Vol 59, No 2 (2017)

By the end of the Archean, the period of active volcanism, plutonism, accretion, and cratonization had been completed by the construction of stable continental plates. Afterward, cratons were subject to intense extension owing to mainly mantle diapirism and ascent of asthenospheric flows, which gave rise to the formation of ensialic intracratonic basins, whereas other linear troughs were expressed in the formation of continental rifts. Zones of continental rifting are characterized by a wide spectrum of mineral resources (Cu, Ni, PGE, Co, Ti, V, etc.) related to igneous complexes. This paper is focused on metallogeny of nickel-sulfide and PGE mineralization in the Fennoscandian Shield. The results of metallogenic analysis of Paleoproterozoic riftogenesis, along with the account of previous achievements, have shown that the aforementioned mineralization is related to three consecutive plume-tectonic pulses of mantle activization, which are expressed in (i) upwelling of the subcontinental mantle enriched in LREE, (ii) intrusion of mafic and ultramafic melts derived from enriched and depleted Archean mantle sources, and (iii) formation of low-sulfide Pt–Pd and Pt-bearing Cu–Ni sulfide deposits.

The geological–structural features and gold-potential perspective of the Tokur ore–placer cluster in the Amur Province have been studied. This ore–placer cluster is a syncline composed of Paleozoic blackshale sequence, which is cut through by Late Paleozoic and Late Mesozoic intrusions. A granitoid massif is suggested at the depth on the basis of geophysical data. The cluster is distinguished by high productivity. Approximately 37 t gold from ore deposits, primarily from the Tokur deposit, and 60 t from placers have been mined out. The Tokur deposit is compared with the Natalka and Degdekan deposits from the Yana–Kolyma Province. Perspectives of the cluster area for large gold–quartz deposits and technogenic gold placers have been estimated.

The degree of concentration and REE and Zr distribution and occurrence in uranium ore samples from paleovalley deposits are considered. Various types of REE distribution in ores with variable uranium content has been revealed: the negative type with predominance of LREE in ordinary ore and the V-shaped type with significant growth of Y, MREE, and HREE contents in high-grade ore. In addition, the relationship between U, on the one hand, and MREE, HREE, Y, and Zr, on the other hand, has been established. Predominant isomorphic incorporation of these elements into various uranium constituents is suggested. The conclusion was arrived at about the most probable gain of REE and Zr along with U on various geochemical barriers from postvolcanic thermal carbonated and sulfuric-acid aqueous solutions enriched in these chemical elements. The significant enrichment of uranium ore in REE confirms the real possibility of recovery of them as a by-product from working solutions in the process of in situ uranium leaching.