Late Proterozoic Acid Magmatism and Associated Tungsten Mineralisation in Northwest India

The crustal evolution of northwestern India is marked by several episodes of acid magmatism during Late Proterozoic period (900-700 Ma). These events occurred during the culmination of Delhi orogenic cycle and continued till the emergence of a stable Aravalli craton. Some of these granites emplaced within the Delhi Supergroup of rocks in central and southern parts of Rajasthan are associated with tungsten mineralisation. This includes three important tungsten deposits, namely those of Degana, Sirohi and Sewariya areas. The geological setting, petrography and geochemical characteristics of the mineralised granites in these deposits are comparable while these features are quite different in non-mineralised granites of this region. ison of mineralised granites in the three areas indicates that: (1) these are relatively small plutons, (2) they are emplaced at high crustal level, (3) the roof of the pluton is either just exposed or lies closely beneath ground surface, and (4) the granites are geochemically specialised with enrichment of alumina, W, B, F, Rb and Li, and depletion of Sr.