MIGRATION OF GOLD TO THE SHEAR ZONE: MINERAL AND FLUID INCLUSION STUDIES OF THE INTRUSIVES OF THE HUTTI GOLD MINE, KARNATAKA, INDIA

The active Hutti Gold mine is located in the Raichur district of Karnataka in the Archean greenschist belt of the peninsular region, India. The area has experienced several phases of Archean to Proterozoic deformation, including well-preserved granite intrusions. Mineral and fluid-inclusion studies of intrusive rocks reveal relationship of the intrusive rocks to gold-mineralization in the Hutti shear zone.

Samples from various levels within the gold mine and around the mine were collected for detailed examination of fluid inclusions and mineralogy. Investigations were done on fluid-melt inclusions in the granite and associated quartz veins. A tentative paragenetic sequence of mineralization was constructed with respect to the deformational events in the area. There are three kinds of inclusions in the quartz reefs (1) mono-phase CO2, which is predominant; (2) bi-phase, low-salinity CO₂-H₂O inclusions; and (3) poly-phase fluid inclusions.

The sources of these inclusions are either magmatic hydrothermal fluids and/or metamorphic fluids. The fluid inclusions are of low salinity (0.9 to 3.8 % NaCl equivalence), and negative crystals are rare. Temperature of homogenization after pressure correction (2.5 kb) is approximately 330-350°C. Gold mineralization in the Hutti gold mine area may be explained by a magmatic-hydrothermal model. The most obvious source of gold in the study area is greenschist rocks in the Hutti schist belt. The emplacement of the gold deposit in this area can be linked to regional structural, metamorphic and intrusive igneous histories of the greenschist belt.