TECTONIC SETTING AND GOLD-COPPER MINERALIZATION IN CENOZOIC MAGMATIC ARCS OF SOUTHEAST ASIA

Most gold and copper deposits in Southeast Asia occur in 30 to 1 Ma magmatic arcs. The most common include porphyry, skarn, high- and low-sulfidation epithermal, disseminated sedimentary rock-hosted and volcanogenic massive sulfide deposit styles. The combined past production and current resources of these deposits exceeds 8,500 tonnes (t) gold and 65 Mt copper.

Fourteen major Cenozoic magmatic arcs form a complex volcanic-plutonic chain that extends >12,000 km along the edge of the Sundaland craton of the Eurasian Plate and the northern margin of the Australian platform. The arcs formed on oceanic and continental crust. The geometry of individual arc segments is complex and the product of subduction, locally involving polarity reversals, seamount subduction, obduction, arc-arc and arc-continent collisions, rifting and transcurrent faulting.

The large abundance of Plio-Pleistocene deposits relates to periods of plate tectonic reorganization, including the 5 Ma collision of the Philippine Sea Plate with the Eurasian Plate near Taiwan and the 4 to 3 Ma docking of the Australian platform with the Banda arc in Indonesia. The subduction of buoyant, aseismic oceanic plateaus beneath Sumbawa, Indonesia and northern Luzon, Philippines have localized mineralization at Batu Hijau (3.7 Ma) and Far Southeast - Lepanto (1.4 Ma), respectively. These collisional tectonic events and subduction of aseismic ridges vary the orientation of predominantly arc-orthogonal compressive stress fields and induce episodic reactivation of crustal-scale fault systems in transpressional to transtensional settings.

The distribution of deposits reflects differences in tectonic setting and composition of crustal basement. In both continental and oceanic arcs, kinks or tears in the subducting slab, slab rollback or instabilities in the mantle, localize asthenospheric upwelling. The spatial coincidence of kinks in the down-going slab with fault zones in the overlying arc promotes magma ascent and high heat flow by providing a link between the mantle and the upper levels of the crust. This zone of enhanced structural permeability facilitates the rapid ascent of magma to high-levels in the overlying arc lithosphere (e.g. depths of < 3 km beneath the paleosurface), where volatile exsolution and metal deposition may occur.