Gold-bearing capacity of local areas of metasomatically altered rhyolites (the Chudnoe deposit in the Subpolar Urals)

The Chudnoe gold-ore deposit, located in the Maldin ore zone of the Subpolar Urals, is of great interest in terms of formation conditions. Gold is mainly concentrated in fuchsitic veinlets of rhyolites, in association with palladium and rare earth minerals. For the first time, the authors conducted a study of the local areas of rhyolite bleaching, characteristic of the deposit, which do not contain fuchsite, but are also gold-bearing. It was found that rhyolite bleaching is a result of Fe evacuation. Along with gold, there are small amounts of sulfides, uranium and rare earth minerals in the bleaching areas. In composition, native gold in bleached rhyolites is not fundamentally different from this in fuchsitic veinlets. Silver, copper, and palladium are established as elements-impurities in it. The deposition of gold in fuchsitic veinlets and areas of rhyolite bleaching was, most likely, due to the manifestation of a single hydrothermal process in the Late Paleozoic. The presence of palladium in native gold, as well as chromium in fuchsite, indicates the important role of deep sources of matter.