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.     

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.     

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 La_N/Yb_N < 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.     

Isotope composition of neodymium in neo-Archean banded iron formations of Karelia and Kola Peninsula

Studies of three deposits of neo-Archean banded iron formations from the West Karelian domain (the Kostomuksha deposit) and from the Central Kola block (the Olenegorsk and Kirovogorsk deposits) showed a pronounced difference in the isotope compositions of Nd from quartz and magnetite–hematite interlayers. The less radiogenic Nd of iron-containing layers compared to that of the quartz component may be considered as an indication of the formation mechanism of the treated banded iron formations. Thus, silicon-containing layers are related to submarine volcanism and iron was supplied to the sedimentation zone from other sources.     

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.     

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 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.     

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.