Abstract

The Ba Tơ area is a favourable condition area for forming vermiculite deposits, especially those of weathering origin. Research results have been determining 4 types of vermiculite deposits of weathering origin in this area.

- Type 1: Type of vermiculite weathered from Mg-Fe-rich biotite-hornblende gneiss of the Sông Re Complex. Ore body is in the form of layer, lens. The typical mineral association is vermiculite-kaolinite-illite-goethite.

- Type 2: Type of vermiculite weathered from ultrametamorphic Mg-Fe-rich biotite metasomatic rocks of the Sông Re Complex. Ore body is in the form of lens, nest, string layer. The typical mineral association is vermiculite-kaolinite-illite.

- Type 3: Type of vermiculite weathered from hydrothermal Mg-Fe-rich biotite metasomatic rock of the Kan Nack and Phù Mỹ Complexes. Ore body is in the form of lens, nest, string layer. The typical mineral association is vermiculite-kaolinite-illite-goethite.

- Type 4: Type of vemiculite weathered from dark coloured, K-high, phlogopite-rich vein rocks of the Hoàng Lan Complex. Ore body is in the form of lens, vein. The typical mineral association is vermiculite-kaolinite-illite-goethite.

Vermiculite ores in all mine types has clear zonation character in material composition, structure, vertical texture, similar to that of their host weathering layers. Vermiculite mineral is concentrated in medium weathering zone and lower part of high weathering layer.

Ba Tơ area is a very promising area of vermiculite of weathering origin, especially the types 2 and 3. The total resources of vermiculite in Ba Tơ area calculated to December 2009 is 5.51 million tons, in this the type 2 resources are about 2.45 million tons, the type 3 – 3.16 million tons of vermiculite.