschau 79:345-353

[7] Hill N J et al. (2013) Geol Soc London Spec Pub 393: 213-247

[8] Swainbank I G and Fortey N J (1981) Correlation of Caledonian Stratabound Sulphides 6:20-26

[9] Clayburn J A P (1988) Earth Plan Sci Let 90:41-51

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session GOLD DEPOSITS

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Pyrophyllite Chemistry as a Vectoring and Fertility Indicator for High-Sulphidation Epithermal Deposits Tonks, E.R.1,2, Wilkinson, J.J.1,2, Armstrong, R.A.2 and Wurst, A.3

1 Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK [email protected] 2 LODE, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK 3 Barrick Gold Corporation, 161 Bay Street, Toronto H9K 1C1, Canada

___________________________________________________________________________ High-sulphidation epithermal ore deposits host important quantities of gold and silver, as well as significant amounts of copper. The ultimate source of the metals contained within these deposits, as well as the fluids that they precipitate from, are thought to be intrusions related to active volcanic centres in the calc-alkaline arcs in which these deposits are typically located [1,2]. Magmatic volatiles condense at shallow depths (1–2 km) to form a hot (200–300oC), highly acidic (pH <2), and oxidised fluid. Consequently, this hydrothermal fluid reacts strongly with the rocks it passes through, producing a characteristic zonation of alteration domains, which decrease in intensity away from fluid conduits due to neutralisation of the fluid by wall-rock interaction. From high to low intensity this ranges from intense advanced argillic, through argillic and propylitic alteration to unaltered rock over several kilometres [2,3]. Disseminated and vein-hosted mineralisation appears to have formed mostly subsequent to the primary alteration stages, also from magmatic-hydrothermal fluids [2]. Pyrophyllite – a hydrated, aluminous, phyllosilicate mineral – is frequently reported in the advanced argillic alteration domain [4], yet knowledge of the controls on its spatial distribution and possible chemical substitutions that could be useful for exploration targeting are limited. Known substitutions into the octahedral sites include Ga, Mg, Ti, Fe2+, and Fe3+, as well as F into OH- sites [4,5]. Due to the lack of previous study, there is a significant opportunity to determine possible chemical substitutions using analytical techniques with very low limits of detection (e.g. LA-ICP-MS) and to decipher the parameters (fluid pH, temperature, oxidation state etc.) responsible for chemical variations in pyrophyllite and its spatial distribution. The relative enrichment or depletion of a given element may be used to determine whether a sample of pyrophyllite is associated with a fertile or barren system. In a potentially fertile system, a knowledge of systematic changes with distance from mineralisation in pyrophyllite chemistry may be employed as a vectoring tool to locate high-sulphidation epithermal deposits. To assess how the chemistry of pyrophyllite varies around a high-sulphidation epithermal deposit, a detailed study of the advanced argillic alteration domain will be conducted at the Pueblo Viejo gold deposit, Dominican Republic. The deposit is a world-class example of a high-sulphidation epithermal gold deposit, which has been actively mined between 1975 and 1999, and 2010 to the present day [6]. Due to the long history of exploration and mining activities at Pueblo Viejo there is abundant drill core available for logging and sampling, permitting the mapping of pyrophyllite chemistry in 3D at a high resolution and the initial development of vectoring and fertility indicators. The main benefits of such vectoring and fertility indicators is to reduce the cost, risk, time, and environmental impact associated with exploration programmes. They may also permit the discovery of “blind” deposits, which may otherwise have been missed by more traditional exploration techniques. References: [1] Sillitoe R and Hedenquist J (2003) SEG Sp Pub 10:315-343 [2] Arribas Jr. A (1995) Min Assoc of Can Short Course 23:419-454 [3] White N and Hedenquist J (1995) SEG Newsletter 23:9-13 [4] Evan B and Guggenheim S (1988) Reviews in Mineralogy 19:255-294 [5] Sykes M and Moody J (1978) Am Min 63:96-108 [6] Nelson C (2015) Econ Geol 110:1101-1110

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MDSG 2020, Natural History Museum, London Poster Session PORPHYRY SYSTEMS

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A Petro-chronological Framework for the Ordubad Region, Azerbaijan, Lesser Caucasus - Implications for Regional Metallogeny Andrews, H.R.1,2, Large, S.J.E.2, Armstrong, R.N.2, Valiyev, A.3, Abdullayev, R.3,. Westhead, S.J.3, and Wilkinson,J.J.2,1 1Department of Earth Science and Engineering, Imperial College London, Prince Consort Road, London, SW7 2AZ, UK ([email protected]) 2London Centre for Ore Deposits and Exploration, Natural History Museum London, Exhibition Road, SW7 5BD, UK 3 Anglo Asian Mining PLC, 3rd Floor, Tower 2, Hyatt Regency Business Centre, 1033 Izmir St, Baku 1065, The Republic of Azerbaijan

___________________________________________________________________________ The Ordubad region in Southern Nakhchivan, Azerbaijan, is regarded prospective for metal deposits

related to porphyry systems based on Soviet era exploration and recent more focussed exploration

by Anglo Asian Mining. However, the lack of a modern regional geochronological framework has so

far restricted the development of a full understanding of the mineral potential of the district. The

district comprises intrusive rocks of the western Meghri-Ordubad plutonic complex and volcanic

rocks of Cenozoic age. Regionally, Ordubad is part of the Zangezur-Ordubad mining district, which is a

southern extension of the Lesser Caucasus covering the southern part of the Nakhchivan

Autonomous Republic (Azerbaijan), southern Armenia and northern Iran. There is currently no active

mining in Nakhchivan and active mines in the area are restricted to intrusion-hosted porphyry- and

epithermal-style mineralisation in the Armenian side of Meghri-Ordubad plutonic complex and in

Iran, with notable examples being the world-class Kadjaran deposit, and the Agarak, Sungun and

Masjed Daghi porphyry-style deposits.

Most studies defining the geological framework of the Ordubad district date back to Soviet times

with most recent studies on the Zangezur-Ordubad district and more specifically the Meghri-Ordubad

pluton having focussed on Southern Armenia. Detailed geochemical and geochronological data

(petrochronology) resolved that the Meghri-Ordubad plutonic complex was assembled from the

Eocene to Early Miocene in three magmatic epochs [1]. Ore deposit formation occurred towards the

end of each cycle with the largest deposits being associated with the culmination of the second cycle

in the Oligocene.

This study presents new whole rock geochemistry and LA-ICP-MS zircon mineral chemistry and U-Pb

geochronology data from plutonic, hypabyssal and volcanic rocks of the Ordubad region in

Azerbaijan. The new data provides the first absolute U-Pb age constraints on the individual

lithologies and places them into the temporal framework of Zangezur-Ordubad region. Based on

comparison with extensive published data-sets [1, 2, 3] our data further allow critical assessment for

the potential of porphyry centres or epithermal plays hosted within the Meghri-Ordubad plutonic

complex and the Cenozoic volcanic domains.

References:

[1] Rezeau et al. (2016) Geology 44(8): 627-630

[2] Moritz et al. (2016) Gondwana Research 37: 465-503 [3] Rezeau et al. (2019) Econ Geology 114 (7): 1365-1388

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Oxidised fluids as a key control on the source and availability of metals for porphyry-epithermal Cu-Au-Te deposits Blanks, D.E. 1 and Holwell, D.A.1 1School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom, [email protected]

___________________________________________________________________________ Recent work has shown the importance of oxidised fluids in transferring S and metals into the mantle wedge during subduction [1]. This provides a fundamental way of metasomatically enriching the mantle wedge in Au, PGE, Cu and S, and ‘priming’ it for fertile magmatism in arc settings. It has also been suggested that oxidised mantle sources are preferential to the formation of Au-rich porphyry deposits [1], which are often also enriched in tellurium (Te). We show that metasomatically enriched mantle contains elevated Au and Te concentrations and suggest this to be a result of their introduction from oxidised, slab-derived fluids. Subduction of Te-rich marine deposits and subsequent transfer into the mantle wedge with other metals by oxidised metasomatic fluids provides a key first order enrichment process in the sub arc mantle, as proposed by Holwell [2]. This Te enrichment is manifest by the common occurrence of tellurides as accessory minerals, alongside carbonate and Cl-apatite, with Fe-Ni-Cu sulfides in mantle rocks and in magmatic systems that tap such sources, and this signature is thought to be a result of metasomatic enrichment of the source [3]. In the deep crustal portions of arc lithosphere, mafic cumulates are generally sulfide saturated, and there is evidence of this in exposed lower crustal cumulates around the world – e.g. the Ivrea Zone, Italy [4]. In such cases, chalcophile metals can be ‘trapped’ by sulfide and potentially render any subsequent magmatic system barren for porphyry-epithermal ore formation. However, we show that Cu-Au-Te-rich sulfides may be present as a liquid phase with the potential to move through a permeable melt network, although how such dense sulfide liquid droplets can be mobilised upwards into the crust is problematic. Oxidised fluids provide one explanation, as they dramatically increase the solubility of sulfide in silicate melt and thus any sulfide can be easily melted/incorporated into the silicate magma, even at relatively low degrees of partial melting (e.g. in post subduction settings). Where oxidised melt is generated by partial melting of a previously metasomatically oxidised source, it is more likely to completely dissolve sulfides in the mantle source [1] and thus the sulfide ‘trap’ becomes less important or even non-existent under such conditions. This process has been suggested to produce Au- and Cu-enriched melts [1] and we propose that Te is similarly enriched via such processes and that oxidised fluids, which are known to be able to transport large amounts of Te [5] are a key control in the development of Te-rich ore deposits in arc settings. Oxidising fluids are therefore critical in fluxing metals and S into the mantle wedge, metasomatically enriching the mantle, and providing a way of removing the issue of the lower crustal ‘sulfide trap’, enhancing porphyry fertility. References:

[1] Rielli A et al. (2018) Earth Planet Sci Let 497:181–192

[2] Holwell D et al (2019) Nat Comms 10:3511

[3] Blanks D et al. (2019) Nat Comms in review

[4] Locmelis M et al (2016) Lithos 244:74-93

[5] Grundler P et al (2013) Geochim Cosmochim Acta 120:298-3252

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Apatite inclusions in Zircon: records of porphyry melt evolution Brugge E.1,2, Wilkinson J.J.1,2, Miles A.J.3 and Buret Y.2 1Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ, UK ([email protected]) 2LODE, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK 3Department of Geology, University of Leicester, Leicester

___________________________________________________________________________ Igneous apatite is a useful mineral in petrological and ore studies. However, in porphyry environments the modification of apatite compositions through metasomatism is common due to the large volume of circulating fluids. In addition, elements key to tracking magmatic-hydrothermal processes (e.g. halogens and S) have fast diffusion rates [1] such that even visibly fresh grains may not preserve a primary igneous composition. In this study we avoid uncertainty through the analysis of fine (< 10 μm) apatite inclusions hosted within zircon. We suggest these apatites are shielded from the effects of metasomatism and diffusion, preserving a record of the melt at the time of zircon growth. This approach also means that trace element analyses can be compared to those of the co-existing zircon from which age and temperature [2] information can be obtained. In this study, zircon-hosted apatite inclusions from the La Granja Cu-Mo porphyry, Peru, and igneous host rocks were analysed. The composition of apatite from older, non-porphyry-related arc magmas can be distinguished from that associated with Miocene porphyry intrusions. Differences in REE concentrations are also observed in the corresponding zircon hosts and are thought to reflect changes in the melt composition linked to deep crustal differentiation. The composition of the apatite inclusions also varies between the porphyry-related intrusions. Some elements, like Cl, decrease in concentration over successive intrusions, inferred to reflect the progressive exsolution of fluid from the source magma region. Other elements, such as S, peak in concentration in apatites from the mineralised intrusions. These differences are likely a record of shallow crustal magmatic processes. These observations are important for understanding what makes arc magmas ‘fertile’ for the formation of porphyry deposits on an arc scale, and also at the deposit scale. Conclusions from this work have implications for the future development of indicator minerals as tools for porphyry exploration. References:

[1] Cherniak D. J (2010) Rev in Min & Geochem 72:827-869

[2] Ferry J. M and Watson E.B (2007) Contrib Mineral Petrol 154:429-437

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Exsolution and migration of mineralising fluids in porphyry magmatic systems - Evidence from the Yerington District, Nevada Carter, L.C.1, Williamson, B.J.1, Armstrong, R.H.2 and Tapster, S.R.3 1Camborne School of Mines, University of Exeter, Cornwall, UK. [email protected] 2Natural History Museum, London, UK 3BGS, Keyworth, UK

