Abstract
Thailand is now very famous for its.large tin production due to the development of many tin deposits in granites and its weathered derivatives accompanying kaolin deposits, especially in the Southern Peninsula of Thailand forming a main tin production area.
The tin-bearing granites, are probably of late Cretaceous age and called "Younger granite". They intrude into the rocks belonging to the upper Cambrian Phuket series consisting of slate, phyllite and quartzite. The distribution of individual granite body has northerly trend in Ranong Province. The tin-bearing granites include much variation of petrographic features due to those of grain size as well as the subordinate mineral species, such as a coarse-grained tourmaline granite, a medium-grained tourmaline granite 'and a medium-grained muscovite tourmaline granite, etc. They suffer intense alterations including tourmalinization, sericitization and kaolinization.
The kaolinization is probably due to remarkably developed weathering under the tropical climate condition, making the formation of placer-type tin and kaolin deposits possible. The primary tin deposits were formed in the granites by dissemination of cassiterite, accompanied by accessory amounts of ferberite (-wolframite), monazite, xenotime, ilmenorutile and spessartine, which are found in the tailing products of the dressing process of tin ores. The kaolin deposits have kaolinite as the dominant ore mineral accompanied by a subordinate amount of sericite.
The laboratory test for the separation of these accessory minerals and kaolinite group minerals was. successfully made. Cassiterite is concentrated at the heaviest part; while the other accessory heavy minerals remains in the tailing.
A rare mineral of ilmenorutile was identified with its microscopic character and X-ray reflection pattern. According to the results of the X-ray, D. T. A. and electron microscopic studies of them, kaolinite is almost pure and equigranular grains with hexagonal tabular form.
As compared with kaolinite from sedimentary origin (e. g. Ipoh, Malaysia), this kaolinite consists of various size of fine crystals because of its unsorted origin. The highest peak of the grain-size histogram is obtained at 5-7μ.
