Peculiarities of formation of the Devonian Au-Ag epithermal mineralization in pipe orebodies

The formation of pipe orebodies of the Yunoe deposit was caused by thermal metamorphism related to intrusions of postmineral basaltic dikes and characterized by heating to a temperature above 500°C, which is evident from index minerals. Based on thermodynamic calculations, the model elaborated suggested that intense heating of pyritized rhyolitic necks resulted in S loss and increase in the S concentration in the hydrothermal system that was favorable for uytenbogaardtite crystallization. The results of thermobarogeochemical investigations are consistent with this model. They show the possibility of fast cooling of the oreforming fluid in subsurface conditions or upon mixing with cold meteoric waters that probably caused the formation of ore mineralization with uytenbogaardtite, acanthite, and native gold. In particular, the results confirm a rise in salinity with a decrease in temperature in fluid inclusions.