Date post: | 03-Mar-2016 |
Category: |
Documents |
Upload: | michelle-calista |
View: | 27 times |
Download: | 0 times |
of 47
1Disseminated Sedimentary Disseminated Sedimentary RockRock--hosted Gold Systems hosted Gold Systems
in Nevadain Nevada
BetzeBetze -- Post, Northern Carlin TrendPost, Northern Carlin Trend
Disseminated Sedimentary Disseminated Sedimentary RockRock--hosted Gold Systemshosted Gold Systems
in Nevadain NevadaSteve GarwinSteve Garwin
Geoinformatics ExplorationGeoinformatics ExplorationCentre for Exploration TargetingCentre for Exploration Targeting
SEG Gold WorkshopSEG Gold Workshop2020--21 October 2007 Cairns, Australia21 October 2007 Cairns, Australia
[email protected]@geoinformex.com
Battle Mtn Eureka trend
Carlin trend
SRHG in Nevada provide 11% of the worlds Au production
Clusters of disseminated Clusters of disseminated sedsed--hosted deposits occur hosted deposits occur as linear trends in the Great Basin province of the U.S.as linear trends in the Great Basin province of the U.S.
Courtesy of Greg Arehart
2Grade/Tonnage of Gold Systems
0.1
1
10
100
1 100 10000 1000000 100000000 10000000000
Tonnes
Gra
de (g
/t)
Epithermal AlkalicEpithermal HSEpithermal LSGreenstone LodeOtherPorphyrySHVVMSWitwaterstrandCarli n
10 Tonnes Au
1000 Tonnes Au
100000 Tonnes Au
Muntean, 2004
(SRHG)
Johnston & Ressel, 2005
(mill
ion
Oz)
Gold Quarry Post-Betze
GetchellPipeline Twin Creeks
Deep Star
Leeville
Deep Post
Cortez HillsMarigold
Sedimentary RockSedimentary Rock--hosted Gold Depositshosted Gold Deposits
3Carlin Trend Gold EndowmentCarlin Trend Gold Endowment(year(year--end 2000; metric end 2000; metric tonnestonnes))
Cumulative Reserves ResourcesCumulative Reserves Resources Total Total ProductionProduction
NewmontNewmont 873873 400400 91*91* 13641364BarrickBarrick 593593 761761 226226 15801580OthersOthers 2525 77 -------- 2525
Totals (t)Totals (t) 14911491 11681168 317317 2976 2976 (million oz) 48 (million oz) 48 38 38 10 96 10 96
Nominal 80% recovery brings total inventory to 3349 t (108 Moz) gold
* denotes mineralized material not in reserve(revised from Teal and Jackson, 1997; Bettles, 2002; unpublished Newmont data)
Carlin Trend Exploration Carlin Trend Exploration and Mining Historyand Mining History
19071907 Lynn Creek placers; originating from Big SixLynn Creek placers; originating from Big Six19461946 Discovery of Au at Bootstrap (57Discovery of Au at Bootstrap (57--60 production)60 production)19591959 Au found in turquoise workings at Blue Star (61 prod)Au found in turquoise workings at Blue Star (61 prod)1961*1961*RRRR Discovery of Carlin (80atDiscovery of Carlin (80at 0.20 opt in 0.20 opt in sedsed rkrk near dike)near dike)19621962 Discovery of Au in Discovery of Au in GoldstrikeGoldstrike areaarea19651965 Carlin production commences (11 Mt at 0.32 opt)Carlin production commences (11 Mt at 0.32 opt)19781978 GoldstrikeGoldstrike production commences (western area)production commences (western area)79/8279/82 Discovery of Gold Quarry / Post OxideDiscovery of Gold Quarry / Post Oxide19841984 Discovery of GenesisDiscovery of Genesis19861986 Discovery of Deep Post Discovery of Deep Post -- Change of strategyChange of strategy8888--8989 Discovery of Deep Star, RodeoDiscovery of Deep Star, Rodeo--GoldbugGoldbug & & MeikleMeikle19941994 Discovery of West Discovery of West LeevilleLeeville19961996 Underground production starts at Deep Star & Underground production starts at Deep Star & MeikleMeikle9696--9797 Deep intercepts in Little Boulder Basin (> 6000 feet)Deep intercepts in Little Boulder Basin (> 6000 feet)20002000 Deep intercepts at Deep intercepts at RenRen0101--0404 Deep intercepts beneath and SSE of Deep PostDeep intercepts beneath and SSE of Deep Post2006 Discovery of Bravo2006 Discovery of Bravo
Outline of PresentationOutline of Presentation
Disseminated Sedimentary RockDisseminated Sedimentary Rock--hosted hosted Gold Systems in NevadaGold Systems in Nevada
1)1) Regional setting and Regional setting and metallogenymetallogeny2) Carlin trend geology & geochemistry2) Carlin trend geology & geochemistry
Styles and settings of gold mineralization Styles and settings of gold mineralization OreOre--related processes and mineral related processes and mineral paragenesisparagenesisOreOre--fluid Pfluid P--TT--X constraintsX constraintsWeathering and Weathering and supergenesupergene effectseffects
3) Global examples of SRHG deposits and3) Global examples of SRHG deposits andConceptual models and controls to mineralizationConceptual models and controls to mineralization(Carlin deposit controversies session (Carlin deposit controversies session SEG / Reno, 2005)SEG / Reno, 2005)
