Gold and copper deposits in Southeast Asia and the west Pacific occur largely in middle to late Cenozoic (25–1 Ma) magmatic arcs. The region contains more than 160 deposits, including porphyry, skarn, high-, intermediate- and lowsulfidation epithermal, volcanic-associated massive sulfide and disseminated sedimentary rock-hosted deposit styles. The combined past production and current resources of these deposits totals about 15,000 tonnes (t) Au and 115 million tonnes (Mt) Cu. The majority of the gold and copper are contained in porphyry (8,742 t Au, 97.1 Mt Cu), intermediate-sulfidation epithermal (2,659 t Au), lowsulfidation epithermal (1,837 t Au), and skarn (983 t Au, 9.2 Mt Cu) deposits.

Twenty major magmatic arcs and several less extensive arcs of Cenozoic age form a complex border to the Sundaland core of the Eurasian plate in Southeast Asia and the northern margin of the Australian continent. The volcano-plutonic chain extends >17,000 km from Japan in the northeast, through Taiwan, Philippines, Indonesia, Malaysian Borneo, and Papua New Guinea, to Myanmar in the northwest. The arcs are constructed on continental and oceanic crust. The geometries of individual arc segments are complex and typically the product of subduction, locally involving polarity reversals, seamount subduction, obduction, arc-arc and arc-continent collisions, rifting, and transcurrent faulting. Three major episodes of platere organization, at ~45, 25, and 5 Ma, have contributed to the present configuration of the arcs. These reorganizations are characterized by collisional events that changed plate boundaries and motions.

Most of the deposits developed during episodes of plate reorganization and local variations in arc stress regimes during the early Miocene, middle Miocene, and the Plio-Pleistocene. Hydrothermal systems were active for durations of <100,000 years. Arc-continent collisions and the subduction of buoyant aseismic ridges vary the orientation of predominantly arc-orthogonal stress fields and induce episodic reactivation of crustalscale fault systems in transpressional to transtensional settings. In both continental and oceanic arcs, subduction hinge retreat, kinks or tears in the downgoing slab, or instabilities in the mantle localize asthenospheric upwelling. The spatial coincidence of kinks in the downgoing slab with arc-transverse fault zones in the overlying arc provides a link between the mantle and upper levels of the crust, which promotes rapid magma ascent and high heat flow. The zone of enhanced permeability creates channels for hydrothermal fluids and the efficient release of metal-bearing volatiles exsolved from melts at high levels in the overlying arc (e.g., <4 km beneath paleosurface).

The distribution of deposits reflects differences in structural and tectonic setting and composition of the underlying crust. Many of the deposits are spatially and temporally related to intrusions and volcanic centers in calc-alkaline to alkaline andesitic-dacitic arcs. Porphyry, skarn, and high- and intermediate-sulfidation epithermal deposits occur typically in contractional to neutral arc settings and are closely related to shallow intrusions, volcanic centers, and, locally, diatremes. Disseminated sedimentary rock-hosted (Carlin-like) deposits occur in calcareous rocks both proximal and distal to intrusive centers in neutral to mildly extensional arc settings. Lowsulfidation epithermal systems are associated with intra-arc and backarc grabens and extensional settings that control bimodal basaltic-rhyolitic volcanism in Japan and K-alkaline magmatism in Papua New Guinea. Volcanic-associated massive sulfide and related deposits are developed in sea floor extensional settings, sharing similarities with onland, lowsulfidation epithermal systems.

The abundance and large size of Plio-Pleistocene deposits are not only related to collisional tectonic events but are also a function of erosion, given the high uplift and exhumation rates (~0.5 mm/yr) of their host arcs. In late Quaternary arcs, uplift and erosion have not exposed mineralized systems concealed beneath coeval or younger rock sequences. In contrast, erosion has mainly removed potentially economic deposits in Cretaceous and Paleogene arcs. Changes in the local stress regime and structural setting may facilitate arc and deposit preservation through the development of extensional basins and concealment beneath younger rock sequences. Hence, the dynamic tectonic environments of Southeast Asia and the west Pacific not only play a part in the formation of hypogene gold and copper deposits but also in their erosion and local preservation.