Vol 64, No 12 (2019)

Conditions of accumulation and fractionation of zirconium and hafnium in alkaline-carbonatite systems
Kogarko L.N.

The patterns of the distribution and fractionation of strategic metals (Zr, Hf) in the Kugda intrusion (Polar Siberia) have been studied. The contents of these elements significantly exceed their concentrations in other rocks (Zr 246 ppm, Hf 7.4 ppm). A significant increase in Zr and Hf from early rocks (olivinite and melilite rocks) to later differentiation products, syenites with up to 570 ppm of Zr and 16 ppm of Hf, has been revealed. During the evolution of the Kuga magmatic system, notable fractionation of Zr and Hf occurred. The Zr/Hf ratios in the dike rock, similar in composition to the primary Kugda Massif magma, and the early intrusions are fairly close to that of chondrite (Zr/Hf = 37 [1]), while in the latest phases this ratio increases by almost 5-fold. Our study showed that the distribution coefficient of Hf (Kd = 0.58) in alkaline pyroxenes is noticeably higher than that of Zr (Kd = 0.40). Consequently, fractionation of this mineral leads to an increase in the Zr/Hf ratio in the residual liquids. Another mineral concentrating up to 400 ppm of Zr and up to 15–20 ppm of Hf is perovskite, which has a very wide crystallization field in the rocks of the Kugda Massif, especially in the earliest olivinite. The data obtained showed that the Zr/Hf ratio in the perovskite of olivinite varies between 23–27, that is, noticeably below both the chondritic and the primary magma values. Early crystallization of perovskite is the main reason for increasing the Zr/Hf ratio in melilitolites (up to 54). Thus, the main process of forming the Kugda Massif was continuous crystallization differentiation, accompanied by a noticeable fractionation of rock-forming and accessory minerals (pyroxene and perovskite).

Геохимия. 2019;64(12):1215-1221
Amphibolites of the metamorphic basement of Wrangel island: age, nature of the protolite and conditions of metamorphism
Sokolov S.D., Silantyev S.A., Moiseev A.V., Tuchkova M.I., Verzhbitsky V.E.

New data on petrography, geochemistry and geochronology of metamorphic rocks sampled from Neoproterozoic basement of Wrangel Island are presented. Oceanic affinity for mafic rocks underwent greenschist to amphibolite facies conditions (350–600°C) has been established by geochemical data. Protolith of this rock belongs to products of the evolution of magmatic melts parental for MORB. Protolith’s age is 617±13 and 698±12 Ma was determined by U-Pb isotope dating of Zircons from these rocks (SHRIMP II and La-ICP MS). There are two main stage of metamorphism could be established: Neoproterozoi – Early Paleozoi (amphibolite and greenschist facies conditions) and Middle Cretaceous (greenschist facies condition only), Last stage of metamorphism related to Chukcha deformation events accompanied by formation of folded nappes structure and consequent extension. An comparison of studied rocks with samples dredged at Chukcha Borderland evidenced for certain similarity existing between these rock assemblages judging by their petrography and chemistry.

Геохимия. 2019;64(12):1222-1246
Equilibrium and kinetic simulation of groundwater demanganation and deironing
Ryzhenko B.N., Mironenko M.V., LImantseva O.A.

Analysis of chemical equilibria among iron and manganese aqueous species at various Eh-pH conditions and aqueous CO2 concentration is done. Thermodynamic and equilibrium-kinetic simulation of iron and manganese aqueous species oxidations is developed for groundwater demanganation and deironing.

Numerical simulation of chemical interactions in the system “groundwater-aqueous oxygen-rock minerals-aqueous carbon dioxide” is shown that deironing is effective enough but aqueous manganese(II) concentration is increased. It occurs because (Fe,Mn)CO3 solubility rate is too slow and (Fe,Mn)CO3 dissolution and removal of aqueous iron species results in secondary MnCO3 formation.

Using published experimental data on carbonate dissolution kinetics, iron and manganese oxidation kinetics and the critical values of rate constants of iron and manganese homogenous oxidation, iron and manganese carbonates solubility, manganese homogenous catalytical oxidation on iron hydroxide suspension are chosen. The kinetics-thermodynamics model of underground oxidation of iron and manganese by dissolved oxygen have been developed. By numerical simulation of chemical interactions in the system “groundwater saturated by oxygen-stratal water-intake rock minerals” shows that deironing occurs effective enough but aqueous manganese concentration increased. It happens due to aqueous manganese slow oxidation and dissolution of (Fe,Mn)CO3. Also secondary MnCO3 formation is possible due to removal of aqueous iron specis. So underground demanganation is possible if there is no (Fe,Mn)CO3 among intake rock minerals or inconvenience of water contact with it.

Геохимия. 2019;64(12):1247-1260
Content of technogenic radionuclides in water, bottom sediments and benthos of the Kara sea and shallow bays of the Novaya zemlya archipelago
Goryachenkova T.A., Borisov A.P., Solov`eva G.Y., Lavrinovich E.A., Kazinskaya I.E., Ligaev A.N., Travkina A.V., Novikov A.P.

