Granite Magmatism in the Tin Belt of South-East Asia

Abstract

The tin belt of SE Asia, which is about 3500 km long and 400–800 km wide (Figure 1), is probably one of the best examples of a metallogenic province. The world's annual tin production (about 230 000 tonnes) is currently valued at about 3 x 109 US dollars and about 60% of this production comes from SE Asia. More dramatically, it is estimated that this metallogenic province has yielded about three-quarters of the world's total tin production during the present century. Most of the tin ore in SE Asia is mined from Quaternary placers, both onshore and offshore, and a steadily rising proportion of the annual production is from offshore dredging operations in increasingly deep water. In 1978, for example, about 35% of Indonesia's tin production was derived from offshore operations. It is anticipated that with the introduction of giant dredgers, designed to work in waters more than 30 m deep, offshore operations will account for about half of Indonesia's tin production by the early 1980s. The tin ore mineral, cassiterite (SnO2), has been concentrated in the alluvial, eluvial or residual gravels of these placer deposits by a fortunate combination of two factors: (a) deep tropical weathering due to the climate (cassiterite is dense and resistant to weathering); and (b) Quaternary topography in relation to changes in erosional base level (producing thick alluvial `flats'). Current tin production from deep mining of primary tin mineralization is less significant, although a large number of small-scale operations do exist.