1.66-Ga-old metamorphosed Pb-Cu deposit in Sargipali (eastern India): manifestations of tidal flat environment and sedex-type genesis

Abstract

The metasedimentary rocks and the unusual PbCu mineralization of the Sargipali mine area are described and discussed to elucidate the processes involved in their deposition. Important lines of evidences used for the interpretation of an inter- to supratidal flat environment are: (1) a general pattern of a shallowing upward sequence from coarse clastics (arenaceous) through finer clastics (argillaceous) to carbonate; (2) the occurrence of metaconglomerate, trough cross-bedding and wave-ripples (within the arenaceous lithostratigraphic unit); (3) intercalations of quartzite, carbonate skarn, dolomite, and convolution of chert laminae (within the argillaceous lithostratigraphic unit); and (4) intercalation of quartz-mica-chlorite schist laminae (within the carbonate lithostratigraphic unit). The ores seems to belong to the same environment. Furthermore, in the assessment of the origin of the Sargipali ores, it is recognized that the orebodies not only represent a sedimentary setting, but also show a high Pb-content, and an older age of mineralization than that of deformation, metamorphism and granite intrusion. Along with the lack of stockwork zones, wall rock alteration, subaerial volcanism, and the presence of chert and tourmalinite, these features are consistent with a sedex-type origin. The idea of this origin finds support by yet another observation, i.e., the ore sulphur was mainly derived from the inorganic reduction of the seawater sulphate (at more than 300°C), while the ore metals were leached from the μ (= 238U/ 204Pb)- enriched Singhbhum soda-granite of 2200 Ma.The present study may help in conceiving a ‘new’ possibility that the sediment-hosted Pb-rich deposits of MVT origin can also be evaluated in terms of the sedex model.