Fluid inclusion study of radioactive granitoids and cherty cataclasite in the southeastern part of Nanded district, Maharashtra: implications for Uranium mineralisation

Abstract

Radioactive granitoids and cherty cataclasites are delineated in Thadisaoli-Khatgaon and Shahpur-Sujayatpur sectors in southeastern part of Nanded district, Maharashtra, which have recorded anomalous radioelemental contents (Granites: upto 1% U 3 O 8 and 0.20% ThO 2 ; Cherty cataclasites upto 0.11% U 3 O 8 and <0.005% ThO 2 ) and enrichment in trace element and rare metal and rare earth element concentration (Nb: upto 146ppm, Y: upto 226ppm, Zr: upto 559ppm and total REE: upto 2010ppm). The mineralised granitoids are affected by profuse pegmatitic/quartzo-feldspathic, quartz and epidote venations and mainly confined along the NE-SW and NNE-SSW faults/shear zones. Radioactive phases are represented by discrete uranium/thorium ore minerals (uraninite, βuranophane and thorite) and high content of resistates viz., apatite, zircon, allanite, sphene, cerianite, monazite and ilmenite.Fluid inclusion studies of the mineralised and sheared granites, quartzo-feldspathic veins (QFV's) and quartz veins indicate the presence of 6 to 32µm size aqueous and carbonic inclusions of three principle types and represented by six phases viz., aqueous mono-, bi-and poly-phases, aqueous-carbonic, carbonic mono-, bi-and poly-phases. Aqueous biphase inclusions show wide range of salinity (0.71 to 19.99 wt.% eNaCl) and homogenisation temperatures (T h : 127.5-280.8ºC ), while aqueous-carbonic inclusions exhibit restricted salinity (5-8.4 wt.% eNaCl ) and T h (28.3-30.9ºC). The composition of these aqueous fluids varies from NaCl-KCl dominant in quartz veins and radioactive granite to MgCl 2 dominant in sheared radioactive granite. Similarly, co-eval aqueous biphase and aqueous-carbonic inclusions have yielded 678-958 bar pressure and 201-233ºC temperature in quartz vein samples while higher values of 1120-1550 bar and 304-360ºC are indicated by sheared granite. The presence of more than one population without much change in fluid composition signifies their origin at different stages of deformation. Besides, mixing of a moderate temperature and low salinity fluid (meteoric/basinal brine) with a comparatively high temperature and hypersaline fluid (magmatic/ evolved brine) might have also played an important role in inclusion characteristics. Based on these fluid inclusion characteristics, it appears that multi-episodic hydrothermal activity under an extensional tectonic regime in this fertile granitic province has led to precipitation of uranium along suitable structural aureoles from uraniferous hydrotherms.