RADIOELEMENTAL EQUILIBRIUM-DISEQUILIBRIUM AND TRACE ELEMENTAL STUDIES OF QUARTZ PEBBLE CONGLOMERATES FROM THE WESTERN MARGIN OF KOIRA-NOAMUNDI IRON ORE BASIN, ORISSA, INDIA

Kalyan Chakrabarti¹*, M. K. Sandilya¹, N. R. R. Ecka¹, P. V. Ramesh Babu² and P.S.Parihar²

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy,
¹Jamshedpur ; ²Hyderabad
*e-mail: kchakrabarthy.amd@gov.in

Abstract

The Late Achaean-Early Proterozoic fluvial pyritiferous gold and uranium bearing quartz pebble conglomerate (QPC) deposited over cratonised granite-greenstone basement is well known across the globe. The QPC represents the earliest sediments (> 2200 Ma age) developed largely under an anoxic atmospheric condition. In eastern India, uraniferous QPC bearing occurrences at the base of Iron Ore Group (IOG) basins and Dhanjori Basin are situated in Orissa and Jharkhand states. They occur as peri-cratonic basins around Singhbhum Granitic batholiths, viz. Badampahar-Garumahisani basin, to the east of Singhbhum Granite, Daitari basin, to the south and Koira basin, located east of Bonai granite (Singhbhum Granite equivalent). This paper discusses the nature of radioactive QPC occurrences at Taladih, Sarlanga, and Soyamba areas situated along the western margin of Koira Basin in terms of their physical characteristics, radioelemental distribution and their disequilibrium behaviour vis-à-vis the trace elemental distribution. The studies showed that the radio-elemental data of Soyamba and Sarlanga samples essentially belong to the same population and are distinctly different from that of Taladih samples. Soyamba-Sarlanga samples show strong disequilibrium in favour of daughters with evidences of post-depositional hydrothermal fluid activity whereas the Taladih samples represent a less open system reflected by lesser order of disequilibrium in favour of daughters and very poor correlation of uranium with Co and Cu suggesting mild post-diagenetic hydrothermal alteration. Low correlation of uranium with thorium in all the areas suggests that the uranium bearing detrital mineral phases were originally impoverished with thorium, indicating their derivation from more evolved granitic and/or pegmatitic sources. Strong correlation of thorium with Y, La, Zr etc. suggests its association in the resitate detrital mineral phases in the QPC matrix.

Keywords: Radioelements, Disequilibrium, Trace elements, Quartz pebble conglomerate, Koira-Noamundi, Iron ore basin, Orissa, India.

URANIUM MINERALIZATION ALONG THE NORTHEASTERN MARGIN OF PROTEROZOIC CHHATTISGARH BASIN AROUND CHITAKHOL, CENTRAL INDIA: A PETROMINERALOGICAL STUDY

P.K. Gupta¹, Rajeeva Ranjan¹, A.R.Mukundan¹, M.S.M.Deshpande²,
V.K.Shrivastava¹ and R.S. Yadava¹

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
¹ Nagpur; ² Hyderabad

Uranium mineralization occurs along the unconformity contact between the basement granites and the overlying Chandrapur sediments of the Chhattisgarh Supergroup along the northeastern margin of the Chhattisgarh basin around Chitakhol area, Korba and Janjgir - Champa districts, Chhattisgarh. A number of uranium occurrences, spread over an area of 20 km², have been delineated with surface samples analyzing up to 0.39 %U₃O₈ in sediments, 2.72 %U₃O₈ in basement granites and up to 0.21 %U₃O₈ in basic dykes. The uranium mineralization is confined to the basement granites and the overlying sediments proximal to the unconformity contact. The basic dykes traversing the basement granites are also mineralized.

