Executive Summary : | Orogenic gold deposits are globally distributed in metamorphic belts and have historically contributed to a significant portion of gold production. However, the processes involved in their formation and the sources of associated metals and fluids remain poorly understood. Previous studies have proposed various models, including metamorphic dehydration, magmatic-hydrothermal fluids, deep-seated meteoric water, CO2-rich fluids from the Earth's mantle, or fluids expelled during the subduction of the oceanic crust. Comprehensive analyses of published data consistently suggest that metamorphic devolatilization and fluids derived from felsic magmatic sources are the most plausible explanations. The Dharwar Craton, known for its world-class gold reserve, hosts several greenstone belts with significant orogenic gold deposits, including Kolar, Ramgiri, Jonnagiri, Hutti-Maski, Gadag, and Chitradurga. Despite numerous studies, the source of the gold ore-forming fluid and the gold metallogeny in the Craton remain subjects of debate. Previous research supports the metamorphic devolatilization model based on analyses of fluid inclusions and metamorphic assemblages in Hutti Mines. However, other studies propose a juvenile origin of auriferous fluids in the Gadag Gold Field based on stable isotope and rare earth element geochemistry. Additionally, a recent study suggests a juvenile granitic source for the Jonnagiri granite-hosted orogenic gold deposits. While variations exist in these perspectives, it is widely accepted that ore fluids in Hutti Gold Mine are derived from metamorphic devolatilization, while both metamorphic devolatilization and mantle-derived/juvenile fluid sources are proposed for the Gadag Gold Fields. The mantle-derived/juvenile fluid sources, however, are subject to scrutiny due to ambiguous isotopic and geochemical evidence. This proposed study aims to address the uncertainties surrounding the sources of ore-forming fluids in the Gadag Gold Fields by comparing them with the established fluid source models in the Hutti Gold Mines. The study will investigate the following research questions: (i) the chemical changes occurring during the metamorphism and deformation of the Gadag and Hutti schist belts, with a focus on elements enriched in the ore deposits of Hutti and Gadag; (ii) spatial variations of elements and isotopes within the Gadag and Hutti schist belts, and identify variations in their background values; (iii) effects of metamorphism on mineral phases hosting the ore-forming elements. By addressing these research questions, the study aims to provide insights into the complex geological processes involved in the formation of the Gadag (and Hutti) gold deposits, particularly regarding the sources of ore-forming fluids and the effects of metamorphism on mineral phases hosting the ore-forming elements. |