___________________________________________________________________________ Porphyry-type Cu ± Mo ± Au deposits (PCDs) are amongst the most studied in the world [1]. One fundamental aspect of PCD formation that is poorly understood is whether the mineralising fluids are derived from: (i) high-level Cu-rich porphyry magmatic stocks; (ii) feeder chambers at mid-upper crustal levels; (iii) a lower crustal reservoir; or (iv) a combination of these in a transcrustal mush system [2]. Magmatic-hydrothermal mineralisation is often spatially, temporally and texturally linked to high-level porphyry stocks but it is unlikely that enough fluid could be derived from such a limited volume of magma [3]. From mass-balance calculations and high-precision CA-ID-TIMS U-Pb zircon studies [4], mineralising fluids must also emanate from a longer-lived, deeper, rarely observed magmatic source, probably at 5 to 15 km depth. The transport mechanism(s) for such fluids is unknown. Due to Cenozoic normal faulting, the Yerington District, Nevada, offers a well exposed, ca. 8 km deep, section through the Jurassic Yerington Batholith, including volcanic rocks, plutons and at least 4 PCDs, the Ann Mason, Yerington, Bear and MacArthur [5]. This provides a rare opportunity to study temporal relationships in the deeper magmatic parts of the system, important in PCD formation, and the magmatic-hydrothermal transition. Existing conceptual models for the Yerington District [5][6] and PCD formation in general [7] commonly suggest that the cupola of the Luhr Hill granite, or dykes emanating from the cupola, were the source of the mineralising fluids. In contrast, our field observations from below the Ann Mason and Yerington PCDs indicate no textural evidence (e.g. miarolitic cavities [8]) for fluid exsolution in the cupola or large porphyry dykes. Rather, we provide evidence, including the presence of unidirectional solidification textures (USTs) [9] and miarolitic cavities, for hypogene fluid exsolution and mineralisation within aplite dykes, which are volumetrically minor yet pervasive from below to within the Ann Mason and Yerington PCDs. These dykes have previously been interpreted as early, and have not been discussed within the context of mineralisation [5]. Further, from our detailed scanning electron microscopy (SEM), cathodoluminescence (CL), electron microprobe (EPMA) and Total Ion Beam Analysis (Total-IBA) studies, the groundmass of the aplites contain a wormy, highly interconnected quartz generation that directly feeds mineralised miarolitic cavities. We interpret this wormy texture as marking an interconnected flow path for mineralising fluids through inter-crystal spaces in a mush framework of magmatic minerals, where we use the term mush to refer to a continuous crystal framework [2]. This is significant as it demonstrates how mineralising fluids would have been able to continually migrate upwards through the aplite dykes, post emplacement, until hydrothermal quartz filled the inter-crystal spaces. Consequently, the volumetrically small but pervasive aplite dykes could have acted as conduits for the upward transport of sufficient volumes of hydrothermal fluids for PCD formation and associated alteration. References:

[1] Richards J P (2018) Econ Geol 113: 1225-1233

[2] Cashman K V et al. (2017) Science 355: 6331

[3] Sillitoe R H (2010) Econ Geol 105: 3-41

[4] Buret Y (2016) Earth Planet Sci Lett 450: 120-131

[5] Dilles J H (1987) Econ Geol 82: 1750-1789

[6] Schopa A et al. (2017) Econ Geol 112: 1653-1672

[7] Seedorff E et al. (2005) Econ Geol 100: 251-298

[8] Candela P A (1997) J Petrol 38: 1619-1633

[9] Kirwin D (2005) IAGOD Guidebook 11: 63-84

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Chlorite and epidote chemistry distinguish between propylitic alteration formed in porphyry versus epithermal environments

Hart-Madigan, L.1 and Wilkinson, J.J.1,2 1 LODE, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK [email protected] 2 Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK

___________________________________________________________________________ Propylitic minerals could hold the key to discovering unknown porphyry and epithermal deposits that

are situated in prospective areas where only distal alteration is visible at surface. Chlorite and

epidote from the propylitic halos of porphyry systems have been shown to have geochemical

characteristics that are unique to this environment [1, 2]. Moreover, systematic changes in their

chemistry are observed with increased distance from a system centre [3, 4, 5] making them useful

vectors to ore.

Epithermal systems often occur close to or within porphyry systems and generate their own

propylitic halos, so their presence has the potential to obscure or complicate any geochemical

patterns. Therefore, in order to improve tools for exploration in propylitically-altered rocks, it is

necessary to be able to distinguish between porphyry and epithermal signals in the alteration

minerals. Primarily, this would facilitate discrimination of different sources of propylitization in and

around a porphyry exploration target. However, this could also be applied in areas that have signs of

an epithermal system at surface, such as advanced argillic alteration. Here, the geochemical signals in

adjacent propylitic rocks could be used to determine if there is are also potential porphyry targets in

the surrounding area. It would then be possible isolate this signal in order to vector towards the

porphyry centre.

In this study, trace elements in chlorite and epidote in samples from high-, intermediate- and low-

sulfidation systems were analysed by LA-ICP-MS. The samples were either donated by academic or

industry collaborators, or they came from the vast ores and minerals collections at the Natural

History Museum, London. With over 30,000 ore specimens and almost 200,000 mineral specimens, it

was possible to select suitable samples from several epithermal deposits from across the globe to

represent each end-member type. The resulting data were compared with published chlorite and

epidote trace element data from several porphyry districts.

The data show that there is a transition in epidote and chlorite chemistry from the porphyry to

epithermal environments that can be tracked by key trace elements. Additionally, each epithermal

end-member has a unique geochemical signature that can be recognised in multivariate space. It has

therefore been possible to create a generic porphyry-epithermal classification scheme that can be

applied in any suitable exploration program to determine the origins of propylitic alteration in that

area.

References:

[1] Hart-Madigan L et al (2019) SGA 2019 Conference Abstract

[2] Wilkinson CC et al (2015) SEG 2015 Conference Abstract

[3] Cooke D et al (2014) Econ Geol Spec Pub 18:127–152

[4] Wilkinson et al (2019) Econ Geol, in press

[5] Pacey et al (2019) Econ Geol, in press

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Favourable tectonic setting and fracture network environment for the formation of the giant Kadjaran porphyry Cu-Mo deposit in Armenia, Lesser Caucasus

Hovakimyan S.1, 2, Moritz R.1, Harutunyan M.2, Tayan R.2 and Rezeau H.1,* 1Department of Earth Sciences, University of Geneva, Rue des Maraîchers 13, 1205 Geneva, Switzerland; E-mail: [email protected] 2Institute of Geological Sciences of the Armenian National Academy of Sciences, Yerevan, Republic of Armenia *Present address: Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, USA

___________________________________________________________________________ The giant Kadjaran porphyry Cu-Mo deposit is situated in the southernmost Lesser Caucasus in Armenia and belongs to the Central segment of the Tethyan metallogenic belt. Cenozoic evolution of this segment was dominated by oblique convergence and final collision of the Arabian plate with the Eurasian margin. The composite Meghri-Ordubad pluton of the southernmost Lesser Caucasus was emplaced during this evolution. It hosts major porphyry Cu-Mo and epithermal Au deposits and prospects, including the giant Oligocene Kadjaran porphyry Cu-Mo deposit. Recent structural investigations of the southernmost Lesser Caucasus emphasize the fundamental control of regional dextral strike-slip tectonics during the emplacement of porphyry Cu-Mo and epithermal Au deposits and prospects, and the associated magmatism of the Meghri-Ordubad pluton. This contribution is focused on the study of district- and deposit-scale faults, and local fracture network characteristics of the Kadjaran deposit to understand the favourable structural conditions leading to the emplacement of this giant porphyry deposit. The Kadjaran deposit is hosted by a mid-Oligocene monzonitic intrusion (dated at 28.3 to 28.1 Ma), and was formed at the intersection of the regional NNW-oriented Tashtun oblique-slip fault and the ~E-W-oriented Voghji strike-slip fault. Paleostress reconstructions in host monzonite indicate NNE-oriented shortening and WNW-oriented extension caused by mid-Oligocene NE-oriented convergence of the Arabian and Eurasian tectonic plates. This tectonic setting resulted in dextral transpression along the regional NNW-oriented Tashtun fault and a sinistral sense of motion along the ~E-W-oriented Voghji fault and initiated the major NE- and ~N-S-oriented district-scale ore-controlling structures under a dextral strike-slip tectonic regime. Dextral kinematics resulted in the formation of dominantly NE- and N-S-oriented extension fractures controlling the porphyry veinlets and veins (dated at 27.3 to 26.4 Ma) along the major N-S- and NE-oriented district-scale faults. During the NNE-oriented shortening regime, many E-W-oriented deposit-scale faults behaved as thrust faults, which was favourable for the opening of gently dipping extension fractures. This fracture network resulted in high permeability around the steeply dipping deposit-scale faults and was the most important structural control for the emplacement of porphyry Cu-Mo mineralization, which consists predominantly of gently to moderately dipping veinlets. During the early Miocene, local relaxation of the convergent stresses resulted in a reversed sense of movement along the regional Tashtun fault, with a sinistral oblique-slip regime and a transtensional environment. This tectonic setting resulted in the emplacement of a porphyritic granite (dated at 22.6 Ma) along the footwall of the Tashtun fault. Paleostress reconstructions in porphyritic granite indicate a WNW-oriented shortening and a NNE-oriented extension. This tectonic event is recorded by reopening of pre-existing ~E-W-oriented deposit-scale faults and porphyry veins with the emplacement of late veins and associated epithermal mineralization (dated at 20.5 Ma). This case study emphasizes the role of interaction between regional structures and district- and deposit-scale faults and extension fractures, which may have generated the favourable fracture network environment for the emplacement of a giant porphyry system.

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Magmatic Arc evolution culminating in porphyry copper formation at Rio

Blanco-Los Bronces

Large, S.J.E.1, Buret Y.1,2, Knott T.R.3 and Wilkinson J.J.1,4 1LODE, Department of Earth Sciences, Natural History Museum, London, UK 2Core Research Laboratories, Natural History Museum, London, UK 3University of Leicester, UK 4Department of Earth Science and Engineering, Imperial College London, UK

___________________________________________________________________________ Giant porphyry deposits along the Andean margin typically form late within an arc segments magmatic evolution. The giant porphyry deposit cluster at Rio Blanco-Los Bronces in Central Chile is such an example having formed towards the end of >20 Myr of recorded magmatic activity within the district. Several km-thick sequences of the Oligocene to Miocene volcano-sedimentary Abanico and Farellones Formations host Miocene intrusive rocks of the San Francisco Intrusive Complex and the Late Miocene to Early Pliocene Cu deposits. The district therefore allows to study the geochemistry of conventional arc magmas unassociated to economic Cu mineralisation and those that sourced fluids, magmas and metals for the giant porphyry Cu deposits. Furthermore, it provides the ideal location to reconstruct the magmatic processes and their changes over time resulting in potentially economic porphyry Cu mineralisation. Here, in-situ zircon geochronology and geochemistry (petrochronology) combined with WR-geochemistry are applied to the rock suite of the San Francisco Intrusive Complex. Results reveal temporally resolved geochemical changes of the intrusive magmatism. We use our new U-Pb geochronology data to refine published geochronology datasets for the district and present the first zircon geochemistry data. We find that compositionally variable magmas were incrementally emplaced from 17 – 4 Ma. Hydrothermal events associated with intrusions before 10 Ma are typically less extensive and Cu-poor, and the majority of Cu was introduced with hydrothermal events related to magmatism younger than ~8 Ma. Geochemistry reveals typical fertile magma signatures, such as elevated Sr/Y in WR (>50) and Eu/Eu* in zircon (>0.4), in porphyry intrusions that are considered to be associated with ore formation, whereas intrusions unrelated to major metal deposition are lacking these signatures (<50 And <0.4, respectively). The combination of geochemistry and geochronology identifies continuous changes in geochemistry over geologically fast timescales and point to modified lower crustal crystallisation assemblages of the source magmas in the latter stages of the area’s magmatic history.

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Porphyry Copper Fertility in the West Luzon Arc, Philippines: an Integrated Accessory Mineral Approach George Stonadge1, Andrew Miles1, David Holwell1, Simon Large2, Daniel Smith1 1School of Geography Geology and the Environment, University of Leicester, University Road, Leicester, LE1 7RH, United Kingdom 2Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK

Porphyry copper deposits (PCDs) are high tonnage, low grade deposits formed in arc environments, and are vital for the future supply of Cu, Mo and a suite of other by-product metals. With demand for Cu forecast to increase due to rapid expansion of the electric vehicle industry, exploration is increasingly reliant on the discovery of new and often concealed deposits. Discovering such deposits requires new techniques capable of tracking the fertility of unexposed arc magmas. Despite much attention on the formation of PCDs in the shallow crust, the deeper processes that determine the fertility of magmas remain poorly understood. The host rocks for PCDs are often not representative of the conditions at which fertility is determined because ore-fluids are produced in regions that are not exposed at the erosion level of the deposit. However, robust accessory minerals such as zircon are commonly inherited from deeper regions and may record early fertility enhancing conditions. By contrast, other accessory minerals such as apatite and titanite document a time-sequential record of processes at the level of magma emplacement such as the generation of mineralizing fluids [1, 2]. These minerals are also known to host inclusions of less robust minerals, including magmatic sulphides important for Cu enrichment and transport. Volatile saturation, fluid extraction and incorporation of sulphur laden mafic magmas into relatively evolved crystal mushes culminate in attractive conditions for PCD genesis. This study aims to test the idea that an integrated accessory minerals approach can be used to investigate where and when these key ore-forming processes occur within a large, trans-crustal arc systems.

