B.DELGERTSOGT

Porphyry Copper Systems

• Schematic illustration of

porphyry Cu system

Sillitoe, 2010

Porphyry stock and underlying pluton, overlying comagmatic volcanic rocks

• Alteration– Sodic-

calcic– potassic– sericitic– advanced

argillic

Sillitoe (2010)

Alteration-mineralization zoning in porphyry Cu deposits

Generalized alteration zoning pattern (Sillitoe, 2010)

Generalized alteration sequence (Sillitoe, 2010)

Generalized alteration zoning and sequence

• Most widely distributed at convergent plate boundaries• Occur with skarn, HS & IS epithermal deposits• Form linear metallogenic belts• Related with plutons (5-15km deep) and porphyry stocks• 100,000 to several million years lifespan (Dep. Clusters or belts 10 m.y or

longer)• Zoned alteration from barren, Na-Ca to potassic, chlorite-sericitic, sericitic,

and to advanced argillic from >700C to <250C• Typical hypogene porphyry Cu deposits have average grades of 0.5 to 1.5

% Cu, <0.01 to 0.04% Mo, and 0.0 – to 1.5 g/t Au. Rarely “Au-only” deposits have 0.9 to 1.5 g/t Au content, but little Cu (,0.1%)

• Ore mineral assemblage of chalcopyrite-bornite• Quartz stockwork sequence, with magmatic-hydrothermal breccia and

phreatomagmatic breccia• Formed by injection of oxidized magma saturated with S and metal-rich

aqueous fluids exolved from cupolas of parental plutons• Early two phase hypersaline liquid and vapor, and later single phase low to

moderately saline liquid associated with mineralization

Characteristics of porphyry type deposits

Porphyry Cu deposits within

and near precursor plutons

a: Los-Bronces-Rio Blanco, Chile

b: El Abra and Conchi Viejo, Chile

c: Highland Valley, British Columbia

Sillitoe (2010)

• Porphyry stocks and dikes– diameter: commonly <1km– 14 km at Chuquicamata- Radomiro Tomic– 4 km Hugo Dummett– Vertical extent: >2-4 km– Multiple phases– I type, magnetite series, metaaluminous, medium K to high

K calc-alkaline– diorite to quartz diorite through granodiorite to quartz

monzonite– Mo-rich porphyry: felsic, Au-rich porphyry: dioritic– Porphyritic texture with feldspar, hornblende, biotite

Deposit-scale characteristics

• Early, quartz- and sulfide-free veinlets containing one or more of actinolite, magnetite, biotite and K-feldspar (EB vein), typically lack in alteration halo, mainly in potassic alteration

• Sulfide-bearing, granular quartz-dominated veinlets with either narrow or no readily recognizable alteration halo (A and B type) in potassic alteration

• Late, crystalline quartz-sulfide veins and veinlets with prominent, feldspar-destructive alteration halo (including D type) in chlorite-sericite and sericite alteration

Porphyry Cu veinlet relationship

Sillitoe (2010)

Schematic chronology of typical veinlet sequence

Sillitoe (2010)

Relation between porphyry intrusions and stockwork mineralization

Early potassic alteration and EB-A vein

B vein at El Salvador

Sericitic alteration and D vein at El Salvador

Latest D vein:Py-tn-tet-en assemblage with muscovite haloLower extension of hydrothermal breccia

Early Transitional Late

EB A B C DBt

Qtz

Anhy

Kfsp

Chl

Ser

And

Bn

Cp

Mo

Py

Vein stages at El Salvador(Gustafson and Quiroga, 1995)

• Diatreme– phreatomagmatic eruptive activity– commonly >1km in diameter, >2km long– composed of cm size clasts in matirx of

volcanic tuff component– post-porphyry Cu mineralization, but

intra-HS epithermal Au mineralization• Magmatic-hydrothermal breccia

– absent in tuffaceous material– steep pipe like to irregular bodies– intramineral porphyry stage with

potassic and sericitic alteration– normally blind to the surface– may host porphyry Cu mineralization

• Phreatic breccia– post-mineral (pebble dike) with

advanced argillic alteration

Sillitoe (2010)

Diatremes & breccia

Tourmaline breccia at El Salvador

• cylindrical orebodies common

• narrow elongated shape (e.g. Hugo Dummett)

• veinlet stockwork at top• gradual or abrupt decrease

of Cu grade downwards• lateral halo of Pb-Zn and Au-

As zones• HS & IS Au-Cu mineralization

above

a: Bingham, Utah, b: Mineral Park, Arizona, c: Sepon, Laos Sillitoe (2010)

Orebody types and geometry

Sulfide zonation at El Salvador, Chile (Gustafson and Hunt, 1975)

