A GIS approach in Mineral Targeting with Narayanpet Kimberlite Spatial Dataset  Fig.1 : The idealised model for kimberlite emplacement in a cratonic block. The above stated facts could serve as conceptual model or exploration model in search of the locales of the primary sources for diamonds. A detailed account on conceptual facts in diamond exploration and identification of prioritised zones in India was dealt in the compilation work of Satyanarayana, 2000. With the advent of GIS technology with tessellation and vector encoding, the integrated approach in search of the primary sources for diamond also get a boost in identification of statistically derived favourable zones from the overlaid predictive thematic layers. The present work constitutes an analysis for mineral targeting in 2953 sq km area falling in the Narayanpet Kimberlite Field, southern India, where integration of evidence maps is attempted on 'Index Overlay Model' coupled with 'Bayesian Probability Principle' in a vector GIS. Narayanpet Kimberlite Field The Geological Survey of India since 1984-85 has been discovering kimberlite bodies in Maddur-Narayanpet area (Nayak et al., 1987: Sarma,1990; Rao, 1995), Mahboobnagar district of Andhra Pradesh. Till date more than 30 kimberlite bodies have been located, now this area which is designated as 'Narayanpet Kimberlite Field (NKF) (Satyanarayana et al., 1997)' is a promicing zone for kimberlites after the well-known 'Wajrakarur Kimberlite Field (WKF)' in Dharwar Craton. The NKF measures about 60 km x 40 km in western part of Mahboobnagar district, Andhra Pradesh and eastern part of the adjoining Gulberga district, Karnataka. The kimberlites of both the fields have broad similarities in mineralogical, petrological characters and major element chemistry, but there are subtle differences in REE distribution, indicator minerals and mantle nodules (Rao et al., 2001). The kimberlites of both NKF and WKF are in similar tectonic set-up, and of contemporary ages (Anil Kumar et al., 1993). Geology The area comprises broadly Archaean gneisses, migmatites and granites with enclaves of schistose rocks, Proterozoic granitic intrusives and sediments of Bhima Group and Cretaceous Deccan Basalts. Emplacement of kimberlites of the NKF is noticed in the gneisses and granites (Rao et al., 1998). For prognostication purpose, the geology is simplified into three litho-domains i.e., gneissic domain, granitic domain and basalt domain. Tectnoic Elements A number of faults, fractures and lineaments of varied dimensions, in different orientation related to different tectonic events are recorded in the area. Some of these are occupied by basic (including ultrabasic) intrusives, pegmatites, quartzo-feldspathic veins, younger acidic intrusives etc.. These intrusives are suggestive of zones of magmatic permeability and repetitive basic and ultrabasic magmatic activity in the area. The various tectonic elements of this area are grouped into E-W, NE-SW, N-S, NW-SE sets on the basis of their orientation. |