Metamorphic Conditions and Raman Spectroscopic Carbonaceous Material Thermometry of Host Schists of Olympiada and Eldorado Gold Deposits (Yenisey Ridge, Russia)

Metamorphic processes play a key role in forming orogenic gold deposits. In this paper, we present new evidence that host schists of the two largest gold deposits of the Yenisey ridge (Russia) Olympiada and Eldorado underwent a single stage of metamorphism in contrast to surrounding blocks. This metamorphism is of moderate thermal gradient and belongs to the Barrovian type, which is typical for the collisional event in the time range 800–850 Ma. The new Ar/Ar age data presented in this paper and the review of magmatic and metamorphic events and ore-forming processes indicate that the most productive stage (gold-sulfide-quartz) correlates well in time with the regional metamorphism of the Barrovian type. This indicates that metamorphic processes can have a crucial role in forming gold deposits of the Yenisey ridge. Carbonaceous material thermometry indicates a wide range of obtained temperatures around 90–150 °C around the mean temperature for each sample. The highest temperatures are close to the peak metamorphic temperatures estimated by garnet-biotite thermometry.

DEFECTS OF MAGMA FORMATION ANALYSIS

The formation analysis of igneous rocks is a great achievement of the Soviet science in terms of classifying natural communities of magmatic rocks for the purpose of forecasting and prospecting of associated deposits. But due to the complexity of the problem itself, the uncertainty of boundaries between formational types in the practice of geological works, there are numerous defects that were clearly observed during the regional and interregional correlation of magmatic complexes of the Altai-Sayan region and Yenisey Ridge. The reasons and consequences of these defects, ways of their correction are analyzed.

Pogor’uy formation of the proterozoic, Yenisey Ridge: age and provenance according to U–Pb-isotopic detrital zircon dating

The results of U–Pb-isotopic dating of detrital zircons from sandstones of the Proterozoic Pogor`uy Fm. from the northern and southern parts of the Eastern-Angara block of the Yenisei Ridge are presented. The sandstones of the northern part of the Eastern-Angara block are dominated by the Archean and Paleoproterozoic populations of detrital zircons, while in the samples from the southern part of the Eastern-Angara block up to 25% of the Mesoproterozoic age grains have been fixed. The dates of detrital zircons allow us to constrain the maximum sedimentary age of the Pogor`uy Fm. and the entire interval of its formation as 1.2–0.9 Ga. The paleogeographic features of the formation of the Pogor`uy Fm. in the context of existing views on a location of Siberia within the Rodinia supercontinent are considered.