Sulfide zoning

Tsagaan Suvarga, Southern Mongolia

Sericitic alteration overprinting on potassic alteration

Watanabe & Hedenquist ( 2001)

Lateral zoning in the sericitic alteration at El Salvador, Chile

Indio Muerto

Mus

Propylitic

Hydrothermal breccia and “lithocap”

Quartz-alunite lithocap

Hydrothermal breccia

Mus

• Sericitic alteration stage (center to margin)– Least altered: igneous feldspar present– Muscovite-andalusite+/-diaspore, tourmaline– Muscovite+/-diaspore, tourmaline– Pyrophyllite overprint– Propylitic (chlorite)

• Advanced argillic alteration stage– Advanced argillic: alunite (AP, APS cores), pyrophyllite,

dickite, diaspore, quartz (zunyite, andalusite)

Mineral assemblage

• absorption of the high-temperature magmatic vapor by ground water and disproportionation of the SO2 – HCl = H+ + Cl- – 4SO2 + 4H2O = 3H2SO4 +

H2S

– H2SO4 = H+ + HSO4-

Advanced argillic lithocaps

Magma Porphyry

Schematic mineralization zones in porphyry Cu deposits (Lowell & Guilbert, 1970)

Hydrothermal alteration

Why center of porphyry system is barren?

• Source magma– Chamber at depth of 5-15km – >50km3 in volume– Porphyry is conduit– water rich (4 wt %), oxidized (high oxidation state

suppresses magmatic sulfide precipitation as pyrrhotite)

– S rich (anhydrite as a magmatic mineral)

Genetic model

Cooling and pressure drop decreased Cu solubility and precipitate Cu-Fe.Sillitoe (2010)

Genetic model

• Target selection– target area selection in

known porphyry Cu belt and associated deposits

– contractional setting– erosion level (sericite-

pyrophyllite level better than advanced argillic level)

– host rock lithology (carbonate)

– climate and age

Exploration

Hedenquist et al. (1998)

Lepanto HS epithermal and FSE porphyry Cu-Au deposit

Angera (1999), modified by Nakayama (2004)

Pre-mineral porphyry

Post-mineral porphyry

Bajo de la Alumbrera porphyry Cu-Au deposit, Argentina

Climax porphyry Mo deposit, USA

Volcanic fronts in SW USA during the Cenozoic

Redmond and Einaudi (2010)

37.07-37.57Ma (Parry et al., 2001)

38.55±0.19Ma (Parry et al., 2001)

Bingham Porphyry Cu-Mo-Au deposit, USA

Hedenquist et al. (1996)

Шүтээний төв хэсэгт бялхсан АГЛОМЕРАТ – ын биет

Шүтээний төв хэсэгт бялхсан АГЛОМЕРАТ –ын биет

• Diatreme– phreatomagmatic eruptive activity– commonly >1km in diameter, >2km long– composed of cm size clasts in matirx of

volcanic tuff component– post-porphyry Cu mineralization, but

intra-HS epithermal Au mineralization• Magmatic-hydrothermal breccia

– absent in tuffaceous material– steep pipe like to irregular bodies– intramineral porphyry stage with

potassic and sericitic alteration– normally blind to the surface– may host porphyry Cu mineralization

• Phreatic breccia– post-mineral (pebble dike) with

advanced argillic alteration

Sillitoe (2010)

Diatremes & breccia

Шүтээн нь нэгэн магмын голомтоос харьцангуй удаан хугацааны туршид хөгжин хэлбэржсэн бөгөөд энэ утгаараа тус структур нь Дөшийн овоогийн вулканоген – пирокласт формаци болон Мандахын интрүзив бүрдэл зэрэг стратиграфи, магматизмийн өөр өөр нэгжүүдээс тогтсон бус харин нэгдмэл нэгэн эх үүсвэрээс гаралтай Шүтээний магматоген–гидротермаль систем болно.

A magma generation model at subduction zone

Examples of the volcanic chains at subduction zones

Tatsumi (1995)

KurileKamchatka

a: Globe-Miami district, Arizona, b: Chuquicamata district, Chile, c: Cadia district, New South Wales, Australia, d: Oyu Tolgoi district, Mongolia.

Arrows: orientation of magmatic arcs

Sillitoe (2010)

Porphyry Cu clusters

Оюу Толгой орд

• Metallogenic provinces– linear, parallel to magmatic arc– some 100 to some 1000km– well defined metallogenic

epoch, typically 10 to 20 m.y.– slab shallowing– crustal thickening & uplift

Porphyry Cu belts and provinces

Sillitoe (2010)

Data sources: Clark (1993), Garwin et al. (2005), Hou et al. (2003), MMAJ (1998)

Cu grade and ore reserves of porphyry Cu deposits

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