Occurrence of paragonite in the hydrothermalwall rock alteration zone of G. R. Halli gold deposit, Chitradurga Schist Belt, Western Dharwar Craton, Southern India

摘要

Paragonite (NaAl2Si3AlO10(OH)2), a dioctahedral sodium mica, occurs as a minor phase in the wall rock alteration assemblage of the Guddadarangavanahalli (G. R. Halli) gold deposit of Western Dharwar Craton, Karnataka. It occurs as colourless to pale yellowish grains and scaly aggregates in chlorite, ankerite and quartz rich matrix of the altered metabasalt. Its presence is noticed in the distal to near proximal wall rock alteration zone, mainly in the southern part of the G. R. Halli gold deposit. Presence of paragonite is identified by X-Ray Diffraction (XRD) and Electron Probe Micro-Analyzer (EPMA) studies. The Na2O content of the paragonite varies between 5.96 wt% and 7.8 wt% whereas K2O ranges from 0.44–2.68 wt%. Al2O3 is measured between 37.73 wt% and 39.72 wt% whereas SiO2 varies from 45.06–47.19 wt%. The relative proportion of Na and K in paragonite varies between Na96K4 and Na77K23. The occurrence of paragonite in the wall rock alteration halo of the G. R. Halli gold deposit is proposed as a result of hydrolysis of metamorphosed plagioclase feldspars during the interaction of the hydrothermal fluids and the wall rock.