The West Luzon Arc, Philippines, hosts fertile and barren magmas with good exposure of mid- to shallow regions of the trans-crustal arc system. Plutonic rocks associated with the Santo Thomas II PCD exhibit geochemical signatures of high Na2O/K2O, Al2O3/TiO2, Sr/Y (>100), Ba/Th and Rb/Th [3]. Several of these are common PCD fertility indicators. Similarly, volcanic rocks from Pinatubo share many of these characteristics and are known to have emitted large amounts of sulphur during the 1991 eruption (c. 17 Mt of SO2); [4, 5]. By contrast, the compositions of volcanic rocks from the nearby Taal volcano show no evidence of Cu fertility and represents a barren volcanic comparator [6]. This study will examine accessory minerals from all three systems to compare and contrast the magmatic processes captured in barren and fertile plutonic and volcanic systems. This work will also help establish the extent to which PCDs achieve connectivity to active volcanic systems. References: [1] Stock M et al. (2016). Nature Geoscience, 9(3), p.249. [2] Kohn M (2017). Reviews in Mineralogy and Geochemistry, 83(1), pp.419-441. [3] Imai A (2002). Resource Geology, 52(2), pp.147-161. [4] Pallister J et al. (1996) Fire and mud: eruptions and lahars of Mount Pinatubo, Philippines, pp.687-731. [5] Kress V (1997). Nature, 389(6651), p.591. [6] Miklius A (1991). Journal of Petrology, 32(3), pp.593-627. Acknowledgements: This work was supported by NERC grants NE/P017053/1 and NE/P017452/1 “ FAMOS: From Arc Magmas to Ores”

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Discriminating porphyry and endoskarn-forming magmatic-hydrothermal systems in the Daye district, China

Zhang F.1, Williamson B.J.1 and Hughes H.S.R.1

1Camborne School of Mines, University of Exeter, Penryn, Cornwall TR 10 9FE ([email protected])

___________________________________________________________________________ Porphyry magmatic systems emplaced within carbonate host rocks constitute a major source of the world’s Cu, Mo, Pb, Zn and Au [1]. Mineralisation is generally either porphyry-style or endoskarn-style within, or porphyry-, exoskarn- or manto-style outside the porphyry intrusion(s) [1,2]. Genetic models for porphyry and skarn mineralisation are well established, however questions remain as to why endoskarn- rather than porphyry-style mineralisation predominates within certain systems and regions. Recent studies show that magmas can assimilate large volumes of crustal carbonates, potentially providing a significant amount of CO2 to late and post-magmatic hydrothermal fluids [3]. High levels of CO2 in magmatic-hydrothermal systems may favour endoskarn formation and affect metal fractionation and solubility of ore minerals [4]. In this contribution, we test the hypothesis that endoskarn alteration may eliminate porphyry-style Cu mineralisation and mobilise Cu into other parts of the pluton and surrounding carbonate wall-rocks (exoskarns). To address this hypothesis, the Daye ore district in the Middle-Lower Yangtze River metallogenic belt was selected for study as it hosts porphyry-, exoskarn- and endoskarn-styles of mineralisation. The porphyry and skarn deposits lie within Late Mesozoic intrusions or along their contacts with Late Triassic carbonates. From among the many porphyry-related systems, the Tonglushan Fe-Cu-(Au) endoskarn-bearing system was selected for detailed field-, light microscopy-, cathodoluminescence-, SEM- and QEMSCAN®-based genetic studies. The current study is mainly based on a comparison of samples from a single core through altered granite, endoskarn and exoskarn. From preliminary data for the Tonglushan system, the granites distal to the endoskarn were affected by Na-Ca alteration (replacement of intermediate composition plagioclase with albite, calcite and chlorite, and hornblende with calcite and chlorite), potassic alteration (replacement of plagioclase with K-feldspar), and later quartz-calcite veining. The endoskarn, which shows relict minerals and textures from the granite, underwent: 1) sericitic alteration, 2) prograde endoskarn formation, 3) retrograde endoskarn formation, and 4) Na-K-Ca metasomatism. Stage 1, sericite replacing feldspar, is tentatively suggested to have resulted from the mixing of CO2, derived from wall-rock de-carbonation, with magmatic-hydrothermal fluids, to produce the required acid [5]. Stage 2 is characterised by diopside, granditic garnet, intermediate to calcic composition plagioclase and K-feldspar, remobilising and utilising Ca, Fe, Mg, Na, K, Si and Al from exiting minerals, magmatic fluids and/or external carbonates. Stage 3 is characterised by the replacement of prograde with retrograde skarn minerals (vesuvianite, epidote, allanite, phlogopite and chlorite). The textural relationships of oxide minerals in exoskarn and endoskarn indicate that magnetite and hematite likely formed during Stage 3. Stage 4, which resulted from alkali and calcic alteration, was mainly produced by magmatic-hydrothermal fluids, with a possible additional component from the carbonates. This stage is widely distributed and caused pervasive replacement of plagioclase by albite and K-feldspar, and the formation of K-feldspar-biotite-albite-phlogopite-calcite veins (potassic alteration), followed by calcite-chlorite veins. Cu-(Au) mineralisation in the exoskarn is considered to be genetically associated with the potassic alteration phase, with precipitation of sulphides caused by acid neutralisation within the carbonates. References:

[1] Sillitoe R (2010) Econ Geol 105:3-41

[2] Meinert L D et al. (2005) Econ Geol 100:299-336

[3] Carter L B and Dasgupta R (2016) Geochem Geophys Geosyst 17:3893-3916

[4] Lowenstern J B (2001) Mineral Deposita 36:490-502

[5] Lentz D R (2005) Springer, Berlin, Heidelberg: 421-424

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Asthenosphere upwelling as a mechanism of remobilizing the Cu-enriched cumulate Deng, C.1, Wan, B.2 and Jenner, F.E.3

1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 10029, China 2School of Environment, Earth and Ecosystem Sciences, The Open University, Walton Hall, Milton Keynes, Buckinghamshire MK7 6AA, UK

___________________________________________________________________________ As arc-related magmas rarely avoid sulphide saturation during cooling in the lower crust, most evolved arc rocks lack Cu [1]. However, it is still debated today whether the resulting Cu-rich cumulates are later remobilised into the shallow crust to form porphyry deposits. To answer this question, we combine melt inclusion and recent geophysical data from 7 Pliocene-Quaternary arcs. Two types of volcano can be identified according to the geophysical data, volcanoes that are related to asthenospheric upwelling and volcanoes that are related to normal subduction processes. These two types of volcanoes display similar FeOT contents. However, primitive asthenospheric upwelling related arc magmas have higher S (up to ~1.08 wt%) and Sr/Y (up to ~314), compared to primitive normal subduction-related arc magmas (S <0.32 wt.% and Sr/Y <50). These geochemical characteristics indicate that asthenospheric upwelling exhibits a control on the S and Sr/Y variability of arc magmas and that asthenospheric upwelling related primitive magmas were sulphide-undersaturated. Consequently, ascending sulphide-undersaturated asthenospheric mantle-derived magmas heat up the lower crust, causing sulphides in the lower crust to become unstable. This is a result of a temperature effect on the sulphide stability field [2]. Hence, these sulphides are easily assimilated during subsequent magmatism, causing the intrusion of Cu-rich magmas (the source of porphyries) into the lower crust.

References:

[1] Jenner F E (2017) Nat Geosci 10: 524

[2] Nash W M (2019) Earth Planet. Sci. Lett.507: 187-198

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Titanite as a recorder of magmatic and hydrothermal evolution in the Los Picos-Fortuna Igneous Complex, Chile Matthews, T.J.1,2, Wilkinson, J.J.1,2 and Loader, M.A.2 1Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK, [email protected] 2Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK

___________________________________________________________________________ Porphyry copper deposits provide a substantial contribution to the global supply of metals, sourcing much of the planet’s Cu, as well as Au and Mo [1]. As part of the green revolution, demand for copper is set to increase but new deposits are becoming increasingly difficult to find. Consequently, it is essential that new methods are developed that can identify prospective systems at an early stage of exploration, hence reducing cost, energy use and environmental impact. Whole-rock and mineral geochemical indicators are increasingly employed in porphyry exploration to assess the ‘fertility’ (i.e. ore-forming potential) of arc segments, igneous complexes and related hydrothermal systems. To date, much work has focused on zircon [2] and apatite [3], although titanite (CaTiSiO5) also offers significant potential as an indicator of magmatic and hydrothermal fertility because it can incorporate a wide variety of trace elements (e.g. REE, HFSE and LILE) into its structure. It is this feature, along with its excellent textural preservation, that has allowed titanite to be utilised as a geochronometer [4], as a thermometer [5] and as a tracker of petrogenetic processes [6]. This study utilises rocks from the Los Picos-Fortuna Igneous Complex (Fortuna Complex), northern Chile. The Fortuna Complex represents a protracted period of calc-alkaline magmatism (> 5 Myr), in the district that culminated in the formation of the El Abra and Chuquicamata porphyry copper deposits [7]. Previous studies have shown that zircon exhibits a systematic compositional change in the lead up to the mineralisation, which has been ascribed to changes in magmatic oxidation state [7]. Titanite major element, trace element and textural data from successive intrusive phases of the Fortuna Complex are presented, firstly in order to ascertain whether titanite is of magmatic or hydrothermal origin (or both) and secondly to identify whether titanite displays systematic compositional changes akin to those observed in zircon. Such an approach will allow us to assess its potential for recording changes in magma and magmatic fluid chemistry in the lead up to porphyry mineralisation. References:

[1] Sillitoe R (2010) Econ Geol 105: 3-41

[2] Lu Y et al. (2016) Econ Geol Spec Pub 19: 329-347

[3] Mao M et al. (2016) Econ Geol 115:1187-1222

[4] Frost B et al. (2001) Chem Geol 172:131-148

[5] Hayden L et al. (2008) Cont Mineral Petrol 155: 529-540

[6] McLeod G et al. (2010) J Petrol 52: 55-82

[7] Ballard J et al. (2002) Cont Mineral Petrol 144: 347-364

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Origin and significance of volatile saturation features in the San Francisco batholith, Rio Blanco-Los Bronces porphyry district, Chile Smith, A.G.G.1,2, Wilkinson, J.J.1,2, Large, S.J.E.2

1 Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK 2 LODE, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK

___________________________________________________________________________ Porphyry Cu deposits source the majority of the world’s copper, forming due to an ideal interplay between magmatic and hydrothermal processes on a crustal scale. It remains unclear which processes are important for, or detrimental to, the eventual size of a deposit, with the chemistry of the ore forming magmatic-hydrothermal fluids having been suggested as one of the key controls [1]. Quartz-hosted fluid inclusions provide a unique opportunity to directly investigate the chemistry of these fluids as they can represent remnants of the original fluids that were trapped during crystal-growth. Investigating these fluid inclusions to understand fluid exsolution processes and fluid compositions from different magmatic-hydrothermal systems could provide insights as to why some igneous systems form giant porphyry deposits and others do not. The San Francisco Batholith in Central Chile is a large, dominantly equigranular diorite to granodiorite igneous complex that was incrementally assembled and hosts several hydrothermal centres with variable metal endowments. Several centres on the eastern side of the intrusive complex constitute the giant Rio Blanco-Los Bronces deposit cluster, which is host to a combined tonnage of >200 Mt Cu [2]. The district thus provides an ideal field area to compare the characteristics of magmatic-hydrothermal systems that have resulted in different degrees of Cu mineralisation. Within the Rio Blanco-Los Bronces deposit cluster, ore formation is thought to have occurred over a 3 million year time period in several discrete events [3]. Copper mineralisation is typically associated with porphyry intrusions and occurs within hydrothermal veins and breccias or is disseminated within the host rocks [2]. The equigranular intrusions that comprise the majority of the San Francisco Batholith are older than the main ore forming events, however, they contain abundant fluid exsolution features, such as miarolitic cavities. These represent pockets of exsolved fluid that have been trapped in a fluid-saturated melt. The mineralogy of these cavities is dominated by quartz, anhydrite, tourmaline and sulphides, remarkably similar to the mineral assemblage associated with the ore stage of the giant deposits. However, economic mineralisation is not associated with these early fluid exsolution events. Here, we present detailed petrography, quartz-hosted fluid inclusion microthermometry and chemical analyses by LA-ICP-MS on Cu-rich tourmaline breccias and tourmaline-quartz veins from the well-endowed San Manuel and El Plomo deposits and from miarolitic cavities within the equigranular, pre-ore host-rocks. Comparison will allow an assessment to be made as to whether the exsolving fluid composition has a control on deposit size within the Rio Blanco-Los Bronces district or whether other prevailing factors, such as the amount of exsolved fluids or the efficiency of metal-precipitation, are of greater influence. References [1] J. P. Richards (2004) Super Porphyry Copper & Gold Deposits: A Global Perspective. [2] V. Irarrazabal et al. (2010) Econ Geol. 15: 253–269. [3] K. Deckart et al. (2014) Min Dep 49: 535–546.

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Processes of metal enrichment displayed by epithermal Pb-Zn±Ag±Au veins in Milos, Greece Schaarschmidt, A.1, Haase, K.M.1, Klemd, R.1, Voudouris, P.C.2 1GeoZentrum Nordbayern, Friedrich-Alexander-Universität (FAU) Erlangen-Nürnberg, Schlossgarten 5, 91054 Erlangen, Germany, [email protected] 2Department of Mineralogy-Petrology, University of Athens, Athens 15784, Greece

___________________________________________________________________________ Epithermal Ag-Au and porphyry Co-Mo-Au mineralizations are associated with subduction-related magmas across the Aegean [1]. The alteration and mineralization paragenesis of epithermal deposits depend on the contribution of magmatic and meteoric water or seawater, and on the physico-chemical fluid conditions (e.g., temperature, pH, redox), which again depend on the volcanotectonic setting and the magma composition [2]. Although numerous epithermal deposits have been studied in detail [3], the metal sources and the processes of metal enrichment are not well understood. Milos Island is part of the South Aegean Volcanic Arc and consists of volcanic and volcaniclastic rocks of Pliocene to Lower Pleistocene age [3]. Western Milos contains at least three shallow submarine epithermal Pb–Zn–Cu–Au–Ag–Te mineralisations that are hosted by calc-alkaline andesites to rhyodacites and are closely related to normal and strike-slip faults [4]. The vein mineralisations have been classified as intermediate (to high) sulfidation deposits and are characterised by a dominant seawater signature. The metals are believed to stem from either the basement or the magmatic host rocks. Mineralised volcanic rocks and epithermal veins were sampled in western Milos to study the main ore minerals and their relation to the surrounding volcanic rocks; in the context of a potential metal source. The north-west trending profile from Kondaros via Katsimouti towards Vani was sampled in detail along 1 km to investigate the spatial variation of metal distribution within these complex vein systems. Major and trace elements of sphalerite, galena, pyrite, marcasite and chalcopyrite were determined by electron microprobe analysis and laser ablation inductively coupled plasma mass spectrometry at the GeoZentrum Nordbayern in Erlangen. The FeS content and the Ga/Ge ratio of sphalerite allow an estimate of the sulphur fugacity (fS2) and the temperature (T) of the parental hydrothermal fluids. The fluid conditions show decreasing fS2 with decreasing T, typical for intermediate sulfidation epithermal fluids. The highest Ag concentrations in galena (up to 3500 ppm) occur in the sample with the highest range of FeS in sphalerite, indicating a highly variable sulfidation state. Marcasite of the same sample shows high As, Sb, and Au contents. This indicates that localised trace element enrichment is related to the variation of the physico-chemical fluid conditions. Changing T and fS2 conditions, indicated by irregular chemical zoning of sphalerite, may have been caused by events like boiling or mixing of different fluids. The lack of correlation of trace elements and fS2 suggests significant chemical variability of the hydrothermal fluid in one vein system.

