Marsh, 2000 Marsh, 2000 Oceanic Crust Oceanic Crust Magma Fossil System Fossil System Active System Active System Crystal Mush Crystal Mush Mantle Walker 2000 Walker 2000 Recent studies in Tasmania & new results from the Ecstall Belt confirm that base metal zoning also exists at belt scales (> 10 km). Study of belt-scale zoning during exploration programs can highlight underexplored areas & permit selection of metal-specific target areas. Study of belt-scale zoning during exploration programs can highlight underexplored areas & permit selection of metal-specific target areas. Belt-scale base metal zoning is driven by the large subvolcanic plutons commonly associated with VMS belts. The latent heat of crystallisation of these batholith-scale plutons sets up a long-lived, regional-scale geothermal gradient. Subvolcanic magma plumes can: Migrate with time Feed multiple volcanoes Belt-scale Zoning The process of selective dissolution & redeposition of Zn & Pb has been termed , & . “hydrothermal reworking” “metal migration” “zone refining” Low Temperature Zn-rich Large 1992 Large 1992 High Temperature Zn-rich Cu-rich Pb-rich Rhyolite Dome Complex Rhyolite Dome Complex Cherty exhalite Cherty exhalite Stockwork ore Stockwork ore Massive ore Massive ore Hydrothermal alteration pipe Hydrothermal alteration pipe Bedded ore Bedded ore White & Herrington, 2000 White & Herrington, 2000 Andesite Proximal Cu-Zn ore Proximal Cu-Zn ore Distal Pb-Zn ore Distal Pb-Zn ore Proximal Cu-Zn ore: massive & stringer types Proximal Cu-Zn ore: massive & stringer types Volcanogenic sediment (chert, jasper, bif, graphitic shales) Volcanogenic sediment (chert, jasper, bif, graphitic shales) Distal Pb-Zn ore: banded pyritic type Distal Pb-Zn ore: banded pyritic type Alteration pipe (cpy-po-py stockwork) Alteration pipe (cpy-po-py stockwork) Felsic volcanic pile with massive lavas & pyroclastic breccias Felsic volcanic pile with massive lavas & pyroclastic breccias Mixed sedimentary-volanic pile Mixed sedimentary-volanic pile Large 1977 Large 1977 Base-metal zoning sulphide lenses at volcano scale (> 1 km) has been recognised in several mining camps. This zoning is attributed to differences in temperature of the enclosing rock packages, with proximal, -rich deposits hosted by felsic volcanics & distal -rich deposits hosted by tuffaceous metasediments. between Cu-Au Zn-Pb-Ag between Observed Zoning Process LIMIT OF DEMAGNETIZED ZONE CHLORITIZED + HEMATIZED BASALT - HYDROTHERMAL REWORKING 100 m SULFIDE TALUS DEBRIS APRON & METALLIFEROUS SEDIMENT WHITE SMOKERS CENTRAL UPFLOW ZONE PYRITE- ANHYDRITE BRECCIAS Zn-RICH MARGINAL FACIES COMPACT ORE ALTERATION PIPE SILICIFIED, PYRITIC STOCKWORK Hannington et al. 1995 ANHYDRITE CONE HYDROTHERMAL REWORKING Py Po Cpy Sph Gn Ba 100 metres 100 metres Alteration Pipe Alteration Pipe Massive Sulphide Mound Massive Sulphide Mound Metal Migration Metal Migration Lydon, 1984 Lydon, 1984 100 m chlorite sericite cpy-py veins cpy-po-py py-sph-cpy py-sph-gn Ba-(Au) modified from Galley, 2001 Felsic Volcanics Chert Massive Sulphide Lens Deposit-scale Zoning Base-metal zoning VMS deposits was documented before the syngenetic nature of these deposits was recognised. Metal zoning results from selective dissolution of metals & the progressive cooling of the metal-bearing hydrothermal fluids as they combine with cold seawater within newly formed sulphide mounds. within Observed Base-Metal Zoning Conceptual Zoning Process Volcano-scale Zoning 4 2 0 -2 -4 150 200 250 300 350 400 ZnS hydrothermal fluids ascending to sea floor Pb-Zn Deposition Zone Pb-Zn Deposition Zone Cu Deposition Zone Cu Deposition Zone Metal Solubility (log ppm) PbS Temperature ºC CuFeS 2 CuFeS 2 Large, 1992 & Barrie et al. 1999 Concept In environments, variations in the temperature & metal solubilities of hydrothermal fluids control the zonation of base metals: Base metal zoning lenses and lenses has long been recogised. volcanogenic massive sulphide (VMS) 1. within single VMS lenses 2. between adjacent VMS lenses 3. along volcanic belts within between Base metal zoning at belt scale is reported here for the first time. Base metal zoning at belt scale is reported here for the first time.
