A holistic approach on the gold metallogeny of the Singhbhum crustal province: Implications from tectono-metamorphic events during the Archean-Proterozoic regime

Abstract

Studies on a wide range of gold deposit types suggest that the crustal accumulation of gold throughout the Earth’s history was a consequence of changing tectonic regimes and variable paleo-redox conditions. The Singhbhum crustal province in eastern India is no exception to these events. The gold occurrences in the Singhbhum crustal province are confined to the Paleo-Mesoarchean greenstone belts within the Archean cratonic core region and the Paleo-to Mesoproterozoic North Singhbhum mobile belt (NSMB). Gold mineralization within the cratonic core region occurs either as greenstone hosted lode-gold or as modified paleoplacer gold terrains, whereas in the North Singhbhum mobile belt, gold is associated with quartz reefs and auriferous sulfides within rocks metamorphosed to greenschist-amphibolite facies. The concentration of gold within these Archean and Proterozoic terrains has been highly episodic with different sedimentary, metamorphic and hydrothermal mineralizing events operating during the respective periods. However, information regarding the genesis of gold in these occurrences remains fragmental and lacks regional-scale integration with the tectonic evolution of the Singhbhum crustal province. The present work provides a comprehensive review of the various gold occurrences/deposits in the Singhbhum crustal province and their possible genesis with respect to the tectonic evolution of the crustal province.This work recognizes that the gold endowment of the Paleo-to Mesoarchean paleoplacers was influenced by the presence of underlying high-MgO komatiites, resulting in the lean Au-assays in these paleoplacer deposits. On the other hand, the Paleo-to Mesoarchean greenstone hosted lode-gold occurrences indicate a mafic proto-source from which Au was mobilized into the Paleoarchean ocean and fixed into the contemporaneous inter-layered carbonaceous sedimentary sinks, which was ultimately reconcentrated to economic grades with the advent of plate-tectonics and coeval metamorphism. From the Proterozoic onwards, tectono-metamorphic events took over as the driving mechanism for gold accumulation in the Singhbhum crustal province. Pervasive intraplate rifting and simultaneous deposition of organic matter rich black shales set the stage for a possible Au-rich carbonaceous sedimentary sink, similar to a wide-range of Proterozoic sediment hosted gold deposits.