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2003 Hedenquist Exploration Notes Geo.PPT

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Research applied to mineral exploration Epithermal High-sulphidation Gold Deposits: Epithermal High-sulphidation Gold Deposits: Characteristics, related ore types, and exploration Characteristics, related ore types, and exploration  Jeffrey W. Hedenquist Jeffrey W. Hedenquist  Colorado School of Mines Colorado School of Mines  & &  Consulting Economic Geologist, Ottawa Consulting Economic Geologist, Ottawa  Hedenquist@aol.com Hedenquist@aol.com BCYCM Roundup 2003
Research applied to mineral exploration Epithermal High-sulphidation Gold Deposits: Epithermal High-sulphidation Gold Deposits: Characteristics, related ore types, and exploration Characteristics, related ore types, and exploration  Acknowledgements: Acknowledgements:  Antonio Arribas R. , Placer Dome Antonio Arribas R. , Placer Dome  Marco T. Einaudi & E. Esra Inan , Stanford Univ. Marco T. Einaudi & E. Esra Inan , Stanford Univ.  Richard H. Sillitoe , London & David John , USGS Richard H. Sillitoe , London & David John , USGS BCYCM Roundup 2003
Research applied to mineral exploration White Island, NZ: 300 t Au flux to atmosphere over life of ~10,000 yrs  Terminology Terminology  Importance and size Importance and size  Principal characteristics Principal characteristics  Origin of features, background Origin of features, background  Case examples Case examples Exploration implications Exploration implications HS epithermal deposits: Outline
Research applied to mineral exploration Epithermal types: Epithermal types: Alternative terminology Alternative terminology Largely synonymous Largely synonymous Type 1 Type 2 Type 3 • Goldfield type, Au-al, 2nd qtzite Goldfield type, Au-al, 2nd qtzite Ag-bms veins Ag-bms veins Gold (Te, Se)-qtz veins Gold (Te, Se)-qtz veins 1906-33 1906-33 • Acid epithermal Acid epithermal Alkaline epithermal Alkaline epithermal 1977 1977 • - - - - Epithermal - - - - - - - - - Epithermal - - - - - 1981 1981 • Au-enargite Au-enargite Hot spring Hot spring 1982 1982 • Acid sulfate, high sulfur, al-kaol Acid sulfate, high sulfur, al-kaol Adularia-sericite, low sulfur Adularia-sericite, low sulfur 1986-89 1986-89 • High sulfidation High sulfidation Low sulfidation Low sulfidation 1987 1987 • High sulfidation High sulfidation High sulfide/bms, High sulfide/bms, Low sulfide/bms, Low sulfide/bms, 1989-94 1989-94 Type 1 ad-ser, Type 1 ad-ser, Type 2 ad-ser Type 2 ad-ser Carbonate-bms-Au Carbonate-bms-Au • High sulfidation High sulfidation Western andesite Western andesite Bimodal basalt-rhyolite Bimodal basalt-rhyolite 1999, 01 1999, 01 • High sulfidation High sulfidation (HS) (HS) Intermediate Intermediate (IS) (IS) Low sulfidation Low sulfidation (LS) (LS) 2000, 03 2000, 03 – Lithocap (barren) Lithocap (barren) Ransome, Emmons, Lindgren, Nakovnik, Sillitoe, Buchanan, Ashley, Giles et al., Bonham, Ransome, Emmons, Lindgren, Nakovnik, Sillitoe, Buchanan, Ashley, Giles et al., Bonham, Bethke, Heald et al., Berger, Albino et al., Leach et al., John, Hedenquist et al., Einaudi et al. Bethke, Heald et al., Berger, Albino et al., Leach et al., John, Hedenquist et al., Einaudi et al.
Research applied to mineral exploration Ore-deposit styles: Relative amounts of gold Ore-deposit styles: Relative amounts of gold (>5 Moz deposits, 1997) (>5 Moz deposits, 1997)  50% 50% Witwatersrand Witwatersrand  12% 12% Epithermal Epithermal  10% 10% Porphyry (+ intrusion hosted) Porphyry (+ intrusion hosted)  12% 12% Sediment hosted (incl. 4% “Carlin”) Sediment hosted (incl. 4% “Carlin”)  9% 9% Greenstone lode (“orogenic”) Greenstone lode (“orogenic”)  7% 7% Other (Fe Fm, VHMS, etc.) Other (Fe Fm, VHMS, etc.)  >40% (non Wits) gold from intrusion-centered >40% (non Wits) gold from intrusion-centered deposits, ~1/4 from epithermal (>5 Moz Au) deposits, ~1/4 from epithermal (>5 Moz Au)  Arribas, UBC, March 2000 Arribas, UBC, March 2000
Research applied to mineral exploration Ore-deposit styles: Giant gold deposits Ore-deposit styles: Giant gold deposits (28 >20 Moz deposits) (28 >20 Moz deposits)  1 (7) 1 (7) Witwatersrand Witwatersrand  7 7 Porphyry (+ intrusion hosted) Porphyry (+ intrusion hosted)  5 5 Epithermal (3 HS; 2 LS) Epithermal (3 HS; 2 LS)  6 6 Sediment hosted (incl. 2 “Carlin”) Sediment hosted (incl. 2 “Carlin”)  5 5 Greenstone lode (“orogenic”) Greenstone lode (“orogenic”)  4 4 Other (Fe ox, Fe Fm, Archean diss.) Other (Fe ox, Fe Fm, Archean diss.)  ~40% giant deposits are intrusion centered ~40% giant deposits are intrusion centered  Sillitoe, GSN 2000 Sillitoe, GSN 2000