Transcript
Marsh,2000
Marsh,2000
Oceanic CrustOceanic Crust
MagmaFossilSystemFossil
SystemActive
SystemActive
System
CrystalMush
CrystalMush
Mantle
Walker2000
Walker2000
Recent studies in Tasmania & new resultsfrom the Ecstall Belt confirm that base metalzoning also exists at belt scales (> 10 km).
Study of belt-scale zoning duringexploration programs can highlightunderexplored areas & permit selectionof metal-specific target areas.
Study of belt-scale zoning duringexploration programs can highlightunderexplored areas & permit selectionof metal-specific target areas.
Belt-scale base metal zoning is drivenby the large subvolcanic plutonscommonly associated with VMS belts.
The latent heat of crystallisation of thesebatholith-scale plutons sets up a long-lived,regional-scale geothermal gradient. Subvolcanic magma plumes can:
Migrate with timeFeed multiple volcanoes
Belt-scale Zoning
The process of selective dissolution & redeposition of Zn & Pb has been termed, & .“hydrothermal reworking” “metal migration” “zone refining”
Base-metal zoning sulphidelenses at volcano scale (> 1 km) hasbeen recognised in several miningcamps. This zoning is attributed todifferences in temperature of theenclosing rock packages, with proximal,
-rich deposits hosted by felsicvolcanics & distal -rich depositshosted by tuffaceous metasediments.
Deposit-scale ZoningBase-metal zoning VMS deposits was documented before the syngeneticnature of these deposits was recognised. Metal zoning results from selectivedissolution of metals & the progressive cooling of the metal-bearing hydrothermalfluids as they combine with cold seawater within newly formed sulphide mounds.
within
ObservedBase-Metal Zoning
ConceptualZoning Process
Volcano-scale Zoning
420-2-4150200
250300
350400
ZnS
hydrothermal fluidsascending to sea floor
Pb-ZnDepositionZone
Pb-ZnDepositionZone
CuDepositionZone
CuDepositionZone
Metal Solubility (log ppm)
PbS
Tem
pera
ture
ºC
CuFeS2CuFeS2
Large, 1992 &Barrie et al. 1999 Concept
Inenvironments, variations in the temperature& metal solubilities of hydrothermal fluidscontrol the zonation of base metals:
Base metal zoning lenses andlenses has long been recogised.
volcanogenic massive sulphide (VMS)
1. within single VMS lenses2. between adjacent VMS lenses3. along volcanic belts
withinbetween
Base metal zoning at belt scaleis reported here for the first time.Base metal zoning at belt scaleis reported here for the first time.
50
0m
E
Sea Level
1000m Elev. 1000m
2000m2000m Elev.
Mt. Phillips
Myra Valley
Myra Mine
Price Mine
Trumpeter ZoneFar West
West Test
Ridge West
25
00
mE
45
00
mE
55
00
mE
50
0m
E
25
00
mE
45
00
mE
55
00
mE
Ridge EastMarshall Zone
Battle Zone
HW Mine
43 Block
Extension ZoneGap Zone
24 Level
21 Level
18 Level 13 Level
5 Level10 Level
15 LevelHWShaft
Lynx Shaft
Lynx Mine
Projected Vertical Section
MYRA FALLS OPERATIONSHW Horizon Ore Zone
LMP Horizon Ore Zone
HW Horizon Potential
LMP Horizon Potential
Sea Level
Thelwood Valley
S. McKinley,
1997
SMcK, 1997
ButtleLake
H-W Mine
Battle Mine
Marshall Zone
Ridge Zone East
Ridge Zone WestExtension
Zone
Trumpeter Zone
Price Deposit
Myra Mine
Lynx Mine
43 Block
Gap Zone
1 km
NB: There can be multipleprospective horizons withinone volcanic succession.
NB: There can be multipleprospective horizons withinone volcanic succession.
