PREREQUISITES TO FINDING OF A CONCEALED AU-MO-(±CU)-PORPHYRY MINERALIZATION IN THE POKROVKSKOE ORE FIELD (GONZHA ORE AREA, UPPER AMUR REGION)
Geological study of some large ore mining regions of the world shows that epithermal (not deep, volcanogenic) deposits existing there spatially and paragenetically associate with meso- and hypothermal (porphyry, plutonogenic) occurrences, with common belonging to the complex, long-time forming and vertically extended ore-magmatic systems. More and more domestic researchers are turning their attention to similar systems in the southeastern metallogenic provinces of Russian Federation: southern Yakutiya, southeastern Transbaikalia, Upper and Middle Amur regions. The Gonzha ore area in Upper Amur region is known for several spatially disseminated epi- and mesothermal (Burinda, Zheltunak, Pionernoe, Pokrovskoe), Au-Cu-Mo-porphyry (Borgulikan, Ikan, Igak, etc.) gold deposits and manifestations of Mo and Pb. Most ore fields occur in peripheral parts of Early Cretaceous intrusive granodiorite-granite massifs framing the Precambrian horst and are juxtaposing with subvolcanic, extrusive bodies and effusive pyroclastic sheets of medium and moderately acid composition. Taking into account the mentioned features of the deposits’ geological disposition, the presence in their areas of dykes, stocks, and paleovolcanic necks, as well as abundant manifestations of zonal metasomatic alterations (from propylite, feldspatholith, cericitolite, and argillizite to secondary quartzite), there is a possibility that deep horizons (to the depth of 4 km) may have sizable epithermal occurrences of Au-Mo-(±Cu)-porphyry mineralization, according to known geological-genetic models. In this connection the Pokrovskoe ore field is worth the prospectors’ prior attention. The odds are that the near-surface epithermal Au-Ag mineralization here spatially conjugates (in vertical extension of more than 1 km) with deeply concealed porphyry mineralization.