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Chaki, Anjan
- Geochemistry of Shales from the Proterozoic Intracratonic Kaladgi- Badami Basin, Karnataka, Southern India as an Indicator of Palaeoweathering and Evolution of the Dharwar Craton
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1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Madhavadhara, Visakhapatnam - 530 018, IN
3 Atomic Minerals Directorate for Exploration and Research, Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, Madhavadhara, Visakhapatnam - 530 018, IN
3 Atomic Minerals Directorate for Exploration and Research, Department of Geological Sciences, Jadavpur University, Kolkata - 700 032, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 71, No 4 (2008), Pagination: 483-501Abstract
Shales of the Proterozoic Kaladgi Supergroup, occupying the intracratonic Kaladgi-Badami Basin in the Dharwar craton, are analyzed for mineralogical as well as major and trace element compositions. Field setting and elemental ratios, critical to provenance, indicate (1) major contribution from highly weathered Archaean silicic source rocks like Peninsular Gneiss and Closepet Granite, (2) the shales lack any systematic time-dependent variation of composition and (3) they record normal weathering history. Compared to the middle Archaean cratonic shales of the Dharwar craton, the Kaladgi shales are enriched in K2O, Th, La, Ce and Yb and depleted in MgO, Cr and Ni suggesting secular change in the Cpper crustal composition towards more felsic nature. The middle Archaean shales document acid leaching as an important weathering process, whereas the Kaladgi shales reflect intense weathering of the source similar to that of present day warm humid climate. In contrast to the extreme variability of the middle Archaean shales, the Kaladgi shales show smaller compositional variation suggesting development of Iarger platformal environment suitable for repeated recycling and efficient mixing. During late Archaean crustal growth, emplacement of juvenile granites into the crust and subsequent intracrustal melting has transferred huge amount of incompatible elements into the upper continental crust. The effect of ths change is clearly imprinted in the evolved composition of the Kaladgi shales.Keywords
Shale, Geochemistry, Proterozoic, Kaladgi Supergroup, Palaeoweathering, Upper Crustal Composition.
- Sedimentary Facies of Gulcheru Quartzite in the Southwestern Part of the Cuddapah Basin and their Implication in Deciphering the Depositional Environment
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1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Nagarbhavi, Bangalore 560 072, IN
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Nagarbhavi, Bangalore 560 072, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 69, No 2 (2007), Pagination: 347-358Abstract
Middle Proterozoic Gulcheru Quartzite marks the onset of sedimentation, after the Eparchaean unconforrnity, in the Cuddapah Basin. In the southwestern margin of the basin it is made up dominantly of orthoquartzites. On the basis of lithology, stratigraphic relationship, bedding characteristics, texture and colour of sediments and sedimentary structures, five lithofacies were recognized within Gulcheru Quartzite. The Gulcheru Quartzite, though dominantly of shallow marine origin, shows imprints of other depositional regimes. Detailed interpretation of the facies and study of their field relationships reveal that pink massive quartzite, the lowermost unit of Gulcheru Quartzite, is of fluvio-aeolian origin. Later marine transgression .led to the development of a moderate to low energy beach, which evolved with time into a barrier: spit complex.Keywords
Depositional environment, Facies analysis, Fluvio-Aeolian, Barrier-Spit, Gulcheru Quartzite, Cuddapah Basin, Andhra Pradesh.- Geochemistry of the Granites from Jharsuguda District, Orissa: Implications for Rare Metal Mineralisation
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Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Jamshedpur-831002, IN
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Jamshedpur-831002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 57, No 6 (2001), Pagination: 539-544Abstract
Jharsuguda Granite is intruded by several pegmatitic bodies, including rare metal bearing ones hosting columbite-tantalite and beryl. Geochemically, it is a silica-rich, metaluminous to peraluminous and potassic granite enriched in trace elements such as Rb, Nb, Zr, Y, Ga and Th, and depleted in Ba, Sr and Ti resulting in high Rb/Sr, Rb/Ba and Ga/Al ratios. The petromineraiogical and geochemical characters indicate Jharsuguda Granite as an A-type, within plate granite (WPG), emplaced around 650°-700°C at an assumed pressure of 5 kb. The granite has characteristics similar to niobium-yttrium-fluorine (NYF) bearing, A-type fertile granites.Keywords
Granitic pegmatites, Rare Metals, Jharsuguda, Orissa.- Cyclic Sedimentation and Classification of the Papaghni Group of Sediments, Cuddapah Basin, Andhra Pradesh
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Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, 6-3-124, Hastinapuri, Secundarabad - 500 094, IN
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN
2 Atomic Minerals Directorate for Exploration and Research, 6-3-124, Hastinapuri, Secundarabad - 500 094, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 71, No 3 (2008), Pagination: 363-370Abstract
The Mesoproterozoic Papaghni Group in the Cuddapah basin of southern Andhra Pradesh comprises mainly arenaceous, argillaceous and calcareous sediments. These sediments occur in sequences that are mappable on large scale (15000) and the sequences are idenified by unconfornities which are recognised by conglomerate/breccia beds in Vempalle Formation (Papaghni Group). Each sequence starts with near shore arenaceous and argillaceous sediments and ends up with relatively deeper marine chemical precipitate, viz dolomitic sediment, with these three constituting one cycle of sediments. The thickness of each cycle ranges from about twenty meters to hundreds of meters and three such cycles of sedimentation are identified. On the basis of the identification of cyclic sedimentation and bounding unconfornuties it is proposed that the Vempalle Formation of Papaghni Group may be classified into Lower, Middle and Upper members, which denote recurrence of similar depositional settings during the Vempalle sedimentation.Keywords
Cyclic Sedimentation, Papaghni Group, Cuddapah Basin, Andhra Pradesh.- Widespread Arkose along the Northern Margin of the Proterozoic Kaladgi Basin, Karnataka: Product of Uplifted Granitic Source or K-metasomatism?