MINE SEQUENCE/MYRA FORMATION
Composite Cross-Section
Upper Rhyolite
HW Andesite
H-W Horizon
Price
Andesite
Upper Rhyolite
Lynx-Myra-Price
Horizon
Thelwood Formation
Thelwood
Formation
SW NE
Andesite
Legend
Massive Sulphides
Stringer Sulphides
Rhyolite
Undifferentiated volcanics
Tuffaceous sediments/mafic sills
H-W Main &
Gopher Lenses
H-W Horizon
H-W North Lens
& Battle Deposit
SMcK, 1997
Core Zone Fault
(strike-slip)
North
Fault
4500.4500.
Stra
itofGeorg
ia
Campbell River
Courtenay
Buttle Lake
VANCOUVER
ISLAND
Strathcona-Westmin
Class ‘B’ Park
Strathcona
Class ‘A’ Park
Pacific
Ocean
British
Columbia
Vancouver
Scale
0 20km
N
Myra Falls MineMyra Falls Mine
Canada
NN
N
10 km
10 km
10 km
Cu ProspectsCu Prospects
Au ProspectsAu Prospects
Zn ProspectsZn Prospects
MurchisonGranite
MurchisonGranite
MurchisonGranite
Limit of
Limit of
Limit of
Mt. Read
Mt. Read
Mt. Read
Volcanics
Volcanics
Volcanics
DarwinGranite
DarwinGranite
DarwinGranite
ML RBHN
HR
MLHN
HR
RB
Extent ofburied granite
ML HN
HR
RB
Extent ofburied granite
Extent ofburied granite
Mines
Mines
Mines
Mount Read BeltTASMANIA
0 50 100
Km
MountReadVolcanics
MountReadVolcanics
Myra Falls
Base metal zoning among VMS deposits isspatially related to a subvolcanic pluton inthe Mount Read volcanic belt of Tasmania.
Prospects in this belt demonstrate clear,proximal-to-distal zoning from copper togold to zinc, both up-section and laterally.
Only two small stocks crop out, but thefull extent of this buried batholith hasbeen revealed by an aeromagnetic survey.
These maps (Large et al., 1996)demonstrate that VMS deposits are
distributed throughout the Mt. Read volcanics,and are not just concentrated near the coeval pluton.
BC
Atl
an
tic
Ocean
8 00'O
CG
CG
CG
CG CG
FARO
BEJA
?
Middle Mississippian
Upper Devonian
Lower Mississippian
They may represent deposits formed neartwo separate thermal or magmatic centres -shown as separate and highson the maps.
However, they may lie within one elongateand contour high - shown here
as a heavy black outline - and nowdissected where erosion has removedfavourable stratigraphy and exposedunmineralised footwall strata.
In the latter scenario, volcanic strataimmediately east-southeast of the Rio Tintomine ( ) are particularly favourable forundiscovered -rich & -rich deposits.
Cu:Zn Cu:Pb
Cu:Zn Cu:Pb
arrowCu Au Mediterranean Sea
Sp
ain
Po
rtug
al
The Rio Tinto mine & Las Cruces deposit are 55 km apart.The Rio Tinto mine & Las Cruces deposit are 55 km apart.
Neves Corvo 80.81 3.12 0.74 4.11 37 0.22 0.76 4.22
Nuestra Senora del Carmen 0.04 1.3 10.3 29 153 1 0.04 0.13
Pena de Hierro 5 1.3 0.42 1.39 0.94 3.10
Rio Tinto 334.5 0.39 0.12 0.34 22 0.36 1.15 3.25
San Platon 1.13 1.16 0.53 12.3 69 2.05 0.09 2.19
San Telmo 4 1.2 0.4 12 60 0.8 0.10 3.00
Sao Domingos 27 1.25 1 2 0.63 1.25
Sierrecilla 1 1.5 5 12 500 0.13 0.30
Sotiel 75.2 0.56 1.34 3.16 24 0.21 0.18 0.42
Tharsis 110.06 0.5 0.6 2.7 22 0.7 0.19 0.83
Vuelta Falsa 1 1.27 8.8 20.7 307 9 0.06 0.14
Application of this contouring technique reveals a simple pattern forthe assorted -rich & -rich deposits of the Iberian Pyrite Belt.