Research applied to mineral exploration Types of epithermal deposits Types of epithermal deposits 3 endmember types 3 endmember types  HS bodies: HS bodies: Cu-Au-As, sulfide rich, andesite arcs Cu-Au-As, sulfide rich, andesite arcs – Barren lithocaps: Barren lithocaps: advanced argillic zones over porphyry systems advanced argillic zones over porphyry systems  IS veins: IS veins: Ag-Au ± Zn-Pb, sulfide rich, andesite arcs Ag-Au ± Zn-Pb, sulfide rich, andesite arcs – Wide variation in metal complement, but continuum Wide variation in metal complement, but continuum  LS veins: LS veins: Au-Ag bonanzas, sulfide poor, bimodal setting Au-Ag bonanzas, sulfide poor, bimodal setting – LS veins: LS veins: Au-Ag-Te, sulfide poor, alkalic association Au-Ag-Te, sulfide poor, alkalic association  HS and IS appear related HS and IS appear related
Epithermal deposits: Production + reserves (~2000) Epithermal deposits: Production + reserves (~2000)
Research applied to mineral exploration Examples of epithermal deposits Examples of epithermal deposits  HS replacements: HS replacements: Goldfield, Summitville, Sauzal, Mulatos, Goldfield, Summitville, Sauzal, Mulatos, Pueblo Viejo, Yanacocha, Pierina, Alto Chicama, El Indio, La Coipa, Pueblo Viejo, Yanacocha, Pierina, Alto Chicama, El Indio, La Coipa, Pascua-Veradero, Lepanto, Chelopech, Bor Pascua-Veradero, Lepanto, Chelopech, Bor – Barren lithocaps: Barren lithocaps: common, W. US, Andes, Asia, etc. common, W. US, Andes, Asia, etc.  IS veins: IS veins: Comstock, Creede, Mexican Ag, Perú bms, ABCD of Comstock, Creede, Mexican Ag, Perú bms, ABCD of eastern Tethys, Philippines (Victoria & Baguio) eastern Tethys, Philippines (Victoria & Baguio)  LS veins: LS veins: Midas, Sleeper, El Peñón, Esquel, Hishikari Midas, Sleeper, El Peñón, Esquel, Hishikari – LS veins, alkalic: LS veins, alkalic: Cripple Creek, Emperor, Porgera, Ladolam Cripple Creek, Emperor, Porgera, Ladolam
Research applied to mineral exploration Location of principal epithermal deposits Location of principal epithermal deposits
Research applied to mineral exploration Geologic setting of HS (and IS) deposits Geologic setting of HS (and IS) deposits Circum Pacific, 43 deposits Circum Pacific, 43 deposits  Neutral - mild extension, calc-alkaline andesite-dacite arcs Neutral - mild extension, calc-alkaline andesite-dacite arcs  22 22 Volcanic domes Volcanic domes (single, complex, summit; not host) (single, complex, summit; not host)  12 12 Central vent volcanoes Central vent volcanoes (including IS) (including IS)  3 3 Calderas Calderas  3 3 Diatremes Diatremes  10 10 Insufficient information Insufficient information  Hosts: A/D flows, bxs, ignimbrites, intrusions, seds Hosts: A/D flows, bxs, ignimbrites, intrusions, seds  LS deposits: Bimodal (rhyolite domes--basalt dikes) in extensional settings: LS deposits: Bimodal (rhyolite domes--basalt dikes) in extensional settings:  Intra, near, and backarc; postcollision rifts (non porphyry) Intra, near, and backarc; postcollision rifts (non porphyry)  Arribas, 1995; White et al., 1995, Sillitoe, 1999 Arribas, 1995; White et al., 1995, Sillitoe, 1999
Research applied to mineral exploration Sillitoe and Hedenquist, 2003 Schematic relations: HS and IS epithermal deposits and porphyry systems
Research applied to mineral exploration Epithermal alteration, gangue minerals Epithermal alteration, gangue minerals  HS replacements: HS replacements: silicic host, alunite, barite, anhydrite silicic host, alunite, barite, anhydrite – Barren lithocaps: Barren lithocaps: silicic core, quartz-alunite halo silicic core, quartz-alunite halo  IS veins: IS veins: quartz, sericite, rhodochrosite, barite, anhydrite quartz, sericite, rhodochrosite, barite, anhydrite  LS veins: LS veins: chalcedony, adularia with illite, calcite (roscoelite) chalcedony, adularia with illite, calcite (roscoelite)
Research applied to mineral exploration HS and IS deposits: sulfide assemblages HS and IS deposits: sulfide assemblages  HS replacements: HS replacements: Cu-Au-Ag Cu-Au-Ag – Initial leaching, vuggy qtz-py Initial leaching, vuggy qtz-py – Early py–enargite–lz-fm Early py–enargite–lz-fm – Late Au– Late Au–py–low-Fe sph– tn/td– py–low-Fe sph– tn/td– ccp–gn, ± Te-Bi-Sn ccp–gn, ± Te-Bi-Sn  IS veins: IS veins: Ag–Au ± Pb–Zn Ag–Au ± Pb–Zn – Py–low-Fe sph–tn/td–ccp–gn, Py–low-Fe sph–tn/td–ccp–gn, ± ± Te Te  HS-IS vs LS distinction related to HS-IS vs LS distinction related to volcanotectonic setting volcanotectonic setting  Barton et al., 1977, John, 2001, Barton et al., 1977, John, 2001, Einaudi Einaudi et al., 2003, others et al., 2003, others
Research applied to mineral exploration Einaudi, Hedenquist and Inan, 2003 Sulfidation states Sulfidation states
Research applied to mineral exploration Einaudi, Hedenquist and Inan, 2003
Research applied to mineral exploration LS deposits HS deposits Hedenquist et al., 1996
Research applied to mineral exploration Steam-heated acid sulfate waters Steam-heated acid sulfate waters
Research applied to mineral exploration Sillitoe, 1993 LS settings only Lithocap (± HS) settings only (steam-heated blanket possible) Any sulfide-rich setting Steam-heated waters, LS, IS, HS possible (HCl, SO2) 3 types only !
