A fluid inclusion and stable isotope study of the Proterozoic Bidjovagge Au-Cu deposit, Finnmark, northern Norway

The Bidjovagge Au-Cu deposit, northern Norway, hosted within a shear zone in the Early Proterozoic Kautokeino greenstone belt, is more base metal-rich than Archaean mesothermal gold deposits. An early phase of gold and copper mineralization is hosted by sheared albitic felsites, within an alteration and oxidation zone to graphitic schists, along with a series of syenodiorite dikes. Fluid inclusions related to gold mineralization comprise varying amounts of H₂O, CO₂, CH₄, and salt, having salinities between 30 to 45 wt % NaCl equivalent. Zonation of the fluid inclusions exists with CH₄ predominantly in the ore zone. Microthermometric data indicate that fluid trapping occurred between 300 to 375 °C and 2 to 4 kbars. Carbon-isotope data display a trend from — 0.7%. in the footwall to — 4.6%. within the ore zone. Fluid inclusion and carbon-isotope data suggest that redox reactions between the fluid and the graphitic schists resulted in gold precipitation from chloride complexes.