Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Transitions from porphyry to epithermal ore environments • • • • • • Processes in active porphyry systems Early and intermediate porphyry stages Transition from porphyry tops to lithocaps Linked porphyry and high-sulfidation deposits Lithocaps and high-sulfidation deposits Intrusion-centered intermediate-sulfidation veins Jeffrey W. Hedenquist Ottawa Hermosillo, Université deMexico: Genève October, : 13 October 2014 2014 Intrusion-centered porphyry Cu deposits: Tectonic and structural control on arc magma emplacement © Richards (2007), from Tosdal & Richards (2001) J.W. Hedenquist 1 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Richards, 2011 (level of neutral buoyancy) Intrusion-centered systems: tectonic setting Cu-Au Intrusion-centered: ~40% of world Au Porphyry: 70% of world Cu From R. Goldfarb, after Groves et al. (2005) J.W. Hedenquist 2 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Sakurajima, Kyushu Bingham Canyon, Utah: >31 Mt Cu Bingham Canyon porphyry deposit, Utah: reconstruction ? ? Advanced argillic lithocap? Waite et al., 1997; Hattori and Keith, 2003 J.W. Hedenquist 3 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Redmondporphyry, et al., 2003 Utah Bingham Redmond et al., 2004 Hypersaline liquid Paleodepth (km) 1.5 - Vapor Critical fluids (Cu) White Island, New Zealand: Quiescent eruption, 1988 High-temperature hypogene vapors, 800oC with HCl, SO2 300 t Au, 1 Mt Cu flux during ~10,000 yr magma discharge; partial loss to atmosphere Photograph: W.F. Giggenbach J.W. Hedenquist 4 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 White Island, New Zealand: fumaroles High-temperature hypogene vapors, 800 oC with HCl, SO2 White Island, New Zealand: drowned fumaroles, 2004 Satsuma Iwojima, Japan Residual (vuggy) quartz pH 0.2 acidic stream, pH ~0.6 J.W. Hedenquist 5 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Satsuma Iwojima, S. Kyushu: passive degassing (no eruption) Summit crater J.W. Hedenquist 880oC, H2O, HCl, SO2 Sampling of 770oC vapor with acidic gases 6 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Residual (vuggy) qtz Satsuma Iwojima, Japan pH 1.7 -- 1.1 Hedenquist et al., 1994 pH 1.1 dissolved rock Satsuma Iwojima White Island (low metals) (~10 ppm Cu) Magmatic fluid: coupled vapor and brine from deep fluid Critical fluid bulk salinity COUPLED vapor + brine hypersaline liquid (brine), within porphyry vapor Critical fluid Fluid exsolved in melt J.W. Hedenquist 7 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Porphyry systems Residual quartz (vuggy), barren pH 1-2, H2SO4 HCl Quartz-alunite, barren Base of lithocap Sillitoe, 2010 Porphyry systems Residual quartz (vuggy) HS enargite, Au Quartz-alunite IS veins Base of lithocap Sillitoe, 2010 J.W. Hedenquist Porphyry Cu (Au) Intermediate: Lower T magmatic, <10 wt% NaCl • White mica (up to pyrophyllite) ( 350oC) • Straight qtz veins, halo • Metals (shallow HS ore, marginal IS veins) 8 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Lowell and= advanced argillic Extreme hydrolytic Guilbert, 1970 Key (accessory) minerals Adv argillic 2 Potassic (early): biotite, K-feldspar (magnetite, actinolite, tourmaline) Time > 4 argillic Advanced argillic: residual quartz, alunite, dickite, pyrophyllite (diasp) sericitic Sodic-calcic (deep): ab/oligo., act. potassic Propylitic (margins): epidote, chlorite, albite, actinolite Sericitic (phyllic): White mica (qtz, chlorite, hematite, anhydrite) High 4 2 ? Argillic (clays): Illite, smectite, kaolinite (later carbonate) Vapor & brine coupled 80% 20% Temperature Depth km ? F - feldspar stable (potassic) H - hydrolytic (attack by H+) (phyllic and advanced argillic) E - caused by external fluids (propylitic and sodic-calcic) potassic sericitic adv. arg. Low argillic Seedorff et al., 2005 J.W. Hedenquist 9 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Chuquicamata, Chile Ridgeway, Australia Hugo Dummett N, Oyu Tolgoi, Mongolia El Teniente, Chile Variable alteration and Cu zoning in large porphyry deposits Sillitoe, 2010 Seedorff et al., 2005 Cooling = change in mineral stability, results in overprinting relationships P - propylitic, IA - inter. argillic AA- advanced argillic S - sericitic, K - potassic Late cool, unseparated fluid Tourmaline [NaFe2+2(Al,Fe3+)Al6Si6O18(BO3)3(OH)4] Dumortierite [Al7BO3)(SiO4)3O3] Brine Vapor Also can add: F = topaz, zunyite log aF-/aH+ Solvus Separation Critical fluid log aK+/aH+ J.W. Hedenquist 10 Porphyry systems: transition to lithocaps Batu Hijau porphyry, Sumbawa Geneva, 13th October 2014 Arif and Baker, 2003 A veins: early, high temperature (potassic stage, no alteration halo - bn, ccp). Wavy veins; ductile plastic rock (high T hypersaline liquid + vapor inclusions): lithostatic P B veins: transitional D veins: later, lower temperature (phyllic stage, with alteration halo - ccp, py, shallow bn + py, cv, en). Straight and center line; brittle rock (350 C 5-10 % NaCl inclusions): hydrostatic P Gustafson and Hunt, 1975 Typical porphyry intrusion and vein relationship Sillitoe, 2010 J.W. Hedenquist 11 Porphyry systems: transition to lithocaps Halilaga Cu-Au porphyry, Turkey Geneva, 13th October 2014 http://pilotgold.com/ Proffett, 2003 J.W. Hedenquist 12 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Bingham Canyon, Utah Gruen et al., 2010 240 Mt of M,I&I at 0.74% Cu and 0.013% Mo (0.5% CuEq cutoff for UG, top 400 m below surface) Copper Creek porphyry Cu-Mo, Arizona 1400 1000 m Riedell et al., 2013 J.W. Hedenquist 13 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Early bt vn A vn Early halo vn D (qsp) vn Riedell et al., 2013 1 km Vein abundance at surface (>5% EH & 5% D), over 0.5% Cu grade shell at ~350-700 m depth J.W. Hedenquist Riedell et al., 2013 14 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Porphyry examples El Salvador, to east c. late 1950s pyrophyllite muscovite Damiana exotic Geology of El Salvador Cornejo et al., 1997 J.W. Hedenquist 15 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Watanabe and Hedenquist, 2001 J.W. Hedenquist 16 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Cu ore at 2600 m Watanabe and Hedenquist, 2001 Watanabe and Hedenquist, 2001, after Hemley et al., 1969 pyrophyllite muscovite 1. Cooling 2. Vapor condensation 2 muscovite + 6 qtz = 3 pyrophyllite KAl3Si3O10(OH)2 + 2 H+ + 6 SiO2 = 3 Al2Si4O10(OH)2 + 2 K+ J.W. Hedenquist 17 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 El Salvador, looking ~SE pyrophyllite alunite lithocap (late) Watanabe and Hedenquist, 2001 J.W. Hedenquist 18 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Breccias w/ adv arg Watanabe and Hedenquist, 2001 Fluids from alteration at presentday level of exposure Volcanic vapor Giggenbach, 1992 Water in felsic magmas B. Taylor et al., 1986 Muscovite overprint Deep potassic (biotite) dickite Vapor-brine fractionation ~20 D ‰ Horita et al., 1995; Schmulovitch et al., 1999 Watanabe and Hedenquist, 2001 J.W. Hedenquist 19
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