Exposing white mica overprint of potassic alteration

Transcription

1 early qtz-alun lithocap?? paleosurface? ~42 Ma retrograde pyroph encapsulated potassic, sulfides 2M1 musc late qtz-alun bx (diasp-pyroph) El Salvador, looking ~SE Erosion at El Salvador: Exposing white mica overprint of potassic alteration Sillitoe, 2010 Economic Geology J.W. Hedenquist 20

2 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 cc-en-bn vn, ser (dk-zy) % Cu, 0.04% Mo Ballantyne, JORC Inferred Resource J.W. Hedenquist 21

3 Manske and Paul, 2002 H E 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. MB-20A (from surface, 1958 m): discovery hole, 1.75 % Cu, >375 m 105 XCS, 3600 L (ft) = ~ sea level (1200 m deep) Manske and Paul, 2002 J.W. Hedenquist 22

4 Manske and Paul, 2002 Manske and Paul, resource: 455 Mt at 1.2 % Cu, 0.02 % Mo m below surface, 1050 x 365 x 305 m J.W. Hedenquist 23

5 N.B: High Cu grades near 1) limestones or 2) Fe-rich rocks All ages ~ 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) % Cu, 0.04% Mo Ballantyne, JORC Inferred Resource Sulfide zoning in porphyries: Greys = potassic Dashed = sericitic overprint, D vns Marco Einaudi, 2002, unpub. J.W. Hedenquist 24

6 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 Mt, magnetite Hm, hematite Py, pyrite Grey = low s n state; yellow, int.; orange, hi; red, v. high Inan et al., 2002 Einaudi et al., 2003 Porphyry Assemblages type II Bingham Chuquicamata Potrerillos El Salvador Gibraltar Sungun Ann Mason Silver Bell Early, higher temp Potassic no pyrite (bn-cp) dg-bn-cp dg-bn-(cp) (mt)-bn-cp mt-bn-cp mt-cp-py (mt-bn-cp) cp bn-cp (dg-bn)-cp bn-cp bn-cp (bn)-cp cp-py (bn)-cp cp-py bn-cp Late, lower temp pyrite Phyllic py-cp-(tn) mt-cp cp-py py-cp-bn, py-bn cp-py cp-py bn-cp, cp-py (SC) py-en, py-bn py, cv, dg, en, cp py-cp-tn py, tn, en py-cp py-hm-(cp) cp cp-py py Bn, bornite Cp, chalcopy Dg, digenite Tn, tennantite En, enargite Cv, covellite Sierrita-Esperanza Butte bn + cp, ss dominant cp-py cp-py (C) py-cp mt-cp-py (EDM) ore mt-cp-py (SC) py, cv, dg, py-cp (S) bn, cp, en cp + py assemblage Mt, magnetite Hm, hematite Py, pyrite Inan et al., 2002 Einaudi et al., 2003 J.W. Hedenquist 25

7 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 SO 2 )? Sulfidation states Hm Cp Mt Einaudi, Hedenquist and Inan, 2003 J.W. Hedenquist 26

8 Sulfidation state evolution cv Arc magmas 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

9 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

10 Cretaceous- Paleogene Lepanto metavolcanics Ma Bagon intrusive complex Late Oligocene to mid- Miocene Apaoan volcaniclastics Slightly younger Balili volcaniclastics Imbanguila dacite porphyry ( Ma) Young cover: <1.2 Ma Bato pyroclastics (1.2 Ma) Bato dacite porphyry (1.2 Ma) 1 km Imbanguila pyroclastics ( Ma) Qtz diorite porphyry Lapangan Tuff (0.19 Ma) Chang et al., 2011 Dickite kaolinite 1 km Quartzalunite Dickite kaolinite NW end of lithocap: qtz-alunite cliffs at unconformity, with kaolinite halo Chang et al., 2011 J.W. Hedenquist 29

11 < 50 ppb Au 1 km X Silicic structures, 1-4 g/t Au Breccias Chang et al., 2011 Lepanto HS:> 0.9 Mt Cu & 102 t Au Buaki porphyry Victoria veins, g/t Au + Ag- Cu-Pb-Zn Teresa veins, g/t Au FSE porphyry: % Cu & 1.2 g/t Au Alteration and Mineralization Guinaoang porphyry, % Cu & 0.4 g/t Au 1 km Nayak veins Mohong Hill porphyry + HS Chang et al., 2011 J.W. Hedenquist 30

12 Lepanto - Far Southeast deposits Ma 2 cm 0.7% Cu Mo 1.45 Ma 1 g/t Au 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

13 Porphyry systems: transition to lithocaps Geneva, 13th October 2014 Arribas et al., 1995; Hedenquist et al., Ma pyroph 1.35 Ma 1.42 Ma Hedenquist et al., 1998; Chang et al., m Residual (vuggy) qtz Qtz-alun (py), dick-kaol What information can we get from a barren lithocap? J.W. Hedenquist 32

14 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): % Cu, 0.69 g/t Au (10 km east of Yanacocha (5-12 Ma) J.W. Hedenquist 33

15 Yanacocha district, Kupfertal valley: High-sulfidation and porphyry deposits, ~10-11 Ma Fault contact between epithermal and porphyry alteration at Kupfertal Epithermal Porphyry Porphyrystyle quartz veins with phyllic alteration 185.3m: pyrophyllite, minor alunite 205.6m: pyrophyllite, alunite 210.6m: pyrophyllite, kaolinite 215.3m: Muscovite Breccia: from 181.5m Pyrophyllite, alunite, kaolinite Fault contact DDH KUP-3 J.W. Hedenquist 34

16 Two origins (environments) of hypogene pyrophyllite: Watanabe and Hedenquist, ) 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 KAl3Si3O10(OH)2 + 2 H+ + 6 SiO2 = 3 Al2Si4O10(OH)2 + 2 K Cooling 2 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

17 Patchy pyrophyllite Replacement /// Petelovo Sericite 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

18 Co. Catedral Al Ma vein zone Al Ma Co. Casale Bt 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

19 Potential for deeper porphyry Cu deposit if lithocap eroded, or on shoulder Assess level of erosion Barren, eroded lithocap: patchy pyrophyllite base?, white mica, veinlets? Sillitoe, 2010 Porphyry Cu-Au? Porphyry systems Lepanto High-sulfidation Au-Cu Co. Catedral (barren) Intermediate sulfidation Au-Ag (Pb-Zn) Base of lithocap FSE Cerro Casale Victoria Resolution El Salvador Porphyry Cu-Au Sillitoe, 2010 Economic Geology J.W. Hedenquist 38