Geochemical Studies Related to Gold Mineralisation at Paramanahalli, Chitradurga Greenstone Belt, Western Dharwar Craton, India: Implications for Gold Mineralisation Processes

ABSTRACT Gold mineralisation at Paramanahalli (Karnataka) is confined to altered metabasalt and Banded Iron Formation (BIF) of the Archean Hiriyur Formation. The addition and/ or depletion of major, trace elements, and the Rare Earth Element (REE) concentrations analysed in mineralised (altered) /non-mineralised (least altered) metabasalt and BIF. The rocks from the proximal alteration zone, such as altered metabasalt, display enrichment in SiO2 (attributed to silicification) and CaO (resulting from the formation of carbonate minerals), accompanied by a marked depletion in MgO due to alteration of mafic ferromagnesian minerals such as pyroxene and amphibole in the original metabasalt. The exchange between fluid and wall-rock contributes to mineral formation, such as chlorite (Fe-rich), quartz, rutile, ankerite, calcite, pyrite, and gold confirming the enrichment of CaO, FeO, K2O, TiO2, SiO2, S, and Au in altered rocks. The enrichment of gold (8-11 ppm) in metabasalt infers that it can be considered as a source and host rock. The study further explores alteration assemblage associated with chloritisation, sulphidation, and carbonatisation marked by the presence of chlorite, sulphides, and carbonate minerals, reflecting extensive fluid-rock interactions that contributed to gold mineralisation in the mineralised zones. The various types of alteration zones are spatially associated with major structural features, including shear zones and lithological contacts, which act as conduits for hydrothermal fluids. The geochemical signature of the Paramanahalli gold deposit, as reflected in the major, trace, and REEs from the mineralised zone, underscores the complex interplay of hydrothermal processes and fluid/rock reaction that led to gold mineralisation.