Abstract:

Vermiculite in Red River and Fan Si Pan zones was formed by weathering processes. The bedrock containing vermiculite crust were rich – Iron - magnesium biotite metamorphic rocks; they were all products of metamorphic mafic rocks, and ultramafic rocks of ancient continental crust fragments formed in the Proterozoi. In the study area, there are three types of potentional vermiculite deposits: 1) Vermiculite - hydrobiotite type weathered from hornblende biotite gneiss, and biotite hornblende schists; 2) Vermiculite - hydrobiotite type weathered from amphibole gneiss, biotite amphibolite gneiss in the complex of the amphibolite migmatite that were been migmatited; 3) Vermiculite - hydrobiotite type weathered from the amphibole gneiss, biotite amphibolite gneiss of the complex amphibolite penetrated by intrusive granites, pegmatites enriched potassium feldspar. The general prospecting criteris for all 3 types of deposit are: Petrologo-tectonic; texturo - structural; geomorphological; and the weathering crust. In addition, each type of deposit has their own criteris. There are 2 groups of prospecting signs for vermiculite in the study area: The direct prospecting signs including ore showings in the weathered crust.; they have different colours: golden brown-brown, yellow, green, turmaline- liked colour. The indirect prospecting signs including rolling fragment containing vermiculite, deluvial vermiculite or in the products of dark brown weathering, the metasomatic zone or biotite - rich contact - metamorphic zone, the exposed hornblende biotite gneiss, biotite hornblende schist, and areas of amphybole, amphybolite gneiss accompanied by migmatite