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.