References:

[1] Voudouris PC et al. (2019) Ore Geol Rev 107:654-691

[2] Simmons SF et al. (2005) Ec Geol 100th Anniversary Vol 485-522

[3] Sillitoe RH and Hedenquist JW (2003) Soc Ec Geol Spec Pub 10: 315-343

[4] Steward AL and McPhie J (2006) Bull Volcanol 68:703-726

[5] Alfieris D et al. (2013) Ore Geol Rev 53:159-180

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session PGE DEPOSITS

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Precious metal geochemistry of ‘lamprophyric’ dykes intersecting the Bushveld Complex: Initial observations and thoughts on the sub-Bushveld lithospheric mantle

Compton-Jones, C.1*, Hughes, H.S.R. 1,2, McDonald, I.3, Bybee, G.M.2, Kinnaird, J.A.2, and Andersen, J.C. Ø 1 1 Camborne School of Mines, College of Engineering, Mathematics & Physical Sciences, University of Exeter, Penryn Campus, Penryn, TR10 9FE, UK (*[email protected]) 2 School of Geosciences, University of the Witwatersrand, Private Bag 3, Wits 2050, Johannesburg, South Africa 3 School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff, CF10 3AT, UK

___________________________________________________________________________ The Western Limb of the Bushveld Complex is host to a recently described swarm of ‘lamprophyric’ dykes [1 and Hughes et al. this conference]. The dykes were first documented by underground platinum mining operations during routine underground mapping and are sometimes associated with gas outbursts. The dykes, which regionally strike WNW-ESE, are significantly younger (177-132 Ma; Ar-Ar dating of phlogopite [2]) than the c. 2.06 Ga Bushveld lithologies they intrude. Lamprophyric and orangeite dykes are thought to be derived from very low-degree partial melting of the subcontinental lithospheric mantle (SCLM), thus their chemistry can provide an insight into the composition of the SCLM beneath the Bushveld Complex. In this ongoing study, we marry bulk geochemistry, bulk platinum-group element (PGE) and Au analysis, detailed mineralogical investigations and radiogenic isotopic geochemistry (Sr, Nd and Hf compositions) of South African lamprophyre and kimberlite dykes from the last 2 Ga. We seek to assess the distribution and controls on precious metals in the SCLM below the Bushveld in order to: (i) identify the mechanisms by which metals such as the PGEs may be mobilised in very low-degree partial melting and metasomatic events, and (ii) understand how the metallogenic record of the sub-Bushveld SCLM has changed through time (using time integrated radiogenic isotopes). Based on isotopic analyses, previous studies have implicated an SCLM component in the Bushveld parental magmas, specifically from an eclogitic component within the SCLM (e.g., [3]) however in situ analysis of sulphide minerals in eclogite xenoliths so far have revealed a general depletion in PGE [4]. In this contribution, we present new bulk geochemical data for the dykes in order to appropriately categorise the lithology and genetic links of the dykes and present some initial observations regarding the precious metal abundance in these rocks. Major element concentrations are generally variable, with evidence of fractionation for some elements, and the dykes have Mg# ranging between 71 and 81, which overlap regional ultramafic lamprophyre and orangeite ranges. The dykes have low total bulk PGE contents of 1.1 – 8.3 ppb and the ratios of IPGE:PPGE are highly variable, for example (Pd/Ir)N ranges from 0.7 – 27.9 (mean = 8.1), highlighting fractionation with PPGE > IPGE, and/or possible incorporation of xenolithic Bushveld material. Ratios of Pt/Pd are more consistent, ranging from 0.8 – 3.1 (mean = 1.8). We plan to establish the radiogenic isotope characteristics of the ‘lamprophyric’ dykes and compare this to kimberlites and lamprophyres with a range of compositions and ages from across Southern Africa. In combination with ongoing mantle xenolith investigations from the region, we thereby aim to unpick the geochemical history of the SCLM beneath the Kaapvaal Craton.

References:

[1] Hughes, H.S.R. et al. 2016. Applied Earth Science, 125(2), 85-86.

[2] Hughes, H.S.R. et al. (in prep). A major swarm of orangeite dykes exposed in platinum mines across the

Western Bushveld Complex, South Africa.

[3] Richardson, S.H. and Shirey, S.B. 2008. Nature, 453.

[4] Compton-Jones et al. (in prep). Metals in the mantle: Eclogite xenoliths and their metal budget.

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Alteration in the Platreef of the Bushveld Complex: A hyperspectral, mineralogical and mass balance study Miron, R.G.1*, Williamson B.J. 1, Hughes H.S.R.1, Lloyd A.2, Stevens F.2, Acheampong K.2,

Spence, M.D.1

1Camborne School of Mines, University of Exeter, Penryn, Cornwall TR10 9EZ, UK. *[email protected] 2AngloAmerican South Africa, 44 Main Street, Johannesburg, 2001, South Africa

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The nature and spatial distribution of alteration is widely used to assess the role of hydrothermal fluids in ore deposit formation (e.g., for porphyry systems) and as a vector towards mineralisation. Comparatively little work has been undertaken on alteration in the PGE-mineralised reefs of the Bushveld Complex and host mafic and ultramafic lithologies. Whilst the main mechanisms of mineralisation in the Platreef were magmatic, it is widely recognised that the system was variably affected by later hydrothermal alteration and remobilisation of ore-forming components [1, 2]. The aim of this MSc study was to describe and quantify mineral reactions and mass changes associated with hydrothermal alteration in the Platreef. Two cores from the Tweefontein-Rietfontein farms were subject to hyperspectral imaging and sampling for traditional mineralogical and geochemical (including Gresens’) analysis in a novel approach to characterising these complex assemblages. Three main alteration styles were found within the Platreef: amphibole-chlorite, talc-carbonate and serpentinisation. Hyperspectral imaging was successful in identifying and spatially resolving the serpentinisation and amphibole-chlorite alteration but not the talc-carbonate alteration, mainly due to the influence of spectral mixing and mineral vs. pixel size limitations. Amphibole-chlorite alteration, which is characterised by two generations of amphibole, variably replaced by chlorite, and a mass gain in MgO, Fe2O3 and SiO2, was found proximal to the calcsilicate rocks as Mg-Fe-Ca-amphibole veins. Very broadly, chlorite varies from Fe-rich to more Mg-rich compositions from the bottom to the top of the Platreef. Talc-carbonate alteration, which is mostly confined to the upper parts of the Platreef, was paragenetically later than amphibole-chlorite alteration and occurs either as veins or surrounds partly remobilised (chemically eroded) sulphide grains. It can be divided into two types, a primary talc-amphibole-mica assemblage and a secondary talc-carbonate/carbonate style. Both types show a mass loss of SiO2, Fe2O3, MgO, and a mass gain of CaO. Serpentinisation resulted in a mass gain in MgO and SiO2, and occurs either as pervasive replacements (prevalent in the lower zones of the Platreef) in the calcsilicate xenoliths, and (to a lesser extent) as veins in the pyroxenites. Remobilised sulphides are encountered in the amphibole-chlorite (pentlandite, pyrrhotite, pyrite and chalcopyrite), talc-carbonate (pentlandite, pyrite and chalcopyrite) alteration assemblages and to a lesser extent with serpentinisation (pyrite). From the spatial distribution of alteration, (i.e., from the calcsilicate rocks upwards this consists of serpentinisation (within the calcsilcates), amphibole-chlorite and then talc-carbonate zones) it is likely that the hydrothermal fluids responsible mainly originated from the metamorphism of sedimentary units found in the lower parts of the Platreef. A second, more local source of fluids may be linked to the later intrusion of A-type granitic dykes, as evidenced from the presence of relatively narrow haloes of talc alteration surrounding them (~1.5 m zone with parallel narrow veins) and from the similitude of element mobility with the talc-carbonate alteration. From textural relationships, mainly sulphide grain boundary alteration and infillings of veins, fractures and tension gashes, sulphide remobilisation was induced by the fluids responsible for the amphibole-chlorite and talc-carbonate alteration, and in a lesser extent with the ones associated with the serpentinisation. References:

[1] Holwell D (2006) PhD thesis. Cardiff University. [2] Harris C and Chaumba J (2001) South Africa Journal of Petrology 42:1321-1347

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Protracted timescales of magmatism documented in the Platreef, Bushveld Complex Tapster, S.R.1, McDonald I.2, Holwell D. 3 and Banks L.1,3

1Geochronology and Tracers Facility, British Geological Survey, Keyworth, NG12 5GG ([email protected]). 2Cardiff University, Park Place, Cardiff, CF10 3AT 3Univeristy of Leicester, Leicester LE1 7RH

___________________________________________________________________________ Models for the formation of the Rustenberg Layered Suite of the Bushveld Igneous Complex continue to be debated. The consensus timescale over which magmatism took place has reduced hand in hand with advancements in geochronological techniques and data precision. The most recent studies by double spiked (202Pb-205Pb) zircon CA-ID-TIMS U-Pb have indicated emplacement in less than 1 Myrs [1][2]. Increasing analytical precision has also seemingly permitted individual magmatic layers to be resolved, leading to the “out of sequence sill” emplacement model [2], albeit contested [3]. We present two new high-precision zircon dates obtained from two continuous core intervals collected <4m apart in a single Ni-Cu-PGE rich pyroxenite unit in the Turfspruit section of the Platreef, Northern Limb of the Bushveld Complex [4]. Grobler et al. [5] correlate this pyroxenite with the Merensky Cyclic Unit of the Upper Critical Zone in eastern and western limbs. Assuming the recommended zircon 238U/235U of Hiess et al. [6] without uncertainties propagated as per previous studies e.g. [1][2], the age interpretations of these two samples define a minimum and maximum temporal interval between 1.01 ±0.16 Myrs and 1.28 ±0.22 Myrs that brackets, or overlaps with, the entirety of previous dates from all preceding studies. The pyroxenite is continuous, without intrusive contacts, and the stratigraphically lower sample produces an apparently younger zircon age than the overlying sample. It seems highly unlikely the entire longevity of the Bushveld’s magmatic evolution was apparently captured within this 4 m section. Therefore, it now seems highly improbable that the Bushveld was emplaced and cooled in less than 1 Myrs, as the current paradigm states [1]. The older date from the Platreef now aligns the isotopic age relationships with the field observations of the overlying Main Zone, in contrast to the interpretation of Mungall et al. [2]. The new dates alone neither support nor contradicts the “out of sequence” sill emplacement model. Rather they merely indicate that melt related process that crystallised zircon was protracted within narrow vertical intervals, and that future work should acknowledge this potential complexity. It raises questions which age of event(s) introduced or modified sulfides within the ore bearing horizon. This requires future work to integrate the geochronological record with ore textures at a high sampling density. However, there also remains a substantial, yet previously overlooked caveat to all geochronological interpretations presented thus far; “out of sequence” sills in particular. This caveat is that the variations in the 238U/235U between samples over observed magnitudes of variations in zircon [4] could account for any offsets in 207Pb/206Pb dates interpreted as real temporal differences. This issue remains to be tested.

