International Journal of Scientific and Research Publications, Volume 3, Issue 4, April 2013 1 ISSN 2250-3153 Delineation of Target Zones for Detailed Uranium Exploration Using Secondary Dispersion Haloes (Pedogeochemical) as a Tool in the NNW Parts of Srisailam Sub Basin, Andhra Pradesh (India) Vishnu Bhoopathi*, S. Niranjan Kumar**, R.S.N. Sastry*, B. Sinivas*, M. Ramana Kumar* * Department of Applied Geochemistry, Osmania University, Hyderabad ** Scientific Officer- E, Atomic Mineral Directorate for Exploration and Research, Begumpet, Hyderabad Abstract- Pedogeochemical sampling over an area of 45 Sq.Km Fracture controlled uranium mineralisation is both was initially taken up in the Chitrial outlier, which is actually basement granite hosted as well as sediment hosted (Gulcheru detached from the main Srisailam sub basin as a result of Formation, the oldest member of the Cuddapah Super Group) topographic low formed through weathering and erosional and occurs along the southern margin of the Cuddapah basin. processes. Pedogeochemical sampling is carried out on a grid of 1Km x 1Km and various geochemically associated trace and ore Strata bound Uranium mineralisation elements viz., U,Th,V,Cr,Co,Ni,Cu,Pb,Zn and As are analyzed The strata bound uranium-mineralisation in southwestern and studied for their dispersion patterns. The pedogeochemical part of the Cuddapah basin is unique in the sense that no such dispersion pattern of trace elements studied in conjunction with strata bound uranium deposit hosted by carbonate rocks is geology and structure has yielded an area of 11 Sq.Km which is reported in the world. Uranium mineralisation is hosted by identified with specific trends (N-S and NNE-SSW), as a impure phosphatic dolostone of the Vempalle Formation of the potential zone for uranium mineralization and is recommended Papaghni Group. It extends from Chelumpalli in the northwest to for detailed and subsurface investigations. Maddimadugu in the southeast over a belt of 160 km with promising mineralisation at Tummalapalle, Rachak-untapalli and Index Terms- Dispersion haloe, pedogeochemical, Srisailam sub Gadankipalli in the central part. basin, uranium. Significance of unconformity uranium deposits An unconformity is a buried erosion surface separating two I. INTRODUCTION rock masses or strata of different ages, indicating that sediment he mid-Proterozoic – Archean basement unconformity is deposition was not continuous. In general, the older layer was Tproved all over the world as the most potential zone hosting exposed to erosion for an interval of time before deposition of some of the world’s largest uranium deposits. The Srisailam sub the younger, but the term is used to describe any break in the basin is geologically mid to late Proterozoic in age and it is sedimentary geologic record. unconformably overlying the Archean granite basement. The Unconformity-type uranium (Jefferson.C., et al., 2005) sediments are essentially arenaceous and are represented by a deposits host high grades relative to other uranium deposits and basal pebbly quartzite, followed by a grey medium grained include some of the largest and richest deposits known. They quartzite with grey to buff coloured shale as intercalations. The occur in close proximity to major unconformities between basement is represented by a coarse to medium grained grey relatively quartz-rich sandstones comprising the basal portion of fractured granite. Srisailam sub basin and cuddapah basin relatively undeformed sedimentary basins and deformed geology with known uranium mineralization. metamorphic basement rocks. These sedimentary basins are typically of Proterozoic age, however some Phanerozoic Unconformity-related Uranium mineralization examples exist. The most significant areas for this style of With the discoveries of high grade mineralisation (~ 0.5% deposit are currently the Athabasca Basin in Saskatchewan, U3O8) of the unconformity-type in the Athabasca basin of Canada, and the McArthur Basin in the Northern Territory, Canada and the Pine creek geosynclines of Australia, (Hoeve , J. Australia. et al., 1980) emphasis on exploration was shifted in early 1990’s The Proterozoic basins all over the world have gained to locate fracture controlled unconformity related uranium importance in the light of high-grade unconformity related mineralisation in Cuddapah basin. Workable deposits of uranium deposits associated with them. The depositional unconformity-related type have been established at Lambapur- conditions for that geologic time favored the chemical mobility Peddagattu, Nalgonda district and Koppunuru, Guntur district, of the uranium from their primary source to the sediments/host Andhra Pradesh, along NW margin of the Cuddapah basin. rocks and got deposited