The offshore tin deposits of Thailand are considered to be specially and genetically related to sea floor outcropping and subcropping granitoid plutons, at distances of up to at least 60 km from the present coastline. The cassiterite has undergone only limited transport. Pay streaks range from a few centimeters to about 1.5 m in thickness, and are locally trapped in extremely incised limestone bottom topography.

To date, most production has come from the east and southeast coast of Phuket Island, where the pioneering, and still active, Tongah Habour dredging operation began in 1907. Thereafter, exploration for offshore tin lapsed until 1957, when the Aokam tin grab-dredge was started, immediately south of Tongah Habour. However, poor recovery soon led to the conversion to bucket dredging.

Modern exploration, including both geophysical methods and drilling, began in 1968 in the eastern Thai penisula, but with little success. The search resumed in 1969 on the west coast from Ranong to Phuket, and resulted in the establishment of the TEMCO 2 (suction-cutter) dredge. Further exploration with the Department of Mineral Resources was carried out in 1972-74 in the area of the Adang-Rawee Archipelago. Although rich streaks were encountered, no mineral has been mined yet.

The most recent development is the initiation of systematic exploration along the west coast of Phangnga and Phuket Provinces, with the cooperation of UNDP and CCOP. This prospect, to commence in 1978-79, will subsequently extend to encompass much of the Gulf of Thailand.

The problems encountered in offshore mining are inherent. They are mainly due to the nature of the deposits--their overburden and subjacent bedrock topographies--and to adverse marine conditions of swell, waves, wind, and corrosion. In addition, many shallow deposits, such as those along the western coast of Phuket and Takua-Pa, are extensively depleted and invariably made sterile by numerous small operators, the majority mining illegally.