EpitermalAuAg_JeffreyHedenquist

EpithermalEpithermal AuAu--AgAg andand AgAg--AuAu veinvein depositsdeposits::

RenewedRenewed interestinterest as as explorationexploration targetstargets

ProExploProExplo 2005: Lima, 2005: Lima, PerPer

Jeffrey W. HedenquistJeffrey W. Hedenquist Ottawa, CanadaOttawa, Canada

Hedenquist@[email protected]

with appreciation to:with appreciation to:Minera PeMinera Peoles de Peroles de PerPlacer Dome del PerPlacer Dome del Per

Why epithermal veins now?Why epithermal veins now?

High grades of Au (10High grades of Au (10--50 50 g/tg/t) and/or Ag (500) and/or Ag (500--1000+ 1000+ g/tg/t)) AgAg--rich may also be rich may also be polymetallicpolymetallic (Zn, Pb, In, etc.)(Zn, Pb, In, etc.)


High grades of Au (10-50 g/t) and/or Ag (500-1000+ g/t) Ag-rich may also be polymetallic (Zn, Pb, In, etc.) Amenable to underground miningAmenable to underground mining Relatively short time for smallRelatively short time for small--tonnage developmenttonnage development


High grades of Au (10-50 g/t) and/or Ag (500-1000+ g/t) Ag-rich may also be polymetallic (Zn, Pb, In, etc.) Amenable to underground mining Relatively short time for small-tonnage development Small surface footprint (mine, tailings)Small surface footprint (mine, tailings) LLess effect on runoffess effect on runoff


High grades of Au (10-50 g/t) and/or Ag (500-1000+ g/t) Ag-rich may also be polymetallic (Zn, Pb, In, etc.) Amenable to underground mining Relatively short time for small-tonnage development Small surface footprint (mine, tailings) Less effect on runoff Potentially high value if moderate mining costPotentially high value if moderate mining cost Peru has underground experience and expertisePeru has underground experience and expertise

More appropriate in areas of high sensitivity to mine More appropriate in areas of high sensitivity to mine development development -- i.e., low impact i.e., low impact -- or difficult terrainor difficult terrain

White Island, NZ: 300 t Au flux to atmosphere over life of ~10,000 yrs

1) Introduction: Terms, sizes1) Introduction: Terms, sizes2) Basic characteristics2) Basic characteristics3) Au3) Au--rich veins: Riftsrich veins: Rifts4) Ag4) Ag--rich veins: Arcsrich veins: Arcs

Exploration implicationsExploration implications

Epithermal vein deposits:

Epithermal types:Epithermal types: Alternative terminologyAlternative terminologyEach column largely synonymousEach column largely synonymous

VeinsVeins VeinsVeins ReplacementReplacementGold (Te, Se)Gold (Te, Se)--qtzqtz Silver, ZnSilver, Zn--Pb Pb Goldfield type, AuGoldfield type, Au--alunite alunite 1900s1900s

RansomeRansome, Emmons, Lindgren, Sillitoe, Buchanan, Bonham, , Emmons, Lindgren, Sillitoe, Buchanan, Bonham,

BethkeBethke, , Heald Heald et al., John, Hedenquist et al., et al., John, Hedenquist et al., Einaudi Einaudi et al.et al.


VeinsVeins VeinsVeins ReplacementReplacementGold (Te, Se)Gold (Te, Se)--qtzqtz Silver, ZnSilver, Zn--Pb Pb Goldfield type, AuGoldfield type, Au--alunite alunite

Alkaline epithermalAlkaline epithermal Acid epithermalAcid epithermalAdulariaAdularia--sericitesericite, low sulfur, low sulfur Acid sulfate, high sulfurAcid sulfate, high sulfur 1980s1980s

Low sulfidation Low sulfidation High sulfidation High sulfidation

RansomeRansome, Emmons, Lindgren, Sillitoe, Buchanan, Bonham, , Emmons, Lindgren, Sillitoe, Buchanan, Bonham,



VeinsVeins VeinsVeins ReplacementReplacementGold (Te, Se)Gold (Te, Se)--qtzqtz Silver, ZnSilver, Zn--Pb Pb Goldfield type, AuGoldfield type, Au--alunitealunite

Alkaline epithermalAlkaline epithermal Acid epithermalAcid epithermalAdulariaAdularia--sericitesericite, low sulfur, low sulfur Acid sulfate, high sulfurAcid sulfate, high sulfur


