Metal transport and ore deposition in porphyry copper ± gold ± molybdenum deposits - contrasting behaviour between deep and shallow environments

High-grade zones typically develop in the Ksilicate- altered centre of porphyry deposits, where copper ą gold ą molybdenum are localised in and around the apex of the intrusion. Mineralisation develops in spatial and temporal association with abundant quartz ą magnetite ą orthoclase ą biotite ą anhydrite as veins, breccia cement and alteration minerals. Multiple generations of stockwork veins ą magmatic-hydrothermal breccias are common and provide evidence for repeated cycles of fluid release from the magma reservoir. Unmixing of brines and vapours from supercritical fluids (deep-level porphyries) and/or direct exsolution of these two phases from the intrusive complex (shallow-level porphyries) are essential prerequisites to ore formation. The brines contain most or all of the oreforming components, and have densities that restrict their occurrence to the apex and shoulders of the mineralising intrusion, where potassic alteration and mineralisation occurs. The vapour passes through the mineralised centre of porphyry deposits, ascending rapidly to the nearsurface environment, where it may form a lithocap.