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ABSTRACT Uranium is one of the most abundant element found in the Earth's crust. It can be found almost everywhere in rock and soil, in rivers and oceans. Traces of uranium are even found in food and human tissue (IAEA, 1996). Uranium is naturally present in all environmental media at very low concentrations (a few parts per million). Higher levels are present in certain areas, including those with natural uranium ores. In its natural state, uranium occurs as an oxide ore, U3O8. Additional compounds that may be present include other oxides (UO2, UO3) as well as fluorides, carbides or carbonates, silicates, vanadates, and phosphates. The environmental transport of uranium is strongly influenced by its chemical form. It is generally one of the more mobile radioactive metals and can move down through soil with percolating water to underlying groundwater. Uranium preferentially adheres to soil particles, with a soil concentration typically about 35 times higher than that in the interstitial water (the water between the soil particles); concentration ratios are usually much higher for clay soils (e.g., 1,600). Uranium can bio-concentrates in certain food crops and in terrestrial and aquatic organisms. However, data do not indicate that it biomagnifies in terrestrial or aquatic food chains. The U.S. Environmental Protection Agency (EPA) established a maximum contaminant level (MCL) for uranium in drinking water of 0.030 milligram per liter (mg/L). The International Atomic Energy Agency (IAEA, 1996) assigns uranium deposits to 15 main categories of deposit types, according to their geological setting and genesis of mineralization, arranged according to their approximate economic significance. 1. Unconformity-related deposits 6. Intrusive deposits (Alaskites) 2. Sandstone deposits 7. Phosphorite deposits 3. Quartz-pebble conglomerate 8. Collapse breccia pipe deposits deposits 9. Volcanic deposits 4. Breccia complex deposits 10. Surficial deposits 5. Vein type deposits 11. Metasomatite deposits 12 12. Metamorphic deposits 14. Black shale deposits 13. Lignite 15. Other deposits UNCONFORMITY RELATED URANIUM DEPOSITS Mid-Proterozoic – Archean basement unconformity is proved all over the world as the most potential zone hosting some of the world’s largest uranium deposits. The Srisailam sub basin is geologically mid to late Proterozoic in age and it is unconformably overlying the Archean granite basement. At present deposits of this type, spatially related to the Lowe-Middle Proterozoic unconformity are known only from Australia and Canada (Hoeve et al., 2005). The ore zones occur above, along and below the unconformity in Canadian deposits (Athabasca) or mainly found in the Lower Proterozoic rocks below the unconformity as in Australian deposits (Pine Creek Geosynclines). Uranium metallogeny for this group of deposits, as inferred from the case studies of deposits envisages a sequence of events that ultimately led to their formation often with high grades and large tonnage forming giant deposits. In Indian scenario the unconformity related uranium deposits, the first unconformity deposit was established in the intra – cratonic proterozoic Cuddapah basin at Lambapur – Peddagattu, Nalgonda district in Andhra Pradesh (Sinha et al., 1995) and then after works at Koppunuru, Guntur District, (Jeyagopal, 1996) at the proximity contact of Meso – Proterozoic Srisailam quartzite/ Neo – Proterozoic Banganapalle quartzite and the basement granite respectively. Unconformity uranium type deposits are divided into some outliers, like Chitrial, Lambapur- Peddagattu, Koppunuru, Amrabad outlier etc. The Geochemical Investigations for Uranium Mineralization in the outliers, NNW of Srisailam sub basin of Cuddapah Basin (Fig 1) has been carried out in the parts of Nalgonda and Mahaboob Nagar districts, Andhra Pradesh. Chitrial and Amrabad areas were selected for the Geochemical investigations. To accomplish the aims of this thesis the Geochemical investigations were carried in two phases in Chitrial and Amrabad areas of Nalgonda district and Mahaboobnagar districts respectively. 