Delineation of Structure over Karara-Tavidar Volcanics of Jalore District, Rajasthan, by Magnetic and Gravity Investigations - An Appraisal of the Integrated Results.

摘要

Worldwide, the fluorite bearing felsic volcanic rocks had been the target of uranium exploration for rich grade uranium deposits, e.g. Streltsvokye-Antei uranium deposit of Rμssia, Idaho & Nevada deposits of U.S.A. In such deposits, fluorite mineralization is prevalent along with Molybdenum (Mo) and Barium (Ba). The uranium mineralization is precipitated along the fractures and intersection of faults. With a similar geological setup, significant uranium mineralization is recorded near Kudi and Tavidar villages in the Karara-Tavidar sector of Jalore district, Rajasthan. The surface samples recorded Uranium values in the range of 51-376 ppm and Thorium in the range of 10-18 ppm. U- Mineralization is associated with felsic volcanic rocks of Mesozoic era (65my) and with the rocks that are highly fractured and faulted with abundant Fluorite and Barite mineralization. Regional geophysical surveys comprising Magnetic / Gravity methods are utilized to delineate structural fabric while identifying favourable locales for U-mineralization in the Karara-Tavidar sector over an area of 80 sq.km. Total Magnetic intensity (TMI) and Reduced To Pole (RTP) anomaly images, deciphered various magnetic anomalous bodies trending in N-S, NE-SW, NW-SE and E-W directions characterized by high magnetic signatures of the order 200-600nT interpreted in terms of basic rock formations. Major/minor faults trending in NE-SW, N-S and NW-SE direction are delineated based on gradient pattern of magnetic anomalies. In addition, well defined fracture zones trending in E-W and NE-SW direction are characterized by magnetic lows to the tune of -350nT. Of these trends, the E-W and NW-SE trends are the younger ones whereas the N-S and NE-SW are considered to be the older trends (Ravinder, 2013), well supported by integrated geophysical results. The prominent intersection zones of these structures occurring in the vicinity of Kudi (lat: 24.85622°, Long: 78.13596°) over an area of 1.5 sq.km; NW portion of Lakhavas (lat: 24.8893°, Long: 78.14566°) village over an area of 2.2 sq.km are considered to be important for further exploration activity. Bouguer gravity anomalies have helped to demarcate the predominant structural trends that are well correlatable with magnetic interpretation. Also, one deep seated fault trending in N-S direction is delineated from the Bouguer gravity anomaly image. Good agreement of the structures identified by geophysical means with surface geology is noticed especially in the central portion of the surveyed area i.e., where the rocks are exposed. To sum up, major/minor structural features trending in N-S, NE-SW, NW-SE, E-W directions & intersection zones of younger structural trends E-W, NW-SE and older structural trends in NE-SW, N-S directions are delineated based on the analysis/interpretation of magnetic/gravity images. These intersection zones are considered to be the potential targets for structurally controlled fluorite/ barite vein hosted Uranium mineralization in the area.