References:

[1] Zeh A et al. (2015) EPSL 418:103-114 [2] Mungall J et al. (2016) Nat. Coms. 13385 [3] Latypov R et al. (2017) South African Jour of Geol. 120.4, 565-574 [4] Nodder SM (2015) MESci dissertation, Cardiff University, 257pp [5] Grobler D et al. (2019) Min Dep 54, 3-28 [6] Hiess J et al. (2012) Science 418, 103-114

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session BASE METAL DEPOSITS

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Variations in White mica compositions in the quartz-sericite-pyrite alteration associated with the Perkoa VHMS, Burkina Faso. Brookes, H.C.Y.1,2*, Armstrong, R.N.2, Herrington, R.J.1,2, James, M.3 1Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK *Corresponding author: [email protected] 2Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD, UK 3Trevali Mining Corporation, 1400 – 1199 West Hastings Street, Vancouver, B.C., Canada

___________________________________________________________________________ The Perkoa Zn mine exploits a bimodal-felsic volcanic hosted massive sulphide deposit (VHMS) [1], situated in the northern part of the N-S trending Boromo greenstone belt, which belongs to the palaeoproterozoic, Birimian-volcano-sedimentary succession [2]. The host stratigraphy consists of transitional to calc-alkaline andesitic volcanics and volcanoclastic tuffs, with rare dacitic/rhyolitic lenses, which are intercalated with minor flysch and epiclastics. Mineralisation occurs as a set of near concordant, steeply dipping, stacked, sulphide-dominated lenses, hosted primarily in the andesitic volcaniclastic tuffs. Primary hydrothermal alteration associated with the lenses has resulted in pyrrhotite-dominated quartz-sericite hanging wall (HW) assemblages and extensive quartz-sericite-pyrite (QSP) footwall (FW) alteration, which entirely envelops the stratigraphically lower lens. The entire deposit was later metamorphosed to greenschist facies during the Eburnean orogeny [2], resulting in the NE-SW structural trend of the deposit and a chlorite overprint. The aim of this study is to assess mineralogical variations in the white mica compositions within the QSP alteration, in relation to the spatial proximity to mineralisation. 20 drill core samples where collected across the sulphide lenses and along strike representing the vertical and lateral changes in alteration. A set of 45 sub-samples from the initial 20 where analysed using X-ray powder diffraction

(XRD), under monochromatic Co K1 radiation. A systematic shift in the 002 white mica peak between 10.3° 2Ɵ and 10.6° 2Ɵ was observed, progressing from HW alteration to deep FW alteration, across both the main sulphide lens and the stratigraphically lower lens. 0-30m above the lenses, a peak position of 10.3° 2Ɵ suggests muscovitic compositions of white mica. FW alteration, 1- 127m below the main sulphide lens and 0-14m below the lower lens, showed a shouldered or double peak at 10.3° 2Ɵ and 10.6° 2Ɵ, indicating a bimodal population of white mica with muscovitic and paragonitic (10.6° 2Ɵ) compositions. All 8 samples taken from the along strike variants of the alteration assemblages (260m along-strike) display prominent peaks at 10.6° 2Ɵ, indicating paragonitic end members. Electron microprobe analysis will be conducted on 8 selected samples to discriminate and confirm the chemistry of the white micas through the QSP alteration. Additionally, a suite of whole rock geochemical pairs from the original samples will be analysed to confirm and investigate any geochemical trends towards mineralisation. This study has the potential to provide a vectoring tool towards other VHMS mineralisation, increase the target area and distinguish between barren and fertile QSP alteration around the district. References: [1] Parker O et al. (2019) SGA conference proceedings

[2] Baratoux L et al. (2011) Precambrian Research 191: 18-45

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Understanding New VMS Prospects in Tigray, Ethiopia: The Ophiolite-Related Teklil Cu Prospect Compared to Potential Au-Rich VMS Prospects of the Zager Licence Area Croft, D.1, Jenkin, G.1, Slater, W.2 and Richards, H.2

1School of Geography, Geology and the Environment, University of Leicester, Leicester, LE1 7RH, UK ([email protected]). 2Altus Strategies, 14 Station Road (Orchard Centre), Didcot, Oxfordshire, OX11 7LL

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The Zager and Daro Projects are Cu-Au greenfield exploration licences operated by Altau Resources, a wholly owned subsidiary of Altus Strategies, and lie within a rapidly emerging VMS district on the Arabian-Nubian Shield (ANS). The ANS hosts numerous other base and precious metal ore deposits including the relatively high grade Zn-Cu-Au-Ag Bisha deposit, Eritrea [1], and the Au(-Cu) Terakimti Project (East Africa Metals). This poster aims to review the mineralisation and geochemical associations of the Zager Licence in contrast to the comparatively better studied Daro Licence, in order to better understand the potential Au-rich nature of the deposit. Both licences lie within the southern shear-extension zone of the Neo-Proterozoic Nafka terrane of the ANS. This portion of the ANS comprises a belt of prospective metasedimentary and metavolcanic rocks which stretches across northern Ethiopia into Eritrea. Both licences contain southwest to northeast trending ophiolite belts obducted during the pan-African Orogeny. Current observations suggest mineralisation is dominated by Cu-oxides and Cu+Pb-sulphides in quartz veins. Geochemical data obtained from rock-chip assay returned grades of up to 27.1 g/t Au and 1.5% Pb from prospects in the Zager licence, while copper grades up to 34% and gold grades of up to 21.6 g/t have been reported in the Daro Licence. Thin section and polished block investigation of samples from both licence areas will be used to constrain relationships between mineralisation and alteration from samples collected during exploration work. Where mineralisation is observed scanning electron microscope (SEM) analysis may be employed to further look at sulphides and other minerals of interest. References: [1] Barrie C T et al. (2007) Econ Geol 102: 717-738

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Ni enrichment associated with Fe isotope fractionation in Ni laterite deposits, Sulawesi Island, Indonesia

Ito, A.1, Otake, T.2, Maulana, A.3, Sanematsu, K.4, Sufriadin5 and Sato, T.2

1Department of Applied Chemistry for Environment, School of Science and Technology, Kwansei Gakuin University, Hyogo, Japan 2Division of Sustainable Resource Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, Japan 3Depertment of Geological Engineering, Hasanuddin University, Makassar, Indonesia 4Geological Survey of Japan, AIST, Tsukuba, Japan 5Department of Mining Engineering, Hasanuddin University, Makassar, Indonesia

___________________________________________________________________________ Ni laterite deposits, formed by intense chemical weathering of ultramafic rocks under tropical to subtropical climate, are important resources of Ni and potential targets for other critical metals (e.g., Co, Sc, PGE) [1]. Ni laterite deposits are well developed in modern and ancient tropical to subtropical regions, such as New Caledonia, Western Australia, and Southeast Asia, including The Philippines and Indonesia, which have been the major Ni supply sources in recent years. However, only a few studies have been conducted for Ni laterite deposits in these countries. In order to understand chemical weathering processes involving enrichment of Ni and other critical metals, we investigated the geochemistry and Fe isotopic compositions of 4 Ni laterite profiles developed on peridotites with different degrees of serpentinisation in the Soroako and Pomalaa areas, Sulawesi Island, Indonesia. The major and minor element concentrations were analyzed by XRF and ICP-MS, the mineralogical compositions were obtained by XRD. Fe isotopes were analyzed by MC-ICP-MS (RIHN, Kyoto) after acid digestion with HNO3+HF and HCl in a stainless bomb and purification using anion exchange column. Si and Mg, major components in the bedrocks, decrease upward through the depth profile at all hills. Conversely, contents of other elements, such as Fe and Al dramatically increase. At Watulabu Hill and Konde Hill, where peridotite is the bedrock, Ni contents show significant enrichment in the upper limonite horizon (<2.44 wt%). In contrast, Petea Hill and Willson Hill exhibit greater concentrations of Ni (up to 3.66 wt%) than those at Watulabu Hill and Konde Hill, with the highest Ni contents found in saprolite horizons. Major and minor element transfer calculations, using Ti as an immobile element, show that Si and Mg display absolute losses in the profiles at all the hills. Conversely, other major elements such as Fe and Al show moderate to large gains in the limonite horizon, whilst Ni shows large gains in the limonite or saprolite horizons. Fe and Ni throughout the profile at all hills are positively correlated, suggesting that Fe behaviour influences Ni enrichment during chemical weathering. Moreover, the greatest gains of Fe and Ni in the profile were found in the profile at Petea Hill, which may indicate that the intensity of chemical weathering and element redistribution is extremely high. Measured δ56Fe values show slight variations in the profiles, except for Petea Hill. Here, the limonite horizon tends to show isotopically lighter δ56Fe values (avg. -0.07‰) than that of the bedrock (-0.02‰), whilst the saprolite horizon shows heavier δ56Fe values (avg. +0.03‰). This suggests that Fe isotopes may be fractionated in a Ni laterite profile, where strong enrichment of Ni accompanies large gains of Fe due to intense chemical weathering. The light δ56Fe values observed in the limonite horizon also indicates that partial reduction and dissolution of oxyhydroxides occurs at the surface, which may be one of the important factors that controls remobilisation and enrichment of Ni in the saprolite horizon [2].

References:

[1] Aiglsperger T et al. (2016) Ore Geol. Rev. 73:127-147

[2] Beard et al. (2003) Chem. Geol. 195:87-117

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Extending the Irish Carboniferous lead-zinc play into northern England? Evidence from basin analysis and seismic interpretation Jenkins, A.P.1,2, Torvela, T.2 1University of Bristol, School of Earth Sciences, BS8 1QU, UK. Corresponding author (A. Jenkins) [email protected] 2University of Leeds, Ores and Mineralisation Group, School of Earth and Environment, LS29JT, UK

___________________________________________________________________________ Stratiform and stratabound base metal ores typically form in sedimentary basins during the overall rifting process. Understanding the detailed structural evolution of the basin is critical for exploration efforts, and adopting approaches from petroleum industry can be very beneficial. In this presentation, we show an example of how seismic interpretation and basin analysis techniques can help to assess the potential for Pb-Zn mineralisation within the Northumberland Trough, northern England, in the context of the wider Carboniferous basin system and the associated base metal ores. Through structural interpretation of seismic reflection data, we consider detailed fault and sedimentation evolution in time and space, to show that Early Carboniferous growth packages exist at depth in the study area: these are, from a structural and basin evolution point of view, capable of hosting mineralisation similar to that in Ireland. We suggest a refined model for the evolution of this part of the basin, including a model where the younger (early Permian) vein-style mineralisation in Northumberland may reflect remobilisation of the older, Early Carboniferous stratabound Pb-Zn mineralisation at depth.

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The recognition of depositional bed-forms on fine sediments in some hydrothermal veins in central Wales

Platten, I.M.1 and Dominy, S.C.2

1Independent, [email protected] 2Camborne School of Mines, Penryn, Cornwall TR10 9FE. [email protected]

___________________________________________________________________________ Old mine tips around Bryn-y-rafr mine in the central Wales Pb-Zn mining district yield small numbers of blocks with a fine (0.2 to <0.05mm, most <0.05mm, where identifiable) sediment accompanying the normal hydrothermal quartz, quartz+galena and quartz+marcasite infills that characterise the A2 assemblage of Mason [1]. These show geopetal structures similar to those seen in situ at Tyndrum [2] but with more residual pore space, allowing structures to be seen in 3 dimensions. Descriptions here are based on the approximate orientation inferred from the geopetal indicators. The fine sediments are seen filling narrow (<20mm) veins and the pore spaces in breccias. The veins show wall lining quartz with terminations buried by axial fills of fine sediment. Drapes of fine sediment within the quartz show that vertical settling from turbid water occurred during quartz growth. Internal layering and layers of upwards growing quartz in the axial fill record former positions of the sediment-water interface and confirm the depositional order. Breccia cavities can show similar features but with irregular walls. Floors of larger (>100mm) breccia cavities show complex fills, with the last event showing well preserved bed-forms. Block fracture surfaces show the whole sequence of floor deposition. Sediment penetrates breccia below the cavity, largely filling pores. Floor accumulations are divided into units by intermittent growth of quartz layers (0.1-5mm) with terminated top surfaces. Internal layering within these unit is visible, best seen in thin section. Sediment deposition is limited on steeper surfaces and absent from overhanging surfaces which show normal hydrothermal mineral growth. Sediment surfaces in 3D show features both independent of, or reflecting, the substrate topography. Nearly planar or gently curved surfaces are common, abutting the steeper walls of the cavity. Block sides show the pre-existing topography is buried and internal layers also abut walls and objects projecting from the floor. Subparallel arrays of round topped ribs occur, oriented close to inferred downslope directions and showing up and/or down slope terminations. Some ribs are the result of local sediment layer thickening. Cone like forms stand above the flatter surfaces and are downslope from notches or chutes in the cavity wall. Fine lineations occur on top surfaces, running downslope. These features all indicate deposition from flowing water. Large clasts projecting above the cavity floor can show accumulation of sediment forming a domed pad on the top. These thin as the clast sides steepen. Overhanging parts of the clast are coated with coarse terminated quartz. The transition in the steepest zone shows discontinuous drapes on up-facing crystal facets of quartz. These show that deposition was occurring from suspension and water flow across the surface was limited. The drapes around the clast sides provide limits to the dip of surfaces capable of holding sediments before avalanching occurred and also show that turbid water was more than 30mm thick. Sediment deposition shows influence from flow of water and settling in water filled pores. The development of ribs suggests deposition from suspensions in flowing water, consistent with silt size particles. The deposits would also indicate a limited amount of downflow in the hydrothermal system. Further work is aimed at particle/cement petrography and the roles of avalanching, localised turbidity flows and bulk water movement.

References:

[1] Mason J (1997) Trans Inst Min Met, 106:B135-143

[2] Platten I and Dominy S (2007) Expl Mining Geol, 16:37-66

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The Syrymbet tin deposit, Northern Kazakhstan Seltmann, R.1, Dolgopolova, A.1, Zhang, R.2, Kiseleva, G.3 and Shatov, V.4

1Natural History Museum, CERCAMS, London, UK; [email protected] 2Nanjing University, China 3IGEM RAS Moscow, Russia 4VSEGEI St. Petersburg, Russia

__________________________________________________________________________ Syrymbet, situated in northern Kazakhstan and discovered in 1985, is in global scale one of the

largest tin deposits and currently under development by “JSC Tin One Mining”.

The complex anatomy of the deposit comprises three deposit types and mineralization styles [1,2]:

1) Sn enriched weathering crust (aiding the initial discovery);

2) metasomatic ore bodies in the exocontact of the multiphase Syrymbet granite pluton intruding

skarnified carbonate rocks and hornfelsed shales of Vendian age;

3) high-grade mineralization structurally confined to steep shear / thrust faults in exocontact rocks

intruded by stocks and dikes forming a subvolcanic-cataclasite complex of bimodal composition. The

ore-bearing intrusions are dominantly leucocratic Li-F porphyritic microgranites (tin porphyries”).

Mineralization sequence and ore stages can be characterised as follows: in the thermal aureole of

the multiphase granitoid intrusions formed first prograde garnet– pyroxene – vesuviane - magnetite

skarns, followed by retrograde replacement comprising amphibole, chlorite, epidote, and sulphides.

The garnet contains up to 0.7 wt.% Sn. The main mineralization relates to hydrothermal greisen veins

(cassiterite, sulfostannates) that are spatially and temporally associated with leucogranite dikes and

stocks. Our ongoing study has established a robust U-Pb cassiterite mineralization age of ~ 405 + 5

Ma (Emsian, Lower Devonian).

