Two types of uranium mineralization in Gulcheru quartzite:Fracture-controlled in Ambakapalle area and litho-controlled in Tummalapalle area,Cuddapah Basin,Andhra Pradesh,India

摘要

The Cuddapah Basin in southern India has a potential for uranium mineralization due to some favorable factors such as its temporal, stratigraphic and tectonic settings. Systematic exploration program conducted by the Atomic Minerals Directorate for Exploration and Research (AMD) within the Cuddapah Basin resulting in the recognition of distinct types of uranium mineralization, viz., strata bound type, fracture/shear-controlled type and tabular type. The Gulcheru Formation which is the lowermost unit of the Cuddapah Basin is dominantly arenitic in nature. During the exploration works, a number of uranium anomalies were identified with dimensions ranging from 1 m to 1.5 km. Gulcheru quartzite hosted uranium mineralization is intermittent and inconsistent in nature. The anomalous outcrops are distributed over a strike length of ca. 60 km between Gandi in the SE and Ambakapallein the NW. Presently, two different types of uranium mineralization are characterized on the basis of field observations, mapping and structural interpretation, petro-mineralogy and geochemistry. Although the host rock is same for both types, the mechanism of uranium enrichment is totally different. The Ambakapalle uranium mineralization is controlled by fault zone and associated hydrothermal activity. Whereas, the Tummalapalle uranium mineralization is litho-controlled in nature influenced by suitable four ‘P’ factors, i.e., provenance, porositypermeability, precipitation and preservation. The geochemical characterization of Gulcheru quartzite suggest a passive margin type of provenance setting. Petro-mineralogically the quartz arenite suggests enough textural as well as mineralogical maturity. Ambakapalle quartzite is slightly strained and deformed due to faulting. Analysis of selected samples recorded 0.01% to 0.048% U3O8 and <0.01% ThO2. Petrographic observation revealed that the anomalies were appeared due to secondary uranium minerals occurring as surficial encrustations, fracture filling and lesser irregular patches. Structural analysis suggests the mineralization along E-W trace slip fault is possibly consistent in sub-surface. Tummalapalle quartzite is relatively less deformed arenitic in nature with significant enrichment in MREE. The genetic models for the two types of mineralization is totally different.