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Zakaulla, S.
- A Discussion on the Physico-Chemical Factors for the Development of Pits in Gulcheru Quartzite in the Southwestern Margin of Cuddapah Basin, A. P.
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1 Atomic Minerals Directorate for Exploration and Research, Bangalore-560072, IN
2 Atomic Minerals Directorate for Exploration and Research, Hyderabad-500016, IN
1 Atomic Minerals Directorate for Exploration and Research, Bangalore-560072, IN
2 Atomic Minerals Directorate for Exploration and Research, Hyderabad-500016, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 72, No 4 (2008), Pagination: 467-470Abstract
Miniature pits of varying size and shape are found in the topmost arenaceous layers of the Gulcheru quartzite. Though pits in sedimentary rocks form in a variety of ways, in clean beach sands they owe their origin to mainly physical processes. Small pits, found in the Gulcheru quartzite, have been formed as a result of interplay of difierent physico-Chemical factors which prevailed in syn- as well as post-Depositional environments. In addition to different agents of physical weathering, which played a vital role in the formation of pits in the Gulcheru quartzite, syn-depositional precipitation of iron oxides and their syn-to post-diagenetic chemical changes are believed to be the main chemical factors.Keywords
Pits, Ferric-Hydroxide, Gulcheru Quartzite, Cuddapah Basin, Andhra Pradesh.
- Petrology and Geochemistry of Meso-Proterozoic Arenaceous Sediments of the Barapani Formation of Shillong Group in Parts of Meghalaya and Assam
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Affiliations
1 Atomic Minerals Directorate, Department of Atomic Energy, Bangalore, IN
2 Atomic Minerals Directorate, Department of Atomic Energy, Hyderabad, IN
3 Atomic Minerals Directorate, Department of Atomic Energy, Nagpur, IN
4 Atomic Minerals Directorate, Department of Atomic Energy, Shillong, IN
1 Atomic Minerals Directorate, Department of Atomic Energy, Bangalore, IN
2 Atomic Minerals Directorate, Department of Atomic Energy, Hyderabad, IN
3 Atomic Minerals Directorate, Department of Atomic Energy, Nagpur, IN
4 Atomic Minerals Directorate, Department of Atomic Energy, Shillong, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 71, No 5 (2008), Pagination: 683-692Abstract
In the Proterozoic Shillong Group, the Meso-Proterozoic arenaceous Barapani Formation, unconformably overlies the Paleo proterozoic Tyrsad Formation. Argillaceous quartz arenite, quartzite and quartz wacke are the constituents of Barapani Formation, in both Meghalaya plateau and Mikir Hilis in Assam. Samples from both the domains contain same type of detrital grains. Monocrystalline quartz forms about 70 to 90 % and feldspars and lithic fragments form minor part of the framework constituents. Sericite is the major mineral in matrix. Geochemical data (major and trace elements) of these arenites show overall similar elemental composition of all the samples from both Meghalaya plateau and Mikir Hills, Assam, indicating constancy of provenance. However, samples from the Mikir Hills as compared to that from Meghalaya Plateau show depletion in FeO(t), CaO, and MgO and enrichment in V, Cr, Co, Ni and Cu. Samples from both the Meghalaya plateau and Mikir Hills indicate a passive margin tectonic setting of sedimentation.Keywords
Petrology, Geochemistry, Mid-Proterozoic, Barapani Arenite, Meghalaya, Mikir Hills, Assam.- Geological and Geochemical Appraisal of Uranium Bearing Gulcheru formation of Cuddapah Supergroup, Gandi Area, Cuddapah District, Andhra Pradesh
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1 Atomic Minerals Directorate for Exploration and Research, Nagarabhavi, Bangalore, IN
2 Atomic Minerals Directorate for Exploration and Research, Nagarabhavi, Shillong, IN
1 Atomic Minerals Directorate for Exploration and Research, Nagarabhavi, Bangalore, IN
2 Atomic Minerals Directorate for Exploration and Research, Nagarabhavi, Shillong, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 64, No 6 (2004), Pagination: 719-730Abstract
