Vaikijaur Cu-Au-(Mo) deposit, northern Sweden : preliminary results from fluid inclusion and (O, H) isotope studies

The Vaikijaur Cu-Au-(Mo) deposit is located in the ca. 1.88 Ga calc-alkaline Jokkmokk granitoid near the Archaean-Proterozoic palaeoboundary within the Fennoscandian shield in northern Sweden. The Vaikijaur deposit occupies an area of 2×3 km within the Jokkmokk granitoid and includes stockwork quartz-sulphide veinlets and disseminated sulphides and gold. The mineralized area is characterized by potassic, phyllic and propylitic alteration. A conductive pyrite-rich central part is surrounded by a conductive and magnetic zone with pyrite, chalcopyrite, and gold. Analyses of one metre drill core sections have shown up to 5% Cu and 7 ppm Au. Molybdenite is distributed irregularly in the deposit. Re-Os age data suggest that primary porphyry-style mineralization was associated with the calc-alkaline magmatism at ca. 1.89-1.87 Ga. Molybdenite records also a later metamorphic event at about 1750 Ma (Lundmark et al., 2005).Preliminary fluid inclusion data reveal no evidence for the involvement of high-salinity fluids typically for the Norrbotten Fe oxide-Cu-Au ores. By contrast, fluid inclusions in quartz veinlets associated with the sulphides at Vaikijaur indicate deposition from inflowing low- to medium-salinity aqueous and carbon dioxide-rich fluids. Oxygen and hydrogen isotope compositions of quartz, biotite, chlorite and amphibole in ore-related samples have mixed magmatic and seawater signatures. Godkänd; 2006; 20111007 (andbra)