Vol 51, No 5 (2016)

C and O isotope composition of Middle-Upper Miocene and Lower Pliocene carbonates from Kerch-Taman Region (Eastern Paratethys) have been studied in order to reconstruct palaeoenvironmental variability and post-sedimentation changes. The δ¹³C and δ¹⁸О values of the Upper Sarmatian to Lower Pliocene organogenic carbonates reflect the desalinization of paleobasins, global Late Miocene Cooling, and increase in seasonal temperature fluctuations. Isotopic composition of the Middle Sarmatian organogenic carbonates was strongly influenced by evaporation processes, high bioproductivity, and local submarine methane emissions. Warm climate and low bioproductivity together with unstable hydrological regime during the Late Chokrakian and the Karaganian times influenced the isotope composition of primary carbonates. Calcite shell of Spiratella sp. (δ¹³C =–0.4‰ and δ¹⁸О =–0.4‰) from Tarkhanian sediments was formed in warm marine environment. Dolomitization prevails over other secondary mineralization in the studied carbonate rocks. Two groups of secondary dolomites that are characterized by negative and positive δ¹³C values have been recognized. Lowe δ¹³C values (up to–31.4‰) in dolomites indicate the influence of both dissolved inorganic carbon (DIC) from oxidized organic matter (С_org) and methane. Dolomites with positive δ¹³C values (7.0 and 7.8‰) associat with migration of CO₂- and CH₄-containing saline groundwater.

It has been established that large ferromanganese deposits enriched in noble metals, Co, U, V, and REE in the Kimkan sedimentary basin are confined to Vendian–Cambrian black shales. Lithostratigraphy plays an important role in the localization of such deposits and promising ore-bearing fields. Deposits and occurrences of complex iron and ferromanganese ores are polygenous and polychronous, because they underwent intense hydrothermal alterations with the superposition of noble metal and uranium mineralization in the Cretaceous. Efficient utilization of complex iron ores in the Kimkan open pit needs the construction of a metallurgical plant.

Over 60 minerals, including native elements, intermetallic compounds, haloids, sulfides, sulfates, arsenides, oxides and hydroxides, silicates, borosilicates, wolframates, phosphates and REE phosphates, were established in Triassic siliceous rocks of Sikhote Alin. Allothigenic and authigenic minerals in the carbonaceous silicites were formed over a long period through several stages. Judging from morphology, chemical composition, and structural position, K-feldspar (K-Fsp), illite, kaolinite, metahalloysite, monazite, xenotime, zircon, rutile, or its polymorphs are the disintegration products of sialic rocks of continental crust. Authigenic sulfides are dominated by diagenetic pyrite (fine-crystalline, microglobular, framboidal, as well as those developed after biogenic siliceous and carbonate fragments), which has been formed prior to precipitation of siliceous cement and lithification of siliceous rocks. Most of other sulfides (sphalerite, galena, chalcopyrite, pyrrhotite, argentite, pentlandite, antimonite, ulmanite, and bravoite), arsenides and sulfoarsenides (arsenopyrite, nickeline, skutterudite, cobaltite, glaucodot, and gersdorffite), wolframates (scheelite and wolframite), intermetallides (Cu₂Zn, Cu₃Zn₂, Cu₃Zn, Cu₄Zn, CuSn, Cu₄Sn, Cu₈Sn, Cu₄Zn₂Ni, Ni₂Cu₂Zn, Ni₄Cd), and native elements (Au, Pd, Ag, Cu, Fe, W, Ni, Se) were crystallized later (during catagenesis after the lithification and brecciation of siliceous beds) from metals involved in the easily mobile fractions of bitumens. Supergene mineral formation was mainly expressed in the sulfide oxidation and replacement of diagenetic pyrite by jarosite and iron hydroxides.