Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

A. K. Dwivedi ¹, A. K. Bajpai ¹, H. C. Srivastava ², R. K. Thakur ¹, N. K. Lal ¹

Affiliations
1 KDM Institute of Petroleum Exploration, ONGC Ltd. Dehradun, IN
2 Geo-Science Division, ONGC Ltd. Jorhat, IN

Abstract

The use of seismics to recognise and map stratigraphic traps is becoming an important phase of exploration activity in mature hydrocarbon provinces, world over. The stratigraphic wedge-outs have provided excellent trapping mechanism in some of the giant fields of the world. Surat depression is known to be the main kitchen for the hydrocarbon occurrences in Bombay High and around. Commercial accumulations have been encountered in Mid-Tapti and South Tapti fields of Surat depression. These accumulations are in structural traps. However, further updip, over Saurashtra shelf, the exploratory efforts have remained limited due to the absence of any structural prospects, The present paper deals with the interpretation of close grid seismic data with an objective to: i) identify seismic sequences and the depositional environments and ii) to map stratigraphic trap at levels equivalent to Eocene sands with oil indications encountered in the earlier drilled exploratory wells.

Keywords

Surat Depression, Sequence Analysis, Seismic Markers, Bombay Offshore.

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A. K. Dwivedi ¹, Joydip Sen ¹, C. Murugan ¹, G. Bairwa ¹, A. K. Bhatt ¹, P. V. Ramesh Babu ¹, S. A. Pandit ²

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Jamshedpur-831002, IN
2 Atomic Minerals Directorate for Exploration and Research, Hyderabad-500016, IN

Abstract

Hydrogeochemical exploration were earned out over an area of 700 sq km in Barabazar-Manbazar area of Purulia district, West Bengal, in order to identify target areas for the uranium mineralization. Water samples were collected from 504 borewells in the Singhbhum Group meta-Sediments and Chhotanagpur Granite Gneissic Complex (CGGC) including South Purulia Shear Zone (SPSZ). For individual Iithological domains, univariate and multivariate statistical techniques were applied to the analytical data on 10 variables, i.e. U, Na⁺, K⁺ , Mg⁺², Ca⁺², SO₄^-2, HCO₃, Cl^-, conductivity and pH. Five hydro uranium anomalous zones withm CGGC were delineated at Raghunathpur, Tentla, Chepua-Dighi, Ban and Jitujon areas. However, distinct pattern of high uranium values along with uranium/Conductivity are observed only in Raghunathpur-Tentla and Chepua-Dighi areas in the proximal tectonized zones of SPSZ. Based on the distinctive hydrogeochemical attributes, and favourable geology and structure, the areas in the vicinity of Raghunathpur-Tentla and Chepua-Dighi in the northern proximal contact of SPSZ, are designated as potential target areas for detailed geological and geophysical exploration.

Keywords

Hydrogeochemistry, Uranium, SPSZ, CGGC, Singhbhum Group, Purulia, West Bengal.

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A. K. Dwivedi ¹, G. N. Hegde ², K. Umamaheswar ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Jamshedpur- 831 002, IN
2 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Bangalore - 5 60 072, IN
3 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Shillong - 793 011, IN

Abstract

New occurrences of uranium mineralisation have been discovered in quartzite and siltsone/Shale units of the Gulcheru Quartzite Formation in the area to the north of E-W trending Idupulapaya fault around Idupulapaya, Malayalamma Bhavi, Tipparajupalle and Cheruvula Bodu. Mineralisation occurs in the form of lensoid bodies of 5 m x 0.5 m to 50 m x 1.5 m and is traced intermittently over an extent of 2000 m. Physical assay result of rock samples (n=66) has indicated values from 0.011% to 1.769% eU₃O₈, 0.017% to 1.848% U₃O₈ and <0.01% ThO₂. Samples (n=21) also analysed higher concentration of Cu (<25 ppm to 3202 ppm), Mo (<25 ppm to 472 ppm), Pb (<25 ppm to 2015 ppm), V (<25 ppm to 1010 ppm), Ag (<0.25 ppm to 3.92 ppm) and Au (<0.25 ppm to 1.40 ppm). Uranium minerals identified are uranophane, autunite, uranitite, pitchblende and U-Ti complex in association with pyrite, chalcopyrite, specular haematite and limonite. The above findings have opened up new potential target areas to look for uranium in the southwestern margin of Cuddapah basin.

Keywords

Uranium, Gulcheru Quartzite, Cuddapa Basin, Andhra Pradesh.

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A. K. Dwivedi ¹, U. K. Pandey ¹, C. Murugan ¹, A. K. Bhatt ², P. V. Ramesh Babu ¹, Mallikarjun Joshi ³

Affiliations
1 Atomic Minerals Directorate for Exploration and Research (AMD), Hyderabad - 500629, IN
2 Atomic Minerals Directorate for Exploration and Research (AMD), Jamshedpur - 831 002, IN
3 Banaras Hindu University, Varanasi - 221005, IN

Abstract

The Barabazar granite, exposed at the northern margin of Singhbhum craton, Eastern India, occurs along the South Purulia Shear Zone (SPSZ) and is emplaced into the Palaeoproterozoic metapelites and felsic volcanics of Singhbhum Group. Geochemical, petrographical and geochronological studies on the Barabazar granite addressed in the work have wide implications on understanding the geodynamics of SPSZ during Palaeoproterozoic to Mesoproterozoic. Geochemically, Barabazar granite displays limited range of major oxides, alkali enrichment and highly fractionated features (SiO₂ > 75%; Eu/Eu^* = 0.16-0.33; enrichment of K, Rb, Th, U and Nb; depletion of Ba, Sr, P and Ti). It is predominantly peraluminous (molar Al₂O₃/CaO+Na₂O+K₂O (A/CNK) = 1.14-144) and contains abundant alkali feldspar, perthite, and minor plagioclase, biotite and accessory minerals. Geochemical and petrological data indicates that it is A-type granite, which formed in 'Within plate granite' tectonic set up. The Barabazar granite was emplaced at ca. 1771 Ma (Pb-Pb) in rift related environs and evolved by partial melting of stabilized lower/middle crust (initial ⁸⁷Sr/⁸⁶Sr = 0.7302 ± 0.0066 and μ₁ = 8.5 ± 0.5). Subsequently, the shear zone (SPSZ) developed during the closure of the riftogenic basin and was reactivated during the Grenvillian orogeny (Ca. 900-1300 Ma), resulting in rehomogenisation of the strontium isotopes and thereby yielding younger whole-rock Rb-Sr isotope age of c. 971 Ma for the Barabazar granite. Probably during this tectonic event, the Singhbhum craton (Southern India Shield) would have finally juxtaposed with Northern Indian Shield along Central Indian Tectonic Zone (CITZ) during the global Grenvillian orogeny.

Keywords

A-Type Barabazar Granite, Geochemistry, Geochronology, Grenvillian Orogeny, Singbhhum Craton, SPSZ, West Bengal.

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