Multiple Origins of Gahnite Associated with Hydrothermal Alteration from the Bhuyari Base Metal Prospect of Proterqzoic Betul Belt, Madhya Pradesh

Multiple origin of gahnite of different generations and their relationship with other coexisting minerals like garnet, biotite, chlorite and sphalerite were studied in metamorphosed synvolcanic hydrothemally altered rock associated with base metal mineralisation from the Proterozoic Bhuyari prospect, Betul Belt, Central India. The present assemblages appear to be the result of overprinting of arnphibolite grade metamorphism on primary hydrothermal alteration products. Gahnite is found in a quartz + biotite + muscovite + pLagioclase + gahnite + garnet + chlorite assemblage. Petrographic evidence with supporting mineral composition data suggests the presence of two generations of gahnite. The first generation gahni te is found surrounding sphalerite grains and may be the product of desulphidation of primary sphalerite involving first generation garnet. Second generation gahnite show petrographic evidence of transformation from biotite and might be the result of overstepping of the zinc saturation limit of biotite during alteration to chlorite. The Bhuyari area was subjected to one prograde event followed by a retrograde metamorphic event and mineral paragenesis is in conformity with the metamorphic hlstory.