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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
Thank you for your attention