4SRHG Systems and Mineral Trends in the Great BasinSRHG Systems and Mineral Trends in the Great Basin
Muntean, 2004
CrustalCrustal Structure Structure Radiogenic Isotope LinesRadiogenic Isotope Lines
Muntean, 2004
(Pb 206/204 >19.3)
Gravity Worms and Crustal Structural InterpretationGravity Worms and Crustal Structural Interpretation
5Great Basin
Sierra Nevada M
tns ColoradoPlateau
Snake River Plain
Thorman, 2002
Thorman, 2002
Thorman, 2002
6Thorman, 2002
Thorman, 2002
Thorman, 2002
7Thorman, 2002
Thorman, 2002
TectonostratigraphicTectonostratigraphic Units in the Great BasinUnits in the Great Basin
Hofstra and Cline, 2000
8Patterns of Tertiary Patterns of Tertiary MagmatismMagmatism
Humphreys, 1995
Patterns of Patterns of Tertiary ExtensionTertiary Extension
Hofstra and Cline, 2000
~34 to 17 Ma ~34 to 17 Ma PostPost--MineralMineralExtensionExtension
Heterogeneous ~50% to
locally >400% extension in north-central Nevada
Tilted post-mineral Oligocene ignimbrites, Caetano tuffMuntean, 2004
9TectonicTectonicTimeTime--EventEvent
Chart for theChart for theGreat BasinGreat Basin
Late Proterozoiccontinental rifting
Paleozoic passive margin sequence
Orogonies & Thrusts:Dev-Miss Antler,P-Trias Sonoma,J Luning-Fencemaker,K Sevier & Laramide(plutonism)
Tertiary extension & magmatism
Muntean, 2004
Great Basin Gold DepositsGreat Basin Gold Deposits
Total gold endowment ~220 Total gold endowment ~220 MOzMOzfor Nevada alonefor Nevada alone
SedimentSediment--hosted deposits are Late hosted deposits are Late Eocene, as are Bingham Porphyry and Eocene, as are Bingham Porphyry and
Fortitude SkarnFortitude Skarn
Bonanza lowBonanza low--sulfidationsulfidation deposits are deposits are MiddleMiddle--Miocene (13Miocene (13--16Ma) and related to 16Ma) and related to
rifting and birifting and bi--modal volcanism modal volcanism
Large disseminated epithermal Large disseminated epithermal deposits (e.g. Round Mountain) related to deposits (e.g. Round Mountain) related to
Early Miocene silicic calderasEarly Miocene silicic calderas
Intermediate and highIntermediate and high--sulfidationsulfidationdeposits related to the Walker Lane deposits related to the Walker Lane
Neogene magmatic arc and calderasNeogene magmatic arc and calderas
Crustal Provinces and Structural SystemsCrustal Provinces and Structural Systems
Major surface thrusts, folds and crustal Major surface thrusts, folds and crustal provinces including radiogenic isotope provinces including radiogenic isotope
lineslines
Gold deposits and belts shownGold deposits and belts shown
10
Extensional Domains and Gold DepositsExtensional Domains and Gold Deposits
Extension began in the N part of Extension began in the N part of the Great Basin in the Late Eocene the Great Basin in the Late Eocene (~40 Ma) and migrated SW with time to (~40 Ma) and migrated SW with time to pass through the Walker Lane in the pass through the Walker Lane in the MioceneMiocene
Gold deposits display a similar temporal /Gold deposits display a similar temporal /spatial patternspatial pattern
Leading edge of extension through time (Ma) indicated by blue lines.
Favourable Stratigraphic Units and Major ThrustsFavourable Stratigraphic Units and Major Thrusts
Black units indicate SilurianBlack units indicate Silurian--Devonian marine slope facies and Devonian marine slope facies and
Antler Antler OrogenyOrogeny (Dev(Dev--Mississippian) Mississippian)
overlap assemblages, which contain overlap assemblages, which contain
reactive and porous / permeable reactive and porous / permeable
mixed carbonate / mixed carbonate / siliciclasticsiliciclastic rocksrocks
Major thrusts shown as light blue Major thrusts shown as light blue lineslines
Favourable Stratigraphic Units, Thrusts and Gold DepositsFavourable Stratigraphic Units, Thrusts and Gold Deposits
Black units indicate SilurianBlack units indicate Silurian--Devonian marine slope facies and Devonian marine slope facies and Antler Antler OrogenyOrogeny (Dev(Dev--Mississippian) Mississippian) overlap assemblages, which contain overlap assemblages, which contain reactive and porous / permeable reactive and porous / permeable mixed carbonate / mixed carbonate / siliciclasticsiliciclastic rocksrocks
SRHG deposits lie in anticlinal SRHG deposits lie in anticlinal domes and windows beneath the domes and windows beneath the Roberts Mountains and Golconda Roberts Mountains and Golconda AllochthonsAllochthons, typically in reactive , typically in reactive calcareous rocks; exceptions do calcareous rocks; exceptions do occur (e.g. Marigold deposit in occur (e.g. Marigold deposit in fractured fractured ValmyValmy Quartzite)Quartzite)
11
Favorable Host RocksFavorable Host Rocks
Muntean, 2004