Seven -rich centres are present around the Lousal, Aljustrel,Neves-Corvo, Cabeza del Pasto, La Zarza, Rio Tinto & Las Crucesmassive sulphide deposits. Other large VMS deposits, such asTharsis, Aznalcollar & Los Frailes, have relatively low &ratios. Contour distributions indicate favourable areas within thisextensive belt to search for -, -, - or -rich VMS deposits.
Each high & area represents a region where coevalplutonic rocks might be preserved & exposed.
Cu Zn
Cu
Cu:Zn Cu:Pb
Cu Au Zn Pb
Cu:Zn Cu:Pb
The Iberian Pyrite Belt
the Rio Tinto & Neves-Corvo mines, the 2nd & 3rd largest VMSdeposits in the world, after Windy Craggy.
Favourable volcanic strata are covered by athin veneer of unmineralized slates. Recentdiscoveries include deposits located bydrilling through these cover rocks. So
c
hosts 140 VMSdeposits in the Early MississippianVolcanic-Siliceous Complex.
The IPB includes
the& ontours were drawn to
project up through overlying strata.Cu:Zn Cu:Pb
This technique reveals underexplored areas
and highlights metal-specific target areas.
This technique reveals underexplored areas
and highlights metal-specific target areas.
Iberian Pyrite Belt
Published Reserves & & ratiosCu:Zn Cu:Pb
SEVILLE
Alldrick DJ & Jackaman W (2002): Metal zoning in the Ecstall VMSBelt; BCMEM, GF 2001, Paper 2002-1, p151-170Alldrick DJ
Alldrick DJ
Alldrick DJ Friedman RM & Childe FC
Alldrick DJ & Gallagher CS (2000)
(2001a): Geology & mineral deposits of the Ecstallgreenstone belt; BCMEM, GF 2000, Paper 2001-1, p279-305
(2001b): Geology & mineral potential of the Ecstall VMSbelt; BCYCM, Cordilleran Roundup, January, 2001, Abstracts, p3-4
(2001): Age & geologichistory of the Ecstall belt; BCMEM, GF 2000, Paper 2001-1, p269-278
: Geology & mineral potential ofthe Ecstall VMS belt; BCMEM, GF 1999, Paper 2000-1, p249-265
Friedman RM Gareau SA & Woodsworth GJ
Gareau SA
Gareau SA
Jackaman W
(2001): U-Pb datesfrom the Scotia-Quaal metamorphic belt; Radiogenic Age & IsotopicStudies 14, GSC, CR 2001-F9, 11p
(1991): The Scotia-Quaal metamorphic belt; CJES, v28,p870-880
(1997): Geology of the Scotia-Quaal metamorphic belt;GSC, Map 1868A, scale 1:100 000, 1 sheet
(2001): Stream sediment & water geochemistry of theEcstall Greenstone Belt; BCMEM, OF 2001-13, 216pScott B (2001): Geology of the Amber-El Amino area; BCMEM,
VMS &GeneralVMS &
GeneralBarrie CT et al
Galley AG
Galley AG
Hannington MD et al
Large RR
Large RR et al
Leistel JM et al
Lydon, JL
Marsh BD
Walker GPL
White NC & Herrington RJ
(1999): Heat & fluid flow in VMS-forming hydrothermalsystems; in Volcanic-associated massive sulphide deposits, SEG, Reviews inEconomic Geology, v8, p201-219
(1995): Target vectoring using lithogeochemistry: applications toexploration for VMS deposits; CIMM, v88, n990, p15-27
(2001): Characteristics of VMS deposits; Kamloops ExplorationConference, Short Course Notes, 56p
(1995): Processes of seafloor mineralisation at mid-ocean ridges; AGU Geophysical Monograph 91, p115-157
(2000): Mineral Deposits Associated withVolcanism; Encyclopedia of Volcanoes, Academic Press, p897-912
Galley AG (1996): Subvolcanic intrusions associated with massive sulphidedistricts; GAC Short Course 12, p239-278
REFERENCES
METAL ZONINGRGS
SAMPLESITES
RGSSAMPLE
SITES
N
km
0 10
N
km
0 10
N
km
0 10
N
km
0 10
29
35
27
2523
2426
15
2219
211817 2016
121413
87
3536
37
38
32
36
33
119
10
6
5
34
2
1
3130
31
28
25252323
24242626
1515
22221919
212118181717
42
20201616
121214141313
8877
40
3839
34
36
35
111199
1010
66
55
3344
22
11
31
39 38
4341
Cha
nnel
Dougla
s
Skeena River
Ecstall River
Big Falls Tonalite
Mixed metavolcanics& metasediments
Mid-DevonianBig Falls Igneous Complex
0 5 10 kmScale
ScotiaPendant
Mineral prospects (44)
3232
2829
5 km
27
3333
37
42
43
44
RGS sample sites (228)[sites extend off map to southeast]
N
RGS DATA(Jackaman, 2001)
RGS DATA
All prospects in this belt crop out. Creeks are actively eroding massive sulphide lensesat the Ecstall & Packsack deposits. Silt samples from these creeks show high contentsof , as expected.
