Lithocaps and high-sulfidation epithermal deposits

Sociedad Geológica de Chile: : July 2011�

III

I

II

H2S + 2 O2 = H2SO4

H2O, NaCl, SO2, HCl, CO2, H2S, ...

H2SO4, HCl

CO2, H2S

4 SO2 + 4 H2O => 3 H2SO4 + H2S

pH >2

pH <1

Steam-heated blanket

Lithocap formed by hypogene condensate

Formation of advanced argillic alteration: hypogene & steam heated

HCl, SO2, CO2, H2S hypogene alteration

CO2, H2S steam-heated

alteration

HS IS LS HS IS LS LS(a)

Ya

RMt

Hedenquist et al., 1996, 2000

Vi To

Wa

Sl

LS, shallow (<300-400 m) <220-230 C

IS, deeper (~300-800 m) >220-230 C)

musc

  Lithocaps and high sulf’n: Cu-Au-Ag

  Initial leaching: vuggy qtz, qtz-alun lithocap w/ crs py, <50 ppb Au

Einaudi, Hedenquist and Inan, 2003

Summitville, Colorado

Steven and Ratté, 1960

pH ~ 4-6 2-4 <2 Summitville, Colorado

Steven & Ratté, 1960

pH ~ >6 4 - 6 2 - 4 <2

10 - 100s m

>10 g/t 500 m

Residual quartz, vuggy: Summitville Quartz-alunite, Summitville

Hypogene alunite, El Tambo Residual quartz, vuggy: Pierina

Arribas et al., 2000

Residual quartz, vuggy : Tucari

High-temperature hypogene vapors, !850 C with HCl, SO2

vadose zone: steam-heated blanket

Arribas et al. (2005) Arribas et al. (2005)

Arribas et al. (2005) Arribas et al. (2005)

Supergene alunite, Rodalquilar

Steam-heated advanced argillic blanket, La Coipa

Supergene alunite, Riaza Supergene alunite, Rodalquilar

Massive supergene alunite, Rodalquilar; post-mineral weathering oxidation

Arribas et al., 2000

Supergene oxidation critical to economics!

Rodalquilar, Spain: looking ~east

Rodalquilar, Spain

Arribas et al., 1995

Drilling beneath supergene alunite blanket; a mistake here....

Sonomi volcano

1 km

Nansatsu district, S Kyushu, looking east: Iwato HS deposit, Maruyama pit Inset: qtz-alun halo, sharp ctc with vuggy qtz, to r.)

Urashima et al., 1981

Tuff breccia Nansatsu Group

Iwato, Arabira rebody: Structural control to alteration and ore (in feeders)

30 m

MMAJ, 1986 250 m

NB: 27 drill holes on pseudo-section outside mine

http://www.iamgold.com/presentations2006.asp

Exploration and discovery histories: Use of models 1991

10 holes, 1869 m, av. 185 m

82 holes, 7656 m, av. 93 m (inclined)

IMG-122 (#40); 71 holes, 23,242 m, av. 330 m

2 km

Diatreme breccia w/ porphyry Cu fragments

Strong lithologic control to residual quartz llithocap: tuffs

“Stacked” lithocaps! “Stacked” lithocaps, upper barren...!

http://www.iamgold.com/presentations2006.asp Longitudinal section, N-S

Pierina, Peru

Volkert et al., 1998

Calipuy volcanic units

Yanacocha

oblique aerial to NE

Cajamarca District

Tantahuatay

Perol-Cocanes

Kupfertal

Cerro Yanacocha

Tertiary volcanic rocks

Paleozoic-Mesozoic sedimentary rocks

Cretaceous-Tertiary

intrusive rocks

Gustafson et al., 2004

40 km

Quilish; 4

La Quinua; 9

Tapado-Corimayo; 4

San Jose; 4 Kupfertal porphyry:

KUP-3

Carachugo-Chaquicocha; 6

Cerro Negro; 1

Leach pad

Cerro Yanacocha; 25 Norte, Oeste, Sur, Encajon

(Verde - sulfide)

Maqui Maqui; 3 Antonio

Carachugo-Chaquicocha; 6

Encajon

Sur Oeste

Norte

Giuliana

5 km

Yanacocha cluster

Longo and Teal, 2005

Perol, Cocañez: 8 km

5 km

Kupfertal

From Longo, 2005; Perol and Coca

11.5 – 13.5 Ma (Cerro Negro, Quilish)

10.7 – 11.1 Ma (Corimayo-Carachugo-Tapado)

10 – 10.5 Ma (San Jose)

8.2 – 9.2 Ma (Yanacocha Complex)

15.8-16.1 Ma (Perol porph, Cocañez litho)

10.7 Ma (Kupfertal porph)

From Longo, 2005, et al. 2010; Perol and Cocañez dates from Gustafson et al., 2004

Late dacite

Alunites

Bell et al., 2005 Longo and Teal, 2005 Longo et al., 2010

Longo et al., 2010

(7 Moz) (20 Moz) (25 Moz)

Longo, 2005; et al., 2010

Cerro Negro Quilish

San Jose Tapado

Corimayo Carachugo

Maqui Maqui

Yanacocha Complex

Km3

Moz

2 km

Hydrothermal breccia body Lithologic horizon (70% of ore in welded pyroclastics)

Margin of dome intrusion

220-ton haul truck

pH ~ >6 4 - 6 2 - 4 <2

Dome moat, laminated siliceous sediments, paleosurface...

Chaquicocha Carachugo

KUPFERTAL PORPHYRY

Patchy

Wormy

Low Au-Ag-Hg-As

Bi-Ba-As-Sb

Au-Ag-As-Sb

Cu-Au-As-Ag

oxide

sulfide

Zn-Pb

Hg

CHAQUICOCHA

~100 m

1

2 2. Cooling

1. Vapor condensation

215.3m: Muscovite

205.6m: pyrophyllite, alunite

Breccia: from 181.5m Pyrophyllite, alunite,

kaolinite

185.3m: pyrophyllite, minor alunite

Porphyry-style quartz veins with phyllic alteration

Epithermal Porphyry

DDH KUP-3

210.6m: pyrophyllite,

kaolinite

Fault contact between epithermal and porphyry alteration at Kupfertal

Fault contact

Patchy texture outcrop 0 500 m

Milagros porphyry prospect, Alto Chicama, Peru

Garia, 2009

Arribas et al., Gold in 2000

Residual quartz (silicic) and advanged argillic size matters...

El Indio 8 Moz

...much of the time, cf. El Indio

Jannas et al., 1990

100 m

Jannas et al., 1990

Qtz-alunite

Pyrophyllite- kandite

White mica

NB: Mixing will not cause amorphous silica saturation and colloform gels

Erosion level?

Lepanto,

FSE

Victoria

Perol

Co. Cocañez (barren)

Relation of porphyry, lithocap, HS ore, and marginal IS ore

Alto Chicama, Peru 10.5 Moz resource, 2003 Lagunas Norte, 1.24 g/t Au, 14 Moz

Chimu qtzites Calipuy volcanics