GEOLOGICAL, MINERALOGICAL, AND GEOCHEMICAL STUDIES OF VOLCANOGENIC MASSIVE SULFIDE DEPOSITS IN BETUL BELT, CENTRAL INDIA

Abstract

The Paleoproterozoic polymetallic sulfide deposit in the Betul belt is located in the southwestern part of the Central Indian Tectonic Zone, Central India. These deposits are known for low ore-grade, zinc-rich sulfide mineralisation. The origin, size, and low ore grade have been a matter of academic interest for the last two decades. Volcano-sedimentary rocks are the principal rock types that cover the area. The sulfide mineralization is hosted mainly by the meta-rhyolites and metapelites. Sulfide mineralization and syn-volcanic hydrothermal alteration in the Betul belt are associated with bimodal submarine volcanism. The mineralization and hydrothermal alteration are overprinted by upper amphibolite facies metamorphism. The principal sulfide minerals (sphalerite, chalcopyrite, pyrite, galena, and pyrrhotite) are intimately associated with metamorphic mineral assemblages (gahnite, garnet, sillimanite, staurolite, anthophyllite, biotite, ilmenite, and chlorite). Eight prominent deposits have been discovered across the belt so far, and exploration activities are proactively being undertaken in the area by the Geological Survey of India. The geochemical studies reveal that sphalerite, the most abundant sulfide mineral, contains high Mn (3533 ppm) and In (33 ppm). Elements like Ga, Ge, and Ag are low in abundance, while Bi, Pb, and Sb are detected in sphalerite. Similarly, pyrites show high Co/Ni >1 with variables Ni, Ti, Se, As, and Mn. Sphalerite and pyrite geothermometry unveil the ore formation temptemperatures0C to 4020C and 2250C to 4840C, respectively. Geochemical discrepancies in the sulfide minerals are because of overprinted metamorphism, which recrystallizes and remobilizes sub-microscopic inclusions from the minerals. Sphalerite, pyrite, and chalcopyrite show distinct and a range of δ34S values 7.27–7.79‰, 8.37–8.61‰, and 6.58– 6.72‰, respectively. The total sulfur in ore-fluid is mainly derived from the seawater sulfate by thermochemical reduction (TSR) and little input from a magmatic fluid source. The carbonate veins indicate that the carbonate formed due to seawater mixing with the hydrothermal fluid. The carbon and oxygen isotope values for the carbonate veins are δ13C: −6.0 to −13.45‰ with an average value of −9.51‰, n = 7; δ18O: 7.32‰ to 20.58‰ with an average value of 15.65‰. All these processes collectively led Zn-Pb-Cu mineralization in the Betul belt.