S. B. Felitsyn

Mobility of Phosphorus during the Weathering of Volcanic Ashes

Data are presented on phosphorus mobility during the weathering of rhyolite–dacite tephra of the modern and ancient eruptions. Distal tephra cannot be considered a phosphorus source, since phosphorous has low mobility during weathering both in subaerial and subaqueous sedimentation conditions. However, volcanic ashes exert a fertilization effect, providing the supply of nutrient elements into the ecosystem of internal basins and coastal zones.

Mobility of cerium in the 2.8-2.1 Ga exogenous environments of the Baltic Shield: Data on weathering profiles and sedimentary carbonates

The absence of Ce anomaly and significant positive correlation between Ce and Fe in the weathering profiles and sedimentary carbonate rocks of the Baltic Shield with an age of 2.8–2.1 Ga indicate that Fe3+ was the main form of Fe migration in the Archean-Paleoproterozoic exogenous environments in the Baltic Shield. The Ce distribution was mainly controlled by hydrogen index rather than redox conditions.

The Content of Gold in Vendian-Cambrian Phosphorite Concretions from the East European Platform

High Au contents in phosphorite concretions and Vendian-Cambrian enclosing shales are attributed to the concentration function of microbial biota of Precambrian epiplatformal basins. Microorganisms and organic detritus served as intermediate collectors of gold delivered with the continental runoff from provenances of the East European Platform.

The Redistribution of Phosphorus in Basic Volcanic Rocks

This work presents data on phosphorus content in the central and peripheral sectors of primary jointing blocks in olivine basalts of the Baikal rift zone (Khamar-Daban Range), as well as basaltic andesite flows and dolerite sills on the Karabakh Highland of the Lesser Caucasus. The P2O5 content decrease near cracks in volcanic rocks of the Baikal rift zone is caused by leaching of phosphorus during humid weathering. Estimates of the amount of mobilized phosphorus suggest that alkaline basic volcanic rocks can serve as the continental source for the formation of phosphates.

Rare earth elements and Rb–Sr and Sm–Nd systematics in the peat bog iron ore and moss of the NW East European Platform

Spectra of the REE distribution in the Quaternary–Recent peat bog ore of southern Karelia and Leningrad region are characterized by LaN/YbN < 1.0, presence of positive Eu and negative Ce anomalies, and higher Y enrichment (relative to Ho and Dy) because of the REE sorption by Fe-bearing minerals in acid boggy waters. The 87Sr/86Sr ratio is 0.7175 in iron oxyhydroxides of the Somino deposit (Leningrad region) and 0.7283 in the Polovinkino ore (southern Karelia). The 143Nd/144Nd ratio in them is 0.511844 and 0.511617, respectively.

Fractionation of Rare Earth Elements in the Acid Treatment of Granitoids

The relative enrichment of authigenic clay minerals with heavy rare earth elements (HREE) in Paleoproterozoic weathering profiles on the Baltic Shield is related to the presence of strong acids in drainage water. This is confirmed by the results of laboratory experiments on the treating granitoids by sulfuric acid solutions. Solutions obtained in the experiments exhibit the prevalence of potassium over sodium, whereas the concentration of potassium and sodium in initial granitoids is nearly the same.

Gold in Vendian-Cambrian organic macrofossils of the East European platform

According to the neutron activation analysis (NAA) data, the average Au content makes up 0.004 μg/g in sabelliditid tubes, 0.08 μg/g in vendotaenid ribbon remains, and 0.28 μg/g (the maximal value) in sapropelic films. Sorption of soluble compounds at the epigenesis stage is the most probable mechanism of Au concentration in Vendian-Cambrian rocks from the East European Platform.

The content of gold in Lower Paleozoic phosphatized biogenic remains in Baltoscandia

According to instrumental neutron activation analysis (INAA) data, the average content of Au in conodont elements and phosphate brachiopod shells from Lower Paleozoic sections in Baltoscandia is 4.9 and 0.79 μg/g, respectively. Concentration of Au in phosphatized biogenic remains suggests that they served as an important intermediate concentrator of this metal in the sedimentary cover of the East European Platform.

Redistribution of Au in volcanic ashes in the course of their postsedimentary alterations

The redistribution of Au in Late Precambrian volcanic ashes from the Vendian section of the East European Platform and the Sinian section of the South China Platform is characterized by high Au concentration (up to >20 ng/g) in Fe3+-rich samples. The Au content decreases to ∼2 ng/g in Fe2+-rich volcanic ashes from the Vendian section of the East European Platform. This distribution pattern suggests the mobility of Au-bearing compounds in postsedimentary processes.

Alkali earth elements in Vendian-Cambrian clayey rocks, the East European Platform

Low Sr and Ca contents in fine-grained terrigenous rocks of the Vendian sedimentary cover in the East European Platform may be related to the following reasons: (1) the absence of authigenic carbonates in Vendian mudstones owing to desalination of epiplatformal sedimentary basins; (2) significant contribution of the chemically weathered rocks in the formation of the Vendian cover of the East European Platform.