Research applied to mineral exploration Lewis-Crofoot, NV: Lewis-Crofoot, NV: LS veins, steam-heated overprint (falling water table) LS veins, steam-heated overprint (falling water table) Similar blankets common in lithocap and HS, IS deposits Similar blankets common in lithocap and HS, IS deposits
Research applied to mineral exploration McLaughlin, CA LS sheeted veins beneath sinter Sinters never in HS setting
Research applied to mineral exploration El Chichon, 1979: El Chichon, 1979: magmatic vapors degassing magmatic vapors degassing
Research applied to mineral exploration Kawah Ijen, Java: Kawah Ijen, Java: magmatic vapors condensed into ground water magmatic vapors condensed into ground water
Research applied to mineral exploration Satsuma Iwojima, S. Kyushu: passive degassing of dome (~1000 yrs)
Research applied to mineral exploration
Research applied to mineral exploration Werner Giggenbach, Werner Giggenbach, geochemist, 1937-1997 geochemist, 1937-1997 Condensation of magmatic Condensation of magmatic vapor with HCl and SO vapor with HCl and SO2 2 generates acidic (pH ~1) generates acidic (pH ~1) waters, causes leaching of rocks waters, causes leaching of rocks to leave residual silica: re-xstal to leave residual silica: re-xstal to vuggy quartz or silicic rock to vuggy quartz or silicic rock View: “rhyolite”, 99.9% SiO View: “rhyolite”, 99.9% SiO2 2
Research applied to mineral exploration Flux of rock-forming components to sea: Flux of rock-forming components to sea: 0.4 Mt/yr 0.4 Mt/yr of rhyolite cations leached, of rhyolite cations leached, i.e., 400 Mt of vuggy quartz over life of degassing dome i.e., 400 Mt of vuggy quartz over life of degassing dome
Research applied to mineral exploration after Gray and Coolbaugh, 1994, by Arribas, 1995 after Gray and Coolbaugh, 1994, by Arribas, 1995
Research applied to mineral exploration Steven & Ratté, 1960 Summitville, CO Vuggy qtz zone flares upward pH ~ >6 4 - 6 2 - 4 <2
Research applied to mineral exploration Summitville, CO: vuggy qtz with alunite halo
Research applied to mineral exploration Research applied to mineral exploration Arribas, 1995 Advanced argillic lithocap, host to HS ore deposits Summitville, CO: Summitville, CO: Alteration zoning Alteration zoning and ore bodies and ore bodies after Gray and Coolbaugh, after Gray and Coolbaugh, 1994 1994 Magmatic vapor Magmatic vapor condensation; Arribas, 1995 condensation; Arribas, 1995
Research applied to mineral exploration Advanced argillic slides: 11 Advanced argillic slides: 11 (if scanned can be reduced to 5) (if scanned can be reduced to 5) Vuggy quartz, Summitville Quartz-alunite, Summitville Hypogene alunite, El Tambo Residual quartz, Pierina Arribas et al., 2000
Research applied to mineral exploration Supergene alunite, Rodalquilar Steam-heated advanced argillic blanket, La Coipa Supergene alunite, Riaza Supergene alunite, Rodalquilar Massive supergene alunite, Rodalquilar Arribas et al., 2000
Research applied to mineral exploration La Coipa: Steam-heated cristobalite- alunite blanket over vuggy quartz zone
Research applied to mineral exploration Chalcedony blanket at paleowater table
Research applied to mineral exploration Urashima et al., 1981
Research applied to mineral exploration MMAJ, 1986
Research applied to mineral exploration Rodalquilar, Spain: looking ~east Research applied to mineral exploration Arribas, 1995
Research applied to mineral exploration Rodalquilar, Spain Arribas et al., 1995 Drilling beneath supergene alunite blanket
Research applied to mineral exploration
Research applied to mineral exploration
Research applied to mineral exploration
Research applied to mineral exploration Arribas et al., 2000
Research applied to mineral exploration
Research applied to mineral exploration
Research applied to mineral exploration
Research applied to mineral exploration
Research applied to mineral exploration
Research applied to mineral exploration Pierina, Perú: long section, alteration + ore Volkert et al., 1998 Volkert et al., 1998
Research applied to mineral exploration El Indio: Chile
Research applied to mineral exploration Siddeley and Areneda, 1986 El Indio: HS with late high-grade IS vein Jannas et al., 1990
Research applied to mineral exploration Jannas et al., 1990
Research applied to mineral exploration El Indio 3500 vein: quartz-pyrite-Au (tn- ccp) with sericite halo, post enargite DSO: 200 g/t Au av., cutoff 100 g/t (1.5 Moz of 8 Moz total)
Research applied to mineral exploration Hedenquist et al., 1998
