Gold exploration in the Mahakoshal belt has been carried out for the past thirty years and mostly quartz veins were identified as the host targets. The recent study based on the concept of mineral system has indicated that gold occurs in mafic and ultramafic rocks also, besides the quartz veins. The mineralisation in Agori Formation is generally confined to Algoma type BIF, meta-volcanics and phyllites, while in Parsoi Formation it occurs predominantly in quartz veins. The metavolcanics have acted as source rocks and the crustal deep faults have acted as conduits for mineralizing fluids, in the continental back arc type tectonic setting with two mineral systems viz. (i) basin related fluid flow with active magmatism, and (ii) magmatic related hydrothermal system.

An investigation for limestone was undertaken by Geological Survey of India, in Daba Gamlin area, West Siang district, Arunachal Pradesh (toposheet no. 82L/12). The area lies in the Lesser Himalayan region. The metasediments comprising sericite-quartz phyllite, garnetiferous phyllite and schist, graphite schist, carbonaceous phyllite, quartzite, carbonates, and chert constitute the Khetabari Formation of Palaeoproterozoic Bomdila Group. Carbonaceous phyllite is exposed near Daba Gamlin and extends in the south westerly direction. It is dark grey to black in colour, very fine grained and soils the finger. Two foliation planes can be inferred. It has thin graphitic bands (1-5mm). Graphite is of amorphous nature. It is also observed as thin flakes admixed with micaceous minerals. At places carbonaceous phyllite has very thin silica veins and occasional ferruginous patches having small pyrite grains and oxidised cavities. The carbonate bands are within the carbonaceous phyllite and at places it is also in contact with mica schist. Dolomitic crystalline limestone is exposed in Daba Gamlin-Liromoba sector, to the southwest of Daba Gamlin. The physical character of the rock indicates that it is a hard, compact, fine-medium grained, bluish grey limestone having banded character with elephant skin weathering pattern on the surface, hence characterised as dolomitic limestone. The MgO content varies from 1% to 15%. The rock specimen when stained with Alizarin Red does not stain the maximum part of the rock. The dolomitic limestone is coarse and crystalline at places, with grain size of the crystals ranging from 2-5mm and concentrated as 1-2 cm bands having translucent calcite grains. The limestone is siliceous and composed of interlocking crystalline grains of the constituent minerals viz. calcite/ dolomite and of phaneritic texture, thus representing a recrystallised limestone. Thin silica/quartz-calcite veins and veinlets (1-2mm) are intruding the dolomitic limestone and are parallel as well as oblique to the banding. The limestone occurs as lenses within carbonaceous phyllite and associated graphitic schist. It is fine grained, carbonaceous in the lower part, while the upper part is siliceous and crystalline. Specks of pyrite and chalcopyrite occur occasionally. During the investigation, five different bands/lenses of dolomitic limestone were delineated.

The Palaeoproterozoic eastern Mahakoshal belt of Central India Tectonic Zone (CITZ) is known for gold occurrences. Gold occurs predominantly in quartz veins and quartz-carbonate veins. It is associated with pyrite, pyrrhotite and arsenopyrite mineral assemblages. The secondary alteration products such as ‘scorodite’ and ‘mansfieldite’ are also associated with gold mineralisation. Recent investigations carried out in Parsoi area, have indicated the association of gold with bismuth, bismuthinite and telluride. This is the first record of bismuth from the Mahakoshal belt. The studies of the bismuth tellurides contribute to the assessment and evaluation of concentrations of gold resources.

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Pahardia-Rungikocha area lies at the south-western end of the north Singhbhum mobile belt (NSMB). The terrain of NSMB is known for gold occurrences. Systematic exploration by the authors have established significant resource (0.48 million tonnes ) with appreciable grade (3.43 g/t) of gold, for the first time. This has added to the National Mineral Inventory on gold and the area has now been granted mining lease.