13 First Phase: Geochemical Reconnaissance Survey Second Phase: Detailed Geochemical Survey In Chitrial around 45 sq.km and in Amrabad around 20 sq.km area has been covered for Geochemical investigations. The Chitrial area falls into the toposheet No. 56L/13, 56L/14 and is located between , latitude and longitudes are N 160 29’ 42.3” and E 780 56’ 28.3” to N 160 34’ 45” and E 790 04’ 55.2. Amrabad belongs to toposheet No. 56L/15 and is located between latitudes and longitudes are N 160 25’ 15” to E 780 50’ 10” and N 160 27’ 15.5” to E 780 54’ 25”. Amraba d Fig 1 Location of Chitrial and Amrabad in Srisailam Basin belonging to Cuddapah formation (AMD, 1996) 14 GEOLOGICAL MAP OF SRISAILAM SUB BASIN Amrabad Uranium Deposit Fig 2 Location of Chitrial and Amrabad in the north eastern fringes of Srisailam sub-basin (AMD, 1996). OBJECTIVES: The following objectives are set for the Geochemical Investigations for Uranium Mineralization in the outliers – NW of Cuddapah Basin in the parts of Nalgonda and Mahaboob Nagar, Andhra Pradesh. 1. To understand the geology and geochemistry of the Srisailam quartzite outlier with reference to U- mineralization. 2. To establish geochemical signatures. 3. To study geochemical dispersions and mobility of U & its associated elements 4. The pH & EC environment around in unconformity zone. 5. To study the geochemical behaviour of U & its associated elements in primary and secondary environment. 15 6. Study of alteration effects and controls of mineralization. 7. Correlation of anomalies in rocks & soils. 8. A comparative study of U behaviour in Chitrial, and Amrabad. 9. Establishing pathfinders for U mineralization. METHODOLOGY (for accomplishing objectives): 1. Reconnaissance and detailed survey according to grid pattern 2. Litho, Pedogeochemical sampling and gamma ray survey. 3. Petrographic studies - Detailed Petro - mineralogical studies. 4. Geochemical analysis of samples for Rocks & Soils 5. Determination of pH and EC for soil samples 6. Kankar (Calcrete) formation and U mineralization. 7. Geochemical analytical data generation 8. Data processing and preparation of geochemical maps. 9. Statistical Analysis and. Data interpretation. 10. Correlation between U & its associated elements. Geology The major rock types are a) basement granites with cross cutting dykes and pegmatites, and b) quartzites around the Chitrial & Amrabad outliers. However thin and discontinuous shales and clays were present along the unconformity between granites and quartzites. Geological set - up: Chitrial and Amrabad outliers are located at NNW of Srisailam sub basin (Fig 2). There is a major Dindi River flowing between the two faults with strike direction as NW to SE separating Chitrial and Akkavaram. The Cuddapah Basin is situated in the eastern part of the Dharwar Craton and is one of the largest Proterozoic, intra-cratonic, sedimentary basins in India. It is crescent shaped and covers an area of around 44 500 km2 with a maximum length and breadth of 440 km and 145 km, respectively. The basin is in filled by a >10 km thick succession of igneous and sedimentary rocks of the Cuddapah and Kurnool Groups. This basin comprises five sub- 16 basins VIZ. Chitravathi, Nallamalai, Krishna, Srisailam, Kurnool and Palnad (Table 1). The western part of the basin has been relatively unaffected by tectonic activity; sedimentary rocks dip gently (10–15°) to the east. In contrast, the eastern part was severely folded and highly metamorphosed during the Middle to Late Proterozoic (∼1·3– 1·6 Ga). Eastern Ghat Orogeny Extrusive and intrusive mafic volcanic rocks are exposed at lower stratigraphic horizons in the Cuddapah Basin and are mostly sub aerial basaltic lavas and sills, occurring an arcuate pattern, parallel to the margin of the basin. There are fourteen major types of basins in India; among these Cuddapah Basin is the one of the biggest and most important for Economic geology. The geological succession of the Cuddapah