However, these are not the most metal-rich samples collected in the survey. The mostmetal-rich stream sediment samples collected in the belt come from 3 streams with noknown mineral occurrences anywhere within their drainage basins.
3
12 morepolymetallic anomalies have been identified from 12 more streams with no knownmineral occurrences.
Cu, Pb, Zn Ag Au&
The strongest values are clustered close to mid-Devonian tonalite bodies; few high valuesare located away from these stocks.
The highest stream sediment values overlap the area of the highest values, but alsoextend further to the south.
The strongest anomalies are broadly dispersed along the belt compared to the tighterclustering of the and values. There is also a small area in the center of the Ecstall belt witha noticeable absence of strong values that coincides with an area primarily underlain by thetonalite stocks. Overall, the zoning pattern of resembles the pattern in theTasmanian study.
Stream sediment sample results for also fit the pattern of lateral zoning well. The strongestvalues are well dispersed along the whole of the belt. Proximal to the tonalite bodies, there is aconspicuous absence of the strong concentrations in the stream sediment samples.
Cu Cu
Au Cu
ZnCu Au
ZnCu Au Zn
Pb Pb
Pb
, &
Concentric zoning of & ratiosdecreases outward from the central coeval stocks.
A -rich zone occurs near the Packsack deposit,despite the apparent absence of mid-Devoniantonalite stocks. However, early mapping workidentified several small bodies of "diorite" alongthis part of the valley.
There is no -rich zone in the SW part of the belt,where a large tonalite body is shown. The tonaliteintrusion in this area was extrapolated from asmall exposure mapped far to the north. Theabsence of any -rich signature, combined withthe presence of two low- mineral occurrenceshosted in , suggest that the tonalite is muchless extensive than shown on maps.
A prominent high at the West Grid AlterationZone contrasts with a conspicuous absence of a
high at the same location. This reflects thelack of analyses from these showings.
Stratified rocks of the belt are grouped into 4principal units: metavolcanic rocks,metasedimentary rocks, quartzite & layered gneiss.
The basal mid-Devonian metavolcanic unit consistsof mafic & intermediate metavolcanic rocks,interlayered with lesser felsic metavolcanic & clasticmetasedimentary rocks & rare limestone & chert.
Mid-Devonian metavolcanic rocks are intruded by large, elongate,mid-Devonian plutons. Mid-Devonian intrusive & extrusive rocks aregrouped together as the Big Falls Igneous Complex.
In greenstone belts, subvolcanic plutons provide camp-scalecontrols for localization of massive sulphide deposits (Galley, 1986;Barrie et al., 1999) and for metal zoning among deposits (Large etal., 1996). Consequently these plutons are an important componentof the evolving metallogenic model for the Ecstall camp.
These rocks are overlain by late Devonian clastic metasedimentary rocks -a lower metapelitic unit & an upper quartzite unit.
Metasedimentary strata are overlain by banded mafic gneiss interpreted as aLate Devonian mafic volcanic package.
This main metavolcanic package hosts 36 of the 40sulphide prospects in the belt.
Felsic volcanic members, preserved as pyritic quartz-sericite schist, typically host these mineraloccurrences. Industry exploration programs havetraced out many favourable felsic units, as well asexhalative horizons (chert) and extensive stockwork-style mineralized zones.
Cu:Zn Cu:Pb& ratios were calculated & contouredfor assays from deposits & prospects in theEcstall belt.
In most mining camps, assay data is more readilyavailable than high quality stream sediment surveyresults, so it offers a more universal database.
EcstallBelt
EcstallBelt
These results reveal that exploration potential throughout this belt is high everywhere,but -rich deposits will be most abundant near the central tonalite bodies while& -rich deposits will be concentrated progressively further away from these intrusions.
