Volcanogenic massive sulfide deposits contain Cu, Zn, Pb, Sb, Bi, Te, Se, Ag, Co and variable amounts of Ag and Au. In some of them gold reserves exceed 100 t while gold grades reach several dozens ppm. Original data base was used to establish statistically meaningful criteria for identification of deposits with large gold reserves and/or anomalously enriched in gold. Some peculiar features of deposits with high Au grades were investigated including distribution in geological history and among the principal metallogenic provinces, association with volcanogenic formations and paleovolcanic structures, geochemical and mineralogical features and factors that caused enrichment in gold.
New data on the radiolarians and foraminifers (planktonic and benthic) from the lower part of Struganik limestones (Brežđe Section, Western Serbia) were presented. Radiolarian data show the presence of Afens perapediensis Zone (uppermost Santonian) [Bragina, 2016]. Planktonic foraminifers are represented by abundant Marginotruncana (extinct in latest Santonian) and Globotruncana linneiana (d’Orbigny) (appear in early Santonian). Radiolarian and planktonic and benthic foraminiferal data agree with one another.
Composition and origin of Callovian–Oxfordian deposits of the Sudak Bay based upon generalizations of our own results and analysis of published and unpublished data were specified. A botanic feature for geological prospecting of Oxfordian limestones was used for the first time.
Based on the lithofacies and structural analysis we consider a new variant of the structuralfacies zonation of the Bazhenov horizon (Tithonian — lower Berriasian) in the north-eastern part of West Siberia. The low content of terrigenous sedimentary material in high-carbon facies the bazhenov formation, due to its capture of relatively deep Pur-Tazovsky paleobasins, which formed the cone of the Yenisei-Khatanga sea strait. Pur-Tazovsky basin filled with the yanovstanskaya formation, he adjoined from the north-east to extensive relatively shallow Obsky paleobasin — the accumulation of black shale bazhenov formation.
The study of heavy metal speciation in bottom sediments of the Vyshnevolotsky water reservoir is presented in this paper. Sequential selective procedure was used to determine the heavy metal speciation in bottom sediments and thermodynamic calculation — to determine ones in interstitial water. It has been shown that Mn are mainly presented in exchangeable and carbonate forms; for Fe, Zn, Pb и Co the forms are related to iron and manganese hydroxides is played an important role; and Cu and Ni are mainly associated with organic matter. In interstitial waters the main forms of heavy metal speciation are free ions for Zn, Ni, Co and Cd, carbonate complexes for Pb, fulvate complexes for Cu. Effects of particle size and organic matter content in sediments on distribution of mobile and potentially mobile forms of toxic elements have been revealed.
Equilibrium mineral assemblages at temperatures from 50 °C to 350 °C and pressure of saturated water vapor were established by the thermodynamic modeling of hydrothermal reaction on the Bazhenov Formation rocks. The calculation results show that the mineral parageneses vary slightly with the temperature increase: for zeolites stilbite-laumontite-wairakite row is typical, kaolinite is replaced by montmorillonite and/or albite, pyrite — by pyrrhotite, calcite — by dolomite, brannerite — by uraninite. The simulation results are confirmed by experimental data.
Ore mineralogy of the largest quartz vein Osinovaya at the Kedrovskoye gold deposit has been studied. Three stages of mineral formation are identified: marcasite-pyrrhotite-pyrite, gold-polysulphide and hypergenic ones. Native gold belongs to gold-polysulfide stage and is represented by two generations. The earlier high fineness (600–870, prevails 780–820) generation cements fragments of pyrite grains and forms inclusions in pyrite, and the later low fineness (520–580, prevails 540–580) generation associates with sphalerite-chalcopyrite-galena veinlets in pyrite. The disappearance of arsenoan pyrite, the increase in iron content of sphalerite, the change of pyrite to pyrrhotite with depth is noted.
The water contents in silica and salt alumina-fluoride melts are estimated. Solubility of water in silica melt increases up to 7–8 wt.%, in alumina-fluoride salt melt up to 15–19 wt.%. Solubility of alumina-fluoride salt melt (brine) increases with increasing concentration of water in the model granite system.
