Gravity and Magnetic Techniques to Decipher the Basement Structures for Uranium Mineralization - A Case study from Subbareddy Palem area, Palnad Sub-Basin, Guntur District, Andhra Pradesh, India

摘要

The Crescent-shaped Cuddapah basin is one of the major Proterozoic basins in India that host a number of mineral deposits of economic interest. In this basin, uranium mineralization is mostly controlled by basement structures faults/fractures, shear and unconformity related stratiform/stratabound types. Subbareddy Palem area falls in the southwestern part of the Palnad Sub-basin of Cuddapah basin. The primary uranium mineralization mostly occurs as veins, fractures/cavity fillings in basement granite and in sediments above the unconformity. The fertile basement granitoid is the main source of uranium in this area, carbonaceous matter acts as a reducing agent. Geophysical surveys comprising gravity and magnetic methods are carried out to decipher the favorable basement structural features for uranium mineralization. An area of about 12 sq km was covered by gravity and magnetic methods. The magnetic and gravity anomalies trend in NW-SE direction representing the general strike of the formations in the area. A major basement fault (Fl) has been identified in the northeastern part of the survey area from Bouguer gravity map. Part of the fault/ fracture zone is emplaced by basic dyke of limited strike extent as inferred from magnetic data. First vertical derivative image of gravity as well as magnetic data reveal another basement fault parallel to the above major fault. This fault/ fracture (F2) trending in WNW-ESE direction is characterized by high order of gravity and magnetic linears by intrusion of basic material. The fault/fractures delineated in WNW-ESE direction in this area are sympathetic to the regional Kandlagunta basement fault to the south of Koppunuru area and corroborate with the established mineralized trends/basement features observed in that area. The inferred basement structures and undulations in the basement topography form favorable geological environment for the deposition of uranium mineralization.