Abstract - Hydrothermal copper & gold deposits associated with felsic intrusives, particularly porphyry related and epithermal ores, are found in a series of extensive, narrow, linear metallogenic provinces throughout the world. These are predominantly associated with the great Mesozoic to Cainozoic orogenic belts. Major deposits however, are also found within Palaeozoic orogens, while a few are known from the Precambrian. The style and setting of these deposits is variable and diverse, although many common features emerge from a global comparison.

Porphyry Cu deposits in the Chilean and Argentinian central Andes occur in a series of orogen-parallel magmatic arcs, which migrated episodically eastward since the Early Cretaceous. The three Cenozoic belts, corresponding to Paleocene-early Eocene, middle Eocene-early Oligocene, and Miocene-early Pliocene epochs, cut obliquely across a composite belt of subeconomic porphyry Cu mineralization formed at several times during the Late Carboniferous to Triassic interval.

Copper-molybdenum and copper-gold porphyry deposits in the Quesnel terrane occur in association with either calc-alkalic or alkalic intrusive suites respectively, emplaced within a succession of island arc volcanic rocks that are of Late Triassic to Middle Jurassic or Late Cretaceous to Eocene age. The Highland Valley porphyry district, in southern British Columbia, consists of five major copper-molybdenum deposits, Valley, Lornex, Bethlehem, Highmont and J A, located within a fifteen square kilometre area in the centre of the Guichon Creek batholith. The batholith is a Late Triassic calc-alkalic intrusion that REE data suggest was derived from either subducted oceanic crust or depleted mantle. The crystallisation age of the batholith, based on U-Pb zircon analyses, is 210 Ma. Mineralisation occurred in late magmatic and early post magmatic time. Oxide analyses suggest a single source magma but younger phases were locally injected into older due to tectonic forces. The earliest deposits occurred after separation of a fluid phase that is marked by a sharp discontinuity in the evolution path of the alkali oxides.

Newly-recognised porphyry-style mineralisation within the Ertsberg intrusion displays significant differences from porphyry mineralisation at the Grasberg porphyry Cu-Au deposit. Stockwork mineralisation in the Ertsberg occurs near the giant East Ertsberg Skarn System, close to the northern margin of the intrusion. Stockwork mineralisation in the diorite is spatially associated with 5-15 m wide, E-striking, dykes of porphyritic hornblende monzonite that cut equigranular Ertsberg diorite. The porphyry dykes strike parallel to major district structures and occur where those structures project into the Ertsberg intrusion. Hornblende abundance greater than biotite, the much greater content of sphene, a paucity of broken phenocrysts, and the aplitic groundmass distinguish the porphyry dykes in the Ertsberg Stockwork Zone from the finer-grained groundmass Kali dykes of the Grasberg deposit.