The mineralized samples are characterized by high content of total FeO (up to 27.23%) and Ba (up to 857ppm). Sympathetic relation of uranium with Fe₂O₃ in surface samples indicates involvement of Fe-rich hydrothermal activity in the process of uranium mineralization. High V (up to 319ppm) and Cr (up to 77ppm) indicate involvement of basic activity. Since the host rocks are highly altered, major and trace elements content shows a wide range.

Petromineralogically, the mineralized sediments of Chandrapur Group are immature, medium to coarse-grained chlorite-subarkose, ferruginous sublithic arenite, ferruginous shale and carbonaceous shale – siltstone intercalations. Wacke and quartz conglomerate are characterized by the presence of chlorite, sericite, pyrite and hydrous iron oxide (goethite). Presence of intermittent fine and coarse layers indicates the fluctuations in the energy regime of depositing medium. Poorly sorted and immature nature with angular to sub angular shape of their clasts reveal short to moderate distance of transportation from the provenance, which are comprised of igneous, metamorphic and basic volcanic rocks. Accessory glauconite grains indicate marginal marine to marine environment of deposition. The basic rocks in the area are altered glass-bearing basalts. QAP plots of basement granites fall in the field of syeno- to monzo-granites. The granites are highly altered (chloritised, kaolinised and ferruginized) particularly near the unconformity contact.

Uranium mineralization at the depth is associated with carbonaceous black shale and is represented by coffinite and pitchblende. Uraninite, brannerite with “U-Fe-Ti” complex, meta-autunite and uranophane also contribute to the mineralization. However, in surface and near surface samples uranium occurs in adsorbed state on to goethite and also as filling the criss-cross fractures. Fracture filled, epigenetic, hydrothermal type of uranium mineralization related to the Proterozoic unconformity is manifested.

Keywords : Uranium Mineralization, Chhattisgarh Basin, Chitakhol, Central India.

PETROLOGY OF THE REE- AND Y-BEARING GRANITOIDS FROM THE RAIKERA-KUNKURI AREA, CENTRAL INDIA

Yamuna Singh¹ and L.S.R. Reddy²

Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy,
¹Hyderabad ; ²Nagpur
¹E-mail : yamunasingh2002@yahoo.co.uk

Abstract

The granitoids of the Raikera-Kunkuri area form a part of the Precambrian Chhotanagpur granite gneiss complex (CGGC) terrain. This paper presents the results of petromineralogical, modal compositional, and petrochemical studies of three textural types of granitoids: (i) coarse-grained porphyritic granitoid (PRG), (ii) medium-grained (a) grey granitoid (GG) and (b) pink granitoid (PG), and (iii) fine-grained grey granitoid (FGGG). Based on the IUGS recommended parameters, the granitoids, in general, can be classified as: (i) PRG: hornblende-biotite granite (2 no) and biotite granite (9 no), (ii) GG: muscovite-biotite granite (24 no) and muscovite granite (1 no), and (iii) FGGG and PG: biotite granite and muscovite-biotite granite, respectively. Despite apparent mineralogical similarities, significant differences characterise the various types of granitoids.

The whole-rock chemical data suggest that, similar to the modal compositions, the chemical compositions of the granitoids are also, by and large, similar. Chemically, like the classification based on modes, all the granitoids can also be classified as granite (ss). Nevertheless, the PRG shows a distinct chemical transition from adamellite to granite, whereas, the GG, FGGG, and PG are, chemically, truly restricted to granite composition. However, the petrochemical characteristics of the PRG and GG clearly demonstrate that the former is chemically less evolved than the latter. The FGGG has highest SiO₂ (av. 73.35%), whereas, the PG has SiO₂ (av. 72.08%) and K₂O/Na₂O ratio (av. 2.08) close to that of the GG. The similarity of SiO2 contents and K₂O/Na₂O ratios of the PG and GG might be because both possibly represent the same initial episode of granite magmatism.