Research applied to mineral exploration Surface projections: Lepanto, Far Southeast and Victoria From Palidan slide
Research applied to mineral exploration Hedenquist et al., 1998
Research applied to mineral exploration Hedenquist et al., 1998
Research applied to mineral exploration Hedenquist et al., 2001
Research applied to mineral exploration Hedenquist et al., 2001
Research applied to mineral exploration Arribas et al., 1995; Sajona et al., 2001, Hedenquist et al., 2001
Research applied to mineral exploration  Lithocap collapse Lithocap collapse  HS ore, if present, HS ore, if present, overprints porphyry overprints porphyry  Varying depths and Varying depths and intervals between intervals between base of lithocap and base of lithocap and top of porphyry top of porphyry
HS ore HS ore deposits deposits
Research applied to mineral exploration HS deposits: HS deposits: Observations relevant to exploration Observations relevant to exploration  Shallow, lithologic host; deep, structural control Shallow, lithologic host; deep, structural control  Vuggy quartz main host: steep (can be barren!) Vuggy quartz main host: steep (can be barren!)  Ore (sulfides + Au) introduced after leaching (or not) Ore (sulfides + Au) introduced after leaching (or not) – Low-grade bodies: evidence for oxidation Low-grade bodies: evidence for oxidation  Identify center(s) from alteration: size can be critical Identify center(s) from alteration: size can be critical  Local high-grade zones (late): cf. El Indio Local high-grade zones (late): cf. El Indio  Marginal IS veins, locally significant Marginal IS veins, locally significant  Pyrophyllite and sericite roots: porphyry tops Pyrophyllite and sericite roots: porphyry tops
Research applied to mineral exploration Masupa Ria, Kalimantan: IS veins cut barren lithocap
Research applied to mineral exploration Arcata, Perú, IS Ag vein Arcata, Perú, IS Ag vein (100 Moz Ag, 1 Moz Au): argillic halo at surface (100 Moz Ag, 1 Moz Au): argillic halo at surface
Research applied to mineral exploration Arcata, Perú: Arcata, Perú: IS Ag vein: qtz- IS Ag vein: qtz- rhodochrosite rhodochrosite Zacatecas, Mexico
Research applied to mineral exploration
Research applied to mineral exploration IS veins IS veins  Common on margin of HS deposits Common on margin of HS deposits – Typically small, but exceptions (Victoria) Typically small, but exceptions (Victoria)  Principle IS deposits: Ag-Au (Zn-Pb, Cu) Principle IS deposits: Ag-Au (Zn-Pb, Cu) – Simple sulfide mineralogy, gangue Simple sulfide mineralogy, gangue  Large veins: up to several km long Large veins: up to several km long  Up to 800 m vertical Up to 800 m vertical – Tops and bottoms not uniform Tops and bottoms not uniform
Research applied to mineral exploration
Research applied to mineral exploration Marte, Maricunga district, Chile
Research applied to mineral exploration Exploration for HS epithermal gold deposits Exploration for HS epithermal gold deposits General guidelines General guidelines  HS-IS epithermal: Neutral (~extensional) setting vs. HS-IS epithermal: Neutral (~extensional) setting vs. contraction (large porphyry) contraction (large porphyry)  HS: Define silicic (± vuggy) core, alteration halo HS: Define silicic (± vuggy) core, alteration halo  HS: Beware barren lithocaps vs. oxidized sulfide HS: Beware barren lithocaps vs. oxidized sulfide  Lithocaps: overlie porphyry Cu-Au systems Lithocaps: overlie porphyry Cu-Au systems  IS veins: Potential importance near HS prospects IS veins: Potential importance near HS prospects – Large lateral and vertical ranges, not uniform top or base Large lateral and vertical ranges, not uniform top or base Sillitoe and Hedenquist, 2003 Sillitoe and Hedenquist, 2003
Research applied to mineral exploration Exploration for HS epithermal gold deposits Exploration for HS epithermal gold deposits Conclusions Conclusions  Prospective to target for world-class ore bodies Prospective to target for world-class ore bodies – Low-grade oxide ore (local bonanza veins) Low-grade oxide ore (local bonanza veins)  Potential for related deposits in a district Potential for related deposits in a district – Cu-Au porphyries, polymetallic Ag-Au-Zn-Pb veins Cu-Au porphyries, polymetallic Ag-Au-Zn-Pb veins  Basic questions: regional to district implications Basic questions: regional to district implications – Arc vs. rift, ligand source (porphyry, alkalic, mafic), Cu vs Arc vs. rift, ligand source (porphyry, alkalic, mafic), Cu vs Pb-Zn (zoning), barren lithocaps, etc. Pb-Zn (zoning), barren lithocaps, etc.
