Original paper

Garnet-gahnite-staurolite relations and occurrence of ecandrewsite from the Koparpani base metal sulfi de prospect, Betul Belt, Central India

Ghosh, Biswajit; Praveen, M.N.


The origin of gahnite and its relationship with coexisting porphyroblasts of garnet and staurolite (zinc-bearing) was studied in metamorphosed syn-volcanic hydrothermally altered rocks associated with base metal mineralization from the Proterozoic Koparpani Zn-Pb-Cu sulfide occurrence, Betul Belt, central India. Gahnite and zincian staurolite are the product of desulfidation of primary sphalerite during metamorphism. Garnet was present all along as the sole Mn-bearing phase. All these porphyroblasts were formed in a single metamorphic regime of continually decreasing growth kinetics generally linked to progressive cooling (diffusion zoning). Mineral composition data are in conformity with the metamorphic history. We report the first description of zincian ilmenite-ecandrewsite from the area. Two compositionally and petrographically distinct populations (Zn-poor and Zn-rich) of ilmenite-ecandrewsite solid solutions are recorded. The compositions of coexisting zincian ilmenite and gahnite suggest that these two minerals did not form in equilibrium over the range of metamorphic conditions.


gahniteecandrewsitezincian staurolitehydrothermal alterationbetul belt