抄録
The tin in Indonesia is mainly exploited from placers containing cassiterite. Chemical analysis by the author made clear that mother rocks which liberate the placers belong to the tin granites of the Collision type, which has more popularity in Europe and the United States than the Cardilleran type of Japan.
One hundred and nine sampling sites which are located within placers to check the grade distribution indicated that economically rich cassiterite concentrations are limited to an area within 14 to 15 km from the fringes of the granitic mother rocks under the existing topographic and climatologic environment of the Tin Islands of Indonesia.