Low sulfide/Low sulfide/bmsbms High sulfide/High sulfide/bmsbmsBimodal basaltBimodal basalt--rhyoliterhyolite Western andesite Western andesite 1990s1990sLow sulfidation Low sulfidation (LS)(LS) IntermediateIntermediate (IS)(IS) High sulfidationHigh sulfidation (HS) (HS)

RansomeRansome, Emmons, Lindgren, Sillitoe, , Emmons, Lindgren, Sillitoe, BuchananBuchanan, Bonham, , Bonham,



VeinsVeins VeinsVeins ReplacementReplacementGold (Te, Se)Gold (Te, Se)--qtzqtz Silver, ZnSilver, Zn--Pb Pb Goldfield type, AuGoldfield type, Au--alunitealunite

Alkaline epithermalAlkaline epithermal Acid epithermalAcid epithermalAdulariaAdularia--sericitesericite, low sulfur, low sulfur Acid sulfate, high sulfurAcid sulfate, high sulfur


Low sulfide/Low sulfide/bmsbms High sulfide/High sulfide/bmsbmsBimodal basaltBimodal basalt--rhyoliterhyolite Western andesite Western andesite Low sulfidation Low sulfidation (LS)(LS) IntermediateIntermediate (IS)(IS) High sulfidationHigh sulfidation (HS) (HS)

LS (LS alkalic)LS (LS alkalic) IS zoned, IS IS zoned, IS MexMex HS & HSHS & HS--IS zonedIS zoned evolvingevolving

RansomeRansome, Emmons, Lindgren, Sillitoe, , Emmons, Lindgren, Sillitoe, BuchananBuchanan, Bonham, , Bonham,


Einaudi, Hedenquist and Inan, 2003

Sulfidation statesSulfidation states

Einaudi, Hedenquist and Inan, 2003

Sulfidation stateSulfidation stateevolutionevolution

Wallro

ck

Wallro

ck bu

ffer

buffe

r

Rift Rift magmasmagmas

ArcArcmagmasmagmas

OreOre--deposit styles: Relative amounts of golddeposit styles: Relative amounts of gold

(>5 (>5 MozMoz deposits, 1997)deposits, 1997)

50%50% WitwatersrandWitwatersrand 12%12% Epithermal (8 >20 Epithermal (8 >20 MozMoz gold)gold) 10%10% Porphyry (1 intrusion hosted)Porphyry (1 intrusion hosted) 12%12% Sediment hosted (incl. 4% Carlin)Sediment hosted (incl. 4% Carlin) 9%9% Greenstone lode (Greenstone lode (orogenicorogenic)) 7%7% Other (Fe Fm, VHMS, etc.)Other (Fe Fm, VHMS, etc.)

>40% (non Wits) gold from intrusion>40% (non Wits) gold from intrusion--centered centered deposits, ~1/4 from epithermal (>5 deposits, ~1/4 from epithermal (>5 MozMoz Au)Au)

A. A. ArribasArribas, UBC, March 2000, UBC, March 2000

Epithermal Au(Ag) deposits: Production + reserves Epithermal Au(Ag) deposits: Production + reserves (~2000)(~2000)

Inter. sulfidation

Alkalic LS subtype

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Ag $Au $

LS (alkalic)

Low sulfidationIntermediatesulfidation

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$

(

U

S

)

Value of Epithermal Deposits (Au & Ag)Value of Epithermal Deposits (Au & Ag)Au $390 US/ozAg $6 US/oz

N=6

N=12

~5 Moz Au eq.

N=4

Values compiled by Gemmell, in prep.

M

M

M

M

M: Mexico

MD

D

D: diatreme related

D

D

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Metal budgets:Metal budgets:

Ag x 100

Au x 1000

Zn + Pb + Cu

Calcatreu

r ath

Cerro Vanguardia

ManantialEspejo

Ma

hica

Cerro Bayo

Esquel

Qda C

Navidad

Sta Teresa

Katerfeld

HalconesChacabuco

Au x 1000

Ag x 100Zn+Pb (Cu)

Rifts:Rifts:

