Geological and mineragenic characteristics of the new Urkachik gold-bearing area of the Ulban terrane (Khabarovsk Krai, Russia)

The paper presents geological and metallogenetic characteristics of the Urkachik ore-bearing area within the southern adjacent areas of the Magu volcanogen. There are described petrographic, mineralogical, and geochemical features of metalliferous metasomatites and veinlet-disseminated hydrothermalites (stockworks) of the Talgiy gold ore deposit and Pikhtovy ore occurrence. Mineralization is confined to linear stockworks of quartz-carbonate veinlets in beresite halos in fault zones and is paragenetically associated with small quartz diorite intrusions that form stocks or along-fault intrusions among Jurassic sedimentary rocks (sandstone, siltstone, siliceous rocks). Steeply dipping faults predominantly control ore mineralization in intrusion endocontacts. Gold and rare metal ores differ in mineral composition, including various native elements, intermetallides, sulfosalts, and precious metal chalcogenides. The continuous development of gold-silver submicron dispersed impregnation in all types of secondary rocks characterizes the ores. Native minerals of precious metals occur as natural Au–Ag, Au–Cu–Ag, and Au–Cu alloys, as well as native gold and silver. With depth, metasomatites exhibit an increase in Cu, Sn, rare earth and siderophile elements, with As, Se, and Sb declining. High Au concentrations and elevated Cu, Bi, Ag, As, Sb, and Te concentrations are typical of the ores that fall into the gold-bismuth geochemical subtype of gold and rare metal hydrothermal deposits formed at the subvolcanic level. In terms of sulfide content, the ores in the Urkachik ore-bearing area correspond to poor and lowsulfide types of metalliferous sediments.