Presented are data on the conditions of moissanite nanoparticles detection in the unusual for this high-baric mineral environment formed in the zones of quartzitizing of rhyolites. The analyzed electron microscopy data on moissanite nanoparticles' localization in the minerals of disseminated multi-metal mineralization (which was formed, as previously shown, under conditions of medium-temperature propylites) indicate that their crystallization proceeded out of this mineral monocrystals' stability region. It's suggested that the conditions favorable for moissanite nanoparticles formation, as well as for associating with them nanoparticles of ore minerals, were realized at penetration into the near-surface fluidal rhyolites' porous layer of reduced fluids, their spontaneous overcooling and super-saturation.