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Abstract
A fluid inclusion study of ores from the Harmsarvet deposit, 15 km NW of Falun, Sweden, was made by means of microthermometry and Raman spectroscopy. Two main types of fluid inclusions can be distinguished: gaseous and aqueous inclusions. The gaseous fluids consist of 3 components: CO2, CH4 and N2; aqueous inclusions are essentially complex brines of varying concentration. Most frequent are CO2-rich inclusions with up to 30 mole % CH4 and less N2; CH4 and N2-rich inclusions are free of any CO2. The present data indicate that the first ore minerals formed already during the regional metamorphic conditions estimated at 600 ± 50°C and about 3 kbar. Late phase minerals (e.g. acanthite) formed during retrograde conditions as trails associated with CO2-CH4-bearing inclusions. It is suggested that the gaseous fluid evolved from a CO2-rich fluid to higher CH4-contents by abstraction of CO2 during the formation of carbonates (siderite). Hydrothermal water probably evolved from high saline brines of metamorphic origin to solutions of lower salt contents by mixing with meteoric water. Brines and gaseous fluids remained immiscible during retrograde conditions.