Aspects of the historical and physical geology of the Sunda Shelf essential to the exploration of submarine tin placers

Abstract

After a short summary of the geology of the region, mainly based on observations on the tin islands, the original exploration concept is explained: the off-shore area is the drowned continuation of the land area, as studied and explored on the islands, only covered by a relatively thin layer of Recent to Holocene marine mud. The formation of cassiterite placers mainly depends on four genetic factors: primary tin occurences in the basement rocks, chemical weathering of these primary occurences, elutriation or washing out, and the presence of traps. Submarine acoustic profiling has greatly helped in identifying the depositional and erosional sequences, which would not have been possible with the aid of drilling samples only. Contrary to the situation on land, there are at least three sedimentation cycles and one erosion cycle (with a total sediment thickness of up to at least 60 m), covering the Permian basement. In the last chapter the new stratigraphical data are linked up with the principles of tin placer formation, thus leading to a new, considerably less simple, exploration concept.