Structural analysis of the shear zone within the basement of Cuddapah Basin at Gondipalle-Eguvapalle Area, Kadapa District, Andhra Pradesh

Epigenetic vein type uranium mineralization is generally associated with or hosted by evolved felsic igneous rocks and some of which are peralkaline. Fracture controlled uranium mineralizations have always been highlighted for high grade deposit. The ENE- WSW trending fracture zone reported earlier for uranium mineralization of Gondipalli area is characterized as brittle-ductile shear zone. Mesoscopic and microscopic study of the shear zone rocks reveal that the ductile nature of the shear zone was superimposed by brittle character. Ductile features like mylonitic foliation is mesoscopic scale and undulose extinction, kink bands, bent or wavy twin plane and flame perthite in microscopic scale were superseded by tension fracture and faults in mesoscale and micro fracture and micro faults in microscopic scale, respectively. Ductile fabric developed earlier in the shear zone perhaps facilitated the infiltration of the oxidizing fluid that leached uranium from fertile granite. Later brittle fracture enhanced the permeability within the shear for fluid circulation. Basic dyke associated with the shear zone might have provided the thermal gradient and sulphides which probably acted as reductants enabling fixation of uranium in the system. (author)