Evaluation of the available data indicates that the granitic melt was generated in response to deformation and extensive regional metamorphism coeval to F3 deformation and M3 metamorphism known from the CGGC terrain. After generation of the melt, its initial emplacement and crystallisation took place at deeper level, where an early differentiate as porphyritic granite formed. Later, a relatively more chemically evolved melt moved to a shallower level, where crystallisation of the medium-grained GG, including the associated coarse-grained muscovite, took place. The distinctly fine-grained nature and limited areal extent of the FGGG make it possibly a phase different from the PRG-GG phase. Accordingly, it may be taken to represent a localised granitic activity, unrelated to the widespread former granitic activity. As against 1005 Ma age of the GG, the distinctly younger isochron age of the pink granite (815 Ma), with signatures of metasomatism in PG and the proximity of PG to FGGG, it appears that the FGGG was, perhaps, responsible for the genesis of the PG. Accordingly, the genesis of the FGGG melt and PG might be linked with the younger metamorphic processes at ~815 Ma. Significantly, the Na₂O/Al₂O₃ vs. K₂O/Al₂O₃ plots reveal that the PRG, GG, FGGG, and PG are the products of the melts derived from crustal material by metamorphism and anatexis of metasedimentary suite.

The first phase of the LREE mineralisation was associated with the emplacement of the large-scale granitic bodies in the form of PRG-GG at ~1005 Ma, whereas, the second (and younger) phase was linked with granitic activity at 815 Ma, represented by the FGGG and pink granite. In contrast, the heavy rare earth element (HREE) mineralisation in the form of xenotime, hosted in the FGGG and PG, took place at ~815 Ma, which was accompanied by a second phase of the LREE mineralisation.

Keywords : Petrology, Granitoids, Monazite, Xenotime, Raikera-Kunkuri, Central India.

URANIUM MINERALIZATION IN THE MESOPROTEROZOIC BANGANAPALLE FORMATION NEAR NAGAYAPALLE, CUDDAPAH BASIN, ANDHRA PRADESH

Himadri Basu¹*, D. Hanumanthappa², B. Saravanan³, T. Harikrishnan¹, M. Rengarajan², Sangeeta Bhagat³ and Mahendra Kumar⁴

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
¹Hyderabad, ²Shillong, ³Bangalore and ⁴Jamshedpur
*Author for correspondence. E-mail: himadribasu.amd@gov.in

Abstract

Cuddapah Basin is the hub of uranium exploration for years together in India. Initial efforts were for quartz-pebble-conglomerate type mineralization. However, the emphasis later shifted towards dolostone-hosted mineralization and finally to unconformity-associated uranium mineralization. The recent finding of uranium mineralization associated with the Banganapalle Formation near Nagayapalle is the outcome of continuous exploration input in the Cuddapah Basin over years.

Uranium mineralization (up to 0.278% U₃O₈) associated with the Mesoproterozoic Banganapalle Formation near Nagayapalle is represented by pitchblende and autunite. Pitchblende occurs as tiny grains in the intergranular spaces and along grain boundaries; and also at places replaces pyrite and covellite grains. The geological set-up indicates that the geodomain is favourable for uranium mineralization.

