地球科学と気候変動ジャーナル

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Implications for Gold Mineralisation in the Gopapur Area, Keonjhar District, Orissa: A New Discovery

Manaswini Kar* and Venkatesh AS

Gold deposits of Orissa can be broadly divided into three broad zones of Keonjhar, Mayurbhanj, and Sundargarh districts. In Keonjhar district gold occurrences have been reported from Saleikana-Dimirimunda-Kardangi sector in Telkoi block and Gopapur, Gajipur, Adal, Kushkala sector in Banspal block. Out of these localities Gopapur area seems to be the most promising one. The Precambrian metavolcanics of Gopapur in the Keonjhar district host auriferous quartz vein. In this area detailed exploration is carried out by GSI in 1:10000 scales with pitting, trenching, drilling, geological mapping and geochemical survey. The Quartz veins are found in the metavolcanics being emplaced along the prominent schistocity planes. Three sub parallel sets of quartz veins with high angle dip of are delineated. Gold mineralization is associated with the sulphides and oxides in quartz veins, basalts and laterites and ultramafic and is exposed on the surface as well as in underground trench faces. Gold occurs as refractory form and in free grains within quartz and intimate association with pyrite and chalcopyrite and oxides (haematite, goethite, magnetite and cuprite) in the form of refractory gold. The gold content of the mineralized quartz veins and lateritic wall rocks varies widely from 1 to 9 ppm. Fluid inclusion study shows the temperature ranges 250°C to 37°C and the gold deposit is of mesothermal type. The gold is formed by the remobilisation from sulphide bearing minerals to oxide bearing minerals. From the mineralogical and lithological assemblages the Gopapur prospect can be compared with Iron-formation-hosted vein and disseminated deposit that is Homestake gold deposit.