Fluid mode of quartz vein formation of Yarotashor gold placer (Subpolar Urals)

By the methods of homogenization, cryometry, gas chromatography and Raman spectroscopy we have studied fluid inclusions in quartz of conformable and intersecting veins of Yarotashor gold placer composed of Precambrian highly metamorphosed rocks. Based on the obtained data, three main stages of quartz formation were identified. The first stage was related to the formation of fine-crystalline quartz of conformable veins, which had occurred at temperatures of 255-380 °C. The ore-forming solutions contained sodium and magnesium chlorides, the salinity of the solutions was up to 14 wt. % NaCl eq. In the gas phase, the dominant role was often played by nitrogen ore carbon dioxide. The second stage was confined to the beginning of the formation of coarse-crystalline quartz of intersecting veins, also developed in conformable veins. Crystallization of quartz occurred at temperatures of 310-385 °C. The ore-forming solutions contained sodium and magnesium chlorides with impurities of other salts, the salinity of the solutions was up to 12.5 wt. % NaCl eq; carbon dioxide and nitrogen predominated in the gas phase. The second stage was associated with the transformation of coarse-crystalline grained quartz of intersecting veins, which had occurred at lower temperatures (200-225 °С). The mineral-forming solutions were enriched with carbon dioxide. On the basis of the obtained data, the final stage of formation of quartz of intersecting veins can be considered as potentially gold productive.