New 1.9-2.0 Ga, Pb-Pb (PbSL), age of dolomites from Vempalle Formation, Lower Cuddapah Supergroup, Eastern Dharwar craton, India

Abstract

Uranium mineralised and non-mineralised dolomites from Vempalle Formation, Lower Cuddapah Supergroup, were analysed by Pb-Pb systematics (Pb Sequential Leaching-PbSL), to ascertain the age of deposition, uranium mineralization, diagenesis and dolomitisation. PbSL technique is a well established tool to be used for direct dating of carbonate rocks world wide. Based on present study, using PbSL technique, it is established that the age of deposition, diagenesis, dolomitisation and syn-diagenetic uranium mineralization, in the Vempalle dolomites, is c. 1900-2000 Ma. Such older ages were not reported earlier from any part of the Cuddapah basin.The present age is within the existing stratigraphic time frame, as mafic sill intruding the Vempalle Formation is dated as c.1885 Ma and this indicates that Vempalle dolomites and syn-diagenetic uranium mineralization in it, have to be older than c.1885 Ma. The deposition of carbonate sediments, diagenesis, dolomitisation and syn-diagentic uranium mineralization in the Vempalle Formation took place in a short duration of 100 Ma, similar to the Wittenoon Formation and Carawine Dolomite of Hamersley Group,Western Australia, in which time between initial deposition, diagenesis and late dolomitisation is 100-150 Ma. The Cuddapah basin might have formed during the period c. 2200–2100 Ma, as evidenced by widespread mafic dyke activity around Cuddapah basin during that time. Present study infers that the minimum age of the onset of sedimentation in the Cuddapah Supergroup was at around c. 2000 Ma and the diagenesis, dolomitisation and syn-diagenetic uranium mineralisation took place up to 1900 Ma.