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Madawara ultramafic complex (MUC) in the southern part of Bundelkhand Craton, Central India comprises peridotite, olivine pyroxenite, pyroxenite, gabbro, and diorite. Coarse‐grained olivine, clinopyroxene (Cpx), amphibole (Amp), Al‐chromite, Fe‐chromite, and magnetite with rare orthopyroxene (Opx) are common minerals in peridotite. Chromites are usually coarse‐grained euhedral found as disseminated crystals in the olivine matrix showing both homogeneous and zoned texture. Al‐chromite, primarily characterizes Cr‐spinels and its subsequent fluid activity and alteration can result in the formation of Fe‐chromite, chrome magnetite, and magnetite. Mineral chemistry data suggest that Al‐chromite is characterized by moderately high Cr2O3 (38.16–51.52 wt.%) and Fe2O3 (3.22–14.51 wt.%) and low Al2O3 (10.63–21.87 wt.%), MgO (1.71–4.92 wt.%), and TiO2 (0.22–0.67 wt.%), whereas the homogeneous Fe‐chromite type is characterized by high Fe2O3 (25.54–47.60 wt.%), moderately low Cr2O3 (19.56–37.90 wt.%), and very low Al2O3 (0.06–1.53 wt.%). Subsequent alteration of Al‐chromite and Fe‐chromite leads to formation of Cr‐magnetite and magnetite. The Cr# of Al‐chromite varies from 55.12 to 76.48 and γFe3+# from 8 to 19, whereas the ferrian chromite has high Cr# varying from 94.27 to 99.53 while its γFe3+# varies from 38 to 70. As a whole, the primary Al‐chromite shows low Al2O3, TiO2 contents, and high Fe#, Cr# values. Olivines have forsterite ranging from 75.96% to 77.59%. The bulk‐rock geochemistry shows continental arc geochemical affinities indicated by the high concentration of large‐ion lithophile elements and U, Th relative to the low concentration of high‐field strength elements. These petrological and mineralogical as well as primary Al‐chromite compositions plotted in different discrimination diagrams suggest an arc environment that is similar to Alaskan‐type intrusion.

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.

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We report here an Alaskan-type mafic-ultramafic complex at Padhar from the Precambrian Betul Belt of Central India. The Padhar intrusive bodies show lithological zoning defined by olivine-bearing ultramafic rocks in the core and gabbroic rocks at the margins, and are commonly accompanied by Cr-Cu-Ni sulphide mineralization. Mineral chemistry and whole-rock geochemistry of these rocks indicate that they are derived from the crystallization of hydrous magmas. The Padhar complex is characterized by high Mg and low abundance of incompatible trace elements. Flat REE pattern with negative Nb anomaly suggests arcmagmatism typical of Ural-Alaskan type. Presence of Mg-rich clinopyroxene and hornblende-rich rock types in the Padhar mafic-ultramafic intrusives along with paucity of orthopyroxenes in them further distinguish its from different types of complexes, i.e. ophiolite, Alpine and stratiform layered-type. These features are akin to Alaskan-type rocks as seen in Alaska, Canada and Urals of Russia. This finding of Alaskan-type ultramafic complex in the Padhar area of Betul Belt, Madhya Pradesh, is significant and has important implications in the tectonics and geodynamics of the Central Indian Tectonic Zone in general, and in the search of platinum group of minerals in particular.