Henley, 1985, 1990Henley, 1985, 1990

RiftsRifts

ArcsArcs

Examples of epithermal deposits Examples of epithermal deposits

LS veins:LS veins: El El LimnLimn; Rio Blanco; (Ares); El ; Rio Blanco; (Ares); El PenPen; Cerro ; Cerro VanguardiaVanguardia, , EsquelEsquel; ; HishikariHishikari; Midas, Sleeper, Lewis; Midas, Sleeper, Lewis--CrofootCrofoot

vs.vs. LS alkalic: LS alkalic: Cripple Creek, Emperor, Cripple Creek, Emperor, PorgeraPorgera, , LadolamLadolam

IS veins:IS veins: Arcata, Arcata, OrcopampaOrcopampa + + JulcaniJulcani, , ColquiColqui & & QuiruvilcaQuiruvilca (w/ (w/ HS); Victoria, HS); Victoria, BaguioBaguio; ; ToyohaToyoha, , KushikinoKushikino; ; KelianKelian; Comstock; ; Comstock; TethysTethys

vs.vs. Mexican Mexican Ag:Au:bmsAg:Au:bms, e.g., , e.g., GuanajuatoGuanajuato, , PachucaPachuca, , FresnilloFresnillo

HS replacements: HS replacements: YanacochaYanacocha, , PierinaPierina, Alto , Alto ChicamaChicama; ; VeladeroVeladero

Location of principal epithermal depositsLocation of principal epithermal deposits

?? ?? ??

Age not necessarily a limitAge not necessarily a limit

Geologic setting of lowGeologic setting of low--sulfidation depositssulfidation deposits

Americas and globalAmericas and global

BasaltBasalt--rhyolite association in extensional settings:rhyolite association in extensional settings: Intra, near, and backarc; Intra, near, and backarc; postcollisionpostcollision rifts (non porphyry)rifts (non porphyry)

Host rhyolite (Host rhyolite (dacitedacite) domes and flows) domes and flows

Sedimentary accumulations; sintersSedimentary accumulations; sinters

SynSyn--hydrothermal mafic dikes commonhydrothermal mafic dikes common

Extension, alkaline magmatism for TeExtension, alkaline magmatism for Te--rich typerich type

John, 2001; John, 2001; SillitoeSillitoe, 2002, 2002

Geologic setting of intermediateGeologic setting of intermediate--sulfidation depositssulfidation deposits

SW Pacific, SW USSW Pacific, SW US

CalcCalc--alkaline alkaline andesiteandesite--dacitedacite arcs, ~neutral extension:arcs, ~neutral extension: Intrusion centered, zonedIntrusion centered, zoned

Andesite Andesite stratovolcanostratovolcano: : common dikes, common dikes, diatremesdiatremes

Cordilleran volcanism: Cordilleran volcanism: large intrusive centers, high relieflarge intrusive centers, high relief

Silicic depression: Silicic depression: large calderas, small intrusionslarge calderas, small intrusions

Hosts: dominant A/D flows, Hosts: dominant A/D flows, bxsbxs, tuffs; , tuffs; sedsseds, basement, basement

White et al., 1995White et al., 1995

Epithermal alteration, gangue mineralsEpithermal alteration, gangue minerals

LS veins:LS veins: illiteillite, clays; chalcedony, adularia, calcite (, clays; chalcedony, adularia, calcite (roscoeliteroscoelite))

IS veins:IS veins: sericitesericite (muscovite); quartz, (muscovite); quartz, rhodochrositerhodochrosite, barite, , barite,

anhydrite (local advanced argillic, e.g., kaolinite, alunite)anhydrite (local advanced argillic, e.g., kaolinite, alunite)

HS replacements:HS replacements: silicic host, quartzsilicic host, quartz--alunite halo; alunite, barite, alunite halo; alunite, barite,

anhydrite; anhydrite; pyrophyllitepyrophyllite--sericitesericite rootsroots

Barren lithocaps:Barren lithocaps: silicic core, quartzsilicic core, quartz--alunite haloalunite halo

LS & IS deposits: sulfide assemblagesLS & IS deposits: sulfide assemblages

IS veins:IS veins: AgAgAu PbAu PbZnZn

PyPy lowlow--Fe Fe sphsph tntn/td/tdccpccpgngn, , Te (Bi, Te (Bi, SnSn, In), In)

LS veins:LS veins: AuAuAg, bonanzasAg, bonanzas

PyPy highhigh--Fe Fe sphsph asp or asp or popo, , Se or TeSe or Te

Barton et al., 1977, John, 2001, Barton et al., 1977, John, 2001, EinaudiEinaudi et al., 2003, otherset al., 2003, others

