Importance of Fracturing in Uranium Mineralization in Gulcheru Quartzite Host: A Case from Ambakapalle Area, Cuddapah Basin, Andhra Pradesh, India

Abstract

AbstractFracture and fault zones can tap the uranium-bearing fluid and help to migrate into the structural trap where the hydrothermal fluids cool and precipitate the uranium mineral. Such a structural setting gives sufficient time to react the fluid with receptive country rocks. Fracture zones have played a major role in the mineralizing event in Ambakapalle area, where uranium anomalies are located along fracture zone strike for about 1.4 km intermittently. The localization of uranium is influenced by E-W fault zone which have provided the pathway for uprising hydrothermal fluids with decreasing heat and pressure. In this context, the structural attributes are studied by mapping the fault zone and by projecting the subsurface geometry. Intersections of fractures are observed as better locations of uranium anomalies and hence given attention for prospecting the uranium mineralization. The block movement along fault is characterized as diagonal slip normal fault with a net slip direction parallel to the trace of bedding on the fault plane, which is also called trace slip fault. Therefore, from plan view, there is no apparent displacement of lithocontact across the fault. This trace slip fault with respect to the strata is interpreted as the most important structure from uranium mineralization point of view. The alteration index values for the host rocks are determined for different types of chemical as well as hydrothermal alteration, and their bearing with uranium mineralization is interpreted. High values of chlorite-carbonate-pyrite index [CCPI = (MgO + FeO) × 100/(MgO + FeO + Na2O + K2O)] indicate intense alteration of Fe- or Mg-rich minerals, such as chlorite. Low to medium ranges of Chemical Index of Alteration [CIA = Al2O3 × 100/(Al2O3 + CaO + K2O + Na2O)] values indicate variable intensity of chemical weathering due to removal of labile cations (Ca2+, Na+, K+) relative to stable residual constituent (Al3+, Ti4+). The correlation among different alteration indices and uranium is noteworthy. It is interpreted that the initial hydrothermal alteration along fault zone is masked by later low-temperature alterations. Therefore, the surficial manifestation of uranium anomalies is disturbed, and intermittent patches of uraniferous anomalies are seen along the trend of fault.KeywordsFracture-controlled uranium mineralizationAmbakapalleGulcheru quartziteHydrothermal alterationAndhra Pradesh