Vol 68, No 6 (2023)

The Rudny Altai metallogenic province, which is concordant to the structures of the eponymous terrane and located in the Central Asian orogenic belt (CAOB), is one of the largest volcanic massive sulfide (VMS) provinces in the world. Lead isotopic composition of galena (61 samples in total) was measured for the first time with high accuracy (±0.02%, SD) for 20 sulfide base metal deposits representing the dominant Kuroko type in the Rudny Altai. They are enclosed in the Early–Middle Devonian volcano-sedimentary sequence in association with volcanic rocks of the bimodal basalt-rhyolite series. We studied the large and superlarge deposits of this type: Ridder-Sokol’noe, Tishinskoe, Novo-Leninogorskoe, Zyryanovskoe, Zmeinogorskoe, and Korbalikha. In the province, the isotope ratios 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb vary within narrow limits. At average values of 206Pb/204Pb = 17.820, 207Pb/204Pb = 15.517 and 208Pb/204Pb = 37.669, the root mean square variations (variation coefficient, %) are 0.22, 0.038 and 0.063% respectively. Even more homogeneous composition is observed within ore districts of the province (0.054, 0.012 and 0.020%) and especially within deposits (0.025, 0.010 and 0.013%), where the scale of variations of lead isotope ratios reaches their measurement error (±0.02%). The lead isotopic composition in the province shows no isotopic “signatures” of juvenile (asthenospheric) origin. The evolutionary characteristics of the lead source (its depletion in uranium, the old model Pb-Pb age, and moderate values of the µ2 parameter) together with the persistent isotopic composition allow us to regard the lithospheric mantle consisting of metasomatized and recycled rocks as its source. This source was of regional significance, chemically (U-Th-Pb) and isotopically (Pb-Pb) homogeneous, and common for all deposits. Among other CAOB terranes, including the Chinese Altai, the 206Pb, 207Pb and 208Pb isotopes in the ore lead of the Rudny Altai terrane have the least radiogenic composition. The previously noted (Chiaradia et al., 2006) systematic decrease of radiogenic isotope content in the lead of ores and rocks of the CAOB terranes from the southwest to the northeast correlates with a decrease in the lower crustal contribution in the same direction in their composition, where fragments and blocks of Precambrian crust are also involved. The peculiarity of the Pb isotopic composition of the Rudny Altai terrane is largely determined by the absence of Precambrian crustal blocks in its composition.

Colloids of metals have been studied much more poorly in hydrothermal solutions than in surface and underground waters. Nevertheless, literature data indicate that colloidal particles containing metals are present in hydrothermal minerals, in geogas, in groundwaters above orebodies, in fluid inclusions of minerals, and in geothermal solutions. These particles are usually thought to be formed at nucleation in supersaturated solution, which is generated in conversion reactions of minerals or when fluids boil. Published experimental data confirm that colloidal particles can be formed and preserved in hydrothermal conditions. Experimental data on the filtration of supersaturated and colloidal solutions in porous media at elevated temperatures are still too scarce to enable a comprehensive and reasonably accurate assessment of the mobility of colloidal particles under these conditions. The involvement of colloids in the hydrothermal ore-forming process is most clearly manifested at formation of rich epithermal Au deposits. The example of a quartz geothermometer is employed to demonstrate that metals can be transferred in true supersaturated solution, and this mechanism may be even more efficient than colloidal transfer. Metals can thus be transferred in the hydrothermal process in significantly higher concentrations than it follows from the traditional approach based on equilibrium thermodynamics.

Sedimentation transport of 137Cs can lead to the significant accumulation of this radionuclide at depths that could not be reached through the vertical water exchange alone; therefore, a comparative assessment of its contents for different types of suspended matter (SM) and regions of the Black Sea is of particular interest. For this purpose, we have collected samples of SM and seawater at deep-water and coastal stations for the subsequent determination of the 137Cs activity in the surface water layer. To calculate the fraction of lithogenic matter, the potassium content in the SM was additionally determined. The range of 137Cs content on SM at different stations differed by more than an order of magnitude: from 7 to 111 Bq/kg for specific activity, and from 0.03 to 0.69% for its content on SM, in % of the total content in the surface water layer. Stations located farther away from the coast were characterized by the lowest percentage of 137Cs in SM, while its content at the coastal stations was more variable. The comparison of the lithogenic and biogenic contribution to SM and data on 137Cs for different stations suggests that the content of this radionuclide on SM is primarily determined by the dynamic variations of the lithogenic matter. Based on the 137Cs migration on SM, the Black Sea is divided into at least two types of regions. One regions are water areas far removed from sources of lithogenic matter where SM is formed mainly due to the hydrobiont activity. The 137Cs content in SM due to the predominance of biogenic matter and an insignificant concentration of lithogenic matter in this case accounts for hundredths of a percent of its total content in the surface water layer. Other regions are coastal and shelf water basins, which, on the one hand, are subjected to the significant coastal and river lithogenic runoff, and on the other, they are characterized by the elevated trophicity and biological productivity. In these water areas, 137Cs content on SM owing to the variability of biotic and abiotic factors is more variable and can fluctuate from values typical for the open sea to an order of magnitude higher.