Redox Redox distinction related to distinction related to volcanotectonic volcanotectonic settingsetting

Sillitoe and Hedenquist, 2003Low sulfidation vein setting: riftLow sulfidation vein setting: rift

5050--100 m100 m

Champagne Pool, Champagne Pool, WaiotapuWaiotapu, New Zealand, New Zealand

McLaughlin, CA:McLaughlin, CA:LS sheeted veins beneath LS sheeted veins beneath sinter with Hgsinter with Hg

HydroHydro--thermal thermal brecciabrecciawith with sintersinter

Sheeted Sheeted veinvein

Sherlock et al. (1995)

LewisLewis--CrofootCrofoot, NV:, NV: LS veins, steamLS veins, steam--heated overprint (falling water table)heated overprint (falling water table)(NB: remnant (NB: remnant qtzqtz veins + Au within overprinted zone)veins + Au within overprinted zone)

Steam-heated mudpool, kaolinite

H2S + 2 O2 = H2SO4

Hishikari, southern Kyushu

Footprint of9 Moz Audeposit

Hishikari:Gold-quartz veinsin greywacke basement

Long Long sections, sections, Honko Honko vein vein system, system, HishikariHishikari

Faure et al., 2002

Greywacke basement

100 m

Unconformity

Unconformity

500 m

Hishikari, S Kyushu

Izawa et al. (1990)

tridymite gone

smectite,kaolinite

smectite-chl

highes

t

paleot

emp

Zoned clays around vein projections: high T paleo-plume

HishikariHishikari vein cross sectionvein cross section

Izawa et al. (1990)

smectite-chl

chlorite

smectite, kaolinite

Patagonia, Argentina

Midas, Nevada:Midas, Nevada:

Ken Snyder LS mine, 110 t AuKen Snyder LS mine, 110 t Au

from from GoldstrandGoldstrand and Schmidt, 2000and Schmidt, 2000

Ken Snyder mine: Ken Snyder mine: Long section, Colorado Grande veinLong section, Colorado Grande vein

300 m

100 g*m)

HS IS LSHS IS LS

Ya

RMt

Hedenquist et al., 2000

Vi To

LS epithermal veins: LS epithermal veins: Extreme disequilibriumExtreme disequilibrium

Rapid ascentRapid ascent Rapid boilingRapid boiling Rapid coolingRapid cooling Rapid Rapid supersaturationsupersaturation, silica, Au, silica, Au

cfcf. Saunders 1994; . Saunders 1994; Saunders et al., 1996;Saunders et al., 1996;

Sillitoe and Hedenquist, Sillitoe and Hedenquist, 20032003

Sleeper ore: Au dendrites, silica gelSleeper ore: Au dendrites, silica gel

Exploration implicationsExploration implications Extensional setting, fault offsetsExtensional setting, fault offsets Narrow vertical intervals, bonanzasNarrow vertical intervals, bonanzas

Summary: LS veinsSummary: LS veins

Distinct setting: Distinct setting: riftsrifts, rhyolite, rhyolite--basalt associationbasalt association Sedimentary sequences (Sedimentary sequences (volcaniclasticvolcaniclastic, , lacustrinelacustrine))

PaleosurfacePaleosurface: sinter, steam: sinter, steam--heated blanketheated blanket Alteration around veins may be limited: Alteration around veins may be limited: zoned clayszoned clays Discontinuous bonanza zonesDiscontinuous bonanza zones

Can be very localized IF presentCan be very localized IF present Ore zones tend to have flat tops/bottomsOre zones tend to have flat tops/bottoms

Outcrop may be low gradeOutcrop may be low grade Must drill test through chalcedony zone (to Must drill test through chalcedony zone (to paleopaleo >200>200--220 C)220 C) Ore zone typically 100Ore zone typically 100--300 m vertical300 m vertical

Sillitoe and Hedenquist, 2003

Schematic relations: IS (and HS) epithermal deposits, adv Schematic relations: IS (and HS) epithermal deposits, adv arg arg alteration:alteration:Intrusion centered, marginalIntrusion centered, marginal

Surface projections: Lepanto: enargite-Au Far Southeast: porphyry Cuand Victoria: IS Au-Ag veins

From Palidan slide

Surface projections of Surface projections of VictoriaVictoria--Teresa IS vein & Teresa IS vein & LepantoLepanto HS enargite, HS enargite, over Far Southeast over Far Southeast porphyryporphyry

Hedenquist et al. (2001)

Teresaveins

Bulalacao ?porphyry

X Biot1.18 Ma

X Illite1.15 Ma

X Horn1.45 Ma

Hydro Biot1.40-1.45 Ma

Alunite1.40-1.45 Ma

Ser ~1.35 Ma

Bt 2.2-1.8 Ma

Enargite-AuPorphyry Cu

IS Au-Ag veins

Arribas et al. (1995)Claveria (2001)

Claveria (2001); Hedenquist et al. (2001)

AlterationAlteration zonationzonation??

