Metallogenesis in SE Asia

Abstract

Southeast Asia may be subdivided into three distinct metallogenic provinces— ( a ) peripheral Cenozoic volcanic arc, ( b ) Mesozoic Sundaland core, and ( c ) cratonic China north of the Red River Suture: a is a major producer of copper with minor gold and silver; b is the World's foremost producer of tin with subordinate tungsten and antimony; c is the World's premier tungsten and antimony province, with subordinate tin and mercury. Ophiolites, obducted since the Palaeocene from Pacific and marginal basin lithosphere, yield substantial chromite, increasing amounts of nickel from residual laterite, and massive Cyprus-type sulphides. Palaeocene to Miocene dioritic stocks, within the ensimatic arcs of the Philippines and north Sulawesi, contain important porphyry coppers. Gold and silver are important associates, but molybdenum is rare. Kuroko-type sulphides and mesothermal copper-gold vein deposits are important in the Philippines and Taiwan. Epithermal gold-silver telluride vein deposits are more widespread throughout the Cenozoic volcanic arc. Tin mineralization, spatially related to acid granitoids of Permo–Triassic age in Indonesia and the Malay Peninsula and of Cretaceous age in Phuket and Tenasserim, is widespread in province b. Important lode deposits are confined to Billiton and the East Coast Belt of the Peninsula, emplaced within the zone of fracture around high level granitoids. Some stratiform iron-tin deposits characterize this Eastern Belt. Other tin fields, which yield the bulk of the region's production, contain few worthwhile lode deposits. Huge amounts of tin have been produced from the contact zones of large deep-seated batholiths in Bangka, along the Main Range of the Malay Peninsula, and in the Phuket region of Thailand. The tin has been concentrated in Quaternary placers by the favourable combination of climate and topography. In the Southern Shan States and north Thailand, the deposits are associated with Triassic granites and have yielded more tungsten than tin, as well as significant amounts of antimony. Major tungsten and less important tin deposits are associated with Mesozoic granitoids in the Caledonian foldbelt of southeastern China. The important antimony and mercury occurrences lie on the continental side of the tungsten-tin belt. Gold, antimony and mercury mineralization is associated with Tertiary igneous rocks in West Borneo, and mercury occurs in Palawan island. Iron contact-metasomatic and sedimentary ore deposits are associated with the Mesozoic igneous rocks in China and Sundaland, and with Cenozoic dioritic rocks in the Philippines. The metallogenic zonation of China may be related to subduction of oceanic material beneath a continental margin, persistent since the early Mesozoic. In SE Asia, more complex patterns of subduction have resulted in less well defined metal zonation in the continental regions. Cenozoic mineralization in the Philippines and Indonesia resulted from convergent tectonics of great complexity involving both continental and oceanic crust of diverse origins.