From Rice University...

Porphyry Cu systems host some of the most widely distributed mineralization types at convergent plate

boundaries, including porphyry deposits centered on intrusions; skarn, carbonate-replacement, and sedimenthosted Au deposits in increasingly peripheral locations; and superjacent high- and intermediate-sulfidation epithermal deposits. The systems commonly define linear belts, some many hundreds of kilometers long, as well as

occurring less commonly in apparent isolation. The systems are closely related to underlying composite plutons,

at paleodepths of 5 to 15 km, which represent the supply chambers for the magmas and fluids that formed the

vertically elongate (>3 km) stocks or dike swarms and associated mineralization. The plutons may erupt volcanic

rocks, but generally prior to initiation of the systems. Commonly, several discrete stocks are emplaced in and

above the pluton roof zones, resulting in either clusters or structurally controlled alignments of porphyry Cu

systems. The rheology and composition of the host rocks may strongly influence the size, grade, and type of

mineralization generated in porphyry Cu systems