Mineralogycal features of ores and fluid inclusions in vein quartz of occurrence Sekushchy (Chukotka)

The study of mineral composition of ores and fluid inclusions in quartz veins of gold ore veins of the occurrence Sekushchy (Chukotka) were carried out. Such minerals as gold, pyrite, arsenopyrite, pyrrhotite, chalcopyrite, galena, sphalerite were described. The authors noted the presence of xenotime, monazite and rare-earth phases of erbium and thulium in the ores. In the vein quartz various fluid inclusions were found: a) three-phase inclusions with a gas phase content of 50-70 vol. %, b) three-phase inclusions with a gas phase content of 25-70 vol. %,c) two-phase inclusions, consisting completely of liquid and gaseous carbon dioxide. It is shown that the formation of the gold occurrence Sekushchy resulted from intensive hydrothermal activity in the Cretaceous (Late Cretaceous) time that was initiated by the processes of regional metamorphism and injection of granitoids. Initially, mainly in the areas of dislocation with a break of continuity occurred the formation of quartz, quartz-carbonate veins and veinlets. Later ore mineralization superimposed on this veins and host rocks. Mineralization was phasic, accompanied by interruptions and tectonic movements. Two main ore stages were distinguished: pyrite-arsenopyrite and gold-chalcopyrite-galenasphalerite. The temperature of the mineral formation was 300-350°C, hydrothermal solutions were essentially saturated by carbon-dioxide.