Research applied to mineral exploration
Research applied to mineral exploration Temperature- dependent alteration mineralogy Useful for paleo- isotherm zoning in epithermal deposits Hedenquist et al., 1996

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2003 Hedenquist Exploration Notes Geo.PPT

  • 1. Research applied to mineral exploration Epithermal High-sulphidation Gold Deposits: Epithermal High-sulphidation Gold Deposits: Characteristics, related ore types, and exploration Characteristics, related ore types, and exploration  Jeffrey W. Hedenquist Jeffrey W. Hedenquist  Colorado School of Mines Colorado School of Mines  & &  Consulting Economic Geologist, Ottawa Consulting Economic Geologist, Ottawa  Hedenquist@aol.com Hedenquist@aol.com BCYCM Roundup 2003
  • 2. Research applied to mineral exploration Epithermal High-sulphidation Gold Deposits: Epithermal High-sulphidation Gold Deposits: Characteristics, related ore types, and exploration Characteristics, related ore types, and exploration  Acknowledgements: Acknowledgements:  Antonio Arribas R. , Placer Dome Antonio Arribas R. , Placer Dome  Marco T. Einaudi & E. Esra Inan , Stanford Univ. Marco T. Einaudi & E. Esra Inan , Stanford Univ.  Richard H. Sillitoe , London & David John , USGS Richard H. Sillitoe , London & David John , USGS BCYCM Roundup 2003
  • 3. Research applied to mineral exploration White Island, NZ: 300 t Au flux to atmosphere over life of ~10,000 yrs  Terminology Terminology  Importance and size Importance and size  Principal characteristics Principal characteristics  Origin of features, background Origin of features, background  Case examples Case examples Exploration implications Exploration implications HS epithermal deposits: Outline
  • 4. Research applied to mineral exploration Epithermal types: Epithermal types: Alternative terminology Alternative terminology Largely synonymous Largely synonymous Type 1 Type 2 Type 3 • Goldfield type, Au-al, 2nd qtzite Goldfield type, Au-al, 2nd qtzite Ag-bms veins Ag-bms veins Gold (Te, Se)-qtz veins Gold (Te, Se)-qtz veins 1906-33 1906-33 • Acid epithermal Acid epithermal Alkaline epithermal Alkaline epithermal 1977 1977 • - - - - Epithermal - - - - - - - - - Epithermal - - - - - 1981 1981 • Au-enargite Au-enargite Hot spring Hot spring 1982 1982 • Acid sulfate, high sulfur, al-kaol Acid sulfate, high sulfur, al-kaol Adularia-sericite, low sulfur Adularia-sericite, low sulfur 1986-89 1986-89 • High sulfidation High sulfidation Low sulfidation Low sulfidation 1987 1987 • High sulfidation High sulfidation High sulfide/bms, High sulfide/bms, Low sulfide/bms, Low sulfide/bms, 1989-94 1989-94 Type 1 ad-ser, Type 1 ad-ser, Type 2 ad-ser Type 2 ad-ser Carbonate-bms-Au Carbonate-bms-Au • High sulfidation High sulfidation Western andesite Western andesite Bimodal basalt-rhyolite Bimodal basalt-rhyolite 1999, 01 1999, 01 • High sulfidation High sulfidation (HS) (HS) Intermediate Intermediate (IS) (IS) Low sulfidation Low sulfidation (LS) (LS) 2000, 03 2000, 03 – Lithocap (barren) Lithocap (barren) Ransome, Emmons, Lindgren, Nakovnik, Sillitoe, Buchanan, Ashley, Giles et al., Bonham, Ransome, Emmons, Lindgren, Nakovnik, Sillitoe, Buchanan, Ashley, Giles et al., Bonham, Bethke, Heald et al., Berger, Albino et al., Leach et al., John, Hedenquist et al., Einaudi et al. Bethke, Heald et al., Berger, Albino et al., Leach et al., John, Hedenquist et al., Einaudi et al.
  • 5. Research applied to mineral exploration Ore-deposit styles: Relative amounts of gold Ore-deposit styles: Relative amounts of gold (>5 Moz deposits, 1997) (>5 Moz deposits, 1997)  50% 50% Witwatersrand Witwatersrand  12% 12% Epithermal Epithermal  10% 10% Porphyry (+ intrusion hosted) Porphyry (+ intrusion hosted)  12% 12% Sediment hosted (incl. 4% “Carlin”) Sediment hosted (incl. 4% “Carlin”)  9% 9% Greenstone lode (“orogenic”) Greenstone lode (“orogenic”)  7% 7% Other (Fe Fm, VHMS, etc.) Other (Fe Fm, VHMS, etc.)  >40% (non Wits) gold from intrusion-centered >40% (non Wits) gold from intrusion-centered deposits, ~1/4 from epithermal (>5 Moz Au) deposits, ~1/4 from epithermal (>5 Moz Au)  Arribas, UBC, March 2000 Arribas, UBC, March 2000
  • 6. Research applied to mineral exploration Ore-deposit styles: Giant gold deposits Ore-deposit styles: Giant gold deposits (28 >20 Moz deposits) (28 >20 Moz deposits)  1 (7) 1 (7) Witwatersrand Witwatersrand  7 7 Porphyry (+ intrusion hosted) Porphyry (+ intrusion hosted)  5 5 Epithermal (3 HS; 2 LS) Epithermal (3 HS; 2 LS)  6 6 Sediment hosted (incl. 2 “Carlin”) Sediment hosted (incl. 2 “Carlin”)  5 5 Greenstone lode (“orogenic”) Greenstone lode (“orogenic”)  4 4 Other (Fe ox, Fe Fm, Archean diss.) Other (Fe ox, Fe Fm, Archean diss.)  ~40% giant deposits are intrusion centered ~40% giant deposits are intrusion centered  Sillitoe, GSN 2000 Sillitoe, GSN 2000
