• M S Pandian

      Articles written in Journal of Earth System Science

    • Fluid inclusion, geochemical, Rb–Sr and Sm–Nd isotope studies on tungsten mineralized Degana and Balda granites of the Aravalli craton, NW India

      Sundarrajan Vijay Anand M S Pandian S Balakrishnan R Sivasubramaniam

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      Granitic plutons occurring within and to the west of the Delhi Fold Belt in the Aravalli craton, northwestern India are the result of widespread felsic magmatism during Neoproterozoic, some of which are associated with greisen and skarn tungsten deposits. In this paper, we present the result of our study on fluid inclusions, geochemistry and geochronology of two such tungsten mineralized granite plutons at Degana and Balda, and interpret the nature of ore fluid, and petrogenesis and age of these mineralized granites. Fluid inclusion study reveals coexistence of moderate and hyper-saline aqueous fluid inclusions along with aqueous-carbonic inclusions, suggesting their origin due to liquid immiscibilityduring fluid–rock interaction. Geochemically, the granites are peraluminous, Rb enriched, Sr and Ba depleted and highly differentiated. The Rb–Sr isotopic systematics yielded 795±11 Ma for Balda granite and 827 ± 8 Ma for Degana granite. We show that major phase of widespread granitoid magmatismand mineralization during the Neoproterozoic (840–790 Ma) in NW India is coeval with breakup of the Rodinia supercontinent and infer a causal relationship between them.

    • 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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