IsopachIsopach Map Map Lower Silurian & Middle DevonianLower Silurian & Middle Devonian
7
6
5
4
3
2 3 4 56
SRHG deposits lie along inferred SRHG deposits lie along inferred NWNW--trending basement structures trending basement structures that controlled deposition of that controlled deposition of SiluroSiluro--Devonian rocksDevonian rocks
Sedimentary Sedimentary isopachsisopachs in 100sin 100sof meters of meters
Zinc in stream sediment samplesZinc in stream sediment samplesas a proxy for Devonian SEDEXas a proxy for Devonian SEDEXmineralizationmineralization
Emsbo et al, 2006
50 km
CT
BMT
Rb-Sr dating of Galkhaite:(Cs,Tl)Hg6(As,Sb)4S12trace Cu, Zn, Cd, Rbno Sr
found at: Getchell, Rodeo, Carlin, SSX
dated at: Getchell (39.5 Ma), Rodeo (39.8 Ma)
paragenetically late ore stage
Photo: Dave Tretbar
3mm
Late Eocene Mineralization EventLate Eocene Mineralization Event
Muntean, 2004
12
Apatite Fission Track Data for Apatite Fission Track Data for CarlinTrendCarlinTrend Gold DepositsGold Deposits
Apatite fission track dates, lesser certainty: ~ 37- 41 Ma, Carlin, hydrothermal apatite
Carlin district associated with large (~250 sq km) late Eocene thermal anomaly
Muntean, 2004
Carlin Trend: FissionCarlin Trend: Fission--track Annealing and Heat Flowtrack Annealing and Heat Flow
(Cline et al, 2005)
Age Data for Disseminated Age Data for Disseminated SedSed--hosted Gold Depositshosted Gold Deposits
Very good maximum age constraints ages on mineralized Eocene dikes: 38 Ma, Ratto Canyon, Tonkin Springs, Alligator Ridge,
Cortez, Chert Cliff
Good minimum age constraints ages on post-mineral supergene alunite: as old as 30 Ma (Gold Quarry), mostly Miocene
Porphyry-related deposits overlap in time with SRHG deposits: 37.5-39 Ma, Bingham Canyon, Copper Canyon, McCoy/Cove,
Hilltop, Tenabo
Muntean, 2004
13
Eocene Eocene PaleotopographyPaleotopography NorthNorth--central Nevadacentral Nevada
2 2.52.5
2.5
2
22.5
2
2
2
3
1.5
1.5
1
2.5
JC
G
AR
CTBMT
Syn-mineralizationtopographic contoursin 1000s of meters
Ruby Mountains (RM) as major topographic high
Eocene intrusive centersas loci for local surfaceuplift
SRHG deposits occuron paleo-highs nearbasin margins
RM
50 km
Eocenesediments
1Disseminated Sedimentary Disseminated Sedimentary RockRock--hosted Gold Systems hosted Gold Systems
in Nevadain Nevada
BetzeBetze -- Post, Northern Carlin TrendPost, Northern Carlin Trend
Disseminated Sedimentary Disseminated Sedimentary RockRock--hosted Gold Systemshosted Gold Systems
in Nevadain NevadaSteve GarwinSteve Garwin
Geoinformatics ExplorationGeoinformatics ExplorationCentre for Exploration TargetingCentre for Exploration Targeting
SEG Gold WorkshopSEG Gold Workshop2020--21 October 2007 Cairns, Australia21 October 2007 Cairns, Australia
[email protected]@geoinformex.com
Outline of PresentationOutline of Presentation
Disseminated Sedimentary RockDisseminated Sedimentary Rock--hosted hosted Gold Systems in NevadaGold Systems in Nevada
1)1) Regional setting and Regional setting and metallogenymetallogeny2) 2) Carlin trend geology & geochemistryCarlin trend geology & geochemistry
Styles and settings of gold mineralization Styles and settings of gold mineralization OreOre--related processes and mineral related processes and mineral paragenesisparagenesisOreOre--fluid Pfluid P--TT--X constraintsX constraintsWeathering and Weathering and supergenesupergene effectseffects
3) Global examples of SRHG deposits and3) Global examples of SRHG deposits andConceptual models and controls to mineralizationConceptual models and controls to mineralization(Carlin deposit controversies session (Carlin deposit controversies session SEG / Reno, 2005)SEG / Reno, 2005)
SRHG Systems and Mineral Trends in the Great BasinSRHG Systems and Mineral Trends in the Great Basin
Carlin Trend
Muntean, 2004
2Regional Structural High Regional Structural High -- GeologyGeology
StratigraphicStratigraphic Column / DepositsColumn / Deposits
(Recent work at GQ assigns more gold ore to Rodeo Creek unit)
Primary Host Lithologies of SRHG deposits calcareous silty/sandy pyritic carbonaceous dolomitic sedimentary
breccias (e.g., debris flow breccias) shelf-slope boundaries
fossiliferousgrainstones
commonly shallow dipping and thin-bedded/ laminated
Roberts Mountains Formation, Maggie Creek Canyon, NV
Photo by Greg Arehart
3Northern / CentralNorthern / CentralCarlin TrendCarlin Trend
Maggie Creek
BoulderValley
Major Deposits:Major Deposits:MeikleMeikle 7 7 MozMozBetzeBetze--Post 27 Post 27 MozMozCarlin 7 Carlin 7 MozMozMike ~7 M ozMike ~7 M ozGold Quarry 22 Gold Quarry 22 MozMoz
> 35 km x 7 km x 2 km> 35 km x 7 km x 2 kmMike
Panoramic Photo / Section Looking East
NRM
Overburden
Bedrock
Roaster
GQSL
?
oxide
?