The ores have a complex character where fine-grained cassiterite and intergrowth with silicates and

sulphides create challenges for ore processing and geometallurgy, delaying the exploitation of the

deposit for the past decades. Besides of Sn, the ores contain W, Nb, REE, Cu, Pb, Zn, In, F, Mo, Bi, Te,

Au, U, Th – some of which are economic.

References:

[1] Sirina TA (1994) Geol Ore Dep 36,5: 1-10 (Geol Rudn Mest 36,5:442-452 [Russ.])

[2] Halls et al. (2004) Atlas Min Dep Models Kazakhstan, CERCAMS NHM, 142p.

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session MAGMATIC AND HYDROTHERMAL PROCESSES ASSOCIATED WITH ORE FORMATION

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Magnetic fabrics: measuring the orientation of different hydrothermal fluid events? Dixon, O.1, Richardson, K.1 and McCarthy, W.1 1University of St. Andrews, Irvine Building, North Street, St Andrews, KY16 9AL. Email: [email protected].

___________________________________________________________________________ Magmatic fabric analysis using anisotropy of magnetic susceptibility (AMS) is used to define and quantify magnetic fabrics of granitoid rocks in a variety of different tectonic settings. While AMS has often been used to determine the tectonic strain acquired during ductile microstructure development [1], very few studies have focused on the effect hydrothermal alteration [2,3] and brittle deformation has on these magnetic fabrics. This study utilises both in-phase (ip) and out-of-phase (op) AMS to distinguish the orientation of different vein generations in diamond drill core samples from a large porphyry copper system. From petrographic studies conducted on samples from the Cu-Mo Aktogay Mine in East Kazakhstan, six distinct generations of veins were identified based on their mineralogy. Through AMS and magnetic characterisation experiments it has been shown that these different vein sets have different magnetic mineralogies, defined by vein sets with minerals that have an op magnetic response and those that do not. In the samples that have an op magnetic mineralogy, AMS is picking up two distinct fabrics, which includes a sub-fabric associated with the orientation of the veins and one that is associated with the magmatic fabric of the sample. These findings show that the different hydrothermal fluid flow events that occur during porphyry deposit generation display different magnetic mineralogies and, with careful analysis of ip and op AMS results, the orientation of these fluid flow events can be identified. Therefore, this can be utilised to map and track alteration related to different fluid phases in the evolution of a porphyry system. Further rock magnetic experiments are being carried out to fully understand the causes of the distinct ip and op AMS signals measured in these diamond drill cores.

References:

[1] Hrouda F (1994) Geophy J Int 118: 604-612

[2] Just J et al. (2004) Geol Soc 238: 509-526

[3] Just J and Kontny A (2012) Int J Earth Sci 101: 819-839

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The fluid and melt inclusion record of the magmatic-hydrothermal transition in magma chambers and its bearing to ore formation Fiedrich, A.M.1, Laurent, O.1, Heinrich, C.A.1 and Bachmann, O.1 1Institute of Geochemistry and Petrology, Department of Earth Sciences, ETHZ, Clausiusstrasse 25, 8092 Zürich, Switzerland; [email protected]

___________________________________________________________________________ The magmatic-hydrothermal transition represents one of the first steps in a chain of events that may lead to the formation of economic ore deposits. This separation of fluid from the silicate melt at depth can be recorded in the form of fluid and melt inclusions, entrapped in magmatic minerals. However, magmatic-hydrothermal ore deposits such as porphyry copper deposits represent a non-ideal environment for preserving the original element concentrations in such inclusions because of relatively slow cooling in the Earth’s crust and possible hydrothermal overprinting. Explosively erupted volcanic rock samples, on the other hand, are rapidly quenched so that diffusion of elements is minimized. Here, we present two sample sets that characterize fluid exsolution in the magma chamber and allow the estimation of element distribution between fluid and melt. The results are based on extensive microthermometry and laser ablation inductively-coupled plasma mass spectrometry analyses. The rhyolitic Kos Plateau Tuff (KPT; Greece; 160 ka [1]) and the dacitic Escorial Ignimbrite (Argentina; 460 ka [2]) both brought clasts to the surface that sampled the magmatic-hydrothermal transition. While the KPT formed in thin continental crust (ca. 30 km) characterized by slow subduction, the Escorial Ignimbrite formed in thickened crust of the Andean Puna (ca. 60 km) characterized by fast subduction. These contrasting geodynamic environments have important consequences for the ore-forming potential of the magmas [3, 4]. The KPT clasts are granites derived from the margin of the magma chamber seated at ca. 2 kbar. The origin of large (cm-sized) quartz clasts in the Escorial Ignimbrite is more complex, as indicated by their trace element budget. In both cases there appears to be a two-stage development with a higher-pressure stage recorded by low-salinity, intermediate-density fluid and a lower-pressure stage indicated by co-existing brine and vapor. At least in the case of the KPT, decompression likely resulted from volcanic eruption. In terms of element distribution, the first results indicate: (a) strong partitioning of economically important metals such as Cu, Mo, Sn, and W from the silicate melt into the fluid and (b) relatively low Cu concentrations in the fluid (ca. 100-500 ppm), suggesting that indeed fluid inclusions from ore deposits may have suffered post-entrapment Cu enrichment. Even relatively low Cu concentrations, however, are sufficient to form economic Cu mineralization [5].

References:

[1] Smith PE et al (1996) Geophys Res Letters 23: 3047-3050

[2] Richards JP and Villeneuve M (2002) JVGR 116: 161-200

[3] Lee CT and Tang M (2020) EPSL 529: 115868

[4] Sillitoe RH and Perelló J (2005) Econ Geol 100th Anniv Vol: 845-890

[5] Chelle-Michou C et al (2017) Sci Rep 7: 40566

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A pyroxenite xenolith record of subduction-related metal and metalloid mobilisation in the upper mantle and lower crust Hughes, H.S.R.1*, McDonald, I.2, Matusiak-Małek, M.M. 3, Rollinson, G.K.1, Buczko, D.3

1Camborne School of Mines, College of Engineering, Mathematics & Physical Sciences, University of Exeter, Penryn Campus, Penryn TR10 9FE, UK (*[email protected]) 2School of Earth and Ocean Sciences, Cardiff University, Main Building, Cardiff CF10 3AT, UK 3University of Wrocław, Wrocław, Poland

___________________________________________________________________________ Mineralisation in the crust is the culmination of multiple factors from the source of the

magma/metals to the location of ‘deposition’ of the ore body. Whilst the main concentrating events

that lead to mineralisation are predominantly crustal processes (e.g., magmatic differentiation, S-

saturation, etc) the fertility of the source region is important. The lower the concentration of metals

in the source region, the more ‘upgrading’ is required by later (crustal) processes. By understanding

the principals dictating source composition and fertility, we may inform mineral exploration models.

Partial melting of mantle peridotites releases base metal sulphides (BMS) and their metal

budget into silicate magma generated, but what proportion of these metals become trapped in the

lithospheric mantle and lower crust during magma ascent? Pyroxenite xenoliths are material from

the melting, assimilation, storage and homogenization (‘MASH’) zone overlying subduction

environments and hence provide a unique insight into the magma and metallogenic processes.

We use clinopyroxenite xenoliths, biotite-clinopyroxenite xenoliths, websterites and

clinopyroxene megacrysts (in comparison to various peridotite xenoliths) from the Hebridean and

Midland Valley terranes of Scotland and Scania of Sweden. These xenoliths are entrained in Permian

(Midland Valley Terrane basanite vent), Jurassic (Scania basanite vent) and Eocene (Hebridean

Terrane monchiquite lamprophyre dyke) host rocks. We present in situ mineralogical and

geochemical analyses of BMS in pyroxenite xenoliths and pyroxene megacrysts to measure the metal

and metalloid budget of the MASH zone and gain an insight into the mobility of HSE and chalcophile

elements in a suprasubduction mantle wedge.

The concentration of Au in BMS ranges from < 0.02 to 2.2 ppm (mean = 0.1 ppm), Te from <

0.06 to 74 ppm (mean = 2.9 ppm), Se from < 10 to 598 ppm (mean = 142 ppm) with S/Se ranging

from 635 to 76,000 (mean 5664), and total PGE ranging from 0.11 to 9.5 ppm (mean = 0.44 ppm).

Overall we find that Cu-Fe-rich sulphides dominant BMS present within pyroxenite xenoliths (as

opposed to Ni-(Co)-Fe-rich sulphides in peridotite xenoliths). These have low to very low Ir-group

PGE (IPGE) concentrations and low total PGE abundances. Palladium and platinum are present in low

abundances in BMS of pyroxenite xenoliths but these are variable Pd and Pt due to the presence of

micro-nuggets of platinum-group minerals. Initial results suggest that the Au and Te budget of

mantle pyroxenites may not be strictly controlled by BMS and therefore sulphide liquids in the

mantle and lower crust.

Combined with thermometry for the pyroxenite xenoliths to contextualise them within

lithospheric pile, and xenolith mapping by QEMSCAN to investigate the petrographic siting of BMS

(e.g., interstitial vs included) and texture, we aim to assess the mobility of sulphides, metals and

metalloids in parental melts and/or metasomatic agents within the uppermost mantle and lower

crust.

This research is funded by the Polish National Science Centre grant no. UMO-2016/23/B/ST10/01905.

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Micas, Melting and Mineralisation Kunz B.E*., Warren C.J., Jenner F.E., Argles T. and Harris N.B.W.

1School of Environment, Earth and Ecosystems Sciences, The Open University, Milton Keynes MK7 6AA, UK. *Corresponding author: [email protected]

___________________________________________________________________________ The origin of critical metal (Li, Cs, Ta, Sn & W) mineralisation in S-type granites has long been a matter of debate. Classical models involve formation from pre-enriched protoliths [1] or extreme fractional crystallisation and late fluid exsolution from an enriched magma [2,3]. Previous work has suggested that a combination of protolith composition and temperature-dependent mineral breakdown might be critical for concentrating critical metals during prograde solid-state metamorphic reactions and then releasing them during subsequent partial melting [4].

Micas, along with certain accessory mineral phases (e.g. rutile), are an important host for many critical metals. Micas form a major part of the mineral assemblage in many metamorphic rocks, spanning a large range of P-T conditions and lithologies. Their high modal abundance in many metasedimentary rocks are likely a key factor in whichever process(es) act to concentrate and release critical metals. We have analysed critical metal concentrations in muscovite and biotite in a number of metasedimentary samples of different metamorphic grade in order to investigate the abundance and partitioning behaviour. Samples from a section across the Main Central Thrust Zone in the Sikkim Himalaya record changes in mica composition from greenschist to upper amphibolite facies. Samples from the Ivrea Zone in Italy changes in mica composition from mid amphibolite to granulite facies. Together these crustal sections cover geochemical changes related to fluid absent melting of both muscovite (Himalaya and Ivrea Zone) and biotite (Ivrea Zone).

Preliminary in situ LA-ICP-MS trace element data from both muscovite and biotite in both continuous crustal sections shows distinctive and predictable changes in concentration during prograde metamorphism. These trends provide a preliminary framework in which to observe and predict systematic changes in mica metal concentration from solid-state metamorphism through partial melting at a range of temperatures.

References:

[1] Romer R.L. and Kroner U. (2014) Min Dep 47:327–338

[2] Lehmann B. (1987) Geol Rund 76:177–185

[3] Štemprok M. (1990) Geol J 25:413–417

[4] Wolf M. et al. (2018) Lithos 310-311:20–30

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Mineral Deposits Studies Group Annual Meeting 2020 Poster Session NEW METHODOLOGIES

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High precision geochemical analysis on low amounts of sample by low-volume solution ICP-MS Banks, L.A.1,2, Tapster, S.R.1, Horstwood, M.S.A.1, Chenery, S. R.1, Smith, D.J.2, Barry, T.L.2

1British Geological Survey, Nottingham, NG12 5GG, [email protected] 2University of Leicester, Leicester, LE1 7RH

___________________________________________________________________________ Ore deposit research and geochemical exploration techniques are underpinned by trace element, isotopic and geochronological studies. These methods are used to explore variation across an orebody, with the aim of understanding the genesis of the deposit itself. Material limited samples, both in terms of the amount of mineral and amount of element can make such analyses impossible, meaning that there is a significant ‘gap’ in the analytical spectrum. For example, certain elements and isotopes are out of the reach of microbeam analysis methods, such as laser ablation (LA) ICP-MS, and heterogeneity of an orebody can be at a finer scale than can be resolved using bulk crystal analysis. Here, we demonstrate a new, novel method of solution-mode ICP-MS, known as low-volume sampling [1]. We demonstrate with the use of uranium isotopes that by changing the way a sample is introduced to the plasma, comparable precision can be achieved with four times less material than conventional solution ICP-MS. When using the same amount of material (2 ng U), a 2.5 times improvement in the precision is gained over the conventional method. Uranium is an extremely redox sensitive element with a very large range in relative abundance of the isotopes. These step-changes in analytical capability bring significant benefits to geochemical techniques. Low-volume solution ICP-MS will allow single crystal analysis of orthodox minerals to become routine, improving upon bulk dissolution. This method will also open new doors to routine analysis of novel minerals with concentrations of element previously too low to measure, realising the spatial resolution of LA-ICP-MS with the precision of solution ICP-MS. Linking these single crystal analyses to trace element, petrographic and geochronological records will allow a much deeper understanding of geochemical models for ore deposits. References:

[1] Bauer A.M. and Horstwood, M.S.A. (2018) Chem Geol 476:85-99

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The Natural History Museum’s ore collection: A unique sample repository for ore deposits research Kocher, S.1 1 Natural History Museum, Cromwell Road, London SW7 5BD, UK, [email protected]

___________________________________________________________________________ The origins of the Natural History Museum’s (NHM) ore collection date back to the Museum of

Practical Geology founded in 1838 by Sir Henry de la Bêche. The museum built an extensive

collection of geological materials, including ores from all areas of the British Empire to “exemplify the

applications of the mineral productions (…) to purposes of use and ornament”. Today the collection

supports ongoing research within the Museum and the wider academic community. It also acts as a

teaching and training resource for undergraduates, postgraduates and exploration geologists.

