Porphyry systems: transition to lithocaps Geneva, 13th October 2014 early qtz-alun lithocap ?? retrograde pyroph paleosurface? ~42 Ma late qtz-alun bx (diasp-pyroph) encapsulated potassic, sulfides 2M1 musc El Salvador, looking ~SE Erosion at El Salvador: Exposing white mica overprint of potassic alteration Sillitoe, 2010 Economic Geology J.W. Hedenquist 20 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Looking east over Superior, Arizona dashed - base of Apache Leap dacite tuff Magma mine, Arizona: 1875~1990s; Ag, cc hm-py-cp-bn (gn-spl) mantos 1.34 Gt @ 1.51% Cu, 0.04% Mo 2008 JORC Inferred Resource J.W. Hedenquist cc-en-bn vn, ser (dk-zy) Ballantyne, 2003 http://riotinto.msgfocus.com/q/1cRLO25OxfDl/wv 21 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Manske and Paul, 2002 H E MB-20A (from surface, 1958 m): discovery hole, 1.75 % Cu, >375 m Deposit identified by underground drilling. S27E (Feb 1995, subhorizontal) cut sericitized rocks with pyrite and hypogene chalcocite veins (1 m bncc-dg vein, 38% Cu, >385 g/t Ag); porphyry copper potential recognized. S27H (Jan 1996, inclined) cut sericite-pyrite alteration, then biotitealtered rocks with chalcopyrite. The last 43 m of S27H averaged 1.94% Cu. 105 XCS, 3600 L (ft) = ~ sea level (1200 m deep) Manske and Paul, 2002 J.W. Hedenquist 22 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Manske and Paul, 2002 Manske and Paul, 2002 1998 resource: 455 Mt at 1.2 % Cu, 0.02 % Mo 1250-1550 m below surface, 1050 x 365 x 305 m J.W. Hedenquist 23 Porphyry systems: transition to lithocaps N.B: High Cu grades near 1) limestones or 2) Fe-rich rocks Geneva, 13th October 2014 All ages ~63.5-65 Ma, indicating: 1) Magma vein and related mantos, 2) Superior East deposit, and 3) Resolution deposit are all the same age (M. Einaudi, pers. comm., 2003) 1.34 Gt @ 1.51% Cu, 0.04% Mo 2008 JORC Inferred Resource Ballantyne, 2003 http://riotinto.msgfocus.com/q/1cRLO25OxfDl/wv Sulfide zoning in porphyries: Greys = potassic Dashed = sericitic overprint, D vns Marco Einaudi, 2002, unpub. J.W. Hedenquist 24 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Porphyry Assemblages I Potassic Phyllic Cp, chalcopy CuFeS2 Bn, bornite Cu5FeS4 Dg, digenite Cu9S5 Cc, chalcocite Cu2S Tn, tennantite Cu12As4S13 En, enargite Cu3AsS4 Cv, covellite CuS Grey = low s n state; yellow, int.; orange, hi; red, v. high Mt, magnetite Hm, hematite Py, pyrite Inan et al., 2002 Einaudi et al., 2003 Porphyry Assemblages type II ‘Early’, higher temp ‘Late’, lower temp pyrite Phyllic Potassic no pyrite Bingham (bn-cp) bn-cp py-cp-(tn) Chuquicamata dg-bn-(cp) (dg-bn)-cp mt-cp Potrerillos (mt)-bn-cp bn-cp cp-py py-cp-tn El Salvador mt-bn-cp mt-cp-py bn-cp py-cp-bn, py-bn py, tn, en cp-py py-cp Gibraltar (mt-bn-cp) Sungun Ann Mason cp Silver Bell Sierrita-Esperanza (bn)-cp cp-py (bn)-cp cp-py cp-py bn-cp bn-cp, cp-py (SC) py-hm-(cp) cp cp-py py cp-py cp-py (C) py-cp mt-cp-py (SC) py, cv, dg, bn, cp, en py-cp (S) mt-cp-py (EDM) Butte bnss + cp, dominant J.W. Hedenquist py-en, py-bn py, cv, dg, en, cp dg-bn-cp cp + py ore assemblage Bn, bornite Cp, chalcopy Dg, digenite Tn, tennantite En, enargite Cv, covellite Mt, magnetite Hm, hematite Py, pyrite Inan et al., 2002 Einaudi et al., 2003 25 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Porphyry styles: Cu introduction and alteration • Porphyry type I: • early high T potassic with low to inter. sulf n state sulfides • most Cu introduced early, with magnetite (lower redox) • minor late high sulf n sulfides + advanced argillic alteration • Porphyry type II: • less Cu introduction during early high T, low sulf n state • more Cu in later lower T phyllic stage, w/out magnetite • pyrite plus inter. to high sulf d state sulfides common • more abundant advanced argillic alteration • more oxidized magma (abundant SO2)? Sulfidation states Hm Cp Mt Einaudi, Hedenquist and Inan, 2003 J.W. Hedenquist 26 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Sulfidation state evolution Arc magmas cv Lithocap Einaudi, Hedenquist and Inan, 2003 Early to intermediate (potassic to phyllic), high to low T, progressively higher sulf d state in porphyry; -metals introduced early or intermediate residual qtz (alunite) host phyllic potassic illite Einaudi, Hedenquist, Inan, 2003 J.W. Hedenquist 27 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Mankayan district, Philippines Mohong Hill quartz-alunite lithocap dacite pyroclastics volcaniclastic basement Lepanto high-sulfidation ores Most ore (~70%) in root zone of lithocap, in Lepanto fault or its splay branches Lepanto fault Hedenquist et al., 1998; Chang et al., 2011 J.W. Hedenquist 28 