GEOLOGY AND URANIUM MINERALISATION AROUND AMPULLI AREA, PAPUM-PARE DISTRICT, ARUNACHAL PRADESH, NORTH- EAST INDIA

Ajay Kumar ¹, S. N. S. Birua ¹ and A. R. Raju²

Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy
¹Jamshedpur; ²Hyderabad

Abstract

Uranium mineralisation associated with Middle Proterozoic Bomdila Group (Daling equivalent) metasediments have been located intermittently over a strike length of 310 m with 0.11 to 2.0 m thickness around Ampulli area of Papum-Pare district, Arunachal Pradesh. The metasediments trend NE-SW and dip 20^o- 85^o due either side. The grab and trench samples assayed 0.012 - 0.36 %eU₃O₈, 0.006 - 0.19 %U₃O₈ (beta/gamma), 0.009 - 0.235 %U₃O₈ (Chem.) and less than 0.010% ThO₂. The host rocks have been identified as tourmaline bearing biotite-quartz schist, garnet bearing muscovite-biotite-quartz schist and muscovite-biotite schist. Uraninite, brannerite and U-Ti complex are observed with uranocircite and meta-uranocircite, the secondary uranium minerals. Replacement of uraninite by molybdenite and pyrite suggested earlier oxide and later sulphide phase. Partial chemical analysis indicated aluminous nature of the host rock and their high K₂O/Na₂O (3.3-10.73) ratios are suggestive of predominance of potash feldspar over sodic and effects of potash metasomatism. Both syngenetic as well as epigenetic hydrothermal origin of uranium mineralisation has been suggested .

Keywords : Uranium mineralisation, Bomdila Group, Ampulli, Arunachal Pradesh, India.

URANIUM MINERALIZATION IN THE LOWER MAHADEK SANDSTONES OF LAITDUH AREA, EAST KHASI HILLS DISTRICT, MEGHALAYA

K. Mahendra Kumar ¹, P. Bhattacharjee² and N. Ranganath³

Atomic Minerals Directorate for Exploration & Research,
Department of Atomic Energy,
¹Jamshadpur, ²Shillong, and ³ Nagpur

Abstract

Significant uranium mineralization hosted in feldspathic sandstone of Upper Cretaceous Lower Mahadek Formation has been located at Laitduh, East Khasi Hills district, Meghalaya. Two mineralized horizons have been identified within Lower Mahadek Formation with vertical separation of 30m. Samples from upper horizon have assayed upto 0.17% U₃O₈, whereas samples from lower mineralized horizon have assayed upto 0.50% U₃O₈. The radioactive minerals identified are coffinite and pitchblende occurring in association with carbonaceous matter.

Keywords : Uranium mineralization, Sandstone, Laitduh, Meghalaya

U-Th MINERALISATION IN BERACH GRANITE AROUND BELWA, DEVTALAI AND GUDALIA, BHILWARA, RAJASTHAN

S.N.Saini¹, G.S. Yadav² and Sohail Fahmi³

Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy ,
¹Shillong,²Jaipur, and ³Hyderabad

Abstract

Uranium – thorium mineralization in Belwa, Devtalai and Gudalia areas is hosted in pink phase of Berach Granite (BG) at the western intrusive contact with the rocks of Mangalwar Complex (MC) in the northern apical region of the granite body. It occurs at the foot wall side of copper mineralization that is associated with quartz reefs. Although surface manifestation of mineralization is limited, its subsurface continuity has been traced over 5km length in between Belwa and Gudalia. Core samples of pink granite have radiometrically assed from 0.014 to 0.036 %U₃O₈, <0.01 to 0.032% U₃O₈ and <0.005 to 0.015 ThO₂. The Berach Granite (BG) has two phases. An early grey and later pink phase. The pink variety hosts mineralization and is a high silica, low-Ca and peraluminous granite, while the grey granite is characterised by low–silica and high-Ca content. Mineralisation falls along the Bharatpur-Mount Abu lineament, close to thrust zone of Mangalwars and Jahazpurs. Raioactivity due to uranium and thorium in pink granite is associated with titanomagnetite, zircon, ilmenite and monazite.

Keywords : Uranium mineralisation, Berach granite, Bhilwara, Rajasthan.

URANIFEROUS RHYOLITIC VEIN IN THE BASEMENT FRACTURES OF SINGHORA PROTOBASIN NEAR JUBA VILLAGE, RAIPUR DISTRICT, CHHATTISGARH