and Kurnool are as follows. Table.1 Geological succession of the area (after Saha and Ttripathy, GSI, 2012) Nandyal Shale Koilkunta Limestone Paniam Group Owk Shale Narji Limestone Banganapalli quartzite KURNOOL GROUP Nallamalai Group ----------Unconformity-------SrisailamFormation ---------Tectonic Contact-----Cumbum Slate Bairenkonda Quartzite (=Nagari Quartzite) CUDDAPAH SUPER GROUP ---------Tectonic Contact------- ChitravathiGroup Papaghni Group Gandikota Quartzite Tadpatri Shale Pulivendla Quartzite Vempalle Slate Gulcheru Quartzite ---- ------- Unconformity--------- Archean Granite & gneisses 17 Cuddapah Basin: Salient Features Area: 44,500 sq km Age: Proterozoic Sub-basinsKurnool, Palnad Papaghni, Nallamalai, Srisailam Lithology: 12 km thick volcano-sedimentary pile consisting of Arenaceous, Argillaceous, Carbonates, and Volcanic (basic and acidic) Structure: Western part is flat lying and Eastern part is folded, faulted and thrusted Intrusives: Gabbro, Dolerite, Basalt, Kimberlite and Lamproite, and Younger granites, syenite Mineralization: Uranium, Base metals, Asbestos, Barytes, Diamond, Phosphorite, Limestone Three genetic types of U-mineralization 1. Stratabound: Impure dolostone hosted syngenetic stratabound uranium mineralization in the Vempalle Formation in the SW part. 2. Unconformity Associated: Uranium mineralization at the base of the Srisailam and the Banganapalle Formations in the N part of the basin. 3. Vein Type: (a) Uranium mineralization localized along fractures/shears in the basement crystallines in the southwestern part. (b) Uranium mineralization localized along shears in the basement schists in the E margin. (c) Uranium mineralization hosted in the Gulcheru Formation in the SW part Petrography and Mineralogy of the host rocks: The host rock for uranium mineralization at Chitrial & Amrabad outlier is mainly granite, which is medium to coarse-grained and composed with phenocrysts of microcline, orthoclase - and quartz. Microcline-microperthite shows post-crystalline deformation with fractures hosting clusters of chlorite, epidote etc. and uraninite with secondary development of uranophane. The host Srisailam arenite varies from feldspathic sandstone to arkose. Uraninite and secondary uranophane are hosted by fractures within the granite. The host dolerite dykes are highly altered, consist of plagioclase and chlorite (altered from 18 pyroxene/amphiboles) with minor calcite, epidote, apatite, biotite and some opaque minerals. Mineralization: Basement granite and quartzite are the host rocks for uranium mineralization in the unconformity area and is akin to high-grade and large-tonnage unconformity-related uranium deposits in Canada and Australia. Uranium mineralization is confined mostly to the joints trending NS, NNE, and SSW direction. The mineralized zones contain Uraninite, pitchblende in addition of pyrite, hematite and secondary silica. The Verma etal (2009) states that several uranium occurrences reported from Chitrial and adjoining areas. In the entire Chitrial and adjoin areas, Uranium mineralization of 0.130% U3O8 x 7.20 m intercepted along the boreholes in the western sector with rich radioactive band. The thickness of orebody varies from 1.0 to 7.20 m with an average value of 2.45 m. Secondary Uranium minerals are identified in Chitrial and Amrabad in following forms. Secondary Uranium minerals are present as micro fracture fillings in Sericite. Secondary uranium minerals observed in Veins Radioactive Allanite and Zircon are also observed associated with Epidote, Chlorite, Sericite and Biotite. Uraninite occurs as inclusion in biotite and feldspar. Where as, pitchblende of later generation, lower temperature, hydrothermal type occurs as fracture filling and veins shows epigenetic nature. Uranophane is present as secondary uranium minerals close to the fracture zone basement granitoid. Large scale alteration illitization of feldspar and chloritization of biotite is noted in the ore zone granitoids. Chitrial granites are considerably rich in chlorite, which aids in the