paleo-channels of singkawang waters west kalimantan and its relation to the occurrences of sub-seabottom gold placers based on strata box seismic record analyses

Strata box seismic records were used to analyze sub-seabottom paleochannels in Singkawang Waters, West Kalimantan. Based on the analyses, it can be identified the distribution and patterns of paleochannels. Paleo channel at northern part of study area interpreted as a continuation of Recent coastal rivers; and at the southern part, the pattern radiates surround the cone-shaped morphology of islands, especially Kabung and Lemukutan Islands. Paleochannels of the study area belong to northwest Sunda Shelf systems that terminated to the South China Sea. A study on sequence stratigraphy was carried out to better understanding sedimentary sequences in the paleochannels. This study is also capable of identifying placer deposits within the channels. Based on criterias of gold placer occurrence such as existence of primary gold sources, intense chemical and physical weathering to liberate gold grains from their source rocks of Sintang Intrusive. Gravity transportation that involved water media, stable bed rock and surface conditions, caused offshore area of Singkawang fulfill requirements for gold placer accumulations. Chemical and physical whethering proccesses from Oligocene to Recent, approximately 36 million, might be found accumulation of gold placer on the seafloor. Based on grain size analyses, the study area consisted of sand 43.4%, silt 54.3% and clay 2.3%. Petrographic examination of the sample shows gold grains about 0.2%.