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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 HO + NaCl + KCl ± MgCl ± CaCl 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 $$ {\text{X}}_{{{\text{CO}}_{2} }} $$ . 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 PT $$ {\text{X}}_{{{\text{CO}}_{2} }} $$ 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. [ABSTRACT FROM AUTHOR]

Graphite is widely associated with the meta sedimentary rocks of the Almora Group, predominantly in the Gumalikhet Formation, which were metamorphosed up to the upper amphibolite grade. This graphite occurs in the form of layers, bands, pockets and lenses, hosted within the garnetiferous mica schist and quartzite. The carbon isotope analyses of the representative samples of Almora graphite are presented there. The δ 13C values range from –23.2‰ to –31.7‰, however with mean value of –29.08‰, which attributes that graphite is crystallized from the biogenic carbon during the metamorphism of the host sediments. [ABSTRACT FROM AUTHOR]