Yadav P. K and Avadich P. C
Rocks of Bhilwara Supergroup are endowed with some of the best zinc resources of country. These are sediment hosted and include massive sulphides (SHMS) of Pb-Zn. SHMS deposits occur in intracratonic rift in half graben sediments. At the basin floor hydrothermal discharges were focused at the intersection of extensional and transform faults. Presence of mafic bodies in most of the ore environments suggest that hydrothermal convection systems were driven by high level magma bodies. In most cases low rigidity, permeability and thermal conductivity of host sediments helped to focus and prolong hydrothermal discharge to a number of limited sites. Rajpura Dariba deposit displays biphase mineralisation including stratiform sulphides and post metamorphic epigenitacally melt introduced independently. Salient features of vein ores such as occurrences as pods, segregation veins or open space fillings traversing the banded ores, absence of deformation and recrystalisation textures indicate that these veins are post-metamorphic and could have formed from a different ore fluid. The cavity filling nature of vein ore and their occurrence in irregular shear planes suggest their environment of ore formaton was different than imprints of metamorphism in banded ores. The source of this fluid could be intrusive granite located during present studies (Misra, B. and Mookerjee, A. 1984; Mishra, B., 2000). Ore search would require identification of faults as sites of ore concentration in environment of favourable host rocks using magnetic data for selecting regional targets. Identification of volcanoclastic rocks, graphite mica-tuffaceous schist and, marble coupled with hydrothermal alteration and element / metal zones will demarcate local targets for selecting drill sites.
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