  • 7. Research applied to mineral exploration Types of epithermal deposits Types of epithermal deposits 3 endmember types 3 endmember types  HS bodies: HS bodies: Cu-Au-As, sulfide rich, andesite arcs Cu-Au-As, sulfide rich, andesite arcs – Barren lithocaps: Barren lithocaps: advanced argillic zones over porphyry systems advanced argillic zones over porphyry systems  IS veins: IS veins: Ag-Au ± Zn-Pb, sulfide rich, andesite arcs Ag-Au ± Zn-Pb, sulfide rich, andesite arcs – Wide variation in metal complement, but continuum Wide variation in metal complement, but continuum  LS veins: LS veins: Au-Ag bonanzas, sulfide poor, bimodal setting Au-Ag bonanzas, sulfide poor, bimodal setting – LS veins: LS veins: Au-Ag-Te, sulfide poor, alkalic association Au-Ag-Te, sulfide poor, alkalic association  HS and IS appear related HS and IS appear related
  • 8. Epithermal deposits: Production + reserves (~2000) Epithermal deposits: Production + reserves (~2000)
  • 9. Research applied to mineral exploration Examples of epithermal deposits Examples of epithermal deposits  HS replacements: HS replacements: Goldfield, Summitville, Sauzal, Mulatos, Goldfield, Summitville, Sauzal, Mulatos, Pueblo Viejo, Yanacocha, Pierina, Alto Chicama, El Indio, La Coipa, Pueblo Viejo, Yanacocha, Pierina, Alto Chicama, El Indio, La Coipa, Pascua-Veradero, Lepanto, Chelopech, Bor Pascua-Veradero, Lepanto, Chelopech, Bor – Barren lithocaps: Barren lithocaps: common, W. US, Andes, Asia, etc. common, W. US, Andes, Asia, etc.  IS veins: IS veins: Comstock, Creede, Mexican Ag, Perú bms, ABCD of Comstock, Creede, Mexican Ag, Perú bms, ABCD of eastern Tethys, Philippines (Victoria & Baguio) eastern Tethys, Philippines (Victoria & Baguio)  LS veins: LS veins: Midas, Sleeper, El Peñón, Esquel, Hishikari Midas, Sleeper, El Peñón, Esquel, Hishikari – LS veins, alkalic: LS veins, alkalic: Cripple Creek, Emperor, Porgera, Ladolam Cripple Creek, Emperor, Porgera, Ladolam
  • 10. Research applied to mineral exploration Location of principal epithermal deposits Location of principal epithermal deposits
  • 11. Research applied to mineral exploration Geologic setting of HS (and IS) deposits Geologic setting of HS (and IS) deposits Circum Pacific, 43 deposits Circum Pacific, 43 deposits  Neutral - mild extension, calc-alkaline andesite-dacite arcs Neutral - mild extension, calc-alkaline andesite-dacite arcs  22 22 Volcanic domes Volcanic domes (single, complex, summit; not host) (single, complex, summit; not host)  12 12 Central vent volcanoes Central vent volcanoes (including IS) (including IS)  3 3 Calderas Calderas  3 3 Diatremes Diatremes  10 10 Insufficient information Insufficient information  Hosts: A/D flows, bxs, ignimbrites, intrusions, seds Hosts: A/D flows, bxs, ignimbrites, intrusions, seds  LS deposits: Bimodal (rhyolite domes--basalt dikes) in extensional settings: LS deposits: Bimodal (rhyolite domes--basalt dikes) in extensional settings:  Intra, near, and backarc; postcollision rifts (non porphyry) Intra, near, and backarc; postcollision rifts (non porphyry)  Arribas, 1995; White et al., 1995, Sillitoe, 1999 Arribas, 1995; White et al., 1995, Sillitoe, 1999
  • 12. Research applied to mineral exploration Sillitoe and Hedenquist, 2003 Schematic relations: HS and IS epithermal deposits and porphyry systems
  • 13. Research applied to mineral exploration Epithermal alteration, gangue minerals Epithermal alteration, gangue minerals  HS replacements: HS replacements: silicic host, alunite, barite, anhydrite silicic host, alunite, barite, anhydrite – Barren lithocaps: Barren lithocaps: silicic core, quartz-alunite halo silicic core, quartz-alunite halo  IS veins: IS veins: quartz, sericite, rhodochrosite, barite, anhydrite quartz, sericite, rhodochrosite, barite, anhydrite  LS veins: LS veins: chalcedony, adularia with illite, calcite (roscoelite) chalcedony, adularia with illite, calcite (roscoelite)
  • 14. Research applied to mineral exploration HS and IS deposits: sulfide assemblages HS and IS deposits: sulfide assemblages  HS replacements: HS replacements: Cu-Au-Ag Cu-Au-Ag – Initial leaching, vuggy qtz-py Initial leaching, vuggy qtz-py – Early py–enargite–lz-fm Early py–enargite–lz-fm – Late Au– Late Au–py–low-Fe sph– tn/td– py–low-Fe sph– tn/td– ccp–gn, ± Te-Bi-Sn ccp–gn, ± Te-Bi-Sn  IS veins: IS veins: Ag–Au ± Pb–Zn Ag–Au ± Pb–Zn – Py–low-Fe sph–tn/td–ccp–gn, Py–low-Fe sph–tn/td–ccp–gn, ± ± Te Te  HS-IS vs LS distinction related to HS-IS vs LS distinction related to volcanotectonic setting volcanotectonic setting  Barton et al., 1977, John, 2001, Barton et al., 1977, John, 2001, Einaudi Einaudi et al., 2003, others et al., 2003, others
  • 15. Research applied to mineral exploration Einaudi, Hedenquist and Inan, 2003 Sulfidation states Sulfidation states
  • 16. Research applied to mineral exploration Einaudi, Hedenquist and Inan, 2003
  • 17. Research applied to mineral exploration LS deposits HS deposits Hedenquist et al., 1996
  • 18. Research applied to mineral exploration Steam-heated acid sulfate waters Steam-heated acid sulfate waters
  • 19. Research applied to mineral exploration Sillitoe, 1993 LS settings only Lithocap (± HS) settings only (steam-heated blanket possible) Any sulfide-rich setting Steam-heated waters, LS, IS, HS possible (HCl, SO2) 3 types only !
