Geologic setting, genesis and transformation of sulfide deposits in the Northern part of Khetri copper belt, Rajasthan, India- an outline

Abstract

The present study is confined to the northern part of the Khetri copper belt that extends for about 100 km in northern Rajasthan. Mineralization is more or less strata-bound and is confined to the garnetiferous chlorite schist and banded amphibolite quartzite, occurring towards the middle of the Proterozoic Delhi Supergroup. Preserved sedimentary features and re-estimation of the composition of the pre-metamorphic rocks suggest that the latter were deposited in shallow marine environment characterized by tidal activity. Cordierite-orthoamphibole-cummingtonite rock occurring in the neighbourhood of the ores is discussed, and is suggested to be isochemically metamorphosed sediment. The rocks together with the ores were deformed in two phases and metamorphosed in two progressive and one retrogressive events of metamorphism. Study of the host rocks suggests that the maximum temperature and pressure attained during metamorphism are respectively 550-600°C and < 5.5 kb. principal ore minerals in madan kudan are chalcopyrite, pyrrhotite, pyrite and locally magnetite. in kolihan these are chalcophyrite, pyrrhotite and cubanite. subordinate phases are sphalerite, ilmenite arsenopyrite, mackinawite, molybdenite, cobaltite and pentlandite. the last two are very rare. gangue minerals comprise quartz, chlorite, garnet, amphiboles,biotite, scapolite, plagioclase and graphite. the ores are metamorphosed at temperatures > 491°C. Sulfide assemblages are explained in terms of f_S2 during metamorphism. Co-folding of the ore zone with the host rocks, confinement of the ores to the carbonaceous pelites or semi-pelitic rocks, strata-bound and locally even stratiform nature of the orebodies, lack of finite 'wall rock alteration', metamorphism of the ores in the thermal range similar to that for the host rocks, absence of spatial and temporal relationship with the granitic rocks of the region led the authors to conclude that the entire mineralization was originally sedimentary-diagenetic. Any loss of primitive features and development of incongruency are due to subsequent deformation and metamorphism to which the ores and their hosts were together subjected.