Research on the collection is supported by the Ores research team and state-of-the-art analytical

facilities at the NHM.

Through its continuous development, the ores collection now contains over 30,000 specimens

representing more than 2,600 localities in 108 countries. Due to its long history, this collection offers

a unique opportunity for economic geology researchers to sample material from defunct or

inaccessible localities or parts of ore deposits long since completely mined out. Representative

sample suites from various deposits and mine camps, including mineralisation and alteration, have

been added systematically in recent years to utilise the collection for current research on

mineralising processes.

To maintain the collection’s significance and to increase its potential we strongly encourage

colleagues from academia and industry worldwide to make use of this unique sample repository for

research and bespoke training. We also seek donations of suites of samples with good geospatial

data and geological context representing the mineralogy, mineral and host rock assemblages,

mineral textures and mineralization styles present at each location/deposit. By lodging material with

the Natural History Museum, donors are preserving representative materials for future generations

of mineral explorers and researchers. Industrial partners who help us to enhance the collection are

given in return access to use our collection as a 'training ground’ for their exploration geologists.

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Portable XRF analysis for porphyry fertility indicators Marquis, E., Hamp-Gopsill, L.J., Pearse, M., Marvin-Dorland, L., Knott, T. R., Smith*, D.J. School of Geography, Geology and the Environment, University of Leicester, United Kingdom, [email protected]

___________________________________________________________________________ Modern exploration strategies for porphyry copper mineralisation include the application of “fertility indicators”. These are geochemical or mineralogical indicators that processes or conditions were consistent with, and favourable for, a model for ore genesis [1, 2, 3]. Typically, these would target rocks genetically linked to mineralisation, but are not dependent on them containing mineralisation or even alteration. Thus, fertility indicators can be used in regional- or district-scale targeting and screening to prioritise specific igneous complexes or even intrusions. Sampling strategies for fertility indicators may include the collection of detrital, resistate accessory minerals (such as zircons), or the collection of fresh to lightly altered/weathered igneous rocks. Key analytes include major oxides, large ion lithophile elements, high field strength elements, and rare earth elements. Thus, a range of elements must be quantified, and ideally at low cost (given that they are indirect indicators of mineralisation). X-ray fluorescence (XRF) represents an excellent tool for major and trace element analysis in the parts per million to weight percent range. As a solid-state technique there is no risk of resistate minerals being under-represented in final analyses due to incomplete digestion. Modern XRF analysers are available in hand-held and portable form factors, suitable for camp or field deployment, and are capable of generating multi-element analyses in under two minutes per sample. We have completed a series of experiments to determine the accuracy and precision of an Olympus Vanta VMR handheld XRF analyser (50 kV X-ray tube and Rh anode) across its elemental range, and differing levels of sample preparation (crushed-milled-pelleted in a hydraulic press, and in handheld die; crushed and presented in polythene bag; unprepared rock face). Performance on elements used in igneous classification and in fertility indicators (e.g. Y, Sr, V, Mn) were particularly scrutinised. The accuracy and precision of the handheld analyser was high for optimally prepared samples (pressed pellets). Quality decreases for less-well prepared samples, with the worst performance from coarsely crushed and bagged samples. In optimally-prepared samples, performance across a range of trace elements was excellent, with accuracy and precision sufficient to allow the analyser to be used as a fully-quantitative instrument. Performance on major elements (Si, Al, K, Ca) is somewhat lower. Our results mirror those of a previous study on pellets and slabbed samples for the Sr/Y fertility indicator [4], but we note that rough sample faces or coarsely crushed sample lead to reduced data quality due to X-ray scattering [5] – sample preparation is a key contribution to overall error. Fertility indicators based on LILE and HFSE trace elements have good performance; those requiring careful discrimination based on total alkali-silica need to be used with caution. Those that are based on lanthanide elements were not possible with the configuration or our instrument. Field portable XRF analysers represent an excellent opportunity to collect large amounts of quantitative fertility indicator data cheaply and quickly. References:

[1] Sun et al. (2013) Geochim Cosmochim Acta 103:263-275

[2] Loucks (2014) Aust J Earth Sci 61:5-16

[3] Loader et al. (2017) Earth Plan Sci Lett 472:107-119

[4] Ahmed et al. (2019) GEEA [online: 10.1144/geochem2018-077]

[5] Lemière (2018) J. Geochem Explor 188:350-363

This work was supported by NERC grant NE/P017053/1 “FAMOS: From Arc Magmas to Ores”.

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Direct dating of hydrothermal copper-gold systems using calcite U-Pb geochronology from the central Yukon Territory, Canada Mottram, C.M.1, Kellett D.2 and Baressi T.3 1 SEGG, University of Portsmouth [email protected] 2Geological Survey of Canada 3Triumph Gold Corp.

___________________________________________________________________________ Interaction between magmatic intrusions, fluids and the surrounding rocks causes enrichment of metals such as Cu, Au, Mo in porphyry style deposits. In these settings the metals are intimately associated with veins containing minerals such as quartz and calcite. In order to develop predictive models for mineralised systems it is imperative to understand the timing of emplacement of these veins. Dating of hydrothermal veins, however, has proved challenging in the past due to lack of suitable ‘datable’ material. Here we aim to use the newly-developed U-Pb calcite dating technique to test the capabilities of calcite dating for providing robust and critical timing constraints for ore-deposit models. The Canadian Cordillera is one of the Earth’s foremost examples of an accretionary mountain belt, formed over the last >200 million years. The central Yukon region of the northern Cordillera underwent a prolonged history of deformation, faulting, magmatism and related mineralisation during Cordilleran accretion. The Dawson Range in the central Yukon is locally enriched in Au, Cu, Mo and other metals largely association with magma bodies (porphyry, epithermal and skarn type deposits) hosted in large continental-scale strike-slip fault zone systems, such as the Big Creek Fault (BCF) system. Here, we use in-situ laser ablation U-Pb calcite dating to directly-date mineralised carbonate veins from the Late Cretaceous porphyry deposits associated with the BCF. Initial results indicate two unambiguous carbonate veining events, one during the Late Cretaceous (~73 Ma) and a second during the Paleocene (~55-60 Ma). This suggests that there were distinct pulses of mineralisation associated with granitoid emplacement and faulting on the BCF. Our results represent a significant contribution to tectonic and mineralisation models for the region and explore the role of major faults, such as the BCF for hosting and facilitating deposition of economic Cu-Au deposits. Furthermore, our results demonstrate the potential for calcite U-Pb dating to provide timing constraints for hydrothermal mineralisation processes in a variety of deposit-type settings.

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Advantages and challenges of integrated automated mineralogy (TIMA X-

analyser, TESCAN) for the characterization of Ni-Co laterite ores: the example

of the Wingellina deposit (Western Australia)

Santoro, L.1*, Putzolu, F.2, Mondillo, N.1,2, Boni, M.1,2, Herrington, R.2, Dosbaba M.3,

Maczurad, M.4

1Earth Sciences Department, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK 2Dipartimento Scienze della Terra Università di Napoli “Federico II” Complesso Universitario di Monte S.

Angelo, Via Cintia 26 80126-Napoli, Italy 3TESCAN, Libusina trida 1, 623 00, Brno, Czech Republic 4Metals X Limited, L5/197, St Georges Terrace, Perth WA, 6000, Australia

*Corresponding author: [email protected]

___________________________________________________________________________ The successful Ni and Co extraction from laterite deposits is strictly related to the accuracy of the chemical, mineralogical and textural characterization of the ores. Due to their very complex ore-bearing mineralogy and chemistry, the routine evaluation of laterite ores can be a knotty challenge. In this study, we present an accurate characterization and a quantitative evaluation of samples deriving from the limonite and smectite ore zones of the Wingellina laterite deposit (Western Australia) [1,2]. The analyses were carried out by a combination of conventional analytical methods (XRPD, SEM-EDS, ICP-MS/AES), and by automated mineralogy methods (TIMA-X analyser, TESCAN), with the aim of investigating their effectiveness in quantifying the amounts of Ni- and Co-bearing Mn-(hydr)oxides (MnO/OH) and in assessing the nature of amorphous material, which by using only XRPD-related methods is hardly classified either due to the absence of structures in the mineralogical dataset (e.g. complex MnO/OH as asbolane) or due to the structural complexity of some mineralogical phases (e.g. smectite clays). The results obtained with the different methods were then compared for validation.

In the limonite ore, goethite and MnO/OH, together with significant amounts of amorphous material, are the main phases. TIMA analyses were able to re-classify the amount of the amorphous as Fe-oxy-hydroxides (FeO/OH) and MnO/OH. Based on their chemistry (i.e. Al/[Ni+Co] ratio), Co- and Ni-bearing MnO/OH were classified as lithiophorite, lithiophorite-asbolane intermediates and as asbolane. In the smectite ore, XRPD detected remarkable amounts of amorph, which TIMA reclassified on the basis of the chemistry as smectite with subordinate FeO/OH and trace amounts of MnO/OH. Even though smectite hosts high Ni amounts, MnO/OH also deports significant amounts of Ni and Co. Another interesting outcome is that part of Co in both ore types deports in mixed classes (i.e. montmorillonite-asbolane-goethite and asbolane-goethite), which correspond to fine minerals intergrowths that have not been discriminated by TIMA.

In conclusion, the main advantages of automated analyses on Ni-Co laterite ores are: i) identification and classification of complex ore-bearing MnO/OH on the basis of their chemistry that are hardly detected by XRPD. This can be a useful information to choose the processing methods, as the presence of abundant Al-bearing MnO/OH (i.e. lithiophorite) during High Pressure Acid Leaching (HPAL) can promote the formation of alunite, which is detrimental for the efficiency of the ore treatment [3]; ii) compilation of element assays and deportment, which helps to predict the metal recovery. The main limitation of TIMA is related to the size of the TIMA excitation beam, which hardly resolves the fine-grained texture of laterites ores [4]. References: [1] Putzolu et al. (2018) Ore Geol Rev 97:21–34. [2] Putzolu et al. (2019) J Geochem Expl 196:282-296. [3] Kaya and Topkaya Miner Eng 24:1188-1197. [4] Santoro et al. (2014) Miner Eng 69:29-39.

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AUTHOR INDEX A Abdullayev, R., 50 Abramova, V.D., 20 Acheampong, K., 35, 64 Allibone, A., 15 Andersen, J.C.Ø., 34, 35, 63 Anderson, M., 32 Andrews, H.R., 50 Argles T., 75 Armstrong, R.A., 49 Armstrong, R.H., 53 Armstrong, R.N., 19, 50, 66 Azevedo, S., 40 B Bachmann, O., 73 Baisalova, A., 42 Bambi, A., 40 Banks, L., 66, 76 Baressi, T., 79 Barrote, V., 36 Barry, T., 25, 76 Beard, C., 9, 41 Berry, J., 22 Blanks D.E., 26, 51 Blenkinsop, T., 13, 15 Boni, M., 12, 30, 80 Borst, A.M., 9, 40 Boyce, A., 13, 31, 48 Brookes, H.C.Y., 66 Broom-Fendley, S. 9, Brugge, E., 21, 52 Buczko, D., 74 Buret, Y., 17, 18, 19, 21, 23,

52, 56 Butcher, A.R., 37 Bybee, G.M., 27, 63 C Carter, L.C., 19, 53 Caruso, S., 36 Chenery, S.R., 76 Chirico, R., 30 Clarke, R.H., 14 Cloutier, J., 48 Compton-Jones, C., 27, 63 Cook, N., 37 Croft, D., 67 Cundari, R., 24 Currie, D., 31 D

Das, S., 38 Daya, P., 27 Deady, E., 41 Dehaine, Q., 37 Deng, C., 59 Dilles, J., 16 Dixon, O., 72 Dolgopolova, A., 42, 71 Dominy, S.C., 70 Dos Santos, A., 40 Dosbaba, M., 80 Doyle, P., 43 E Eskdale, A.E., 47 Essien, B., 31 Estrade, G., 44 Eugenio, A., 40 F Faithfull, J., 31 Ferguson, J.J., 35 Fiedrich, A.M., 73 Finch, A.A., 9, 40 Foury, S., 36 G Gleeson, S.A., 29 Goodenough, K., 8, 9, 13, 41,

44 H Haase, K.M., 32, 62 Hamp-Gopsill, L.J., 78 Hannington, M., 32 Harbidge, R.C., 15 Harris N.B.W., 75 Hart-Madigan, L., 54 Harutunyan, M., 55 Heinrich, C.A., 73 Herrington, R. J., 4, 11, 12, 66,

80 HiTechAlk Carb, 46 Holliday, J., 15 Hollings, P., 24 Hollis, S.P., 36 Holwell, D.A., 22, 25, 57, 65,

14, 26, 51 Horstwood, M.S.A., 76 Hovakimyan, S., 55 Hughes H.S.R., 27, 34, 35, 58,

