Rd. Raju et al., URANIUM MINERALIZATION IN THE SOUTH-WESTERN PART OF CUDDAPAH BASIN - A PETROMINERALOGICAL AND GEOCHEMICAL STUDY, Journal of the Geological Society of India, 42(2), 1993, pp. 135-149
Two types of uranium mineralisation occur in the south-western part of
Cuddapah basin, viz., stratabound type hosted by impure dolostone of
the Vempalle Formation of the Papaghni Group and structurally-controll
ed type hosted by deformed basement granitoid. The carbonate-hosted ty
pe occurs over a 140 km-long belt from Reddipalle in the west to Maddi
madugu in the east with promising mineralisation at Tummalapalle, Rach
akuntapalle and Gadankipalle. It is sandwiched between a lower massive
limestone and upper shale and cherty limestone. The mineralised carbo
nate rock is a stromatolite-bearing 'siliceous, calcitic dolostone' (S
CD+/-phosphate) associated with other impure dolostones, quartzite, ch
ert, phyllite, conglomerate, and intrusive dolerite and basalt. Uraniu
m mineralisation occurs along the bedding plane, carbonate-phosphate c
ontact, micro-stylolites, grain boundaries of clasts and within pelloi
ds, mainly in the form ultrafine pitchblende, in intimate association
with pyrite and as disseminations in collophane-rich parts, besides as
minor phases of coffinite and U-Ti complex. The associated ore minera
ls include pyrite, molybdenite, chalcopyrite, bornite, digenite and co
vellite. The fertile basement granite (s.1.) is the source of uranium
and the mineralisation, which appears to be polygenetic (syn-, dia- an
d epi-genetic), is controlled by impure nature of dolostone and organi
c activity. The mineralisation in the southern part of the belt in Cud
dapah district is typically molybdenum-rich, whereas the northern port
ion, in parts of Anantapur district, is characterised by high content
of copper. The mineralised SCD in the S/SE parts is also marked by hig
h content of P, V and Pb, in addition to Mo. There is a good positive
correlation of U with P and V (r : 0.98 and more). The structurally-co
ntrolled uranium mineralisation occurs around Rayachoti (outside the S
W margin of Cuddapah basin) along a number of fracture zones within th
e basement granitoid, and is hosted by mylonites and cataclasites indi
cative of intense dislocation metamorphism. Of many such zones, the on
e between T. Sundupalle and Sanipaya is promising and has a strike ext
ension of about 16 km. This mineralisation is epigenetic hydrothermal
vein-type, mainly represented by coffinite, pitchblende, U-Ti complex
and secondary uranium minerals.