EARLY PROTEROZOIC METALLOGENY, TECTONICS AND GEOCHRONOLOGY OF THE SINGHBHUM CU-U BELT, EASTERN INDIA

The Singhbhum Thrust Belt hosts three types of mineralisation: sulphides of copper and other metals, uranium oxides and apatite-magnetite. Regional geological investigations reveal that the thrust belt and the mineralisations evolved through several distinct geological episodes: (1) The oldest is the deposition of the protoliths of the Older Metamorphic Group, their subsequent deformation and metamorphism, and the post-kinematic intrusion of the Singhbhum Granite (the Older Metamorphic orogeny, 3.15-3.0 Ga); the Chotanagpur Gneiss to the north is also thought to have originally belonged to this period. (2) The Chotanagpur Gneiss and the Singhbhum Granite together formed an extensive sialic basement of the Archaean period, which subsequently underwent extension, producing a continental basin filled with platform sediments of the Iron Ore Group and deep sea basins (on sialic basements) filled with flysch-like sediments of the Singhbhum Group; this was accompanied by extensive mafic volcanism (the Dalma Volcanics, the Dhanjori Volcanics and the dolerite dyke); the sulphide ores were formed as strata-bound layers associated with the volcanism of the Dhanjori Volcanics; uranium minerals and phosphates were deposited as sediments or related to later felsic plutonic activity; volcanism, sedimentation and mineralisation were controlled by rift fractures forming the basins; these were later subjected to deformation and metamorphism of the Singhbhum orogeny (2.05-2.0 Ga); the rift fractures developed into thrust belts; felsic magmatic activity took place; hydrothermal activity along the thrust belt modified the mineralised belt. (3) A later thermal event (1.6 Ga) was imprinted on the rocks of the thrust belt.