  • 20. Research applied to mineral exploration Lewis-Crofoot, NV: Lewis-Crofoot, NV: LS veins, steam-heated overprint (falling water table) LS veins, steam-heated overprint (falling water table) Similar blankets common in lithocap and HS, IS deposits Similar blankets common in lithocap and HS, IS deposits
  • 21. Research applied to mineral exploration McLaughlin, CA LS sheeted veins beneath sinter Sinters never in HS setting
  • 22. Research applied to mineral exploration El Chichon, 1979: El Chichon, 1979: magmatic vapors degassing magmatic vapors degassing
  • 23. Research applied to mineral exploration Kawah Ijen, Java: Kawah Ijen, Java: magmatic vapors condensed into ground water magmatic vapors condensed into ground water
  • 24. Research applied to mineral exploration Satsuma Iwojima, S. Kyushu: passive degassing of dome (~1000 yrs)
  • 25. Research applied to mineral exploration
  • 26. Research applied to mineral exploration Werner Giggenbach, Werner Giggenbach, geochemist, 1937-1997 geochemist, 1937-1997 Condensation of magmatic Condensation of magmatic vapor with HCl and SO vapor with HCl and SO2 2 generates acidic (pH ~1) generates acidic (pH ~1) waters, causes leaching of rocks waters, causes leaching of rocks to leave residual silica: re-xstal to leave residual silica: re-xstal to vuggy quartz or silicic rock to vuggy quartz or silicic rock View: “rhyolite”, 99.9% SiO View: “rhyolite”, 99.9% SiO2 2
  • 27. Research applied to mineral exploration Flux of rock-forming components to sea: Flux of rock-forming components to sea: 0.4 Mt/yr 0.4 Mt/yr of rhyolite cations leached, of rhyolite cations leached, i.e., 400 Mt of vuggy quartz over life of degassing dome i.e., 400 Mt of vuggy quartz over life of degassing dome
  • 28. Research applied to mineral exploration after Gray and Coolbaugh, 1994, by Arribas, 1995 after Gray and Coolbaugh, 1994, by Arribas, 1995
  • 29. Research applied to mineral exploration Steven & Ratté, 1960 Summitville, CO Vuggy qtz zone flares upward pH ~ >6 4 - 6 2 - 4 <2
  • 30. Research applied to mineral exploration Summitville, CO: vuggy qtz with alunite halo
  • 31. Research applied to mineral exploration Research applied to mineral exploration Arribas, 1995 Advanced argillic lithocap, host to HS ore deposits Summitville, CO: Summitville, CO: Alteration zoning Alteration zoning and ore bodies and ore bodies after Gray and Coolbaugh, after Gray and Coolbaugh, 1994 1994 Magmatic vapor Magmatic vapor condensation; Arribas, 1995 condensation; Arribas, 1995
  • 32. Research applied to mineral exploration Advanced argillic slides: 11 Advanced argillic slides: 11 (if scanned can be reduced to 5) (if scanned can be reduced to 5) Vuggy quartz, Summitville Quartz-alunite, Summitville Hypogene alunite, El Tambo Residual quartz, Pierina Arribas et al., 2000
  • 33. Research applied to mineral exploration Supergene alunite, Rodalquilar Steam-heated advanced argillic blanket, La Coipa Supergene alunite, Riaza Supergene alunite, Rodalquilar Massive supergene alunite, Rodalquilar Arribas et al., 2000
  • 34. Research applied to mineral exploration La Coipa: Steam-heated cristobalite- alunite blanket over vuggy quartz zone
  • 35. Research applied to mineral exploration Chalcedony blanket at paleowater table
  • 36. Research applied to mineral exploration Urashima et al., 1981
  • 37. Research applied to mineral exploration MMAJ, 1986
  • 38. Research applied to mineral exploration Rodalquilar, Spain: looking ~east Research applied to mineral exploration Arribas, 1995
  • 39. Research applied to mineral exploration Rodalquilar, Spain Arribas et al., 1995 Drilling beneath supergene alunite blanket
  • 40. Research applied to mineral exploration
  • 41. Research applied to mineral exploration
  • 42. Research applied to mineral exploration
  • 43. Research applied to mineral exploration Arribas et al., 2000
  • 44. Research applied to mineral exploration
  • 45. Research applied to mineral exploration
  • 46. Research applied to mineral exploration
  • 47. Research applied to mineral exploration
  • 48. Research applied to mineral exploration
  • 49. Research applied to mineral exploration Pierina, Perú: long section, alteration + ore Volkert et al., 1998 Volkert et al., 1998
  • 50. Research applied to mineral exploration El Indio: Chile
  • 51. Research applied to mineral exploration Siddeley and Areneda, 1986 El Indio: HS with late high-grade IS vein Jannas et al., 1990
  • 52. Research applied to mineral exploration Jannas et al., 1990
  • 53. Research applied to mineral exploration El Indio 3500 vein: quartz-pyrite-Au (tn- ccp) with sericite halo, post enargite DSO: 200 g/t Au av., cutoff 100 g/t (1.5 Moz of 8 Moz total)
  • 54. Research applied to mineral exploration Hedenquist et al., 1998
