Quaternary geology related to gemstone deposit in Bo Phloi Basin, Amphoe Bo Phloi, Changwat Kanchanaburi

Bo Phloi district of Kanchanaburi province is one of the major famous source of blue sapphire in Thailand. It is thus the aim of this research is to study the characteristics of gemstone deposits, their paleoenvironment and source rocks and to investigate the relationship among the sedimentary characteristics, gemstone deposition and landforms of the area and finally the gemstone distribution will be delineated. The unconsolidated deposits can be divided by its sedimentary structures and textures into eight lithofacies as massive gravels, forest- bedded gravels, trough and wedge-shaped cross bedded sand, cross-lamination sand, forest laminated sands, planar stratified sand, horizontal laminated silt, and silty and muds. Geomorphologically, landforms in the study area, which consist of hilly and mountainous terrain and lowland area, can be divided into three main units as denudational, fluvial-colluvial and fluvial landforms. From the results of this study, it can be concluded that gemstones are related directly to landforms and their stratigraphic position of the deposits. Low terrace and floodplain are found to be the gemstone depositional landforms. Gemstone paystreaks are normally found in the gravel bed and forest-bedded gravels. Moreover, basalt is believed to be the main source of sapphire in this area. The age of the basalt is late Pliocene and crops out at Khao Lan Tom and Huai Nam Pu (Huai Ma Kah) . Based on landforms, gemstone depositional deposits and carbon-14 dating, it can be concluded that gemstone paystreak developed by river processes during the Quaternary. The distributional area of gem-bearing gravel beds are delineated trending from the north to the south and covered about one hundred square kilometers.