porphyry systems

Some info on porphyry systems for those like myself who lack the technical background.

Porphyry deposits are the world's most important source of Cu and Mo, and are major sources of Au, Ag, and Sn;
significant byproduct metals include Re, W, In, Pt, Pd, and Se. They account for about 50 to 60% of world Cu production
and more than 95% of world Mo production. In Canada, they account for more than 40% of Cu production, virtually
all Mo production, and about 10% of Au production. Porphyry deposits are large, low- to medium-grade deposits
in which primary (hypogene) 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, although they range in size from
tens of millions to billions of tonnes; grades for the different metals vary considerably but generally average less than
1%. In porphyry Cu deposits, for example, Cu grades range from 0.2% to more than 1% Cu; in porphyry Mo deposits,
Mo grades range from 0.07% to nearly 0.3% Mo. 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. A close temporal and genetic relationship
between magmatic activity and hydrothermal mineralization in porphyry deposits is indicated by the presence of intermineral
intrusions and breccias that were emplaced between or during periods of mineralization. Porphyry deposits
range in age from Archean to Recent, although most economic deposits are Jurassic or younger.