295m/4.05g/t Gold
300
+0.34 g/t Gold Shape Oxide+2.40 g/t Gold Shape Refractory
0
Meters
158m/4.15g/t Gold
Gold Quarry Gold Quarry -- Central Carlin TrendCentral Carlin Trend
Deep SulfideDeep SulfideFeederFeeder
2000 x 1200 x 350m
ChukarChukar Footwall Deposit (02)Footwall Deposit (02)Looking Northwest
Core Drill RC Drill
Main Decline Portal
North Vent Portal
Resource (0.2 opt Au):380,000 oz @ 0.37 opt
4Northern / CentralNorthern / CentralCarlin TrendCarlin Trend
Geology and Gold DepositsGeology and Gold Deposits
(generalized from NBMG Bull. 111, 2002)
Dee/Rossi
Boot-strap
RenMeikle
RodeoBetze-Post Deep Post
GenesisBeast Leeville
Carlin
Pete
Lantern
Mike
Mac
GoldQuarry
Deep Star
(Goldstrike Stock - 158 Ma)
Goldstrike
LBB Vivian
Northern / CentralNorthern / CentralCarlin TrendCarlin Trend
Intrusion and Dike Swarm Intrusion and Dike Swarm InterpretationInterpretation
Dee/Rossi
Boot-strap
RenMeikle
RodeoBetze-Post Deep Post
GenesisBeast Leeville
Carlin
Pete
Lantern
Mike
Mac
GoldQuarry
Deep StarGoldstrike
Jurassic Alkaline Jurassic Alkaline GoldstrikeGoldstrike Stock and Associated DikesStock and Associated Dikes
GoldstrikeGoldstrike DioriteDiorite Lamprophyre andLamprophyre andMonzoniteMonzonite DikesDikes
RhyoliteRhyolite PorphyryPorphyryDikesDikes
Johnston & Ressel, 2005
5Finely Finely PorphyriticPorphyritic RhyoliteRhyolite of of BetzeBetze--PostPost--Genesis (40.3Genesis (40.3--39.3 Ma)39.3 Ma)
Coarsely Coarsely PorphyriticPorphyritic RhyoliteRhyoliteof Beast (37.6 Ma)of Beast (37.6 Ma)
PorphyriticPorphyritic HblHbl DaciteDacite of of BetzeBetze--PostPost--MeikleMeikle (40.1(40.1--39.0 Ma)39.0 Ma)
AphyricAphyric HighHigh--SiSi RhyoliteRhyolite ofofDeep StarDeep Star--Genesis (40.3Genesis (40.3--39.3 Ma)39.3 Ma)
Eocene Intrusions of the Northern Carlin TrendEocene Intrusions of the Northern Carlin Trend
Johnston & Ressel, 2005
Eocene Intrusions Eocene Intrusions SRHG depositsSRHG deposits
No deposits within 2 km of coeval stock
Some SRHG deposits have coeval Eocene dikes range from basaltic to rhyolitic, common porphyry textures, locally mgt-poor & ilmenite-rich
Johnston & Ressel, 2005
Northern / CentralNorthern / CentralCarlin TrendCarlin Trend
Geology and Gold DepositsGeology and Gold Deposits
Dee/Rossi
Boot-strap
RenMeikle
RodeoBetze-Post Deep Post
GenesisBeast Leeville
Carlin
Pete
Lantern
Mike
Mac
GoldQuarry
Deep Star
(Goldstrike Stock - 158 Ma)
Goldstrike
LBB Vivian
(generalized from NBMG Bull. 111, 2002)
Section Line
6CrossCross--Section, Northern Section, Northern CarlinTrendCarlinTrend
(Section A A Plate 3, NBMG Bull. 111, 2002)
RMT
Post Fault
Post Anticline
Ore Outline
Northern / CentralNorthern / CentralCarlin TrendCarlin Trend
Geology and Gold DepositsGeology and Gold Deposits
Dee/Rossi
Boot-strap
RenMeikle
RodeoBetze-Post Deep Post
GenesisBeast Leeville
Carlin
Pete
Lantern
Mike
Mac
GoldQuarry
Deep Star
(Goldstrike Stock - 158 Ma)
Goldstrike
LBB Vivian
Section Line
(generalized from NBMG Bull. 111, 2002)
(Modified from Jory, 2002)
Generalized LongGeneralized Long--Section, Northern Carlin TrendSection, Northern Carlin Trend(using Drc/Dp contact as a datum)(using Drc/Dp contact as a datum)
thermalaureole
> 0.03 opt Au
7Folds, Thrusts and LowFolds, Thrusts and Low--Angle FeaturesAngle Features
PostAnticline
Photo: Greg Arehart
Low-Angle Features
Anticlines / domes Thrust faults /
duplexes Sills / flows Low-angle normal
faults Lithologic /
rheologic contrast
Cross-section of Conelea Anticline, Mega-pit, Twin CreeksMuntean, 2004; Stenger et al, 1998
Low-Angle Features
Anticlines / domes Thrust faults /
duplexes Sills / flows Low-angle normal
faults Lithologic /
rheologic contrast
Muntean, 2004; Teal and Jackson, 1997
8Northern / CentralNorthern / CentralCarlin TrendCarlin Trend
Structural InterpretationStructural Interpretation
Dee/Rossi
Boot-strap
RenMeikle
RodeoBetze-Post Deep Post
GenesisBeast Leeville
Carlin
Pete
Lantern
Mike
Mac
GoldQuarry
Deep StarGoldstrike
Dome
Dome
Eocene Extension and Reactivation of Pre-existing Faults
NNE to N faults: dip slip
NWNW faults: oblique right-lateral dip slip
WNW faults: strike slip
Potential for vertical 1 and low dev. stress allows for dilation on steeply dipping faults / fractures