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Authors
Affiliations
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Nagarabhavi, Bangalore-560072, IN
2 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad-500016, IN
1 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Nagarabhavi, Bangalore-560072, IN
2 Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Begumpet, Hyderabad-500016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 71, No 1 (2008), Pagination: 79-88Abstract
The basal conglomerate and sandstone all along the northern margin of the Proterozojc Kaladgi basm are highly enriched in K-feldspar ranging m size from sand to pebble They are believed to have undergone K-metasomatism by earlier workers However, the present study shows that K-feldspar grains present in these rocks are predominantly temgenous detrital This is indicated by sympathetic relation between constituent quartz and feldspar in size, presence of fresh rounded microcline with or without authigenic overgrowth, typical arkosic texture and geochemistry of the rocks, and their sharp erosional contact with the underlying granitoids An uplifted, restncted source, dominantly consisting of K-rich granitoids and pegmatites to the north of the basin supplied the immature arkosic detritus possibly under humid and warm climatic condition The testimony for the presence of a highly K-rich source weakens the theory of K-metasomatism in the Kaladgi basin as proposed by some earlier authors.Keywords
Arkose, Petrography, Geochemistry, Provenance composition and tectonism, Kaladgi Basin, Karnataka.- Geochemistry of Granitoids of Bilgi Area, Northern Part of Eastern Dharwar Craton, Southern India - Example of Transitional TTGs Derived from Depleted Source
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Authors
Affiliations
1 Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN
2 Department of Atomic Energy, Nagarabhavi, Bangalore - 560 072, IN
1 Department of Atomic Energy, Begumpet, Hyderabad - 500 016, IN
2 Department of Atomic Energy, Nagarabhavi, Bangalore - 560 072, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 73, No 6 (2009), Pagination: 854-870Abstract
Mildly deformed granitoids exposed around Bilgi in the northernmost part of the eastern Dharwar craton are divided into two groups viz. granodiorites and monzogranites. The granodiorites contain microgranular enclaves and amphibolite xenoliths, and show low-Al TTG affinity with high SiO2 (71-74 %), Na2O, Y and Sr/Y, moderate to moderately high Mg#, Cr and Ni, low to moderate LILE, and low Nb and Ta. However, compared to similar TTGs from different cratons the Bilgi granodiorites have distinctly higher K2O, K2O/Na2O, Rb and lower REE and Th. The amphibolite xenoliths are characterized by variable enrichment of K2O, Rb, Ba and Th and depletion of Ti, Zr and P compared to MORB. The microgranular enclaves are quartz diorite to granodiorite in composition with high Mg, Ni and Cr, and compared to MORB, are enriched in LILE and depleted in Ti and Y. The monzogranites, compared to the granodiorites, display higher SiO2, K2O and Rb with lower Mg#, although still maintaining the high Na2O, Ni and Cr and low REE character.The Bilgi granodiorites are explained as transitional TTGs late synkinematic with respect to regional deformation. Geochemical signatures and regional geological set up suggest that they are probably derived from partial melting of a highly depleted slab material (metabasalt) followed by variable contamination or assimilation of intermediate crustal rocks in a subduction zone set up. Late stage fluid activity on the granodioritic magma is probably responsible for the generation of monzogranites. The amphibolite xenoliths predate the granodiorites and possibly represent fragments of a schist belt carried away by the granitic magma. They are probably island arc basalt derived from mantle source that has been metasomatized by slab-derived fluids. The microgranular enclaves are coeval with the Bilgi granodiorites and also likely to be island arc magmas derived from mantle variably enriched in slab-derived and within-plate components.
Keywords
Transitional TTG, Petrography, Geochemistry, Petrogenesis, Geodynamic Setting, Dharwar Craton.References
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- Wavelength-Dispersive X-Ray Fluorescence Spectrometric Determination of Tantalum in Columbite-Tantalite Using Takα and an Lif 420 Analysing Crystal
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Authors
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1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
1 Atomic Minerals Directorate for Exploration and Research, Begumpet, Hyderabad - 500 016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 76, No 2 (2010), Pagination: 171-174Abstract
The paper proposes a simple, accurate, precise, and rapid method for determining the high atomic number (Z) major-element, tantalum (Z = 73), in the rare mineral, columbite [(Fe,Mn) (Nb,Ta)2O6] - tantalite [(Fe,Mn) (Ta,Nb)2O6], by wavelength-dispersive x-ray fluorescence spectrometry (WDXRFS). The other major-element in columbite-tantalite is the lower atomic number niobium (Z = 41). The method uses the characteristic radiation, TaKα, and an LiF 420 analysing crystal, to overcome the problems associated with the serious x-ray spectral-line interference of the secondorder NbKα and NbKβ with the first-order TaLα1 and TaLβ1 respectively.
Samples of columbite-tantalite ground to minus 300 mesh are blended with cellulose in the proportion of 1:1, and pressed powder-pellets are made from 1-g aliquots, with boric acid as a backing. The analytical standards consist of chemically analysed columbite-tantalite containing 5 to 80% by weight of Ta2O5. The instrumental parameters include a rhodium x-ray tube (operating voltage = 100 kV; current = 10 mA), air path, fine collimator (150 μm), and scintillation counter. The counting involves fixed time with three readings of 20s each on the peak and three readings of 20s each on one background.
The accuracy achieved is excellent (within 1.6 to 2.2%), as is the precision (within 0.4 to 2.4%). The time taken for determining Ta2O5 in a batch of twentyfour samples of columbite-tantalite, for a replication of four analyses per sample, by one operator using a manual WDXRF spectrometer, is only five hours.