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Late Oligocene to midMiocene Apaoan volcaniclastics Young cover: Slightly younger Balili volcaniclastics Imbanguila dacite porphyry (3.31.8 Ma) CretaceousPaleogene Lepanto metavolcanics <1.2 Ma 12-13 Ma Bagon intrusive complex Imbanguila pyroclastics (3.3-1.8 Ma) Bato pyroclastics (1.2 Ma) Bato dacite porphyry (1.2 Ma) Qtz diorite porphyry 1 km Lapangan Tuff (0.19 Ma) Chang et al., 2011 Dickite kaolinite Quartzalunite Dickite kaolinite 1 km NW end of lithocap: qtz-alunite cliffs at unconformity, with kaolinite halo Chang et al., 2011 J.W. Hedenquist 29 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 < 50 ppb Au X 1 km Silicic structures, 1-4 g/t Au Breccias Chang et al., 2011 Lepanto HS:> 0.9 Mt Cu & 102 t Au Alteration and Mineralization Buaki porphyry FSE porphyry: 650 Mt @ 0.65% Cu & 1.2 g/t Au Victoria veins, 11 Mt @ 7.3 g/t Au + AgCu-Pb-Zn Guinaoang porphyry, 500 Mt @ 0.4% Cu & 0.4 g/t Au Teresa veins, 0.8 Mt @ 5.74 g/t Au Nayak veins 1 km J.W. Hedenquist Mohong Hill porphyry + HS Chang et al., 2011 30 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Lepanto - Far Southeast deposits 1.8-2.2 Ma 2 cm 1.45 Ma 1 g/t Au Mo 0.7% Cu Concepcion and Cinco, 1989; Garcia, 1991 Lepanto - Far Southeast deposits 500 m X-section 1) Residual qtz (early, barren) 2) Breccia-hosted enargite + Au (sericite stage) Long section along Lepanto fault Garcia, 1991; Arriibas et al., 1995; Hedenquist et al., 1998 J.W. Hedenquist 31 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Arribas et al., 1995; Hedenquist et al., 1998 1.41 Ma pyroph 1.35 Ma 1.42 Ma Hedenquist et al., 1998; Chang et al., 2011 500 m Residual (vuggy) qtz Qtz-alun (py), dick-kaol What information can we get from a barren lithocap? J.W. Hedenquist 32 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Alunite peak increases closer to intrusive center High Na/(Na+K) alunite forms at higher temperature, closer to intrusion Chang et al., 2011 • Co. Cocañez: Barren quartz-alunite lithocap (16.1 Ma alun); related to Perol porphyry? • Perol porphyry: (15.8 Ma, bt): 641 Mt @ 0.3% Cu, 0.69 g/t Au (10 km east of Yanacocha (5-12 Ma) J.W. Hedenquist 33 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Yanacocha district, Kupfertal valley: High-sulfidation and porphyry deposits, ~10-11 Ma Fault contact between epithermal and porphyry alteration at Kupfertal Epithermal 185.3m: pyrophyllite, minor alunite 210.6m: 205.6m: pyrophyllite, pyrophyllite, alunite kaolinite Porphyry Porphyrystyle quartz veins with phyllic alteration 215.3m: Muscovite Fault contact Breccia: from 181.5m Pyrophyllite, alunite, kaolinite DDH KUP-3 J.W. Hedenquist 34 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Watanabe and Hedenquist, 2001 Two origins (environments) of hypogene pyrophyllite: 1) Vapor condensation Lithocap environment (roots) Silicic (vuggy), alunite halo, hotter pyrophyllite (below) 2) Simple fluid cooling Cooling: muscovite (A) to pyrophyllite (B) (gusano replacement of silicic) to dickite (C) 2. Cooling 2 2 KAl3Si3O10(OH)2 + 2 H+ + 6 SiO2 = 3 Al2Si4O10(OH)2 + 2 K+ 1 1. Vapor condensation Milagros: Garcia, 2009 Porphyry evolution: High to low T alteration magmatic input Early Intermediate After magma crystallization: heat, but only meteoricwater clay overprint Sillitoe, 2010 J.W. Hedenquist 35 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Patchy pyrophyllite Replacement /// Sericite Petelovo Milagros • Variable interval between base of lithocap and top of porphyry • Rapid syn-hydrothermal uplift causes lithocap to overprint Ppy (telescoping) Wafi-Golpu, PNG Wafi telescoped porphyry Cu-Au Sillitoe, 1999 Cp replaced by py due to phyllic overprint, then bn-dg-cc-cv sulfidation caused by late advanced argillic overprint J.W. Hedenquist 36 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Co. Catedral Al 13.5 0.5 Ma vein zone Al 13.89 0.04 Ma Co. Casale Bt 13.91 0.04 Ma Sillitoe, 1990 Co. Casale and Co. Catedral: relationship? Largely eroded (barren?) qtz-alunite lithocap of Co. Casale, with roots preserved, or…? ? J.W. Hedenquist 37 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Potential for deeper porphyry Cu deposit if lithocap eroded, or on shoulder Sillitoe, 2010 Assess level of erosion… Barren, eroded lithocap: patchy pyrophyllite base?, white mica, veinlets? Porphyry Cu-Au? Porphyry systems High-sulfidation Au-Cu Co. Catedral (barren) Lepanto Intermediate sulfidation Au-Ag (Pb-Zn) Victoria Resolution Base of lithocap Cerro Casale El Salvador FSE Porphyry Cu-Au Sillitoe, 2010 Economic Geology J.W. Hedenquist 38
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