Studies of mineral-forming processes in modern peat bogs can shed light on metal concentrations and their cycling in similar environments, especially in geological paleoanalogs. In terms of the mineralogical and geochemical evolution of peat bog environments, the Vasyugan Swamp in Western Siberia is a unique scientific object. Twelve peat samples were collected from the Vasyugan Swamp up to the depth of 275 cm at 25 cm intervals. The studied peat deposit section is represented by oligotrophic (0–100 cm), mesotrophic (100–175 cm), and eutrophic (175–275 cm) peat, and this is underlain by basal sediments (from 275 cm). About 30 minerals were detected using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. The observed minerals are divided into detrital, clay, and authigenic phases. The detrital minerals found included quartz, feldspar, ilmenite, rutile, magnetite, zircon, and monazite. When passing from basal to oligotrophic bog sediments, the clay minerals changed from illite-smectite to kaolinite. Authigenic minerals are represented by carbonates (calcite and dolomite), iron (hydro-)oxides, galena, sphalerite, pyrite, chalcopyrite, Zn-Pb-S mineral, barite, baritocelestine, celestine, tetrahedrite, cassiterite, REE phosphate, etc. The regular distribution of mineral inclusions in peat is associated with the (bio)geochemical evolution of the environment. The formation of authigenic Zn, Pb and Sb sulfides is mainly confined to anaerobic conditions that exist in the eutrophic peat and basal sediments. The maximum amount of pyrite is associated with the interval of 225–250 cm, which is the zone of transition from basal sediments to eutrophic peat. The formation of carbonate minerals and the decreasing concentration of clay in the association with local sulfide formation (galena, sphalerite, chalcopyrite, stibnite) begins above this interval. The peak of specific carbonation appears in the 125–150 cm interval of the mesotrophic peat, which is characterized by pH 4.9–4.5 of pore water. Kaolinite is the dominant clay mineral in the oligotrophic peat. Gypsum, galena, chalcopyrite, sphalerite, and relicts of carbonate are noted in association with kaolinite. Changes in oxygen concentrations are reflected in newly formed mineral associations in corresponding intervals of the peat. This can be explained by the activity of microbiological processes such as the anaerobic oxidation of methane (AOM) and bacterial sulfate reduction (BSR), expressed in specific carbonatization (100–225 cm) and sulfidization (175–250 cm), respectively.

This study reconstructs the depositional conditions of ironstones within the Chulym-Yenisey basin and assesses the iron source. The detrital minerals of the studied deposits include quartz and feldspar. The authigenic minerals are goethite, siderite, aragonite, dolomite, calcite, apatite, barite, and pyrite. The clay components include minerals of the chlorite group (possible chamosite), nontronite, kaolinite, illite, and beidellite. Local bacterial sulfate reduction led to the formation of pyrite framboids in siltstone layers. The subsequent diagenetic iron reduction promoted the formation of chamosite from siderite. The goethite precipitation occurred in an oxidic aqueous environment. The Cretaceous continental sediments of the Ilek and Kia Formations of the Chulym-Yenisei depression consist of fine- and medium-grained, cross-stratified, poorly sorted litho-feldspatho-quartzose sandstones of fluvial channel origin alternating with bluish-gray siltstones and ironstones of floodplain–lacustrine–bog origin. Thin layers of iron-bearing rocks within siltstones formed in meromictic waters. The changes in geochemical proxies demonstrate fluctuations of paleoenvironmental conditions within the Cretaceous sequence. Siltstones and sandstones formed under humid and arid conditions, respectively. The primary iron source for sediments of the Chulym-Yenisey depression was determined as volcanogenic and igneous rocks of the Altai-Sayan mountainous region.