Identifikasi Keterdapatan Thorium pada Endapan Laterit Bauksit di Daerah Nanga Tayap – Sandai, Kabupaten Ketapang, Kalimantan Barat

The results of regional uranium and thorium surveys in Ketapang District, West Kalimantan Province conducted using RS 125 gamma ray detectors obtained anomalous uranium and thorium zones on bauxite laterite deposits that occupy Kerabai volcanic rock, Sukadana granite and basalt Bunga in Nanga Tayap and Sandai areas. The Sandai and Nanga Tayap areas are a bauxite laterite mining area. The purpose of this research is to know thorium availability at bauxite laterite deposit because bauxite laterite distribution in Indonesia is quite abundant. The method used is by making test pit on Kerabai volcanic rock, Sukadana granite and basatl Bunga, sampling soil / rock at test pit and analyzing thorium and aluminum element content. The results of this study concluded that the highest thorium level is found in the test pit in the basalt Bunga area reaching 115 ppm whereas the lowest is in the Kerabai volcanic rock area of 28 ppm. In the area of Sukadana granite and basalt Bunga elements of thorium and aluminum are not correlated but in the volcanic Kerabai rocks correlate quite well. In the granite area thorium enrichment occurs in the zone between limonite and saprock, whereas in the basalt Bunga occurs in the saprolith zone and in the Kerabai volcanic rock occurs in the limonite zone.