63, 64, 74 Hutchison, W., 9

I Ihlenfeld, C., 17, 18 Ito, A., 68 J James, M., 66 Jenkin, G., 67 Jenkins, A.P., 69 Jenner F.E., 59, 75 Jeremias, E., 40 K Keith, M., 32 Kellet, D., 79 Kerr A.C., 13 Key, R.M., 28 Killeen, J., 38 Kinnaird, J.A., 27, 63 Kiseleva, G., 71 Klemd, R., 32, 62 Knott, T.R., 56, 78 Kocher, S., 43, 77 Kramers, J.D., 27 Kuehnapfel, C., 13 Kunz B.E., 75 L Lambert-Smith, J., 15 Large, S.J.E., 21, 50, 56, 57, 61 Laurent, O., 73 Lindsay, D.H.M., 43 Lindsay, J.J., 34 Lloyd, A., 35, 64 Loader, M.A., 23, 60 Lopes, E., 40 Lyell, C.M., 48 M Maczurad, M., 80 Magnall, J.M., 29 Mann, S., 14 Mark, D.F., 48 Marlow, A.G., 10 Marquis, E., 44, 78 Marvin-Dorland, L., 78 Matthews, T.J., 60 Matusiak-Małek, M.M., 74 Maulana, A., 68 McCarthy, W., 48, 72 McConachy, T., 27, 32 McDonald, I., 35, 63, 65, 74 Menzies, A.H., 37 Miles, A., 22, 52, 57

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Miron, R.G., 64 Mitchell, T.M.., 17 Molnar, F., 37 Mondillo, N., 12, 30, 80 Moore, A.E., 28 Moritz, R., 55 Mota e Silva, J., 30 Mottram, C.M., 79 N Naden, J., 14 Najorka, J., 20 Nathwani, C., 18 Nex, P., 8, 27 O Otake, T., 68 Ovadia, D.C., 28 P Palmer, M.R., 10 Pashley, V., 48 Pearse, M., 78 Platten, I.M., 70 Plotinskaya, O.Y., 20 Porto, C., 12 Price, J.P., 13 Pring, A., 33 Pumphrey, A., 36 Putzolu, F., 12, 80 R Ramokate, V.L., 28 Reynolds, M.A., 29 Rezeau, H., 55 Richards, H., 67 Richardson, K., 72 Rollinson, G.K., 35, 74 S Sanematsu, K., 68 Sangster, C.J., 48 Santoro, L., 12, 80 Sato, T., 68 Sayab, M., 37 Schaarschmidt, A., 62 Schaffalitzky, C., 28 Schwarz-Schampera, U., 32 Seltmann, R., 20, 42, 71 Shatov, V., 71 Shaw, R.A., 8 Shilovskikh, V.V., 20 Siddle, R., 14 Siegfried P.R., 9, 40 Slater, W., 67 Smith, A.G.G., 61

Smith, D., 14, 22, 57, 76, 78 Smith, K., 46 Smith, M., 44, 45 Solferino, G.F.D., 47 Sorjonen-Ward, P., 37 SoS MinErals team, 11 Spence, M., 64 Spratt, J., 21 Stevens, F., 35, 64 Stonadge, G., 57 Strachan, R.C., 17 Strauss, H., 32 Stuart, F.M., 31 Sufriadin, 68 T Tagle, R., 37 Tapster, S., 25, 19, 53, 65, 76 Tayan, R., 55 Tchimbali, G., 40 Thompson, A.J.B., 38 Thompson, J.F.H., 7 Tonks, E.R., 49 Torvela, T., 69 Tuffield, L., 21 V Valdivia, V., 17 Valiyev, A., 50 Vermeesch, P.., 17 Villanova-de-Benavent, C., 44,

45 Voudouris, P.C., 62 W Walker, R., 25 Wall, F., 9, 46 Wan, B., 59 Ward, L.A., 25 Warren C.J., 75 Westhead, S.J., 50 Wilkinson, J.J., 17, 18, 21, 33,

49, 50, 52, 54, 56, 60, 61 Williamson, B.J., 19, 53, 58,

64 Wurst, A., 49 Y Yeomans, C.M., 34 Z Zhang F., 58 Zhang, R., 71

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DELEGATE LIST

A Abdullayev, Rustam, Anglo Asian Mining, plc,

[email protected] Andersen, Jens C, Camborne School of Mines,

[email protected] Andrews, Holly, Imperial College,

[email protected] Argles, Tom, The Open University,

[email protected] Armstrong, Robin, Natural History Museum,

[email protected] Ashton, John, Consultant Boliden Tara Mines,

[email protected] Asgarov, Rashad, Anglo Asian Mining, plc,

[email protected] B Banks, Lewis, British Geological Survey/University of

Leicester, [email protected] Barry, John, CSA Global, [email protected] Bartlett, Ryan, Rio Tinto, [email protected] Bay, Claire, Oriole Resources PLC,

[email protected] Beard, Charles, British Geological Survey,

[email protected] Benham, Antony, SRK Exploration,

[email protected] Berry, Jessica, University of Leicester, [email protected] Blakley, Ian, RPA, [email protected] Blanks, Daryl, University of Leicester, [email protected] Boni, Maria, University Napoli, [email protected] Borst, Anouk, University of St Andrews, amb43@st-

andrews.ac.uk Boyce, Adrian, Scottish Universities Environmental

Research Centre, [email protected] Brookes, Harry, Imperial College London,

[email protected] Brugge, Emily, Natural History Museum,

[email protected] Butcher, Alan, Geological Survey of Finland,

[email protected] C Carter, Lawrence, Camborne School of Mines,

[email protected] Caulfield, Brendan,, [email protected] Chapman, John, Rio Tinto,

[email protected] Chapman, Robert, University of Leeds,

[email protected] Chirico, Rita, University of Naples "Federico II,

[email protected] Christopher, Alex, Independent Exploration Geologist,

[email protected]

Clarke, Rose, University of Leicester, [email protected]

Collins, Lawrence, Geological Survey Ireland, [email protected]

Compton-Jones, Charlie, University of Exeter, [email protected]

Cope, Ian, IC Exploration Ltd, [email protected] Croft, Daniel, University of Leicester,

[email protected] Currie, David, SUERC, [email protected] D D'Angelico, Anthony, Plethora Private Equity,

[email protected] Davey, James, SRK Consulting, [email protected] Dawson, Rob, Consultant Geologist,

[email protected] Deady, Eimear, University of Exeter/British Geological

Survey, [email protected] Deng, Chen, The Open University,

[email protected] Dilles, John, Oregon State University,

[email protected] Dixon, Oliver, University of St Andrews, ojd4@st-

andrews.ac.uk Dodds, Peter, Mineral Prospektering AB,

[email protected] Dolgopolova, Alla, Natural History Museum,

[email protected] Dominy, Simon, Exchange Minerals Ltd,

[email protected] E Earls, Garth, UCC, [email protected] Eskdale, Adam, Royal Holloway University of London,

[email protected] F Fiedrich, Alina, ETHZ, [email protected] Foster, Bob, BFA Ltd, [email protected] G Gallagher, Rachael, RioTinto,

[email protected] Gibbs, Jeremy, Hummingbird Resources Ltd,

[email protected] Gleeson, Sarah, GFZ Potsdam, sgleeson@gfz-

potsdam.de Goodenough, Kathryn, British Geological Survey,

[email protected] H Halsall, Nigel, Rio Tinto, [email protected] Hancox, John, CCIC, [email protected]

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Hancox, Eva, CCIC Coal, [email protected] Harbidge, Reinet, Cardiff, [email protected] Hart-Madigan, Lisa, Natural History Museum, l.hart-

[email protected] Hawkes, Nicholas, Rio Tinto,

[email protected] Hill, Eddy, Zeiss, [email protected] Hilton, Caroline, Pelican GeoGraphics Ltd,

[email protected] Hogg, James, Addison Mining Services,

[email protected] Hollings, Pete, Lakehead University,

[email protected] Hollis, Steven, University College Dublin,

[email protected] Holwell, David, University of Leicester, [email protected] Houlahan, Todd, Olympus,

[email protected] Hovakimyan, Samvel, University of Geneva,

[email protected] Hughes, Joshua, Bluejay Mining plc,

[email protected] Hughes, Hannah, University of Exeter,

[email protected] I Imaña, Marcello, Mineral exploration consultant,

[email protected] Ireland, Timothy, FQM / CODES, [email protected] Ito, Akane, Kwansei Gakuin University,

[email protected] J Jacques Ferguson, Jean, University of Exeter,

[email protected] James, Daniel, Plethora Private Equity,

[email protected] Jefferson, Sean, Great Glen Resources,

[email protected] Jenkin, Gawen, University of Leicester, [email protected] Jenkins, Alexander, University of Bristol,

[email protected] K Keith, Manuel, University of Erlangen,

[email protected] Kelly, Clare, RPA, [email protected] Kelly, Jamie, University Of Southampton,

[email protected] Key, Roger, Kalahari Key Mineral exploration company

(pty) ltd, [email protected] Kocher, Simon, Natural History Museum,

[email protected] Konopelko, Dmitry, Saint Petersburg State University,

[email protected] Kunz, Barbara, The Open University,

[email protected] L Lam, Chloe, Knight Piesold,

[email protected] Large, Simon, Natural History Museum,

[email protected]

Large, Duncan, Geologist, [email protected] Lindsay, Daniel, Imperial College London,

[email protected] Lindsay, Jordan, University of Exeter,

[email protected] Loader, Matt, Natural History Museum,

[email protected] Lunnon, Jack, RPA UK, [email protected] Lyell, Calum, University of Glasgow,

[email protected] M MacKenzie, Chris, Manas Resources,

[email protected] Marquis, Eva, University of Leicester,

[email protected] Marten, Brian, Consultant, [email protected] Matthews, Tom, Natural History Museum,

[email protected] McDonald, Iain, Cardiff University,

[email protected] Menuge, Julian, iCRAG / University College Dublin,

[email protected] Menzies, Andrew, Bruker Nano GmbH,

[email protected] Merry, Alice, Rio Tinto,

[email protected] Miron, Radu, University of Exeter, [email protected] Mondillo, Nicola, Università degli Studi di Napoli

"Federico II”, [email protected] Moon, Charlie, Moon Geology,

[email protected] Morgan, Jack,, [email protected] Mottram, Catherine, University of Portsmouth,

[email protected] Mullen, Gary, University of Glasgow,

[email protected] N Naden, Jonathan, British Geological Survey,

[email protected] Nathwani, Chetan, Natural History Museum,

[email protected] Nazarova, Anastasiya, Rio Tinto,

[email protected] O Orbán, Szabolcs, Consulting geologist,

[email protected] P Palmer, Martin, Southampton University,

[email protected] Penttinen, Karoliina, Rupert Resources Ltd,

[email protected] Platten, Ian, Independent,

[email protected] Plotinskaya, Olga, IGEM RAS, [email protected] Pratelli, Tom, Micromine, [email protected] Pratt, Warren, SGM Ltd, [email protected] Price, Jamie, Cardiff University, [email protected] Pring, Allan, University of Cambridge,

[email protected]

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Pringle, Ian, Ian J Pringle & Associates Pty Ltd, [email protected]

Purkiss, Martin, University of Oxford, [email protected]

Putzolu, Francesco, University of Naples Federico II, [email protected]

R Rajendra, Russell, Mineralogical Society,

[email protected] Ralston, Max, Imperial College London,

[email protected] Reynolds, Catherine, Anglo American,

[email protected] Richards, Huw, Altus Strategies, h.richards@altus-

strategies.com Richardson, Kathryn, University of St Andrews,

[email protected] Roberts, Stephen, University of Southampton,

[email protected] Routleff, Charles, Cardiff University,

[email protected] S Sant, Thomas, Exploration Direction Limited,

[email protected] Schaarschmidt, Anna, Friedrich-Alexander-Universität

Erlangen-Nürnberg, [email protected] Seabrook, Charlie, Rupert Resources Ltd,

[email protected] Seltmann, Reimar, Natural History Museum,

[email protected] Selwyn, Robert, Plethora Private Equity,

[email protected] Sharman, Elizabeth, BHP, [email protected] Siddle, Richard, Addison Mining Services,

[email protected] Sillitoe, Richard, Independent Consultant,

[email protected] Simmons, Adam, Anglo American,

[email protected] Skiggs, Thomas, Rio Tinto,

[email protected] Smith, Daniel, University of Leicester, [email protected] Smith, Martin, Univeristy of Brighton,

[email protected] Smith, Adam, Imperial College London,

[email protected] Spence-Jones, Carl, University of Leeds, C.Spence-

[email protected] Spink, Jack, Oulu mining school, [email protected] Starkey, Roy, The Russell Society,

[email protected]

Stonadge, George, University of Leicester, [email protected]

Strachan, Rebecca, UCL/NHM, [email protected]

T Tapster, Simon, BGS, [email protected] Thompson, Anne, PetraScience Consultants Inc,

[email protected] Thompson, John, PetraScience Consultants Inc,

[email protected] Tonks, Ethan, Imperial College/Natural History

Museum, [email protected] Torvela, Taija, University of Leeds,

[email protected] Tuffield, Lauren, Natural History Museum,

[email protected] V Villanova-de-Benavent, Cristina, University of Brighton,

[email protected] W Walding, Sam, Rolling Road Exploration,

[email protected] Wall, Frances, Camborne School of Mines,

[email protected] Ward, Laura, University of Leicester, [email protected] Warren, Clare, The Open University,

[email protected] Warwick, Tom, Blue Scientific Ltd, tom.warwick@blue-

scientific.com Webster, Timothy, The Open University,

[email protected] Wenborn, Alice, Rio Tinto, [email protected] Wesby, Tom, First Quantum Minerals Ltd,

[email protected] Westhead, Stephen, Anglo Asian Mining, plc,

[email protected] Wilkinson, Jamie, Natural History Museum,

[email protected] Williamson, Ben, Camborne School of Mines,

[email protected] Wilton, John, BeMetals Corp,

[email protected] Wood, Paul, Tescan UK Ltd, [email protected] Wrathall, Jeremy, Cornish lithium Ltd.,

[email protected] Z Zhang, Fei, University of Exeter, [email protected]

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