(after Teal and Jackson, 1997; Nutt and Tosdal, 1999)Muntean, 2004
3
Carlin Carlin -- N. Wall, Main Pit (94)N. Wall, Main Pit (94)
Hardie fault (NE)Looking Northwest
Midway fault (NW)Jki dike-filled
Mill 1
9GoldGold--related Structural related Structural Systems in Carlin AreaSystems in Carlin Area
Early NNEEarly NNE-- and Nand N--trendingtrendingsystemssystems
SynSyn--ore NWore NW-- and WNWand WNW--trending systemstrending systems
Late NELate NE--trending systemtrending system(not shown)(not shown)
(after Madrid, 2001)
Mineralized Fracture SystemsMineralized Fracture Systems
OvOv OutcropOutcrop~ 1500 feet~ 1500 feetabove Rita Kabove Rita Kresource, north resource, north of Carlin mineof Carlin mine
Fractures Fractures typically contain typically contain 1010--50 ppb Au, 50 ppb Au, to 2000 to 2000 ppmppm AsAs
(after Madrid, 2001)
NURE Arsenic NURE Arsenic StreamStreamSediment/SoilSediment/SoilDataData
Strong association with known gold resources(black dots)
Muntean, 2004> 20 ppm As
10
Deposit Morphology by SizeDeposit Morphology by Size
(Modified from Jory, 2002)
Deposit Morphology and SettingDeposit Morphology and Setting
Alteration Zoning - Carlin Mine
Muntean, 2004 Kuehn and Rose (1992)
11
Hydrothermal Mineral Zoning and Abundance, Carlin MineHydrothermal Mineral Zoning and Abundance, Carlin Mine
Bakken, 1990Muntean, 2004
Stratiform Jasperoid outcrop, Gold Point, NVPhoto: G. Arehart
Decarbonatization: Sanded dolomitePhoto: G. Arehart
12
Dickite, Getchell, NVPhoto: G. Arehart
Jasperoid breccia,Gold Quarry, NV
Photo: G. Arehart
Hydrothermal Dissolution Hydrothermal Dissolution BrecciaBreccia, , GetchellGetchell
Photo: G. Arehart
13
Deep Post Underground (02)Deep Post Underground (02)
L 4080W L 4080W realgarrealgar--orpiment ,orpiment ,1.5 opt Au1.5 opt Au
Rock bolterRock bolterin actionin action
Collapse (dissolution) breccia in Roberts Mountains Fm. adjacent to Goldstrike Intrusion, L 4150 W
JKi
SDrmstls2
Deep Post MineDeep Post Mine
2.02 opt Au
0.79 opt Au0.05 opt Au
0.18 opt Au
Dp2
SDrmSDrm
BrecciaBreccia Textures Textures -- Deep Post Deep Post
Carbonate rock clastsin sulfidic matrix
Decalcified-sulfidic
Silica-sulfidic Late realgar after silica-sulfidic
2 cm
(after Marino, 2002)
14
Dissolution Dissolution BrecciaBreccia TextureTexture
Relict clast0.8 mmPhotomicrograph (plane-polarized)
Photo: Tracy CailSEM image 56.6 g/t Au
99NZ008 2732.5-1
As-0.02Au-bdl
As-0.02Au-bdl
As-0.65Au-bdl
As-14.5Au-2100
As-12.7Au-300
As-8.8Au-2100
As-7.0Au-400
50 mImage and data from Jean Cline
Getchell
15
Core
Rim
TU00664 219 1.213 oz/t 148 Zone Image from Jean Cline
Getchell
Interpretation
Inner (early) rims - highest Au (X000 ppm) Metals traveling with Au: As Cu Hg Tl Te Sb (Pb)
Outer (later) rims mod Au (X00 ppm)Metals from wallrocks: Pb, W
(& diminishing ore trace elements)
Rims are a proxy for evolving ore fluid
Cline, 2006
Carlin Jurassic Dikepyrite
Carlin SDrmpyrite
1.1% Au
0.76% Au
0.70% Au
Up to 0.90% Auin bright zones
Up to 0.47% Au
SEM - BSEImages
16
Betze-Post
2.1 oz/t Au
Ore quartz is characterized by jasperoid and drusy quartz lined
vugs, rather than veins
Late ore drusy
Post ore drusy
Ore jasperoid
Lubben, 2004
Cathodoluminescence
Betze-Post, Lubben, 2004
Provides control for fluid inclusion and ion probe isotope analyses
Late-stage orpiment, Twin Creeks
Muntean, 2004
17
25m
stibnite
galkhaite Late-stage intergrown galkhaiteand stibnite, Getchell
Images from Greg Arehart
Late-stage hydrothermal barite,Meikle, NV
Photo from Greg Arehart
18
Processes and Processes and ParagenesisParagenesis
Early
Late
DecarbonatizationDecarbonatization / Decalcification/ Decalcification((DolomitizationDolomitization & & BrecciationBrecciation))
volume lossvolume loss
Replacement: Replacement: ArgillizationArgillization, , SilicificationSilicificationSulfidationSulfidation (Au)(Au)
volume lossvolume loss
Open Space Development / DepositionOpen Space Development / Depositioncavities, fractures and brecciascavities, fractures and breccias
calcitevein quartz
drusy quartzjasperoidgalenaarsenopyritesphaleritechalcopyritepyrite / pyrrhotitesericite
galkhaitefluoriteorpimentmarcasite (Au and As)pyrite (Au and As)marcasite
Fe-oxidescalcite (coarse,euhedral)calcite (clear,coarse)realgarstibnite
illite / kaolinite
? ?
