Relationship between Sn mineralization and geochemical anomalies in non-residual overburden at Tebrong area, Belitung, Indonesia

The Southeast Asia Tin Research and Development (SEATRAD) Centre initiated a project to study the relationship between Sn mineralization and geochemical anomalies in non-residual overburden at and around Tebrong in the Lenggang district of Eastern Belitung, located about 400 km north-northeast of Jakarta. Belitung island, with a land surface area of about 5000 km², forms the easternmost expression of the Southeast Asian tin belt.There is essentially no outcrop, only minor scattered float in the study area. Drainage is very poorly developed and consists of several small creeks. The climate is tropical with a mean daily maximum temperature of 33°C, and an average annual rainfall of about 2000 mm. The watertable is at approximately 5 m depth, depending on seasonal rainfall and local elevation.The oldest rock sequence in the study area is a Triassic metasediment consisting of sandstone, phyllite, claystone, mudstone and quartzite. These rocks are intruded by Triassic granitic plutons. The Tebrong area is underlain by low-grade Sn mineralization consisting of swarms of <0.5-cm-thick subvertical quartz - tourmaline - kaolinite - chlorite - cassiterite veins. In general, cassiterite is present in quartz veins which occur as fracture fillings in the country rocks. These rocks are overlain by Quaternary cassiterite-bearing alluvium (kaksa). Residual lag kaksa typically occurs on Belitung.In the central part of the study area where there is a thick alluvial cover, the soil is mostly transported material. Surface soil geochemically anomalies are absent, but near bedrock, weak anomalies can delineate placer concentration of Sn.Based on the findings of the initial survey, it can be concluded that the distribution of Sn in non-residual overburden does not reflect bedrock Sn distribution. However, geochemical soil profiling, using a motorized auger, can be usefully employed to delineate target areas for further exploration for placer Sn.