Petro-mineralogical and geochemical characteristics of Shahaba Limestone from Gogi-Kanchankayi sector, Bhima Basin, Karnataka with reference to Uranium mineralisation

The Shahabad Limestone Formation of Bhima Basin from Gogi-Kanchankayi area occurs in heterogeneous forms like massive/blocky limestone, argillaceous/ siliceous limestone and laminated/ flaggy limestone. These limestones are primarily composed of micrite, which often alters into sparry calcite on diagenesis with associated impurities of quartz, feldspar, barite, chlorite, glauconite, sulphides and carbonaceous matter. Geochemically, these limestones comprises of variable CaO with low MgO and P2O5 content. Trace elements concentration shows elevated Ba, Rb and depleted Sr. The current study classified these limestones as non-dolomitic and non-phosphatic types deposited in shallow marine carbonate platform setting with low energy conditions. Post-sedimentation, basin tectonics has resulted in reactivation of the basin margin fault causing intense fracturing of limestone. Subsequent hydrothermal movement along those fractures has resulted in re-mobilisation and re-precipitation of sulphides and carbonaceous matter, and along with alteration has facilitated the precipitation of the uranium bearing minerals.

Potentiality of Uranium Mineralisation in the Environs of Chhattisgarh Basin, India: a new occurrence in Chhibra

The Meso-Proterozoic intracratonic basins are known for hosting medium to high grade, large tonnage, low cost unconformity-type uranium deposits in the world like-Athabasca Basin, Saskatchewan, Canada and the Pine Creek Geosyncline, Northern Territory, Australia. Similarly, there are fourteen Proterozoic basins in India, out of which, the unconformity-related uranium deposits are identified at Lambapur-Yellapur-Chitrial in the northern part of the Cuddapah basin. Based on the geological setting, age and fertile basement provenance, the other Proterozoic basins in India also hold promise for uranium mineralisation. In this context, the Chhattisgarh basin which is third largest Proterozoic basin in Central India occupying an area of 33,000 sq. km. with 2500m thick sediments, is identified as one of the major favourable targets for uranium mineralisation. It is located at the northern fringe of Bastar Craton in parts of Odisha and Chhattisgarh and comprises mostly siliciclastic sediments of Singhora, Chandrapur and Raipur Groups. Uranium exploration carried out in the environs of Chhattisgarh basin mostly along the basin margins, have brought to light a number of uranium occurrences having sizeable dimensions hosted by both the basement rocks viz. Malaikhaman (0.026-0.11% U3O8), Makarumunda (0.013-3.3% U3O8), Damdama (0.026-0.43% U3O8) , Kashipali (0.010-0.96% U3O8), Karichhapar (0.011-0.40% U3O8) and the cover sediments viz. Juba-Banjhapali (0.010-0.078% U3O8), Govardhangiri-Bagia Nala (<0.010-0.80% U3O8), Chitakhol-Renkhol-Bokarda (<0.012-0.39% U3O8). The newly located uranium mineralisation in the sandstones of Rehatikhol Formation near Chhibra which is exposed intermittently over a strike length of 800m with grab samples (n=43) physically assayed 0.014 to 0.140% eU3O8, 0.010 to 0.120% U3O8 (β/γ) and <0.005% ThO2. Uraninite and pitchblende have been identified as uranium minerals. The favourable factors like geological, geochemical, geophysical, sedimentological, tectonic framework and presence of fertile granitic rocks (n=33, 5-26ppm U) in the provenance indicate its potentiality for uranium mineralisation. The exploration so far, has been mostly confined around shallow basin margins leaving deeper part unexplored. With the advancement of geophysical techniques like airborne magnetic, radiometric and electromagnetic surveys it would be possible to explore the deeper part of the basin. In addition, geochemical techniques such as hydro and litho-geochemical sampling could also be applied around suitable litho-structural settings, especially along the shear/fault zones trending NNE-SSW to NW-SE and their intersections with the ENE-WSW trending shear/fault zones. The present paper deals with the potentiality of uranium mineralisation in the environs of Chhattisgarh basin with emphasis on recently located significant occurrence of uranium mineralisation near Chhibra in the Rehatikhol Formation of Singhora Group along the southeastern margin of Chhattisgarh basin.

Shear-Hosted Uranium Deposits: A Review

A group of uranium deposits is described that is hosted within polyphase shear zones. The group is economically significant, collectively containing over 500,000 tonnes of uranium and several examples have been or are being mined. Over a hundred individual deposits are known widely spread over many countries. It is proposed that this group be assigned to a new shear-hosted uranium deposit category. Uranium deposition was superimposed upon intense and extensive feldspathic alteration formed during ductile deformation. This intense alteration has led to the alternative albitite-type or metasomatite-type nomenclature. The evidence is clear that in most cases uranium mineralization postdates regionally extensive feldspar alteration and is associated with a range of alteration assemblages which overprint early albite or K-feldspar dominant alteration. Abundance of hydrothermal zirconium and phosphate minerals is a common characteristic of this group which implies high activity of F and P during mineralisation, but the source of hydrothermal fluids remains uncertain. Also uncertain is the geodynamic setting of uranium mineralisation which is a consequence of absolute mineralisation age being poorly defined. Data from three of the four major districts are suggestive that mineralisation was a consequence of fluid migration along shears during regional compression. This paper reviews key aspects of the group in a mineral systems context, focussing on the four major districts of Kropyvnytskyi (Ukraine), Lagoa Real (Brazil), Mount Isa (Australia) and the Central Mineral Belt (Canada).

Lithostratigraphy of the Sinqeni Formation, Pongola Supergroup, South Africa

The Mesoarchaean Sinqeni Formation forms the lowermost unit of the predominantly sedimentary Mozaan Group (Pongola Supergroup) of southern Africa. The formation comprises a dominantly arenaceous succession, which can be subdivided into four members. A laterally discontinuous gold- and uranium-bearing conglomerate package (Denny Dalton Member) is commonly developed at the base of the formation. Overlying the basal conglomerates are two significant quartz arenite packages (Dipka, and Kwaaiman Members) which are separated by a ferruginous shale package (Vlakhoek Member) that locally hosts banded-iron formation. The formation is the most extensively exposed succession of the Mozaan Group, cropping out extensively in the Hartland region, as well as in multiple inliers from Amsterdam in the Mpumalanga to Nkandla in central KwaZulu-Natal, with further exposures in Eswatini. Subeconomic gold and uranium mineralisation occur sporadically within the conglomerates of the Denny Dalton Member, and have previously been mined from multiple occurrences in the White Mfolozi, Mhlatuze and Nkandla Inliers whilst many prospecting trenches are found in the conglomerates of the Hartland and Amsterdam areas. Gold has also briefly been exploited from ferruginous shales and iron formations of the Vlakhoek Member in the Altona area. Litho-correlative equivalents of the formation comprise the Mandeva Formation (White Mfolozi Inlier), Skurwerant Formation (Amsterdam region) and Mkaya Formation (Magudu region).