D.K.Sinha¹ and S.K.Jain²

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
Hyderabad¹, Nagpur²

Abstract

Uraniferous rhyolitic vein occupying fracture (N80°E-S80°W), is reported in the inlier exposed as basement (Sambalpur Granitoid) windows within the eastern margin of Singhora Group of rocks, near Juba village, in Raipur District of Chhattisgarh State. Chemically, vein shows granitic composition which is further confirmed by thin section studies. Presences of phenocrysts of bipyramidal quartz, euhedral senidine and biotite in fine grained glassy to devitrified groundmass classified the rock to rhyolitic category. The rhyolitic vein (5 m X 1 m) analysed uranium (28 to 100 ppm) associated with limonite, goethite and apatite. This Uranium bearing rhyolitic vein is fracture filled in the basement rocks and has significance in the light of uranium-sulphide mineralisation already reported in the overlying sedimentary rocks of Singhora Group exposed very near to this location. Presence of such acid volcanic activity during Singhora sedimentation or post Singhora basement activation is important from the uranium exploration point of view.

Keywords : Uraniferous rhyolitic vein, Singhora-Chhattisgarh basin, Sambalpur Granite.

APPLICATION OF X-RAY DIFFRACTION TECHNIQUE FOR DETERMINING TRICLINICITY OF ALKALI-FELDSPAR FROM THE RARE METAL PEGMATITES OF THE PANDIKIMAL AREA, NORTH ORISSA, INDIA

Yamuna Singh¹ and K.K. Pandey²

Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy,
¹Hyderabad ; ²Nagpur
¹E-mail: yamunasingh2002@yahoo.co.uk

Abstract

The zoned rare metal pegmatites of Archaean age in the Jharsuguda district of north Orissa, eastern India, are well-known for their potentiality for Nb, Ta, and Be minerals. They also contain limited Li, Bi, Th, and U minerals. Because of the economic concentrations of the ore minerals of Nb-Ta and Be, they are being mined for recovering columbite-tantalite and beryl. In this paper, the values of triclinicity of alkali-feldspars, determined by x-ray diffraction, are presented and, based on the same data, the evolutionary history of the rare metal pegmatites is traced. The values of triclinicity range from 0.83 to 0.97 with an average of 0.92. The high values of triclinicity suggest that the investigated alkali-feldspars from the rare metal pegmatites of the Pandikimal area belong to the category of maximum microcline. It would, thus, mean that during the crystallisation of alkali-feldspar, and by implication their host rare metal pegmatites, not only was the rate of cooling slow, the temperature of crystallisation was also falling. Accordingly, it is interpreted that the rare metal pegmatites of the Pandikimal area crystallised slowly under a falling-temperature regime in deep-seated plutonic conditions. The presence of large beryl crystals in the rare metal pegmatites also supports this interpretation.

Keywords : X-ray diffraction. Triclinicity. Alkali feldspar. Rare metal pegmatite. Pandikimal. Orissa.

ANOMALOUS URANIUM CONCENTRATION IN ARCHAEAN BASEMENT SHEAR AT DHANI BASRI AND ITS SIGNIFICANCE ON SOUTHERN MARGIN OF ALWAR SUB-BASIN, RAJASTHAN

B. Panigrahi, T. S. Shaji, G. S. Sharma, O. P. Yadav and L. K. Nanda

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
Jaipur.

Abstract

Prominent shear zones cutting through the basement and cover rocks of Delhi Supergroup have been recognized in Dhani Basri – Ramewala sector of Dausa district, Rajasthan. One such shear zone traversing the granite gneiss (Archaean basement) has been observed at Dhani Basri. The sheared rock is exposed in the form of a small hump and gives appearance of quartzite due to intense silicification. Grab samples collected from the shear zone rock analysed upto 93ppm U₃O₈ and <10ppm ThO₂, which is anomalous in comparison to unsheared rock which analysed 51ppm eU₃O₈, upto 5ppm U₃O₈ and 80ppm ThO₂. Gamma-ray logging of boreholes drilled by GSI across this shear zone indicated uranium mineralization of the order of 0.030% eU₃O₈ x 5.40m and the primary radioactive mineral has been identified as uraninite. The extension of Dhani Basri shear zone inside the cover rocks of Meso-Proterozoic Delhi Supergroup of rocks of Alwar sub-basin is of paramount importance in locating unconformity related as well as hydrothermal vein type uranium mineralization.

