U-Pb Zircon Geochronology and Structural Control of the Hydrothermal Vein-type Uranium Deposit at Chitrial, Eastern Dharwar Craton, India
Abstract
Vein-type hydrothermal uranium deposits represent epigenetic concentrations of uranium minerals that typically fill breccias, fractures, and shear zones (Qui et al., 2018), but the sources of the uranium in such deposits are difficult to identify and poorly understood. This study focuses on the hydrothermal vein-type uranium deposit which formed within WNW-ESE striking fault/fracture set that cross-cut the granitoids and the overlying Srisailam Formation at Chitrial, Eastern Dharwar Craton, India. In the absence of robust age constraints, the relative timing of sedimentation and uranium mineralization in the studied area remains debatable. Five successive deformation phases (D1-D5) have been identified from the granitoid rocks of the study area (Das et al., 2019), of which the last event (D5) has also affected the overlying Srisailam Formation. As both the basement granitoid and the Srisailam Formation host the uranium mineralization, we argue that the uranium bearing hydrothermal activity is related to the last (D5) tectonic event. Structural analysis indicates that the D5 stage faults and fractures are prolifically developed surrounding the uraniferous zones and bear a near one to one relation between increase in fault-fracture density and mineralization. Pitchblende and coffinite are the main uranium minerals occurring in micro-fractures and inter-granular spaces of the host rock, often in association with pyrite. U-Pb petrochronology of hydrothermally altered zircons provide two prominent age spectrums between ~2.52 Ga and ~172 Ma. The older age matches well with the emplacement age of the host granitoids (Mukherjee et al., 2018). The younger age, possibly is related to a thermal event in which high-CL zircon overgrew the ~2.52 age domain. We consider this mid-Jurassic age as the timing of the main uranium ore-forming event. The combined data set speaks for a major, hitherto undetected, tectonothermal activity (D5 stage faults, hydrothermal activity and uranium enrichment) that had affected a large part of the East Dharwar Craton (encompassing the Srisailam-Palnad sub-basins) in the Mesozoic time. The overall stress regime established from fault slip analysis data of the D5 stage faults and fractures has been correlated with a broad extensional to transtensional one. The timing of this ~172 Ma extensional-transtensional D5 event matches well with the breaking up of the Indian crustal fragment from the East Gondwana supercontinent where the present day eastern coast of India presents a significant role as far as large-scale rifting and splitting up of the Indian crustal block is concerned (Rogers and Santosh, 2004). It remarkably broadens the general perception about possible much younger (mid-Mesozoic) timing of uranium enrichment even from a very old cratonic part of the Indian crustal block.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMV019.0013M
- Keywords:
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- 3619 Magma genesis and partial melting;
- MINERALOGY AND PETROLOGY;
- 3625 Petrography;
- microstructures;
- and textures;
- MINERALOGY AND PETROLOGY;
- 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY;
- 8125 Evolution of the Earth;
- TECTONOPHYSICS