NEW GOLD PALLADIUM TYPE OF MINERALIZATION IN THE KOZHIM REGION OF CIRCUMPOLAR URAL (RUSSIA)

Investigations begun in the circumpolar Urals in 1994 of the occurrenc e of Chudnoe (upper part of the Al'kes-Vozh Creek, the left tributary of the Balban-Yu River, Kozhim River basin) native gold ore have shown that the existence of this ore is due to a new type of hydrothermal A u-Pd-REE mineralization in rhyolites. The occurrence of this ore, whic h is deposited in Riphean rhyolites, is localized in the south margin of the Maldin anticline. Four mineralization zones of schistosity with quartz-albite and multiple fuchsite stringers have been discovered. I n two central zones, 15 exposures with visible gold have been found. T he gold content according to two sampling channels was 42 and 84 g/tn. The near-alterations in rhyolites are represented by albite-sericite( +fuchsite)-quartz association. The ores contain the following minerals : quartz; albite; fuchsite; orthite (allanite); barite; zircon; monazi te (?); and leucoxene; as well as Ag-, Cu-, Hg-, and Pd-bearing native Au I and high-grade Pd-bearing Au II; Au-Cu minerals; native Ag; a me rtyite group mineral; atheneite; and an unnamed mineral (palladium ars enide). Two mineralization stages have been distinguished: (I) barren quartz-albite and (II) fuchsite-gold. The sequence of mineral separati on in stage II is fuchsite + orthite (+/-monazite +/- barite?)-Au I-me rtyite + atheneite + the Pd-As mineral. The internal structure of nati ve Au I is complicated by the exsolution structure, which consists of an Au + Ag + Cu + Hg + Pd-matrix and Au + Cu +/- Pd-laminae. Palladium minerals (mertyite, atheneite, and the Pd-As phase) were formed after Au I and are observed in intergrowths with it. In high-grade Au II in clusions of gold and copper, minerals are present. These are assumed t o be formed together with native Ag during supergene changes of Au I. A comparison of the morphology, the internal structure, and the compos ition of gold and platinum group minerals (PGM), from Chudnoe ore occu rrence and from placers, has led to the discovery of their identity.