Mineralogy of Tin and Niobium-Tantalum-Bearing Minerals in Thailand

Abstract

Mineralogical study of panned concentrates from the Omkoi area, Northern Thailand, and several products from the concentrator plant of Patana Mine, Central Thailand, and Chaiyayuth dredge, Tantikovit Mine and Loon Seng Mine in Southern Thailand was carried out by microscopic and electron microprobe examination of polished section. The results show that the common Nb-Ta-bearing minerals associated with cassiterite are columbite-tantalite and Nb-Ta rutile with some samarskite and tapiolite. The associated heavy mineral suite is ilmenite, garnet, monazite, rutile, zircon, tourmaline, maghemite, anatase, xenotime, topaz, scheelite, wolframite, martite, geothite, Mn-oxides, pyrite, arsenopyrite, spinel, lepidocrocite, marcasite and limonite, with some beryl, allanite, magnetite and hematite. In general cassiterite, columbite-tantalite, Nb-Ta rutile and samarskite from the three different areas have similar characteristics as follows: Cassiterite occurs mostly as free particles, anhedral crystals, brownish-grey in colour, weak bireflectance, commonly of twinned habit and showing reddish-white to brownish-white internal reflections. Some cassiterite is intergrown with columbite-tantalite, quartz, and to a lesser extent with Nb-Ta rutile in simple and mottled type intergrowths. Columbite-tantalite in general occurs as free particles, as small inclusions in cassiterite, and intergrown with cassiterite as well as quartz in simple and mottled type of intergrowth. Some columbite-tantalite shows replacement by microlite along the margin and/or along the fractures of the particles. From Omkoi area, columbite-tantalite replaced by tapiolite is also observed. Nb-Ta rutile is present as homogeneous and inhomogeneous particles. Homogeneous Nb-Ta rutile particles show a grey colour with weak bireflectance, strong anisotropism from reddish-grey to dark brown and a common twinned habit, while inhomogeneous Nb-Ta rutile particles consist of a grey Ta-rutile groundmass with dark grey patches of columbite-tantalite inclusions. These columbite-tantalite inclusions form irregular bodies in a wide size range and evenly distributed throughout the groundmass. Some Nb-Ta rutile is intergrown with cassiterite and/or quartz in simple intergrowth. Samarskite occurs as anhedral to subhedral, grey colour, with weak bireflectance and weak anistropism and having distinct light brown to dark brown internal reflections. A comparison of the general characteristics of Nb-Ta-bearing minerals in Thailand and Malaysia are as follows: Nb-Ta-bearing minerals are closely associated with tin-bearing pegmatites along the Western Tin Belt of the Burma-Thai-Malaya orogen. In general columbite-tantalite in Thailand contains higher Ta than Nb, and tends to be high in Fe in the north, whereas in the south, Mn is predominant. In Malaysia, columbite as well as ferro-columbite is more common than tantalite. In the southern part (Bakri) Mn-tantalite with Ta-rich series such as wodginite and tapiolite are also observed. Struverite (Ta-rutile) is more common than Nb-rutile in Thailand and is present as both homogeneous and inhomogeneous particles (with exsolution bodies of columbite-tantalite): whereas in Malaysia Nb-rutile, which occurs as inhomogeneous particles, is more common than Ta-rutile. Tungsten is present everywhere as a trace constituent in columbite-tantalite from Thailand, whereas in Malaysia tungstenian-columbite has been reported. No well-defined zoning of columbite-tantalite relative to cassiterite is apparent from the mineralogical data. From an operation point of view, the data reported here suggest that by carefully applying controlled magnetic and high tension separation to the magnetic products from the mine, is should be possible to obtain a columbite-tantalite concentrate with fairly high recoveries.