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

R. Dhana Raju ¹, G. S. Ravi ², K. Shivkumar ³, L. S. R. Reddy ⁴, Sabita Rohatgi ⁴

Affiliations
1 Hon Visiting Prof, Dept of Applied, Geochemistry, Osmania University, Hyderabad - 500 007, IN
2 Atomic Minerals Directorate for Exploration & Research, Department of Atomic Energy, Visakhapatnam-530 018, IN
3 Atomic Minerals Directorate for Exploration & Research, Department of Atomic Energy, Nagpur-440 001, IN
4 Atomic Minerals Directorate for Exploration & Research, Department of Atomic Energy, Hyderabad- 500 016, IN

Abstract

Estimation of industrial and strategic heavy minerals (HMs) in sands, viz, ilmenite, rutile, garnet, sillimanite, zircon and monazite, is usually carried out by Microscopic Gram-Counting (MGC) technique on heavy Liquid- and Magnetically-Separated fractions. This method is slow, laborious, Time-Consuming, costly, toxic and causes Eye-Strain. Its precision and accuracy depend on Microscope-Operator's skills in mineral identification and preparation, by microsplitting of representative portions of fractions for analysis. Instead, we are proposing here a WDXRFS-Based relatively simple, rapid, low-cost, non-toxic, eye Strain-Free and precise method. This involves (a) magnetic separation of a sand sample into 3 Sub-Samples that are magnetic at 0 4 and 1 2 A and Non-Magnetic at 1 2 A, (b) WDXRFS analysis of these for the oxides and elements in the formulae of HMs, and (c) computation of the contents of HMs, assuming their stoichiometric composition. The contents of HMs in sand samples, determined by this method, are in general agreement with that from MGC method on natural sand samples and prepared samples, with an overall error of <20%and coefficient of correlation (r) of -0 98. Furthermore, our method gives additional information on end-member composition of garnet, Th-content of monazite and proportion of Ortho- to Clino- in pyroxenes.

Keywords

XRF Method, Heavy Minerals, Quantification, Beach Sands.

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R. V. S. Sesha Rao ¹, M. S. M. Deshpande ¹, K. Shivkumar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Central Region Civil Lines, Nagpur - 440 001, IN

Abstract

Uranium mineralisation associated with phosphatic ferruginous breccia has been located for the first time within the Lower Vindhyan Semri Group of basal sediments in Son Valley around Baskati, Sidhi district, M.P. The phosphatic ferruginous breccia occurs along the reactivated basement fracture that follows the structural grain of Son-Narmada megalineament, and also marks the tectonic contact zone between Vindhyans to the north and Crystallines/Mahakoshals to the south. Detailed geological investigations at Baskati reveal uranium enrichment intermittently over a stretch of 2500 m at Baskati block and 400 m in Paniha block further east with an average width of 3 to 5 m. Samples from radioactive horizon analysed upto 670 ppm U and 36. 87% P₂O₅. Petromineralogical studies reveal that the association of uranium is mostly with the phosphatic phase.

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Rahul Banerjee ¹, K. Shivkumar ¹

Affiliations
1 Atomic Minerals Directorate for Exploration and Research, 1-10-153/156, AMD Complex, Begumpet, Hyderabad - 500 629, IN

Abstract

Kinwat crystalline inlier exposes Palaeoproterozoic granitoids belonging to the northern extensions of younger phase of Peninsular gneissic complex (PGC) within Deccan Trap country in Eastern Dharwar Craton (EDC) and bounded in south by a major NW-SE trending lineament (Kaddam fault). Geochemically, the Kinwat granitoids are similar to high-K, calc-alkaline to shoshonite magnesian granitoids and subdivided into two major groups, i.e. felsic group (pink and grey granites) and intermediate to felsic group (hybrid granitoids). The felsic group (∼67-74% SiO₂) shares many features with Neoarchaean to Palaeoproterozoic high potassic granites of PGC such as higher LILE and LREE content and marked depletion in Eu, P and HFSE, especially Nb, Ti, relative to LILE and LREE. The hybrid granitoids (∼58 - 67% SiO₂) have comparatively higher Ca, Mg and Na contents and slightly lower REE content than the granitoids of felsic group. Both, felsic and hybrid granitoids are metaluminous to weakly peraluminous and belong to highly fractionated I-type suite as evidenced by negative correlation of SiO₂ with MgO, FeO^t, CaO, Na₂O, Al₂O₃, whereas K₂O, Rb and Ba show sympathetic relationship with SiO₂. Moderate to strong fractionated REE patterns (Ce/Yb_N: ∼54-387) and strong negative Eu anomalies (Eu/Eu^*: 0.13 - 0.41) are quite apparent in these granitoids. The geochemical characteristics together with mineralogical features such as presence of biotite±hornblende as the dominant ferromagnesian mineral phases point towards intracrustal magma source, i.e. derivation of magma by partial melting of probably tonalitic igneous protolith at moderate crustal levels for felsic granites, whereas hybrid granitoids appear to be products of juvenile mantle-crust interaction, in an active continental margin setting.

Anomalous radioelemental concentration (upto 0.033% U₃O₈ and 0.30% ThO_2; n=61) has been recorded in Kinwat granitoids, especially close to the contact zones with mafic intrusives and shear zones. Distribution patterns of heat producing elements (U, Th and K) in these granitoids have indicated substantially high heat production values (9.55-97.78 μWm^-3), which might have played important role in uranium remobilisation and concentration by supporting hydrothermal gradient along the dilatant structures. Considering highly labile nature of uranium in this reactivated terrain, the Kinwat granitoids form a fertile provenance to mineralisation under favourable conditions, especially in Neoproterozoic cover sediments in adjoining areas.

Keywords

Kinwat Crystalline Inlier, High Heat Producing (HHP) Granite, Radioactivity, Kaddam Fault, Maharashtra.

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V. Rajamani ¹, K. Shivkumar ¹, G. N. Hanson ², J. W. Granath ²

Affiliations
1 School of Environmental Sciences, Jawaharlal Nehru University, New Delhi 110067, IN
2 Department of Earth and Space Sciences, State University of New York at Stony Brook, New York 11794, US

Abstract

The amphibolites in the Kolar schist belt include four textural types, schistoic, granular, massive and fibrous and occur in abundance in that order. The fibrous variety consists of two coexisting calcic amphiboles (A1 rich hornblende and A1 poor actinolite). The other three varieties contain hornblende and plagioclase (An₄₀ to An₈₅). The texture, mineralogy and mineral chemistry suggest metamorphism in the middle to upper amphibolite facies.

Major and Rare earth elements (REE) data indicate that (a) the fibrous amphibolite is somewhat similar to high-Mg basalts of Archean greenstone belts but with a strongly, heavy REE depleted pattern, (b) the other three varieties are similar to low-K oceanic tholeiites with slightly light REE depleted patterns and with strong positive Eu anomalies, and (c) the two groups do not represent primary melt compositions generated by the partial melting of a pyrolite mantle. It is concluded that the Kolar amphibolites must have been evolved from at least two separate parent magmas generated from different temperature and pressure (depth) conditions.

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