? ?
? ???
? ?
??
Pre Ore Carlin Event Post OreLateMain
Depth and Fluid TemperatureDepth and Fluid Temperature--Composition Composition of SRHG Depositsof SRHG Deposits
Depth approx. 1 km (+ 0.5km), inferred from glassy dikes, reconstruction of Eocene volcanic stratigraphy and cooling profiles for apatite closure temperatures (FT and U-Th)
Temperature 115-240, mostly 180-240C for ore deposition Salinity 0-10 wt%, locally as high as 17 wt%
Gas Content CO2-bearing, but less than 4 mole %
Detectable H2S, trace CH4 No evidence for boiling
(Modified from Muntean, 2004)
19
Quartz Quartz MicrothermometryMicrothermometry / Fluid Inclusions/ Fluid Inclusions
160 220 3 6
Cline & Hofstra, 2001
Shigehiro, 2001
Kuehn & Rose, 1992
Lamb, 1995
Lubben, 2004
Hofstra, 1994
Tt =180-240C
Fluid Inclusions Fluid Inclusions -- GetchellGetchell
ore quartz: 180-220Corpiment: 180-200Cfluorite: 140-180C
realgar: ?calcite: 120-160C
Cline & Hofstra, 2000
Oxygen and Hydrogen Isotopes Oxygen and Hydrogen Isotopes
Source fluids for Au mineralization equivocal
Local evidence for deep magmatic or metamorphic ore-fluid overprint by exchanged meteoric fluids(e.g. Getchell, Deep Star)
Cline et al., 2005
20
Sulfur Isotopes Sulfur Isotopes
Cline et al., 2005
S isotope range in ore-pyrite is inconclusive or consistent with sedimentary source
Local evidence formagmatic source(e.g. Getchell, N. Carlin)
SRHG Deposits Carbonaceous MaterialSRHG Deposits Carbonaceous Material
Horse Canyon Pit
Muntean, 2004
SRHG Deposits Carbonaceous MaterialSRHG Deposits Carbonaceous Material
Most SRHG deposits have a close spatial association with carbonaceous rocks
Unaltered rocks generally contain 10 wt%
Indigenous C and mobilized C Most carbon in SRHG deposits is best characterized as
pyrobitumen (overmature, locally bordering on graphite) No consistent relationship between gold grade and the amount
of carbon at the deposit scale In many cases, SRHG deposits appear to occupy pre-existing
hydrocarbon reservoirs Hydrocarbons mainly accumulated and were rendered immobile
prior to mineralization; Au-bearing hydrothermal fluids cooked oil reservoir at Alligator Ridge
Some syn-ore mobilization of hydrocarbons cannot be ruled out
Muntean, 2004
21
Weathering of SRHG deposits
Oxide profile, Twin Creeks megapit
Photo: G. Arehart
Weathering and OxidationWeathering and Oxidation
Weathering generates iron oxides (hematite, goethite), sulfates (alunite-jarosite); phosphates (variscite and similar minerals); and As oxides (e.g. scorodite)
Weathering in Nevada occurred sporadically between 30 0 Ma based on supergene alunite and volcaniclastic rock dates
Depth of weathering varies, but may reach 500 m along structures
Oxidation liberated significant Au to generate oxide ore exploited almost exclusively until 1990
Bio-oxidation to liberate gold from ore-stage pyrite-marcasite
Current debate over supergene mobility of gold
Modified from Muntean, 2004
1Disseminated Sedimentary Disseminated Sedimentary RockRock--hosted Gold Systems hosted Gold Systems
in Nevadain Nevada
BetzeBetze -- Post, Northern Carlin TrendPost, Northern Carlin Trend
Disseminated Sedimentary Disseminated Sedimentary RockRock--hosted Gold Systemshosted Gold Systems
in Nevadain NevadaSteve GarwinSteve Garwin
SEG Gold WorkshopSEG Gold Workshop2020--21 October 2007 Cairns, Australia21 October 2007 Cairns, Australia
Part III
Outline of PresentationOutline of Presentation
Disseminated Sedimentary RockDisseminated Sedimentary Rock--hosted hosted Gold Systems in NevadaGold Systems in Nevada
1)1) Regional setting and Regional setting and metallogenymetallogeny2) Carlin trend geology & geochemistry2) Carlin trend geology & geochemistry
Styles and settings of gold mineralization Styles and settings of gold mineralization OreOre--related processes and mineral related processes and mineral paragenesisparagenesisOreOre--fluid Pfluid P--TT--X constraintsX constraintsWeathering and Weathering and supergenesupergene effectseffects
3) Global examples of SRHG deposits and3) Global examples of SRHG deposits andConceptual models and controls to mineralizationConceptual models and controls to mineralization(Carlin deposit controversies session (Carlin deposit controversies session SEG / Reno, 2005)SEG / Reno, 2005)
SRHG DEPOSITS in SOUTHEAST ASIASRHG DEPOSITS in SOUTHEAST ASIASRHG DEPOSITS in SOUTHEAST ASIA
Bau Mesel
Siana
Kyaukphato
Xepon
SW GuizhouW Hunan
2Bau Limestone - Sarawak, Malaysia
District-Scale Deposit Zoning
1000m
Tai Parit - SRHG
NN
Diss. Au-As-Hg
Polymetallic vein
Central Porph / skarn
Epithermal Au
3Mining Operations Circa 1995
Bau District Sarawak, Malaysia
Host Rocks Lower Cretaceous Pedawan Shale (turbiditic) Jurassic Bau Limestone
Assoc. Igneous Rocks Middle Miocene (13-10 Ma) dacite porphyries
Geologic Setting Host rocks deposited on active margin of Sundaland Caton District in Oligocene-Miocene Central Kalimantan Arc
Deposit Form Zoned from porphyry / skarn center outwards through
polymetallic veins and SRHG deposits to distal disseminated Hg deposits
