Porphyry Copper Gold Deposit Model
Porphyry deposits are the world's most important source of Cu and Mo, and are major sources of Au, Ag, and Sn. They account for about 50 to 60% of world Cu production and more than 95% of world Mo production. Porphyry deposits are large, low- to medium-grade deposits in which primary ore minerals are dominantly structurally controlled and which are spatially and genetically related to felsic to intermediate porphyritic intrusions. They are distinguished from other granite-related deposits such as skarns and mantos by their large size and structural control, mainly stockworks, veins, vein sets, fractures, and breccias. Porphyry deposits typically contain hundreds of millions of tonnes of ore. In porphyry Cu deposits, for example, Cu grades range from 0.2% to more than 1% Cu while in porphyry Au and Cu-Au deposits, Au grades range from 0.2 to 2 g/t Au. Associated igneous rocks vary in composition from diorite-granodiorite to high-silica granite; they are typically porphyritic epizonal and mesozonal intrusions, commonly subvolcanic.
Known deposits within the Lachlan Fold Belt include the world class Cadia/Ridgeway copper-gold system and the Northparkes copper deposits, associated with Silurian alkaline and calc-alkaline intrusions.