Advanced

Advanced argillic argillic lithocap

lithocap

Claveria (2001); Hedenquist et al. (2001)

White Island, NZ: 300 t Au flux to atmosphere over life of ~10,000 yrs

Intrusion-centered active systems

Kyushu epithermal deposits: LS and IS veinsKyushu epithermal deposits: LS and IS veins

Tectonics and age Tectonics and age determine type of determine type of epithermal Au epithermal Au depositsdeposits

Migration of arc (IS), Migration of arc (IS), producing rift (LS)producing rift (LS)

Y. Watanabe (2004)Y. Watanabe (2004)

Hishikari Hishikari (LS) 0.7 Ma(LS) 0.7 MaKushikino Kushikino

(IS) 3.7(IS) 3.7 MaMamigration of volcanism

Kushikino: Mt Kamuridake to eastcapped by silicic zones, adv. argillic halos

Kushikino IS veins 2 km west

Kushikino IS veins: qtz-calcite-Au

Volcanic setting of Volcanic setting of KushikinoKushikino IS deposit, Kyushu IS deposit, Kyushu

((Izawa and Izawa and ZengZeng, 2001), 2001) 55 t Au production55 t Au production

500 m500 m100100--200 m200 m

0 m0 m

Volcanism: 3.6Volcanism: 3.6--3.9 Ma3.9 MaAlunite: 3.4Alunite: 3.4--3.8 Ma3.8 MaAdulariaAdularia--Au:Au: 3.43.4--3.7 Ma3.7 Ma

AdAdzonedzoned

AAAA

Comstock Lode, Comstock Lode, Nevada: Nevada: IS veinsIS veins

6000 t Ag, 257 t Au6000 t Ag, 257 t AuCon Virginia: 1.13 Mt @ Con Virginia: 1.13 Mt @ 87.4 87.4 g/t g/t Au, 1834 Au, 1834 g/t g/t AgAg

Al to Al to pyrop pyrop diasp diasp to to kaol kaol dick dick to to illiteillite

2 km

2M mica

Hudson(2003)

Alunite: Alunite: 1515--16.3 Ma16.3 MaAdularia: Adularia: 12.712.7--14.1 Ma14.1 MaAdAd overprint on AAoverprint on AA

Arcata, Arcata, PerPer:: IS AgIS Ag--Au vein:Au vein: >3,000 t Ag, 30 t Au>3,000 t Ag, 30 t Au

adv. argillic vein halo to veins at surfaceadv. argillic vein halo to veins at surface Candiotti et al. (1990)Candiotti et al. (1990)

Zacatecas, Mexico: IS veins with multiple pulses of saline fluid

PachucaPachuca, Mexico:, Mexico: IS vein and fault patternIS vein and fault pattern45,00045,000 t Ag, 220 t Aut Ag, 220 t Au

Simmons et al. (2005)Simmons et al. (2005)after after Geyne Geyne et al. (1963)et al. (1963)

4 km

PachucaPachuca, Mexico: , Mexico: Cross and long sectionsCross and long sections

Clay cap, variable tops/bottomsClay cap, variable tops/bottoms

Drier, 1982Geyne et al., 1963

500m

100 m

clays

HS IS LSHS IS LS

Ya

RMt


Vi To

IS vein depositsIS vein deposits

CalcCalc--alkaline volcanic alkaline volcanic arcsarcs Principle IS deposits: AgPrinciple IS deposits: Ag--Au (ZnAu (Zn--Pb, Cu)Pb, Cu)

Simple sulfide mineralogy & gangue: MexicoSimple sulfide mineralogy & gangue: Mexico Intrusion related, zoned:Intrusion related, zoned: complex sulfides/sulfosalts complex sulfides/sulfosalts

