GARNET-BEARING ZONES OF POSTMAGMATIC RHYOLITE ALTERATION AT THE DUKAT ORE FIELD AND THEIR RELATION TO THE HIGH-GRADE GOLD-SILVER ORES

Abstract

Some new data concerning the chemical composition of postmagmatic garnets and associating minerals from various alteration zones of potassic rhyolites and granites in the central part of the Au-Ag Dukat ore field are discussed. The garnets studied belong to the grossular-spessartine series. They occur in metasomatic rocks related to the latest stage of evolution of the hydrothermal system and to the formation of the quartz-rhodonite-rhodochrosite orebodies. The mineral assemblage formed at a shallow depth in cavities and fissures under high gradients of physicochemical parameters. The assemblage is nonequilibrium and includes quartz, grossular-spessartite garnet, Ce-containing clinozoisite, Fe-chlorite, phengite, fluorite, calcite, and Mn hydroxides rich with Ag, Zn, Pb, Cu, and Ce. Quartz, spessartine, fluorite, parisite, and allanite dominate below the orebodies. Almandine with associating biotite, chlorite, and titanium oxides occurs in hornfels and graphitization zones. The mineral deposition was accompanied by moderate-temperature propilitization and was related to the heat of the granitic pluton and reduced gas flows.