• P V Ramesh Babu

      Articles written in Journal of Earth System Science

    • Mineral chemistry of tourmaline from Mashak Pahar, South Purulia Shear Zone (SPSZ), eastern Indian Shield

      Santanu Acharjee Jyotisankar Ray Payel Dey Debapriya Bhattacharyya Mousumi Banerjee Basab Chattopadhyay Shyamal Sengupta A K Bhatt D Chowdhury A K Dwivedi Sanjoy Mahato Arka Ranjan Jana P B Maithani P V Ramesh Babu

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      The area of investigation at and around Mashak Pahar, Bankura district, West Bengal, India comprises a number of rock types namely: granite gneiss, migmatized quartz tourmaline gneiss, quartz pebbleconglomerate, ferruginous quartzite, quartz tourmaline veins (as veins) and graphite schists. Interestingly, the study area lies in the region extending South Purulia Shear Zone (∼Tamar–Porapahar Shear Zone) which marks the boundary between two contrasting tectonic blocks of eastern India, namely, the Chhotanagpur Gneissic Terrane (CGC) to the north and Singhbhum Group of rocks to the south. The rocks of the study area are poly-phasedly deformed by three phases of folding, namely, F1, F2 and F3. All the tourmalines are classified to be of ‘Alkali Group’. Chemistry of tourmalines from migmatized quartz tourmaline gneiss and those from quartz tourmaline veins are in conformity with their relation to (earthquake induced) shear system evolution in this terrain. In general, the compositional evolutionof tourmaline during prograde metamorphism (∼400°–730°C) has been supported by both petrographic and chemical evidences. Assessment of mineral–chemical data of constituent tourmaline grains clearly suggests compositional variations across zonal boundaries within tourmaline that was controlled by changing metamorphic milieu in this terrane. Field and petrographic evidences clearly indicate activation of earlier and later shears in this region accompanied by infiltration of boron and formation of zoned tourmaline crystals.

    • Hydrothermal activity in the basement granite associated with the unconformity-related uranium deposit in Chitrial area, Cuddapah Basin, India


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      Uranium mineralization occurs adjacent to the unconformity between Paleoproterozoic granite and Meso- to Neoproterozoic cover sediments in Chitrial prospect of Cuddapah Basin in Indian shield. Hydrothermal activity in the granite is evident by the presence of hydrothermal veins and associated wallrock alteration in the unconformity zone (0–5 m below unconformity), shallow zone (5–100 m), and deep zone (100–120 m). Hydrothermal alteration of granite has produced chlorite in all depth, epidote in the deep zone, muscovite commonly in the shallow zone and illite predominantly in the unconformity zone. Pitchblende and coffinite are associated with sulphides and carbonaceous matter filling micro fractures and occurring along grain boundaries in the granite. Fluid inclusion study of quartz from hydrothermal veins reveals the presence of primary aqueous inclusions (biphase, monophase, polyphase) with a wide range of salinity from 0.2 to >23.2 wt.% (low–high). The fluid composition indicates that MgCl$_{2}$ is present in all depth zones, CaCl$_{2}$ in the deep zone and KCl–NaCl in the unconformity zone. T$_{h}$ of aqueous biphase inclusions is in the range of 275.0–78.9$^{\circ}$C. Available evidence suggests convective circulation of basinal brine between cover sediments and basement granite during which uranium was mobilized from granite and precipitated in the unconformity zone.

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