Typomorphic features of platinum group minerals from alluvium of the Kytlym platinum-bearing cluster (North Ural), Russia

Research subject. The article presents the results of an integrated study of platinum group minerals from platinum-bearing alluvial placers of the river Kosva, draining the Kytlym concentrically zonal ultramafic massif (Northern Urals) and its southern tributary stream Bogaty Log. Materials and methods . Materials were sampled during the fieldwork of 1990–1991. The chemical composition and structural and textural features of platinum group minerals were determined using ore (AxioScope.A1) and scanning electron (MIRA 3 LMU with an INCA Energy 450 XMax 80 microanalysis system) microscopy. Results. Platinum group minerals in placers of the river Kosva and stream Bogaty Log are represented by Pt-Fe(±Cu) alloys, which correspond to isoferroplatinum and ferroan platinum with inclusions of Os-Ir-(Ru) intermetallic compounds, laurite, and irarsite. Most grains of platinum group minerals were subject to postmagmatic alteration, which manifested itself in the formation of replacement rims of a tetraferroplatinum–thulaminite composition. Among the secondary platinum group minerals, the authors encountered a mineral phase – unnamed intermetallic compound of rhodium, copper, palladium, and tin (Rh,Cu,Pd,Pt) 3 Sn that has not been previously described in nature. Conclusions. The main sources of platinum-bearing placers are ultramafic complexes of the Kytlym concentrically zonal ultramafic massif, primarily chromitites from eroded serpentinized dunites. The grains of platinum group minerals do not bear traces of hypergene chemical alteration and completely inherit the composition of platinum mineralization from the primary sources that feed the placers. The influence of intermediate pre-Quaternary reservoirs on the formation of the studied platinum placers is minimal.