Veins He Den Quist

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    Epithermal Au-Ag vein deposits:

    Critical characteristics, variations, and exploration

    Ares, January 2005

    Jeffrey W. Hedenquist Ottawa, Canada

    Epithermal vein deposits Terminology: metal variation

    Background: features, variations and causes

    LS deposits: Back-arc

    IS deposits: Intrusion-centered (vs Mexican)

    Exploration

    Zacatecas, Mexico

    Epithermal types:Alternative terminologyLargely synonymous

    Type 3 Type 2 Type 1

    Gold (Te, Se)-qtz veins Ag, bms veins Goldfield type, Au-al, 2nd qtzite 1903-33

    Alkaline epithermal Acid epithermal 1977

    - - - - Epithermal - - - - - 1981

    Hot spring Au-enargite 1982

    Adularia-sericite, low sulfur Acid sulfate, high sulfur, al-kaol 1986-89

    Low sulfidation High sulfidation 1987

    Low sulfide/bms, High sulfide/bms, High sulfidation 1991, 93

    Type 2 ad-ser Type 1 ad-ser

    Bimodal basalt-rhyolite Western andesite High sulfidation 1999, 01

    Low sulfidation (LS) Intermediate (IS) High sulfidation (HS) 2000, 03

    LS, LSa (alkalic) IS zoned, IS Mex HS, HS-IS zoned evolving

    Ransome, Emmons, Lindgren, Nakovnik, Sillitoe, Buchanan, Ashley, Giles, Bonham,

    Bethke, Heald et al., Berger, Albino, John, Hedenquist et al., Einaudi et al.

    Examples of epithermal deposits

    LS veins:Midas, Sleeper, Mule Canyon, Lewis-Crofoot; El Limn;

    Beroen; Ares?; El Pen; Cerro Vanguardia, Esquel; Hishikari; Balei

    LS veins, alkalic: Cripple Creek, Emperor, Porgera, Ladolam

    IS veins:Comstock, Creede; Tethys, e.g., Rosia Montana,

    Sacarimb; Victoria, Baguio, Philippines (adj. lithocaps); Toyoha, Sado,

    Kushikino, Japan; Kelian; Arcata, Orcopampa, Cordilleran, e.g.,

    Julcani, Colqui & Quiruvilca (w/ HS), all of Per, ; vs. Mexican

    Ag:Au:bms, e.g., Tayoltita, El Oro, Guanajuato, Pachuca, Fresnillo,

    Zacatecas

    HS replacements:

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    Metal Budgets: Function of salinity and volcanotectonics

    LS Au-Ag:

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    Temperature-dependentalterationmineralogy

    LS deposits: sulfide assemblages

    LS veins: AuAg, bonanzas

    Pyhigh-Fe sph asp or po,

    Se or Te

    Distinctly related tovolcanotectonic setting

    Barton et al., 1977, John, 2001,Einaudi et al., 2003, others

    IS and HS deposits: sulfide assemblages

    IS veins: AgAu PbZn

    Pylow-Fe sphtn/tdccpgn, Te (Bi, Sn, In)

    HS replacements: Cu-Au-Ag

    Initial leaching, vuggy qtz-py

    Early pyenargitelz-fm

    Late Aulow-Fe sph

    tn/tdccpgn, Te-Bi-Sn

    Einaudi, Hedenquist and Inan, 2003

    Sulfidation states

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    Einaudi, Hedenquist and Inan, 2003

    Sulfidation stateevolution

    Wallrock

    buffe

    r

    HS IS LSHS IS LS

    Ya

    RMt

    Hedenquist et al., 2000

    Vi To

    Sillitoe and Hedenquist, 2003Low sulfidation vein setting

    Champagne Pool,Waiotapu, NZ

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    Lewis-Crofoot, NV:LS veins, steam-heated overprint (falling water table)(NB: remnant qtz veins + Au within overprinted zone)

    Sulphur, NV, near paleosurface

    Low-sulfidation schematic model

    Hedenquist et al. (2000),modified from Buchanan

    (1981), Sillitoe (1993)

    McLaughlin, CA:LS sheeted veins beneathsinter with Hg

    McLaughlin, CA:Atypical LS host

    Sherlock et al. (1995)

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    Hydro-thermal

    brecciawith

    sinter

    Sheeted

    vein

    Sherlock et al. (1995)

    Mineral deposition in

    conduits, pressureincreases above

    hydrostatic, hydraulic

    fracturing, and

    hydrothermal eruption:

    mineral (+Au) deposition

    Sherlock et al. (1995)

    LS epithermal veins:

    Extreme disequilibrium

    Rapid ascent

    Rapid boiling

    Rapid cooling

    Rapid supersaturation, silica, Au

    Exploration implications Extensional setting, fault offsets

    cf. Saunders 1994;

    Saunders et al., 1996;

