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Green mica (fuchsite or chromian-muscovite) is reported worldwide in the Archaean metasedimentary rocks, especially quartzites. They are generally associated with a suite of heavy minerals and a range of phyllosilicates. We report the occurrence of green-mica quartzites in the Saigaon-Palasgaon area within Bastar Craton in central India. Mineralogical study has shown that there are two types of muscovites; the chromium-containing muscovite (Cr 2 O 3 0.84-1.84%) and muscovite (Cr 2 O 3 0.00-0.22%). Chlorites are chromium-containing chlorites (Cr 2 O 3 3.66-5.39%) and low-chromium-containing chlorites (Cr 2 O 3 0.56-2.62%), and as such represent ripidolite-brunsvigite varieties. Back scattered electron images and EPMA data has revealed that chlorite occurs in two forms, viz., parallel to subparallel stacks in the form of intergrowth with muscovite and independent crystals within the matrix. The present study indicates that the replacement of chromium-containing chlorite by chromium-containing muscovite is found to be due to increasing grade of metamorphism of chromium-rich sediments. However, the absence of significant compositional gap between aforementioned varieties indicates disparate substitution of cations, especially chromium, within matrix chlorites. The chromium-containing muscovite and muscovite are two separate varieties having distinct paragenesis.

The depositional history of the Himalayas has been overprinted by the tectonic activities during the Himalayan Orogeny. A detailed investigation of the sedimentary units can provide crucial information regarding their depositional history and provenance.This study aims at constraining the weathering history, tectonic setting, and provenance of meta-sediments from the Shimla and Chail Groups of Outer Lesser Himalaya. With similar major element chemistry, these meta-sediments comprise a low-silica group (avg. SiO 2 /Al 2 O 3 <3.29). Weathering intensity parameters chemical index of alteration (CIA), plagioclase index of alteration (PIA) and index of chemical variability (ICV) range from 62 to 78 (avg. = 69.41), 70 to 96 (avg. = 85.34), and 0.45 to 1.45 (avg. = 1.01), respectively indicating moderate to severe degrees of weathering. Transition element ratios [Cr/V (1.68-5.18), Ni/Co (1.47-30.99), and V/Ni (0.87-4.61)], and trace element bivariate plots suggest a recycled, felsic to intermediate provenance that has primarily been derived from Post-Archean sources with minor inputs from Archean units. A passive margin depositional setting with arcderived sources is suggested for the Chail and Shimla meta-sediments. Rare-earth element patterns reveal similarities between the studied metasediments with TTG gneisses and sanukitoids from the Aravalli and Bundelkhand Cratons, as well as Chaur and Jutogh granitoids. Therefore, Neoproterozoic Himalayan granitoids and ArcheanAravalli-Bundelkhand granitoids (TTGs and high-K granitoids) could be potential sources of these meta-sediments, as also suggested by the detrital zircon age distribution from the Beas-Satluj-Pabbar valleys and Shimla Group.

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