Deposit types/Copper, Molybdenum, Gold

Porphyry copper

Copper sulphide in many fine veinlets and scattered grains through a large body of altered porphyry rock and the rock around it.

What it is

Copper sulphide in many fine veinlets and scattered grains through a large body of altered porphyry rock and the rock around it.1,2

How it forms

High-level porphyry intrusions with dykes and breccia pipes form during arc volcanism. Chalcopyrite is carried in stockwork veinlets. Alteration runs in zones from sodic-calcic and potassic at the core through phyllic and argillic to propylitic at the edge. Weathering can leach copper from the top and re-deposit it near the water table as chalcocite.1,2

Host rocks

Tonalite to monzogranite or syenite porphyry cutting granitic, volcanic and carbonate rocks.1,2

Where it forms

Rift zones during volcanism along convergent plate boundaries (Andean or island-arc), later uplifted and eroded.1,2

How old

Mainly Mesozoic and Cenozoic, but any age1,2

How geologists look for it

Alteration zoning (potassic core to propylitic edge), copper-molybdenum-gold geochemistry in the centre with lead, zinc and arsenic outside, and leached outcrops stained by iron oxide.1,2

Mines of this type

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Mines

An example ofChuquicamataSee Chuquicamata, an example of this deposit type.1An example ofEscondidaSee Escondida, an example of this deposit type.1An example ofEl TenienteSee El Teniente, an example of this deposit type.1An example ofMorenciSee Morenci, an example of this deposit type.1An example ofBagdadSee Bagdad, an example of this deposit type.1An example ofSierritaSee Sierrita, an example of this deposit type.1An example ofCuajoneSee Cuajone, an example of this deposit type.1An example ofToquepalaSee Toquepala, an example of this deposit type.1An example ofCerro VerdeSee Cerro Verde, an example of this deposit type.1An example ofLas BambasSee Las Bambas, an example of this deposit type.1An example ofOyu TolgoiSee Oyu Tolgoi, an example of this deposit type.1An example ofPanguna mineSee Panguna mine, an example of this deposit type.1

Sources

  1. Mineral Deposit Models (Bulletin 1693, Cox and Singer, eds., 1986) US Geological Survey
  2. Mineral Deposit Models for Resource Assessment, Chapter B: Porphyry Copper Deposit Model (SIR 2010-5070-B) US Geological Survey

From the Prospector Trails mining history dataset: each fact links to the source it was checked against. Figures are as the source gives them, in the money of their day. Not investment advice.

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Cover photos from Wikimedia Commons: Haul trucks by Lechhabmed, CC BY-SA 4.0. Pictures: Falu gruva, Lundberg, Bengt A / Europeana (CC0 1.0); Escondida Mine, Chile, NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team (Public domain (NASA media, no copyright)).