CARBON, OXYGEN AND URANIUM ISOTOPIC STUDY OF URANIFEROUS DOLOSTONE FROM CUDDAPAH BASIN, SOUTHERN INDIA - IMPLICATIONS TO DEPOSITIONAL ENVIRONMENT AND URANIUM ALTERATION

The dolostones show a narrow range of delta(13)C values but a large ra nge of delta(18)O values. The small spread of delta(13)C from 0.1 part s per thousand to -0.9 parts per thousand is typical of marine carbona tes, whereas the large range of delta(18)O from -7 parts per thousand to -14 parts per thousand represents characteristic Proterozoic marine carbonates some of which were exposed to alteration by fresh continen tal waters. A diagenetic environment of mixed marine and fresh water f or the dolostone alteration is also supported by earlier studies in se dimentary structures and petrography. The U-234/U-238 activity ratio o f 0.7 in some of the mineralised samples shows the effect of ongoing c hemical leaching of uranium from discrete uranium minerals like pitchb lende and coffinite.