Peculiarities of accumulation and metamorphism of the triassic metalliferous sediments in the Taukha and Samarka Terranes of the Sikhote-Alin (by the results of geochemical and mineralogical study of Th, U and REE)

Abstract

monazite, allanite, apatite enriched in REE, the Dy2O3, compound, and Th and U minerals were crystallized in the process of the contact metamorphism of metalliferous sediments under the same conditions as the rock-forming minerals of manganese-silicate rocks and silicate-magnetite ores. The presence of the Fe2Ce compound as well as many other intermetallic compounds and native elements is explained by the influence of the organic matter of the underlying carbonaceous silicites. It is connected with the removal from the carbonaceous rocks through heating of the most volatile components, and first of all the poorly bound water and hydrocarbons, that resulted in the origination of some fluid volume with high- and ultra-reductive capacity, which migrated along fractures to other rocks.Differences in the Th-U ratio and the presence of the positive Ce anomaly in the REE-spectra of the manganese-silicate rocks of Samarka terrane and the negative Ce and positive Eu anomalies in the REE-spectra of Taukha terrane are related with the differences in the facial conditions of sedimentation (defined by different position relative the margin of Khanka massif) and with the extent of influence of the mobile metamorpho-genetic fluid phase through the contact metamorphism.