Gold near limestone-shale contact and steeply-dipping faults or intrusive margins
4MESEL GOLD MINE NORTH SULAWESI, INDONESIA
MESEL GOLD MINE NORTH SULAWESI, INDONESIA
5Mesel District - Sulawesi, Indonesia
Host Rocks Middle Miocene silty- to clayey-limestone sequence
Assoc. Igneous Rocks Middle Miocene (14-11 Ma) hbl. andesite laccolith, flows &
tuffs
Geologic Setting Oligocene-Recent North Sulawesi magmatic arc Intersection of arc-parallel and arc-normal faults control local
extensional sedimentary basins, related magmatism & mineralization
Deposit Form Gold near limestone-tuff contact and laccolith margins
SW Guizhou Province, China
6Zimoudang Gold Mine
oreore Permian Calcareous Rocks
oreoreTriassic Calcareous Rocks
Getang Gold Mine,
7Guizhou-Guangxi, China
Host Rocks Upper Permian Middle Triassic shelf carbonates grade to
clastics, including coal
Assoc. Igneous Rocks None evident; no geophysical evidence of intrusions at depth
Geologic Setting Host rocks deposited on south margin of Yangtze Craton;
open folding is only significant deformation (Yangshanian)
Deposit Form Stratabound ore at contact between carbonates and clastics
and within carbonate rocks in anticlines Ore associated with high-angle faults that typically breach
folds
Circum-Pacific SRHG Deposits: Common Attributes
Deposits hosted by sedimentary rock sequences containing carbonate
Gold ore in favourable stratigraphy near controlling faults
Alteration Assemblages: Carbonate dissolution and brecciation Silicification by replacement and deposition Argillic alteration of siliciclastic units Sulfidation of iron to form pyrite / marcasite
Geochemical Enrichment: Au, Ag, As, Sb, Hg, Tl, Ba Sub-micron gold diss. in arsenical py / marc rims
8Conceptual Model Conceptual Model -- Large Deposit Large Deposit (e.g. Gold Quarry)(e.g. Gold Quarry)
Conceptual Model Conceptual Model Muntean (2004)Muntean (2004)
Muntean, 2004
Muntean, 2004
9Muntean, 2004
Controls on MineralizationControls on Mineralization
Structural high Structural high -- anticline or horst blockanticline or horst blockSteep faults, dikes and fracture zones Steep faults, dikes and fracture zones
-- hydrothermal fluid conduitshydrothermal fluid conduitsGentlyGently--moderate dipping moderate dipping lithologieslithologies and thrusts and thrusts
-- traps and thickened prospective sectiontraps and thickened prospective sectionReceptive and reactive host rocksReceptive and reactive host rocksContrasting Contrasting rheologyrheology and porosity/permeability and porosity/permeability
-- competency contrast and fluid channel wayscompetency contrast and fluid channel waysDecalcification, Decalcification, brecciationbrecciation & & silicificationsilicification
-- volume loss;volume loss; preparation to gold depositionpreparation to gold deposition
Restored Late Eocene CrossRestored Late Eocene Cross--sectionsection
Removes Oligocene-Early Miocene extension Shows Eocene granitic intrusions, emplaced at >10 km depth,
could have underlain Carlin trend deposits
Keith Howard, 2003
Muntean, 2004
10
FIGURE ADAPTED FROM HEINRICH (2005)FIGURE ADAPTED FROM HEINRICH (2005)
On the margins of large On the margins of large magmaticmagmatic--hydrothermal hydrothermal systems, where we propose systems, where we propose CarlinCarlin--type deposits form, type deposits form, remobilization of at least some remobilization of at least some wallwall--rock components during rock components during mineralization cannot be ruled mineralization cannot be ruled out, and may be the norm. out, and may be the norm. Circulation of meteoric, Circulation of meteoric, connate, or other fluids and the connate, or other fluids and the associated remobilization of associated remobilization of wallwall--rock components may rock components may account for account for nonmagmaticnonmagmaticsignatures of mineralizing fluids signatures of mineralizing fluids and variable isotopic signatures and variable isotopic signatures for mineralizing components for mineralizing components observed in many Carlinobserved in many Carlin--type type depositsdeposits
-- Johnston and Johnston and ResselRessel (2005)(2005)
FIGURE ADAPTED FROM SILLITOE AND BONHAM (1990)FIGURE ADAPTED FROM SILLITOE AND BONHAM (1990)Johnston & Ressel, 2005
Metal and deposit Metal and deposit zonationzonation around the 39 around the 39 Ma Bingham stock Ma Bingham stock (modified from Gunter (modified from Gunter and Austin, 1997)and Austin, 1997)
Johnston & Ressel, 2005
11
Carlin Trend: Centered on the 39 to 37 Ma NCEP ComplexCarlin Trend: Centered on the 39 to 37 Ma NCEP Complex
PROXIMAL PORPHYRY PROXIMAL PORPHYRY AND/OR SKARN DEPOSITSAND/OR SKARN DEPOSITS
POLYMETALLIC VEIN OR POLYMETALLIC VEIN OR REPLACEMENT DEPOSITSREPLACEMENT DEPOSITS
DISTAL CARLINDISTAL CARLIN--TYPE TYPE (SRHG) DEPOSITS(SRHG) DEPOSITS
PROSPECTIVITY BY TYPE:PROSPECTIVITY BY TYPE:
OUTLINE OF THE NORTHERN CARLINOUTLINE OF THE NORTHERN CARLIN--EMIGRANT PASS INTRUSIVE COMPLEXEMIGRANT PASS INTRUSIVE COMPLEX
CARLIN, ETC.
