Volcanogenic sulphide, precious metal and iron ore deposits in Paleoproterozoic Continental margin settings of Singhbhum Protocontinent, India: Their evolution in time and space
|Location||International Geological Congress,oslo 2008|
|Author||DR. Rai, Kishanlal|
|Holding Date||11 October 2008|
The Paleoproterozoic continental margins of the Singhbhum Protocontinent host several, rift-bounded, linear, along-fabric oriented basins, development of which was initiated mainly during the Archean-Proterozic transition period (C~2.5 Ga).
It is proposed that the metallogency closely related to the lithospheric evolution of the continental margins of Singhbhum Protocontinent took place sequentially in following major stages, in general: (1) Ocean-Basin Opening Stage (C~2.5 to 2.0 Ga): The oldest deposition of ores of this stage is represented by the Au-U bearing quartz-pebble-conglomerates of Witwatersrand-type along the basal or marginal horizons of oldest volcano-sedimentary basins like Iron Ore basin, Dhanjori and equivalent basins in the Protocontinent around 2.5 Ga.
Large-scale deposition of BIF-associated iron and iron-manganese deposits of Superior-type in I.O.G. (Noamundi-type) rocks of Bihar-Orissa and Chhattisgarh (Bailadila and Dalli-Rajhara-type) followed the extensive basic volcanism of this period in the above-stated iron ore basins. Sulphide-facies iron formations of this period host workable occurrences of remobilized gold in preferred tectonic locales e.g. at Sonadehi in Kanker district of Chhattisgarh, the underlying volcanics having been dated as ~2.56 Ga.
(2) crustal Accretionary Stage (2.0 to 1.6 Ga) : The metallogeny of this stage accompanied the large-scale tectono-magmatic activation of continental crust that resulted in widespread mantle-tapping komatiitic and tholeiitic magmatism of both extrusive and intrusive types. The dominant role of mantle magmatism and cogenetic volcanism in the genesis of ores of this stage is thus obvious and is unequivocally substantiated by the observed results of detailed geological-geochemical studies, particularly on the minor- , trace- and rare-earth element geochemistry and sulphur- and lead- isotopic studies on all the studied major ore desposits of the epicratonic domains of this Protocontinent.
The extrusive magmatism of this stage is represented by bimodal (felsic/mafic) submarine to sub-aerial volcanism. Notable mineralisations associated with them include the gold prospects of Sonakhan, iron ore and uranium prospects / occurrences of Khairagarh-basin, zinc and scheelite prospects of Kolari-Bhaonri-type in adjoining Sakoli basin, etc.
The intrusive activity accompanying the thickened crust in later phases of this stage is represented by the calc-alkaline type magmatism with which the giant - size Cu ± Mo ± Au deposit of Malanjkhand (Kotri volcanic basin) is associated. The soda-granite and basic magmatites hosted Cu ± U deposits localized along the of Singhbhum shear zone, which have been considered as volcanogenic strata-bound deposits by few workers are another giant - size base metal deposit of this stage. The SEDEX-type Cu-Au prospects of Pular-Parsori in Sakoli basin and the lead-dominant sulphide deposit of Sargipali in Gangpur basin also belong to this stage.