During the expedition on the Akademik Mstislav Keldysh research vessel in 2016 year it was established that the content of radioactive cesium in the sea water of the Novaya Zemlya archipelago bays and open sea are at a level corresponding to the global fallout (1 Bq /m3). Plutonium content in water is slightly higher .The activity of neptunium

in water is an order of magnitude higher than the activity of plutonium (0.76–1.89 Bq/m3), although its content in global fallout is almost two orders of magnitude lower than the plutonium content. The plutonium content in the bottom sediments of the Kara Sea is 0.2–3.8 Bq/kg. The content of radioactive cesium is as high as possible in the mouth of the Yenisei River (up to 21 Bq/kg) Analysis of benthic samples showed that the content of radioactive cesium and plutonium in samples taken in the bays of the Novaya Zemlya archipelago is below the detection limit. The neptunium content in the benthos samples is above the detection limit and amounts to 1–80 Bq/kg wet weight. It was showed that the content of neptunium in benthos is one of the indicators of radioactive contamination of the marine environment.

Геохимия. 2019;64(12):1261-1268
Short communications
Correlation high-calc undersaturated earth silicon complex of Maymecha-Kotuy province with Siberian flood basalts. New age data of massif Kugda (Polar Siberia)
Anosova M.A., Kostitsyn Y.A., Kogarko L.N.

Perovskite crystals from ore-bearing olivinite and phoscorite of Kugda Massif were analyzed by LA-ICP-MS. Age obtained for alkaline rocks of Kugda Massif is 257±6 Ma. It means that Kugda massif was formed simultaneously with the Siberian flood basalts and Guli Massif (250±9 Ma) which is the largest pluton in the Maymecha-Kotuy Province and is highly differentiated. The melilite-bearing Kugda Complex was formed synchronously with Siberian Trapps and Guli Massif, which suggests that these rocks might be genetically related.

Геохимия. 2019;64(12):1269-1273
Thermodynamic properties of montechellite
Ogorodova L.P., Gritsenko Y.D., Vigasina M.F., Bychkov A.Y., Ksenofontov D.A., Melchakova L.V.

A thermochemical study of natural calcium and magnesium orthosilicate ─ monticellite (Ca1.00Mg0.95)[SiO4] (Khabarovsk Territory, Russia) was carried out on the Tian-Calvet microcalorimeter. The enthalpy of formation from the elements ΔfHоel(298.15 K) = -2238.4 ± 4.5 kJ / mol was determined by the method of high-temperature melt solution calorimetry. The enthalpy and Gibbs energy of formation of monticellite of the theoretical composition of CaMg[SiO4] are calculated: ΔfH0el(298.15 K) = -2248.4 ± 4.5 kJ/mol and ΔfG0el(298.15 K) = -2130.5 ± 4.5 kJ/mol.

Геохимия. 2019;64(12):1274-1280
137CS concentrations in surface waters of the seas of Eurasia: results of expeditionary research in 2017
Miroshnichenko O.N., Paraskiv A.A., Gulin S.B.

According to results of the field work conducted in 42nd cruise of the research vessel “Akademik Boris Petrov” (January-March, 2017) and 68th cruise of RV “Akademik Mstislav Keldysh” (June-August, 2017), the data on concentration of the man-made radionuclide caesium-137 in surface waters of the East China Sea, the South China Sea, Equatorial part of the Indian Ocean, the Red Sea and Mediterranean, Biscay Gulf, the English Channel, the Baltic Sea, North Atlantic, Norwegian Sea and the Barents Sea have been obtained. It was found that concentration of caesium-137 in the surface water of studied Eurasian seas is at a low level. The exception is the Baltic Sea, where the level of caesium-137 is much higher than the values observed before the Chernobyl accident. A higher concentration of caesium-137 in the surface waters of the East China Sea, compared with previous estimates, was found, which may be due to the significant discharge of a high-level liquid radioactive waste after the Fukushima-1 accident in 2011.

Геохимия. 2019;64(12):1281-1287
Estimation of the formation conditions of the Bishuli thermomineral water (Crimean Plain) by isotope geochemical methods
Amelichev G.N., Tokarev I.V., Tokarev S.V.

The formation conditions of the Bishuli thermomineral waters from the Crimean Plain were determined by a complex of isotopic methods. The absence of tritium (3H < 0.1 TU) and considerable radiocarbon age (τ = 28 ± 3 ka) are in line with the light isotopic composition of the mineral water (δ18O = –13.4‰ and δ2H = –96‰), which is strongly different from that of the recent precipitation, river water, and groundwater of the region (δ18O from –7.4 to 8.7‰ and δ2H from –50 to –62‰). The formation of the mineral waters should be assigned to the Dnestr pluvial interstadial of the last glaciation, which reached the maximum in the region approximately 27 ka ago. The recharge zone is probably located on the northern slope of the Crimean Mountains (at a distance of ~60 km), which, together with the absence of tritium, indicates that the mineral waters are protected from an anthropogenic impact.

Геохимия. 2019;64(12):1288-1292

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