Up to many km long and 800 m verticalUp to many km long and 800 m vertical Tops and bottoms not uniformTops and bottoms not uniform

Common on margin of HS deposits (barren lithocaps)Common on margin of HS deposits (barren lithocaps) May be associated w/ adv. May be associated w/ adv. argarg. Alteration. Alteration

Zoned alteration (AA to SerZoned alteration (AA to Ser--Ad): think laterally, orAd): think laterally, oroverprinted (Ad? after AA): drill deep if surface barrenoverprinted (Ad? after AA): drill deep if surface barren

from Simmons from Simmons et al.et al. (2005)(2005)

HS

10 km

Comparative Comparative sizes of vein sizes of vein districtsdistricts

LargeLarge

Co. de Pasco IS(46,000 t Ag,

Zn, Pb, Au)

Acupan IS(200 t Au) (45,000 t Ag, 220 t Au) IS

(131 t Au, 1,605 t Ag) LS (34,850 t Ag, 175 t Au) IS

1 km(2x)

Waihi Waihi (220 t Au) (220 t Au) LSLS

Hishikari Hishikari (260 t Au) (260 t Au) LSLS

and smalland small

Zoned around

diatremes

Large variations between deposit types and districtsLarge variations between deposit types and districts

Model the prospect, do not fit prospect to the model Model the prospect, do not fit prospect to the model

Exploration for epithermal AuExploration for epithermal Au--Ag vein depositsAg vein deposits

Beware generalizationsBeware generalizations

Exploration for epithermal AuExploration for epithermal Au--Ag vein depositsAg vein deposits

Large variations between deposit types and districts

Model the prospect, do not fit prospect to the model

Beware generalizations

PaleosurfacePaleosurface estimation, hydrology, erosion levelestimation, hydrology, erosion level LithologyLithology: volcanic (alteration) history, effect on permeability : volcanic (alteration) history, effect on permeability

(size of alteration halo)(size of alteration halo)

Structure: relation to Structure: relation to lithologylithology, , paragenesisparagenesis (and ore)(and ore)

Alteration mineralogy, assemblage, Alteration mineralogy, assemblage, paragenesisparagenesis, and , and zonationzonation

Vein textures and mineralogyVein textures and mineralogy

Distinguish style of deposit and hence possible morphologyDistinguish style of deposit and hence possible morphology

Exploration for epithermal Au depositsExploration for epithermal Au depositsGeneral guidelinesGeneral guidelines

LS: Extension, affiliated with rhyoliteLS: Extension, affiliated with rhyolite--basalt associations basalt associations Timing (arc migration), recognition (abundant andesite; rhyoliteTiming (arc migration), recognition (abundant andesite; rhyolite))

LS: Narrow bonanza zones (vertically, laterally)LS: Narrow bonanza zones (vertically, laterally) Restricted, zoned alteration halo; steamRestricted, zoned alteration halo; steam--heated alteration blanketheated alteration blanket

LS giants: Alkalic centers, quartz poorLS giants: Alkalic centers, quartz poor

Lack of strong surface expressionLack of strong surface expression

Sillitoe and Hedenquist (2003)Sillitoe and Hedenquist (2003)

Exploration for epithermal AgExploration for epithermal Ag--Au depositsAu depositsGeneral guidelinesGeneral guidelines

ISIS--HS: ~Neutral arcs vs. contraction (giant porphyry)HS: ~Neutral arcs vs. contraction (giant porphyry) IS veins on margins of HS deposits or lithocaps, some porphyriesIS veins on margins of HS deposits or lithocaps, some porphyries

IS: Large lateral & vertical range: not uniform top or baseIS: Large lateral & vertical range: not uniform top or base SteamSteam--heated cap and shallow clay zone is common, and barrenheated cap and shallow clay zone is common, and barren

IS: Different guidelines for intrusionIS: Different guidelines for intrusion--related related vsvs Mexican?Mexican? Zoned or overprinted alteration, relation to ore veins Zoned or overprinted alteration, relation to ore veins vsvs

large veins under clay alteration blankets (clay zoning?)large veins under clay alteration blankets (clay zoning?)

Sillitoe and Hedenquist (2003)Sillitoe and Hedenquist (2003)

Epithermal vein deposits LS deposits: Rift setting IS deposits: Intrusion-centered

High-grade underground mines small is beautiful (when out of sight) !

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EpitermalAuAg_JeffreyHedenquist