Gulcheru Formation constitutes 200 m-250 m thick siliciclastic sediments Based on grain size texture and colour of the sediments, four distinct facies are demarcated They are pink massive quartzite, cross bedded grey quartzite, purple siltstone and pitted quartzite The ratios of Si/Al is higher (62 9 to 292 18) in pitted quartzite and lowest (2 122 - 18 247) in siltstone, where as grey quartzite has wide range of 3 78 - 8637 67 Ths difference is essentially due to higher quartz content in pitted quartzite and dominance of clays/shaly component in siltstone The wide range of Si/Al ratio in grey quartzlie is due to interlayering of siltstone/shale laminations/bands Distribution of uranium indicates grey quartzite (av U308= 9 9 ppm) and siltstone (av 15 42 ppm) have higher intrinsic uranium than that of pitted quartzite (average 5 6 ppm) and pink massive quartzite (average 7ppm) which is considered very high in comparison to normal sandstone (av = 0 5ppm, Taylor, 1965) Trace elements like Mo, V, Ni, Cu and Pb are enriched in mineralised grey quartzite Pitchblende is the man uranium mineral in grey and pitted quartzite unlts It occurs as fracture fillings and also as interstital material, associated intimately with chlorite Close association between pitchblende and sulphides like pyrite, chalcopyrite and galena is seen when pitchblende occurs as fracture fills Uranium in siltstone, is generally in adsorbed form with ferruginous material, where as associated trace elements like Mo (r = 0 515), V (r = 0 806), Nt (r = 0 4) and even Ti02, (r = 0 87) are well correlated with Al203, suggesting their clays/phyllosilicates U/Pb dating of uraniferous grey quartzite indicated ages of 1336k±4 Ma and 446±29 Ma suggesting remobilisation and concentration of intrinsic uranium.Keywords
Gulcheru Formation, Cuddapah Supergroup, Siliciclastic Sediments, Uranium incidence, Gandi Area, Andhra Pradesh.- Geochemistry and Petrogenesis of Anorogenic(?) Granitoids of West Garo Hills, Meghalaya
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Authors
Affiliations
1 Atomic Minerals Directorate for Exploration & Research, Jamshedpur - 831 002, IN
2 Atomic Minerals Directorate for Exploration & Research, Shillong, IN
3 Atomic Minerals Directorate for Exploration & Research, Bangalore, IN
4 Atomic Minerals Directorate for Exploration & Research, Hyderabad, IN
1 Atomic Minerals Directorate for Exploration & Research, Jamshedpur - 831 002, IN
2 Atomic Minerals Directorate for Exploration & Research, Shillong, IN
3 Atomic Minerals Directorate for Exploration & Research, Bangalore, IN
4 Atomic Minerals Directorate for Exploration & Research, Hyderabad, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 80, No 2 (2012), Pagination: 276-286Abstract
The granite in Samingiri - Dilsekgiri area occurs as discordant, isolated pluton within the migmatitic terrain of West Garo Hills district, Meghalaya. The pluton is exposed over 140 sq km (18 km × 8 km). It exhibits structures of solid state and piecemeal stoping effect proximal to the contact and enveloped by a contact metamorphic aureole of albite-epidote-hornfels facies. Modally, it is biotite-monzogranite and biotite-syenogranite with minor biotite, chlorite, epidote and sericite and accessories like zircon, apatite, allanite, pyrite, magnetite and sphene. Geochemically, it is marked by restricted composition (69-76 wt% SiO2), high alkalies, low Ca, metaluminous to strongly peraluminous (Molar Al2O3/CaO+Na2O+K2O = 0.95-1.54), high FeO/MgO, high Ga/Al, high contents of Rb, Sr, Ba, Y, Zr and Ce and depleted in Ti and P. The field observation, mineralogical and geochemical aspects indicate the post-tectonic nature of West Garo pluton more like as A-type granite formed by partial melting of lower crustal blocks followed by low to moderate degree of fractional differentiation. Low Ca, alkaline nature and peraluminous character point to A-type nature of West Garo granite significantly different from other granites of Meghalaya Plateau. Rb-Sr age (616 ± 86 Ma) of granite, however, corresponds to widespread Middle to Upper Pan African activity, a thermal event prevailed during Late Proterozoic - Early Palaeozoic (500-800 Ma) period, manifested in the form of several granitic intrusions in the basement gneissic complex and the overlying Proterozoic metasediments of the Shillong Group in Meghalaya Plateau.Keywords
West Garo Granite, Shillong Group, Meghalaya, Pan African Activity.References
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