Keywords: Shear zones, Dhani Basri, Dausa district, Rajasthan, Delhi metasediments, Banded Gneissic Complex.

GEOCHEMISTRY OF BARAPANI ARENITES IN UMPHYRNAI-MAWKYNREW- MAWRYNGKNENG AREA, EAST KHASI HILLS, MEGHALAYA: IMPLICATIONS ON PROVENANCE, PALAEOWEATHERING, K-METASOMATISM AND URANIUM MINERALISATION

M. Nagendra Kumar¹, Pradeep Pandey², M. Rengarajan² and R. Mohanty²

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
¹Bangalore; ²Shillong
E- mail: nagendra_amd@ yahoo.com

Abstract

Geochemical studies on Barapani arenites of Shillong Basin, Meghalaya Plateau, around Umphyrnai-Mawkynrew-Mawryngkneng area, East Khasi Hills, Meghalaya were carried out to understand provenance, palaeoweathering and uranium mineralisation along unconformity contact between Tyrsad and Barapani Formations of Shillong Group.

The studies reveal higher concentration of SiO₂ (Avg. 82.7%) in Barapani arenites. Antipathic relationship of SiO₂ with Al₂O₃, K₂O and CaO indicates that Barapani arenites are highly matured. Positive correlation between K₂O and Al₂O₃, Ba and Rb indicates presence of clay minerals which is further substantiated by positive association of Al₂O3 with K₂O, Na₂O, TiO₂ and MgO. Higher ratios of SiO₂/ Al₂O₃ and K₂O/ Na₂O indicates felsic provenance with dominance of K-feldspar (K₂O up to 2.2%). Higher amount of Cr (58 ppm), Ni (41 ppm), Cr/ Ni (1.5 ppm) and Th/ Cr (Avg. 0.98) and Cr/ Th (Avg. 5.18) ratios further suggest the felsic nature of source rocks. The A-CN-K plot shows that Barapani arenites scatter above feldspar join along A-K line due to lowering of CIA values and related K-enrichment. The discriminate diagram between K₂O/ Al₂O₃ vs MgO/ Al₂O₃ ratios reveals illitisation in these arenites. Lowering of chemical index of alteration values and presence of illite also indicate K-metasomatism in Barapani arenites.

Barapani arenites along alteration zones have U (total) and U (leachable) values up to 8ppm and 5ppm respectively in comparison to average uranium content 0.5ppm in quartzite. The K-metasomatism and highly oxidised nature of Barapani arenites suggest migration of uranium and probable uranium enrichment at unconformity surface.

Keywords : Geochemistry, Barapani arenites, East Khasi Hills, Meghalaya.

URANIUM MINERALISATION IN BARAPANI FORMATION OF MAWBEH AREA, EAST KHASI HILLS DISTRICT, MEGHALAYA

C.S. Gupta¹, M. Nagendra Kumar², Amit Majumdar³ and K. Umamaheshwar⁴

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
¹Shillong, ²Bangalore, ³Nagpur and ⁴Hyderabad
e- mail: nagendra_amd@ yahoo.com

Abstract

Proterozoic Shillong Basin of Meghalaya comprises metapelites of Paleoproterozoic Tyrsad and arenaceous siliciclastics of Mesoproterozoic Barapani formations. Two major igneous activities, in the form of basic dykes/ sills and younger granites of Neoproterozoic age, intruding Proterozoic sediments, are reported from Shillong Basin. Significant uranium mineralisation, with values up to 0.1% U₃O₈, associated with NE-SW trending shear zone in Barapani Formation is discovered at Mawbeh area, Pynursla Plateau. The mineralised Barapani has undergone hydrothermal alterations in the form of sericitisation, chloritisation, illitisation and kaolinisation. Petrographic studies reveal that the host rocks are ortho-quartzite, subfeldspathic arenites, quartz wacke, sericite phyllite, quartz-sericite-chlorite rock and quartz wacke. X-ray diffraction (XRD) studies of radioactive Barapani quartzite revealed the presence of uraninite.

