Abstract
Rampura-Agucha zinc-lead deposit, located 15 km southeast of Gulabpura in Bhilwara District, Rajasthan, forms a part of pre-Aravalli Banded Gneissic Complex (3.2 to 2.5 billion years old) consisting of gneisses. schists and intrusives of acidic and basic igneous rocks, that occupy predominantly the southeastern plain of Ajmer and Bhilwara. The sequence of rocks from hanging wall to footwall in the deposit is (a) garnet-biotite-sillimanite gneiss/schist, intercalated with amphibolite, calc-silicate, pegmatite and aplite, (b) graphite-mica-sillimanite gneiss/schist, (c) footwall garnetbiotite- sillimanite gneiss with interlayering of granite gneiss, amphibolite, calc-silicate and pegmatite, (d) granite gneiss. and (e) mylonite. The rock units show northeast-southwest strike with steep dips in hanging wall (75°-80° ) and moderate dips in footwall (60°-65°) towards southeast and are suspected to have undergone more than two stages of deformation. Structurally, the deposit is interpreted to represent a doubly plunging. isoclinal, synformal fold with steep northeasterly plunge (65°-70°) in the south and shallow southwesterly plunge (20°-22°) in the north.
Graphite-mica-sillimanite gneiss/schist forms the host for economic mineralization and have a strike extent of about 1400 m. The ore zone is massive, wider in the middle section with tapering ends on either side along the strike. The persistence of ore has been established upto a depth of about 350m and is still open in depth. The economic minerals occurring in this deposit, in the order of decreasing abundance are sphalerite, pyrite, pyrrhotite and galena. The dominant gangue minerals occurring within the ore zone are quartz, felspar, micas (sericite, chlorite and biotite), graphite and sillimanite with negligible amounts of garnet and amphibole. The genesis of mineralization remains unclear, but presently it is interpreted as a volcanogenic massive sulohide that has later been subjected to high grade metamorphism and tectonic disturbances. The total ore reserves have been estimated to be 61.10 million tonnes with 1.57 % Pb, 13.48 % Zn and 9.58 % Fe.
