A COLLISIONAL COLLAGE—GEODYNAMIC SETTINGS FOR PORPHYRY COPPER DEPOSITS IN SOUTHEAST ASIA, MELANESIA, AND EASTERN AUSTRALIA

The southwestern Pacific region hosts world-class porphyry copper deposits (Batu Hijau, Grasberg, Cadia) that formed in a variety of tectonic settings: subduction-related magmatic arcs developed on continental or oceanic crust, postconvergent magmatic belts unrelated to an identified subduction zone, and composite/accreted arcs and belts. Permissive igneous map units that occur in these settings are the basis for delineating geographic areas (permissive tracts) for assessment of undiscovered porphyry copper deposits. Early Paleozoic orogenic events formed the Tasmanides of eastern Australia, where the Macquarie arc hosts nine porphyry copper deposits. Late Paleozoic subduction of the Paleotethyan Ocean and Mesozoic subduction of the Pacific Plate produced arcs of the Indochina Peninsula, none of which has been thoroughly explored. Igneous rocks associated with Cenozoic island arc-continent collisions, subduction-related magmatic arc systems (Sunda-Banda, Ambon, Halmahera, Sulawesi-Sangihe, Maramuni, Inner and Outer Melanesia), and postconvergent magmatic belts (Medial New Guinea, Central Kalimantan) define permissive tracts for Miocene-Pliocene porphyry copper deposits. Deposits are known in 18 of the 26 permissive tracts; these 47 deposits contain 100 million metric tons (Mt) of copper. An estimated 300 Mt or more of in-place copper in undiscovered deposits is predicted across the 26 tracts. About 40 Mt of undiscovered copper is estimated for a postconvergent belt that outlines hundreds of small Late Oligocene-Pliocene intrusions and volcanic rocks in Central Kalimantan; this tract, an area of active exploration, represents the most prospective tract in the study area. Other highly prospective tracts in the region outline composite arcs on the Indochina Peninsula, the accreted Macquarie island arc, a continental arc on Sumatra, and the postconvergent eastern Medial New Guinea Magmatic Belt. High costs may limit the economic viability of development in some areas.