Keywords: Uranium mineralization, Barapani Formation, Mawbeh, Meghalaya

URANIFEROUS CALCRETES OF THAR DESERT FROM KANJI KI SIRD AND JODHSINGH KI SIRD AREAS, JODHPUR DISTRICT, RAJASTHAN

G. S. Yadav, S. K. Garai and M. K. Khandelwal

Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy,
Jaipur.
e -mail: gsyadav.amd@gov.in

Abstract

Secondary uranium mineral-bearing calcrete formations have been located for the first time in India at Kanji Ki Sird (27°29'30"N, 72°28'06"E) and Jodhsingh Ki Sird (27°29'17"N, 72°29'04"E) areas in Thar Desert environs of the Jodhpur district of Rajasthan. Seven zones of uraniferous calcretes in varying dimensions from 25m x 25m to 500m x 200m have been delineated by pitting and trenching over an area of 2 sq. km. The thickness of the uraniferous (assayed up to 0.047 %U₃O₈ and chemical up to 0.024 %U₃O₈) calcrete horizon varies from 30 cm to about a meter. These zones fall within a half-kilometer wide WNW-ESE trending low gradient drainage channel. Greenish to yellowish coloured secondary uranium minerals occur along cavities, vugs and fractures in calcretes and along rock fragment boundaries. Uranium minerals identified by X-Ray Diffraction technique are tyuyamunite [Ca(UO₂)2(VO₄)2.5-8H₂O], wyartite [Ca₃U (UO₂)6(CO₃)2(OH)163-5 H₂O] and meta-autunite [Ca(UO₂)2(PO₄)2.10-12H₂O]. The Bap Boulder Bed and Badhaura sandstone exposed in the catchment area are the provenance rocks for uranium.

Keywords: Uraniferous Calcrete, Thar Desert, Jodhpur, Rajasthan

GEOCHEMISTRY AND PETROGENESIS OF RADIOACTIVE LAMPROPHYRES ASSOCIATED WITH ERINPURA GRANITES AROUND ISRA, SIROHI DISTRICT, RAJASTHAN

P.B. Maithani¹, Rahul Banerjee^2* and Ravindra Gurjar²

Atomic Minerals Directorate for Exploration and Research
Department of Atomic Energy
¹Hyderabad ; ²Nagpur
* Email: rahul_bnrg@gmail.com

Abstract

Remote sensing studies in parts of Sirohi district resulted in delineation of a number of faults/shear zones, quartz reefs, pegmatites, basic and lamprophyre dykes in the environs of Deesa–Sirohi lineament in Erinpura granite country. Significant uranium anomalies were recorded in lamprophyres at the faulted contact with granites (upto 0.038% U₃O₈) and in two parallel NW–SE trending dykes (upto 0.027% U₃O₈) about 1.5 km SW of Isra. In this part, intersection of N–S, NW–SE and ENE–WSW trending Iineaments is exhibiting intense brecciation, ferruginisation vis-à-vis assimilation of lamprophyre and granite along the fault zone. The granitic rocks of this sector have shown comparatively higher radioelemental concentration (11ppm U₃O₈ and 78ppm ThO₂; n=5) than general abundance, and enrichment of uranium in the vicinity of mineralised zone (U/Th – 0.8) signifying labile nature of uranium in the system. Petrographically, Isra lamprophyres exhibit porphyritic panidiomorphic texture as defined by euhedral phenocrysts of hornblende and occasionally mililite in fine grained groundmass of feldspars, chlorite, augite and titanium-iron oxides, and can be classified as ‘spessartite’ belonging to calcalkaline lamprophyre (CAL) branch. Chemically, these are characterised by relatively low SiO₂ (42.26–53.69%), K₂O (0.40–1.67%), moderately high MgO (1.56–4.76%), CaO (3.1–6.47%) and high Al₂O₃ (10.51–14.15%), FeO(total) (12.84–26.45%), TiO₂ (1.98–6.13%) concentrations with low K₂O/Na₂O ratio (0.13–1.47) and Mg No. (14.63–31.58). In addition, they display enrichment of Zr (488–986ppm) and Y (74–124ppm). Major and trace elemental chemistry points toward subalkaline nature with basalt to basaltic andesite composition. The associated Erinpura granites exhibit typical peraluminous nature (A/CNK: 1.36–1.54) with high-K calcalkaline trend and fall in granite field in various plutonic discrimination diagrams. They exhibit development in syn-collisional tectonic environment. The emplacement of lamprophyre dykes vis-à-vis brecciation have provided the necessary thermal gradient for the mobilisation of uranium from the Erinpura granites while fault zones acted as channelways and iron provided the necessary reducing environments for fixation and concentration of uranium.

