Comparative U-Pb (zircon and sphene based, for the first time) and K-Ar (biotite , amphib ole, and whole rock based) dating of monzonitoids and subalkaline granitoids of the Ket Kap and Uchur vol canic plutonic complexes (Ket Kap-Yuna Igneous Province is one of the areas of tectonic magmatic acti vation of the Aldan Shield), respectively, has been made. The new data, which are chiefly acquired by us for the first time, are close to each other and fall within the relatively narrow time interval of the mid Early Cretaceous. The U-Pb sphene based isochron datings indicate the formation time of the subalkali complexes at the Bar remian-Aptian boundary. The values of SHRIMP age for zircons from the Uchur Complex subalkali diorites vary from 124.4 to 120.1 Ma; variations in U-Pb dates for monzonitoids of the Ket Kap Complex fall in the narrower interval of 125.8-123.6 Ma. The extraordinary cases of highly polymodal distribution of SHRIMP derived zircon based dates are explained by the presence of detrital zircon crystals probably belonging to the protolith; this is interpreted by evidence for participation of the ancient continental crustal material in the formation of the source for the KKYuIP subalkali magmas. The range of the new K-Ar datings based on the whole rock composition of subalkali rocks and on the results of monomineral determinations is wider; how ever, it corresponds to the Early Cretaceous as well. This is significantly in contrast with the data given in the literature and geological survey reports. It was found for the first time that the duration of the subalkali magmatism manifestation in the KKYuIP is only several Ma and, according to the precise U-Pb dating, falls within the Aptian age of the Early Creta ceous epoch; this is sharply in contrast to the previously derived dates that referred to Early Jurassic-Creta ceous age of the magmatism. This time interval probably marks the main stage (relative quiet phase under strong compression) in the evolution of the setting of mutual sliding between the Siberian Craton and Amurian megablock, according to geodynamical reconstructions by A.I. Khanchuk and his colleagues.

The accumulations of massive sulfides, mostly pyrrhotite, and the accompanying Pt-Pd and gold mineralization in the more eroded Lantar part of the Dzhugdzhur massif-type anorthosite, Aldan Shield, Russia, are characterized in detail for the first time. The metamorphic basement host-rocks of the anorthosite massif are crosscut by interlayers and injections of pyroxenite and plagioclase peridotite, which have a different extent of pyrrhotite dissemination. Upward, they give way to olivine-bearing gabbronorites interlayered with bodies of sulfide-bearing pyroxenite and gabbro. Above is a zone 350 m thick of pegmatitic gabbroic anorthosites which hosts the main bulk of the sulfide ores of Nyandoma and Batomga areas. These areas differ from one another by intensity of occurrence of the massive and disseminated pyrrhotite, chalcopyrite nests, and late pyrite-bearing assemblages. Platinum-palladium mineralization is represented by moncheite, sperrylite and kotulskite. Copper-, silver-, and Pt-Pd-bearing gold is found in the pyrite concentrate. SommaireNous décrivons pour la première fois les accumulations de sulfures massifs, surtout la pyrrhotite, et la minéralisation associée en Pt-Pd et en or dans la partie plus érodée (Lantar) de l'anorthosite de type massif de Dzhugdzhur, bouclier d'Aldan, en Russie. Le socle métamorphique qui est l'hôte du massif d'anorthosite est recoupé par des intercalations et des injections de pyroxénite et de péridotite à plagioclase, qui font preuve de différences en teneurs de la fraction sulfurée. Vers le haut du complexe, on trouve surtout des gabbronorites avec interdigitations de venues de pyroxénite et de gabbro porteurs de sulfures. Au-dessus cet ensemble se trouve une zone d'une épaisseur de 350 m d'anorthosites gabbroïques pegmatitiques, qui renferment la plupart des accumulations de minerai sulfuré des régions de Nyandoma et Batomga. Ces régions se distinguent selon la proportion de pyrrhotite massive et disséminée, les accumulations de chalcopyrite, et les assemblages tardifs riches en pyrite. La minéralisation en platine et palladium se manifeste par la présence de monchéite, sperrylite et kotulskite. Les grains d'or contenant cuivre, argent, et Pt-Pd se trouvent dans les concentrés de pyrite. (Traduit par la Rédaction)Mots-clés: minéraux du groupe du platine, or, anorthosite de Dzhugdzhur, bouclier d'Aldan, Russie. §

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