Research - Dept. of Civil Engg.

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Browsing Research - Dept. of Civil Engg. by Author "Joshi, Prabha"

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    Fluid inclusion and geochemical signatures of the talc deposits in Kanda area, Kumaun, India: implications for genesis of carbonate hosted talc deposits in Lesser Himalaya
    (Springer, 2015-06) Joshi, Prabha
    Talc deposits in the Deoban Formation of inner Lesser Himalaya in Kumaun are interpreted to have resulted from low-grade, regional burial metamorphism of the siliceous magnesium bearing carbonates consisting of magnesite and dolomite. These deposits are distributed over a large area, occurring in association with magnesite and rarely with dolomite. They are found as fine-grained, fibrous aggregates of talc restricted to small, irregular patches or pockets in carbonate host rocks. Their petrographic features represent different phases of reactions between magnesite and silica to produce talc, thus equilibrium conditions were attained by the assemblage of magnesite + quartz + talc. Scanning electron microscopy also demonstrates that magnesite has reaction margins, whereas dolomite has perfect grain boundary in the magnesite–dolomite–talc assemblage. The major and trace elements in magnesite/dolomite and talc rule out the possibility of any incursion of foreign material during talc formation. Early fluids in magnesite and dolomite were H2O + NaCl + KCl ± MgCl2 ± CaCl2 in composition, their microthermometry data suggest mixing of the fluids. The fluid inclusion studies also imply that talc was formed under the condition of very low XCO2XCO2. A peak temperature of 300–340 °C and pressure of 2–2.2 kbar are estimated from the coexisting immiscible fluids in talc–magnesite assemblage. It is attributed that the estimated PTXCO2XCO2 conditions in the Upper Proterozoic Deoban carbonate rocks, favored the talc formation from magnesite + quartz, and were not conducive to convert siliceous dolomite to talc on a large scale. Keywords Talc Magnesite Fluid inclusions Lesser Himalaya
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    Fluid Inclusions in the Ca-Mg Carbonates in Kumaun lesser Himalaya and Focus on the Basin Fluid System
    (Indian Institute of Technology Bombay, 2016-11-25) Joshi, Prabha
    The Ca-Mg carbonate rocks of the Deoban - Formation in Kumaun Lesser Himalaya have been extensively studied for field, petrography, and geochemical characters whereby the dolomitization after calcite precursor is well established. Many microlithotypes are identified in them, which are fine grained and preserve the original organic and inorganic fabric. Lack of substantial compaction is evident by the fenestral structure (Fig.1). Polygonal mud cracks and parallel lamination in these carbonates signify their exposure as well as deposition in a quiet, shallow marine tidal flat environment. The studies of the fluid evolved in these carbonates and circulated in the basin have not been comprehensive. Present study aims to understand ,the basinal fluids contributed in the formation of various lithofacies from limestone-dolomite-magnesite to talc. In the present work representative samples from Jhiroli area in, Kumaun Lesser Himalaya have been studied.
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    Genetic issues of some of the non metallic minerals in lesser Himalaya
    (Iranian Journal of Earth Sciences, 2010) Joshi, Prabha
    A brief account of the representative and workable industrial minerals namely magnesite, talc and barite in Lesser Himalaya, is presented here emphasizing their genesis. Deposits of magnesite and talc are found associated with Neoproterozoic, plateform type, shelf-slope limestone-dolomite host rocks from inner Lesser Himalayan sequences. Field, textural, geochemical signatures and fluid inclusions trapped in dolomite and magnesite reveal within basin processes, in an increased burial- diagenetic environment responsible for formation of magnesite replacing dolomite. Talc is formed at the expense of magnesite and silica, and with limited dolomite involvement at transition conditions from diagenetic to metamorphism. Barite deposit is hosted within Neoproterozoic Nagthat quartzite rocks of outer genetic understanding.
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    Petrography and geochemistry of magnesite and talc deposits of Jhiroli, Kumaun Lesser Himalaya
    (Magmatism, Tectonism And Mineralization: Macmillan Publishers India Ltd, 2009) Joshi, Prabha
    The Veitsch type magnesite mineralization in association with talc from Jhiroli is confined within the stromatolitic dolomite of Deoban Formation. The dolomite represents many microlithotypes and characterized by nodules and bands of chert. Microtextures suggest a tidal flat environment where different phases of replacement of dolomite by magnesite were observed. Grain boundary relations, replacement features and different phases of reactions between magnesite and silica explain development of talc in the system. There is a noteworthy similarity in geochemical signatures of dolomite, magnesite and talc except a few major and minor elements, which suggest an external chemical flux is not responsible for the magnesite and talc mineralizations. On the basis of field relation, petrography and geochemistry it can be inferred that the marine, sparry magnesite deposits are product of diagenetic replacement of early dolomite in a protected intertidal carbonate flat environment whereas the associated talc deposits resulted from incipient/low grade regional burial metamorphism of these siliceous, magnesium bearing carbonates.
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    Role of fluids in the formation of talc deposits of Rema area, Kumaun Lesser Himalaya
    (Springer, 2009-02) Joshi, Prabha
    Talc deposits of Rema area in the Kumaun Inner Lesser Himalaya are hosted within high magnesium carbonates of the Proterozoic Deoban Formation. These deposits occur as irregular patches or pockets mainly within magnesite bodies, along with impurities of magnesite, dolomite and clinochlore. Textures represent different phases of reactions between magnesite and silica to produce talc. Petrography, XRD and geochemistry reveal that the talc has primarily developed at the expense of magnesite and silica, leaving dolomite largely un-reacted. Early fluid inclusions in magnesite and dolomite associated with talc are filled with H2O+NaCl+KCl ± MgCl2 ± CaCl2 fluids, which represent basin fluid system during diagenesis of carbonates. Their varied degree of re-equilibration was although not pervasive but points to increased burial, and hence requires careful interpretation. H2O-CO2 fluid with XCO2 between 0.06 and 0.12 was equilibrated with talc formation. The reaction dolomite+quartz → talc was not extensive because T-XCO2 was not favourable, and talc was developed principally after magnesite+quartz. Keywords Talc Fluid Inclusions Re-equilibration Kumaun Lesser Himalaya