Keywords: Lamprophyre, Erinpura granite, uranium mineralisation, Isra, Sirohi, Rajasthan.

GEOCHEMISTRY OF A -TYPE KUILAPAL GRANITE FROM NORTH SINGHBHUM MOBILE BELT, EASTERN INDIA: IMPLICATION FOR RADIOELEMENTAL CONCENTRATION

Joydip Sen¹, C. Murugan, A. K. Dwivedi, A. K. Bhatt, and P. V. Ramesh Babu²

Atomic Minerals Directorate for Exploration and Research,
Department of Atomic Energy
Jamshedpur ; ²Hyderabad
Email : joydipsen@yahoo.co.in

Abstract

The 1.6 Ga old Kuilapal granite (KG), with areal extension of 80 km² area, is intrusive into Palaeo to Meso Proterozoic Singhbhum Group of rocks in the northeastern part of North Singhbhum Mobile Belt (NSMB) of East India Shield. The KG is medium to coarse-grained, and commonly shows gneissic banding parallel to regional foliation of the country rock. After combining field relations, petrographic observations and new geochemical data, it is inferred that Kuilapal granite postdates deformational events of the mobile belt. Geochemically, Kuilapal granite is fairly silica-rich, alkali dominated and has high total FeO/MgO and Ga/Al ratios, but low to moderate CaO content. It is metaluminous (av. A/CNK = 0.95) and contains abundant alkali feldspar and Fe-rich biotite and amphibole. It displays notable enrichment of Rb, Th, U, K, Nb, Zr, Y and REE and depletion of Ba, Sr, P and Ti with negative Eu/Eu* anomaly. The mineralogical and geochemical characters indicate that it is A-type granite, which formed in ‘Within Plate Granite’ (WPG) tectonic set up, which is in contrary to the earlier view of peraluminous S-type suite. Compared to average crustal composition, the A-type Kuilapal granite is distinctly fertile for U, Th, Y, Nb and rare earths elements. Based on zircon solubility model and liquidus phase relation, the temperature of the granitic melt has been estimated around 850°C ± 50°C at 5 Kbar pressure. This P-T estimation is consistent with experimental results for the generation of metaluminous A-type granite. Thus, the granitic melt could be derived from melting of calc-alkaline source (possibly Singhbhum Granite or any other equivalents) beneath supracrustal, but fractional crystallization of alkali feldspar and plagioclase had played prominent role in the subsequent evolution of the magma. The present geochemical data and thermal characteristics are suggestive of generation of the rock in an extensional regime of the mobile belt. In this tectonic milieu, polymetallic-rich intrusive Kuilapal granite offers favourable geological environment for prospecting and exploration of radioactive, rare metals and rare earth minerals in the North Singhbhum Mobile Belt.

Keywords: Geochemistry, A-type granite, Kuilapal, Eastern India, Radioelemental concentration.

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