Tectonic and Stratigraphic Framework of the Lead-Zinc Sulphide Mineralisation at Zawarmala, District Udaipur, Rajasthan

The carbonate-hosted lead-zinc sulphide mineralisation of Zawarmala belongs to the early Proterozoic rocks of the Aravalli Supergroup. The floor of the Aravalli sedimentation was a peneplained Archaean basement whose antiquity, as revealed by the recent Sm/Nd isotope studies, dating back to 3.5 billion years ago. The sedimentary package of the Arava11i Supergroup represents a sequence showing a distinct dichotomy in its depositional and lithological characters. The sulphide mineralisation is entirely confined to the near-shore shelf sequence which shows diverse lithofacies association of carbonates, black shales, argillites and arenites. By contrast, the distal (deep water) facies rocks which do not show any sign of syngenetic mineral deposits of any kind, is a totally carhonate-free sequence of argillites with thin bands of arenites.

The Aravalli Supergroup includes two groups separated by an unconformity marked by conglomerates and palaeo-erosional surfaces. The lead-zinc sulphide ores are confined to the carbonate sequence which occurs in the Upper Aravalli Group. Studies on the host rocks and the orebodies indicate a common plan of deformation and metamorphism. The geometry of the ore lenses suggests a very strong influence of the second deformation (AF2). This is also apparent in the trend surface maps showing distribution pattern of the metals-lead and zinc. Localisation of sphalerite, galena, and pyrite-bearing orebodies indicates differential mobilisation of these minerals in response to repeated deformation and metamorphism under a low temperature condition. The present study reveals a polygenetic history of the Zawarmala ore-bodies comparabte with those proposed for 'Alpine or Mississippi ValIey' types.