Reactivated fracture-controlled uranium mineralization: An example from NNE-SSW Kamaguttapalle–Kammapalle tract, Kadapa district, Andhra Pradesh, India

Abstract

The Cuddapah Basin (CB) and its basement can be considered as an appropriate uranium metallogenic province. The basement complex of CB in the Eastern Dharwar Craton (EDC), India, has been the target for structurally controlled uranium exploration since the early 1980s. Most of the brittle-ductile deformation induced reactivated narrow linear fracture zones often exhibit significant surface and sub-surface uranium occurrence. There are about 10 fracture zones associated with uranium mineralization. Amongst them, the Kamaguttapalle–Kammapalle fracture zone (KKF) in the south of the CB is quite interesting from an exploration viewpoint with a suitable geologic setting in space and time frame. Geomorphic, structural and petro-mineralogic exploration guides imply the possibility of economic uranium concentration along the NNE-SSW trend where tectonic reactivation took place over pre-existing ductile shear zone. Progressive exhumation and transition from ductile to brittle deformation regime led to the development of dominant strike slip tectonics with an associated riedel fracture system, which are subsidiary coeval shear fractures used in depicting sense of movement. Intense illitization and hematitization are often observed. Quartz reefs and veins along the NNE-SSW trend cut the preexisting mylonites at places. About 9 stages of fracturing is observed out of which 3 stages are related to uranium mineralization. All the 9 deformations are related to strike slip tectonics which in turn is part of Grenville orogeny. Paragenetic sequence and mode of occurrences of uranium phases deciphers about the importance of low to moderate level epi‑meso type hydrothermal (100°–250 °C) fluids as carrier of U. Reactivated fractures and quartz veination also act as controlling factors of mineralization. Strain analysis points to positive and negative flower structures at different segments of the fracture zone. Based on the litho-structural attributes it is established that maximum compression (σ1) acted along the NNW-SSE direction. Fractured quartz veins provide well defined permeability and trapping facility by restricting transverse fluid movement as a mechanical barrier. The presented model gives an idea on role of strike-slip tectonics in uranium mineralization for narrowing down the target zone for sub-surface exploration.