  • 55. Research applied to mineral exploration Surface projections: Lepanto, Far Southeast and Victoria From Palidan slide
  • 56. Research applied to mineral exploration Hedenquist et al., 1998
  • 57. Research applied to mineral exploration Hedenquist et al., 1998
  • 58. Research applied to mineral exploration Hedenquist et al., 2001
  • 59. Research applied to mineral exploration Hedenquist et al., 2001
  • 60. Research applied to mineral exploration Arribas et al., 1995; Sajona et al., 2001, Hedenquist et al., 2001
  • 61. Research applied to mineral exploration  Lithocap collapse Lithocap collapse  HS ore, if present, HS ore, if present, overprints porphyry overprints porphyry  Varying depths and Varying depths and intervals between intervals between base of lithocap and base of lithocap and top of porphyry top of porphyry
  • 63. Research applied to mineral exploration HS deposits: HS deposits: Observations relevant to exploration Observations relevant to exploration  Shallow, lithologic host; deep, structural control Shallow, lithologic host; deep, structural control  Vuggy quartz main host: steep (can be barren!) Vuggy quartz main host: steep (can be barren!)  Ore (sulfides + Au) introduced after leaching (or not) Ore (sulfides + Au) introduced after leaching (or not) – Low-grade bodies: evidence for oxidation Low-grade bodies: evidence for oxidation  Identify center(s) from alteration: size can be critical Identify center(s) from alteration: size can be critical  Local high-grade zones (late): cf. El Indio Local high-grade zones (late): cf. El Indio  Marginal IS veins, locally significant Marginal IS veins, locally significant  Pyrophyllite and sericite roots: porphyry tops Pyrophyllite and sericite roots: porphyry tops
  • 64. Research applied to mineral exploration Masupa Ria, Kalimantan: IS veins cut barren lithocap
  • 65. Research applied to mineral exploration Arcata, Perú, IS Ag vein Arcata, Perú, IS Ag vein (100 Moz Ag, 1 Moz Au): argillic halo at surface (100 Moz Ag, 1 Moz Au): argillic halo at surface
  • 66. Research applied to mineral exploration Arcata, Perú: Arcata, Perú: IS Ag vein: qtz- IS Ag vein: qtz- rhodochrosite rhodochrosite Zacatecas, Mexico
  • 67. Research applied to mineral exploration
  • 68. Research applied to mineral exploration IS veins IS veins  Common on margin of HS deposits Common on margin of HS deposits – Typically small, but exceptions (Victoria) Typically small, but exceptions (Victoria)  Principle IS deposits: Ag-Au (Zn-Pb, Cu) Principle IS deposits: Ag-Au (Zn-Pb, Cu) – Simple sulfide mineralogy, gangue Simple sulfide mineralogy, gangue  Large veins: up to several km long Large veins: up to several km long  Up to 800 m vertical Up to 800 m vertical – Tops and bottoms not uniform Tops and bottoms not uniform
  • 69. Research applied to mineral exploration
  • 70. Research applied to mineral exploration Marte, Maricunga district, Chile
  • 71. Research applied to mineral exploration Exploration for HS epithermal gold deposits Exploration for HS epithermal gold deposits General guidelines General guidelines  HS-IS epithermal: Neutral (~extensional) setting vs. HS-IS epithermal: Neutral (~extensional) setting vs. contraction (large porphyry) contraction (large porphyry)  HS: Define silicic (± vuggy) core, alteration halo HS: Define silicic (± vuggy) core, alteration halo  HS: Beware barren lithocaps vs. oxidized sulfide HS: Beware barren lithocaps vs. oxidized sulfide  Lithocaps: overlie porphyry Cu-Au systems Lithocaps: overlie porphyry Cu-Au systems  IS veins: Potential importance near HS prospects IS veins: Potential importance near HS prospects – Large lateral and vertical ranges, not uniform top or base Large lateral and vertical ranges, not uniform top or base Sillitoe and Hedenquist, 2003 Sillitoe and Hedenquist, 2003
  • 72. Research applied to mineral exploration Exploration for HS epithermal gold deposits Exploration for HS epithermal gold deposits Conclusions Conclusions  Prospective to target for world-class ore bodies Prospective to target for world-class ore bodies – Low-grade oxide ore (local bonanza veins) Low-grade oxide ore (local bonanza veins)  Potential for related deposits in a district Potential for related deposits in a district – Cu-Au porphyries, polymetallic Ag-Au-Zn-Pb veins Cu-Au porphyries, polymetallic Ag-Au-Zn-Pb veins  Basic questions: regional to district implications Basic questions: regional to district implications – Arc vs. rift, ligand source (porphyry, alkalic, mafic), Cu vs Arc vs. rift, ligand source (porphyry, alkalic, mafic), Cu vs Pb-Zn (zoning), barren lithocaps, etc. Pb-Zn (zoning), barren lithocaps, etc.
  • 73. Research applied to mineral exploration
  • 74. Research applied to mineral exploration Temperature- dependent alteration mineralogy Useful for paleo- isotherm zoning in epithermal deposits Hedenquist et al., 1996

Editor's Notes