LEEVILLE, ETC.
LANTERN
GENESIS COMPLEX
GOLDSTRIKE COMPLEX
BOOTSTRAP, TARA
DEE, ROSSI
GOLD QUARRY, MIKE, ETC.39 TO 38 Ma WELCHES
CANYON STOCK
5 km5 km
Johnston & Ressel, 2005
District Dimensions and Zoning
A question of scale Size of footprints of Carlin-type (SRHG) systems
are substantially larger than giant igneous-related porphyry and high-sulfidation epithermal deposits
Seedorff & Barton, 2005
Sizes of Intrusions and SRHG Systems
Tuolumne Intrusive Suite, Sierra Nevada Batholith Assembled by emplacement of plutons over 10 m.y.
Carlin trend (figures at same scale) About the same size as a large composite pluton within a batholith
Coleman et al., 2004, Fig. 1
Seedorff & Barton, 2005
12
Regional Hydrothermal Systems
Regional systems are not only large, but they have weak alteration zoning Orogenic gold systems, e.g., Mother
Lode of California Note spatial proximity to igneous rocks
(probably genetically unrelated) Note similarity in scale of Carlin trend to
central Mother Lode
Seedorff & Barton, 2005
Three Possible Scenarios
Magmatic origin Magmatic
fluids Amagmatic
origins Metamorphic
fluids Surface-
derived fluids
Seedorff & Barton, 2005
Fluid Pathways on P-T Diagram
Pathways on diagram contoured for solubilities of quartz and calcite
Note similarity of products at low P and TSeedorff & Barton, 2005
13
Source Rocks for Au in Amagmatic Models
Fine-grained clastic rocks at base of miogeocline may be in appropriate setting and have appropriate chemistry to be the source of metals
Seedorff, 1991, Table 4
Seedorff, 1991, Fig. 20
Seedorff & Barton, 2005
Disseminated SedimentaryDisseminated Sedimentary--rock Hosted rock Hosted Gold Systems Gold Systems -- Looking ForwardLooking Forward
HighHigh--grade u/g deposits (e.g. Deep Star) grade u/g deposits (e.g. Deep Star) -- profitability profitability vsvs ouncesounces
Rendering the upper plate (RMA) transparent Rendering the upper plate (RMA) transparent -- delineate zones of structural complexitydelineate zones of structural complexity
NonNon--traditional host rocks traditional host rocks -- upper plate, subupper plate, sub--SDrmSDrm and intrusive rocksand intrusive rocks
Geological and geochemical vectors to ore Geological and geochemical vectors to ore -- fracture mapping, alteration zoning and 3D modelsfracture mapping, alteration zoning and 3D models
Innovative underground drilling techniques Innovative underground drilling techniques Enhancement of BioEnhancement of Bio--oxidation process oxidation process
-- milling of low/moderatemilling of low/moderate--grade refractory materialgrade refractory material
AcknowledgementsAcknowledgements
J. Muntean, M. Johnston & M. J. Muntean, M. Johnston & M. ResselRessel, , E. E. SeedorffSeedorff & M. Barton, C. & M. Barton, C. ThormanThorman
NewmontNewmont, , BarrickBarrick, Placer Dome, Victoria, Placer Dome, VictoriaGeoinformatics & other Company GeologistsGeoinformatics & other Company Geologists
UNR UNR CREG, UNLV, UWACREG, UNLV, UWA
US Geological SurveyUS Geological Survey
J. Cline, D. Groves, J. J. Cline, D. Groves, J. HedenquistHedenquist, , T. Leach, P. Lewis, R. MadridT. Leach, P. Lewis, R. Madrid
J. Muntean, M. Johnston & M. J. Muntean, M. Johnston & M. ResselRessel, , E. E. SeedorffSeedorff & M. Barton, C. & M. Barton, C. ThormanThorman
NewmontNewmont, , BarrickBarrick, Placer Dome, Victoria, Placer Dome, VictoriaGeoinformatics & other Company GeologistsGeoinformatics & other Company Geologists
UNR UNR CREG, UNLV, UWACREG, UNLV, UWA
US Geological SurveyUS Geological Survey
J. Cline, D. Groves, J. Hedenquist, J. Cline, D. Groves, J. Hedenquist, T. Leach, P. Lewis, R. MadridT. Leach, P. Lewis, R. Madrid
[email protected]@geoinformex.com