mineralization. Large scale intergranular fracturing, recrystellization of quartz, granulation of quartz and feldspar might have further necessitated formation of richer concentration close to the unconformity contact. It aided by the presence of suitable reductants in the form of grey to black coloured, thinly laminated shale and pyrite. Hydrothermal signatures in the form of bleeding pyrite in granite and also predominately seen. 19 Based on the surface radioactivity survey, lithogeochemical and pedogeochemical analysis results, primary and secondary dispersion patterns, petrographic investigations are indicating the occurrence of U mineralization in Chitrial and Amrabad along the unconformity contact between basement biotite granitoid and the Srisailam Formation. The most favorable trend of the ore body is NE-SW (major fracture trend). This feature supports the role of fractures in controlling U-mineralization, besides non-conformity contact with basement granitoid. Surface Radioactivity: The surface radioactivity has been carried-out only in Amrabad but not in Chitrial. The vein-like uranium mineralization along the fractures in the Lower Proterozoic pelitic rocks close to the unconformity, Basement granite of Amrabad outlier belongs to the Middle - Upper Proterozoic Cuddapah of Super group. Based on the surface radioactivity investigations the secondary uranium mineralization was observed, in the basement granite and the overlying Srisailam pebbly arenite and basic dykes and vein quartz within the basement granite close to the unconformity.. The radiometric surveys were conducted on basement granite near Chennakeshavulu Gutta and near the village of the Padhra, the location point is N 160 25’ 55” and E 780 50’ 40.2” at Amrabad outlier. The radiometric counts are shows 195 and 202 ppm measured by the differential spectrometer. The good amount of the secondary uranium may occur in granite at Padhra. Mineralization appears to be controlled by NNE-trending vertical fracture in the basement granite, filled with quartz associated with Chlorite and galena. Such an association clearly points to open-space filling and hydrothermal nature of mineralization at Amrabad. Thus, it is evident from the field and geochemical analysis data, prominent sets of fractures/faults in the basement granite, trending NNE-SSW and NW-SE, have proved the concentrating of secondary uranium mineralization at Amrabad. 20 Kankar (Calcium Carbonate Precipitate- (Calcrete) Formation of Calcium Carbonate (CaCO3) is a characteristic feature of semi-arid and arid regions of the world, resulting from a displacive and/or replacive introduction of vadose carbonates in greater or lesser quantities in the weathering profile. The breakdown of feldspars as kaolinite during rock-water interaction, releases Ca2+. Soils/weathered products contribute high CO2 under the open system. The Ca2+ and CO2 are added to the groundwater through the infiltrating recharge water. They subsequently precipitate as fine-grained carbonates in the weathering profile due to evapotranspiration under a freshwater environment (Subba Rao et al, 2009) According to Netterberg (1969), calcrete can be regarded as “a material formed by the in situ cementation and/or replacement of almost any pre-existing soil by calcium carbonate deposited from the soil or ground water”. Thus, although calcrete contains a high proportion of calcium carbonate, it is not a sedimentary rock like limestone which also contains a high proportion of Calcium Carbonate (CaCO3) but which has a quite different origin. Instead, calcrete is a secondary product formed within or on top of an existing soil and is a member of the useful group of road building materials known as pedogenic materials, of which ferricrete (laterite) and silcrete are prominent members. In Chitrial, and Amrabad we find Honeycomb and Nodular type Calcrete. Kankar generally forms when minerals are leached from the upper layer of the soil (the A horizon) and accumulate in the next layer (the B horizon), at depths of approximately three