    Sillitoe and Hedenquist,

    2003

    Sleeper banded ore: Au dendrites Hishikari, S Kyushu

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    Hishikari, S Kyushu

    >8 Moz AuHishikari,

    S Kyushu:Geological and

    geophysicaldiscovery,

    LS veins in

    greywacke

    basement

    Izawa et al., 1990

    500 m

    Hishikari, S Kyushu

    Paleoisotherm reconstruction

    Izawa et al. (1990)

    Hishikari long section

    Izawa et al. (1990)

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    Zuisen vein, -10 mL

    late truscottite

    Patagonia, ArgentinaMidas, NV:Ken Snyder LS mine

    from Goldstrand and Schmidt, 2000

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    Ken Snyder mine: Long section

    300 m

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    Hedenquist et al., 1998

    Surface projections:

    Lepanto,

    Far Southeast

    and Victoria

    From Palidan slide

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

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    Arribas et al. (1995); Sajona et al. (2001); Claveria (2001); Hedenquist et al. (2001)

    Surface projection of Lepanto

    HS, Far Southeast porphyry,and Victoria-Teresa IS vein

    ores, and ages

    Hedenquist et al. (2001)

    Teresa

    veins

    Bulalacao ?porphyry

    X Biot

    1.18 Ma

    X Horn1.45 Ma

    Hydro Biot

    1.40-1.45 Ma

    Alunite1.40-1.45 Ma

    X Illite

    1.15 Ma

    Ser ~1.35 Ma

    Bt 2.2-1.8 Ma

    HS IS LSHS IS LS

    Ya

    RMt

    Hedenquist et al., 2000

    Vi To

    Kyushu epithermal deposits: LS and IS veins

    Metallogenicprovinces inKyushu

    Type, age andgeology ofepithermal Audeposits

    Tectonicinterpretation

    Y. Watanabe (2004)

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    Au provinces in KyushuY. Watanabe (2004)

    Volcanic setting of Kushikino IS deposit, Kyushu

    (Izawa and Zeng, 2001) 55 t Au production

    Kamuridake, capped by silicic zones

    Kushikino veins (insets), 2 - 4 km west Temperature-

    dependent

    epithermal

    alteration

    mineralogy

    compiled byHedenquist et al. (1996)

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    Arcata, Per: IS Ag-Au vein:~100 Moz Au, 1 Moz Au (local Zn)

    adv. argillic vein halo at surface

    Arcata, Per:IS Ag vein: qtz-rhodochrosite

    after Candiotti et al. (1990)

    Comstock Lode, NV

    6000 t Ag, 257 t AuCon Virginia: 1.13 Mt @

    87.4 g/t Au, 1834 g/t Ag

    Hudson (2003)

    Propylite: Richthofen, BeckerAd: 12.7-14.1 Ma, Al: 15-16.3 Ma

    SH

    Al to

    pyrop

    diasp

    to

    kaol

    dick

    to

    illite

    2 km

    2M mica

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    ComstockLode:Ag-Au ISbonanzaveins; longsection plusreconstructionpre-faulting(?), with Slateral flow

    Vikre (1989), flincs,

    Hudson (1993, 2003)

    500

    m

    1 km

    Bartos (1987)

    1 km

    inner stib

    outer tn-td

    outer en

    Quiruvilca, Peru:

    Zoned IS bms vein systemProd. 1987, 8 Mt: Reserves 5.8%Zn, 2.0% Pb, 2.8% Cu, 230 g/t Ag

    Alto Chicama

    ~5 km east

    Calipuy Fm

    Sillitoe and Hedenquist (2003),

    modified from Einaudi et al. (2003)IS vein deposits

    Principle IS deposits: Ag-Au (Zn-Pb, Cu)

    Simple sulfide mineralogy & gangue: Mexico

    Complex sulfides/sulfosalts, zoned: intrusion related

    Up to many km long and 800 m vertical

    Tops and bottoms not uniform

    Common on margin of HS deposits (barren lithocaps?):

    associated w/ adv. arg. alteration

    Typically small (Rodalquilar, Rio del Medio at El Indio), but

    exceptions (Victoria-Teresa)

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    Zacatecas, Mexico: IS veins with multiple pulses of saline fluidMexican Ag-Au bms veins:

    Depth below paleosurface and

    Au:Ag:bms relationship

    Albinson et al. (2001)

    Pachuca, Mexico: IS vein and fault pattern

    45,000 t Ag, 220 t Au

    Simmons et al. (2005)

    after Geyne et al. (1963)

    4 km

    Pachuca fractures, dikes, ore, surface alteration

    Wisser (1948)

    2360 m datum

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    Pachuca:

    Cross and long sections

    Drier, 1982

    Geyne et al., 1963

    500

    m

    from Simmons et al.

    (2005), with permission

    HS IS

    LS IS

    10 km

    Creede IS

    from Simmons et al.(2005), with permission

    2 km

    LSa LSLSa

    HSLSaIS

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    from Simmons et al.

    (2005), with permission

    1 km

    HS w/ IS to N

    LS

    IS w/ lithocap

    IS w/ adv arg

    HS

    LS

    LSa, VIILS

    Sillitoe and Hedenquist (2003)

    Schematic relations: HS and IS epithermal deposits,

    and porphyry systems

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