as different type of uranium deposits specific to their type and nature. In particular, the unconformity Fracture/Shear controlled uranium mineralisation surface between the Proterozoic sediments and the Archean www.ijsrp.org International Journal of Scientific and Research Publications, Volume 3, Issue 4, April 2013 2 ISSN 2250-3153 basement crystalline acted as the most favourable geochemical Nalgonda district (Sinha, 1995), and later at Koppunuru, Guntur front/ surface with host of other favourable criteria like basement district (Jeyagopal, 1996) at the proximity of unconformity faults and folds, along with the clay horizons, reductants and contact of Meso-Proterozoic Srisailam quartzite/ Neo- alteration zones associated with the rocks proximal to the Proterozoic Banganapalle quartzite and the basement granite unconformity surface. The hydrothermal solution activity along respectively. with structural disturbances over the geologic times would have reactivated, remobilized and concentrated uranium along these surfaces. II. GEOLOGY AND STRUCTURE Proterozoic unconformity and their environs are established The Srisailam sub basin is located in the north eastern part potential target areas of medium to high grade, large tonnage, of the Cuddapah basin. The Chitrial, area is located in the north low cost uranium deposits in parts of Canada (Cigar lake) and eastern fringes of Srisailam sub basin (fig no.1). Chitrial outlier Australia (Athabasca basin) and more than 50% of present day is horseshoe shaped and is located to the north of Dindi River world production is recovered from such geological settings. which is flowing from northwest to southeast along lineament The classical geological setting of unconformity type and merges with Nagarjunasagar reservoir. uranium deposits is “the contact between Meso to Neo- The study area (45 Sq.km) falls around the known / Proterozoic sediments and Palaeo-Proterozoic metasediments”. established uranium mineralization at Chitrial. The area is Such deposits are mainly located at or near the unconformity located in the northern periphery of the Srisailam sub-basin. The surface, (Senthil kumar, P., et al 2002) as it provides an effective area represents small Outlier of Quartzite (Srisailam formation). plumbing system for circulation of hydrothermal solutions. The area covers both the quartzite outliers and the basement Precipitation due to intermixing of highly charged metal rich granite, dolerite dykes, shale, clays are presented along the oxidizing solutions from above and reducing solutions from unconformity of the Chitrial outlier (fig no. 2), considering the below the unconformity and repeated recycling/ remobilization importance of both the source and host for uranium are the conspicuous features of such deposits imparting them mineralization. The fertile nature of the granite basement is a unusually high grade. pre-requisite for unconformity type of uranium mineralization in Indian Scenario of Unconformity related uranium deposits: Proterozoic basins. In India, first unconformity deposit was established in the intra- cratonic Proterozoic Cuddapah basin at Lambapur- Peddagattu, Figure 1. Location map of Chitrial outlier in Srisailam Sub basin (AMD) www.ijsrp.org International Journal of Scientific and Research Publications, Volume 3, Issue 4, April 2013 3 ISSN 2250-3153 Figure 2. Geological map of Chitrial outlier (AMD, 2009) Structure: A number of basement-dykes (dolerites) Dindi and Krishna Rivers flow along WNW-ESE and N-S trending N-S and NNW-SSE and a minor trend represented by E lineaments respectively. The joints in the basement show two -W are observed. The mineralization trend as established in the distinct directions along NW-SE and NE-SW, with less Chitrial area is also more or less in the N-S and NNW-SSE developed directions of N-S and E-W. direction (fig 2). The Chitrial area has been dissected by NW-SE; NE-SW; and NS lineaments. The main drainage in the area Viz. www.ijsrp.org International Journal of Scientific and Research Publications, Volume 3, Issue 4, April 2013 4 ISSN 2250-3153 Table-1 - Geological succession in the Cuddapah Basin, after King {1872} Kundair Group Paniam Group KURNOOL SYSTEM Jamalamadugu Group Banganapalli Group ----------------------Unconformity------------------- Kistna Group Srisailam Quartzite Kolamnala Slate Iriakonda Quartzite ---------------------- Unconformity------------------------- Nallamalai Group Cumbum Slate Bairenkonda Quartzite CUDDAPAH SYSTEM ----------------------Unconformity----------------------------- Cheyair Group Tadpatri Shale Pulivendla Quartzite Nagari Quartzite Papaghni Group Vempalle Slate Gulcheru Quartzite --------------------- Unconformity--------------------------- Older Precambrian Figure3. Pedogeochemical