to 10 feet under the surface. It generally consists of carbonates in semiarid regions, while in arid regions, less-soluble minerals will form kankar layers after all the carbonates have been leached from the soil. The calcium carbonate precipitate first and accumulates in the form of small lumps, nodules, then forms a discernible layer, and finally, results in thick solid bed. In Chitrial area kankar is found near the unconformity zone where Uranium mineralization reported by AMD. In Amrabad the kankar formation is observed about 10 meters thick (Fig 3). The observed surface radio activity is high in Amrabad area compared to that as Chitrial. The high surface radioactivity is due to the presence of 21 secondary uranium minerals in granite (Uranophane and Uranyl Carbonate). The Leached Uranium Carbonate form the primary Uranium minerals are trapped in kankar zone. The kankar zone scavenges the further mobility of Uranium resulting in the accumulation of Uranyl Carbonate in calcrete. Hence the high surface radioactivity observed in kankar zone. So kankar formation is play major role in exploration of Uranium mineralization. Quartzite Boulders Kankar Weathered Granite Fig 3 Kankar (Calcrete) formation between quartzite and weathered granite Geochemical Sampling: The geochemical sampling has been carried-out in two stages. 1. Reconnaissance and 2. Detailed Survey. Reconnaissance Survey: The sampling grid of 1 x 1 Sq.Km was prepared and rocks & soil samples were collected with the help of GPS from Chitrial and Amrabad are tabulated. One sample per one square kilometer has been collected (Fig 4). A total of 64 lithogeochemical and 65 pedogeochemical in Chitrial, 20 lithogeochemical and 20 pedogeochemical in Amrabad (Table 2) samples were collected during geochemical reconnaissance survey. 22 Detailed Survey: The target area has been narrowed down based on the dispersion patterns observed in the reconnaissance survey. The sampling grid of 0.25 X 0.25 Sq. Km (Table 2) was planned on narrowed target and carried out in detailed survey in Chitrial and the same was not carried out for Amrabad area (Fig 5), but Gamma ray survey was conducted and secondary Radiogenic minerals of Uranium on basement granite were observed. About 44 lithogeochemical and 44 pedogeochemical samples were collected at Chitrial. Table 2 Geochemical sampling of Reconnaissance and Detailed surveys Chitrial Amrabad Rock Soil Rock Soil Reconnaissance Survey 44 45 20 20 Detailed Survey 44 44 nil Nil Total 88 89 20 20 23 CHITRIAL NARAYANPUR UDIMILLA Amrabad Fig 4 Litho & Pedogeochemical sampling at Chitrial & Amrabad of reconnaissance survey 24 16.59313 16.58411 CTR/S-16 CTR/S-21 CTR/S-31CTR/S-36CTR/S-41 CTR/S-6 CTR/S-11 CTR/S-1 CTR/S-26 CTR/S-27CTR/S-32 CTR/S-2 CTR/S-7 CTR/S-12CTR/S-17CTR/S-22 CTR/S-3 CTR/S-13 CTR/S-18CTR/S-23 CTR/S-8 PEDDAMULA 16.57523 CTR/S-37 CTR/S-42 CTR/S-33 CTR/S-38 CTR/S-28 16.56622 16.55734 CTR/S-43 MADHAVARAM CTR/S-24 CTR/S-29 CTR/S-39 CTR/S-34 CTR/S-44 CTR/S-9 CTR/S-14CTR/S-19 CHITRIAL CHITRIAL BLOCK CTR/S-4 16.54832 CTR/S-45 CHITRAL CTR/S-10 CTR/S-15CTR/S-20CTR/S-25 CTR/S-40 CTR/S-30CTR/S-35 CTR/S-5 16.53944 VENKATGHANI TANDA 16.53043 BUDDONI TANDA DASARIPALLI NP/S-1 NP/S-2 GHANPUR 16.52155 NP/S-5 NP/S-9 NP/S-13 NP/S-17 NP/S-21 NP/S-6NP/S-10 16.50308 NP/S-14 NP/S-18NP/S-22 NP/S-3 NP/S-7 NP/S-11 NP/S-15NP/S-19 NP/S-4 NP/S-8 16.51196 NP/S-12 NP/S-16 NP/S-20 REKALAGADDA 16.49406 NP/S-23 NARAYANPUR BLOCK 16.48519 NP/S-24 16.47617 UD/S-1AKKAVARAM UD/S-5 UD/S-9 UD/S-2 UD/S-6 UD/S-3 UD/S-21 UD/S-13UD/S-17 UD/S-14 UD/S-10 UD/S-7 UD/S-11 UD/S-15 UD/S-16 UD/S-4 UD/S-8 UD/S-12 16.46729 UD/S-18UD/S-22 UD/S-23 UD/S-19 16.45827 16.44939 UDIMILLA BLOCK UD/S-20 UD/S-24 16.44038 Fig 5 Grid pattern lay out - Rock and Soil samples locations and their coordinates at Chitial area of Detailed Survey. 25 79.11711 79.10799 79.09901 79.08989 79.08092 79.07179 79.06267 79.05355 79.04473 79.03546 79.02648 79.01737 79.00839 78.99942 78.99030 78.98133 78.97221 78.96265 78.95354 78.94456 78.93544 78.92647 78.91734 78.90837 78.89925 78.89028 16.43159