Petrology, Geochemistry and Fluid Inclusion Studies of Cu-Au Mineralization in Paleoproterozoic Salumber-Ghatol Belt, Aravalli Supergroup, Rajasthan
Authors: Fareeduddin  , Kirmani I. R. , Chander Suresh 
Published: July 2012

The Salumber-Ghatol belt in Rajasthan, India, situated along southern margin of the Aravalli Craton, hosts a cluster of Cu-Au deposits in calcitic and dolomitic marbles that belong to Debari Group of the Paleo-mesoproterozoic Aravalli Supergroup. The Fe-Mn rich dolomitic marble of the Delwara Formation hosts Cu-Au-Fe-oxide mineralization at Ghagri and associated distal K-Fe-Mg rich altered rocks (cryptocrystalline microcline + magnesioriebeckite + magnetite + phlogopite) and proximal feldspathised carbonate rocks (medium grained albite + microcline + dolomite + magnetite). The calcitic marble of Mukandpura Formation hosts Dugocha Cu-Au deposit with development of distal graphite-tourmaline-bearing albitites and proximal albite-microcline-magnetite rocks. Calcite and dolomite carbonates of Bhukia region with development of albite-actinolite-bearing alteration assemblages host the largest of the Cu-Au deposits in this belt. The second generation folds and associated ductile-brittle shear zones of the multiply deformed events constitute conduits for the mineralizing fluids at all locations in this belt.

Carbon isotope data for the dolomitic marbles of Ghagri area suggest mixed isotopic signatures: (i) normal marine values close to zero per mil (mean= -0.269 ‰) and (ii) enriched positive values (mean= + 4.04 ‰) akin to the 1.9 Ga global event of positive excursion. The calcitic marbles of Dugocha area have significantly depleted δ13C values that are interpreted to be the result of pervasive inter-mixing of isotopically distinct carbon derived from primary depositional carbonates, hydrothermally exchanged carbonates, with significant influence of the organic carbon. The petrographic distinction of calcitic and dolomitic marbles of Bhukia area is corroborated by δ13C values that show a bimodal distribution of near 0 per mil and depleted values of -3 per mil. Fluid inclusion studies suggest predominance of saline brines in the ore fluids. The δ34S values for all the three deposits are narrowly constrained between 10.4 and 15.1 ‰, which suggests a common metasedimentary source for sulfur.

Identical chondrite-normalized REE patterns and primitive mantle-normalized multi-element patterns suggest a common Na- and/or K-source for the formation of Ghagri and Dugocha-Bhukia feldspathic rocks. Based on mineralization styles and attendant alteration patterns, it is argued that the mineral deposits of Salumber-Ghatol belt in the Aravalli Supergroup (i) represent sedimentary carbonate-hosted Cu-Au deposits belonging to the wider class of Proterozoic Iron-Ore-copper-Gold type (IOCG-like) mineral deposits; (ii) the fluids responsible for the mineralization are generated from common sub-crustal source and (iii) during mineralization, the influx of Na-K-rich fluids is so intense that it created ‘artificial’ hyper-saline conditions in the normal depositional basin that facilitated crystallization of scapolite, brucite, spadaite, povondraite and phlogopite bearing mineral assemblage.