Uranium isotopes in groundwater of the Mezen syneclise Vend

Modeling past and present activity of a subarctic hydrothermal system using O, H, C, U and Th isotopes

“…Across the dataset, the U content in the thermal springs ranged from 0.238 ± 0.005 to 0.330 ± 0.007 mg/L, and the 234 U/ 238 U activity ratio ranged from 3.53 ± 0.49 to 4.19 ± 0.75. The high average 234 U/ 238 U activity ratios indicate that the deep water ascends to the surface because the shallow water in carbonate rocks has low 234 U/ 238 U ratios (1.5e2, Andrews, 1993, 2000;Malov et al, 2009). The relatively small dispersion in the uranium-isotope composition parameters of the source waters indicates that their formation occurs in a single hydrothermal system with the same factors and processes.…”

“…According to our data, this water is encountered in the taliks near the village of Karatayka, which is located in the permafrost zone northwest of the Pymvashor sources. NaeHCO 3 -rich shallow groundwaters are also found in sandyeclay Vendian aquifers in areas with kimberlites formation that are north of Arkhangelsk in northwestern Russia (Malov et al, 2009; Table S5). …”

The use of even uranium isotopes as hydrogeological tracers

“…From (3), we have several values of N 1rock /p corresponding to them (6) In addition to radiation impact, U isotopes into water pass into water through chemical dissolution of U contained in rock domains undisturbed by radioac tive decay. To take this process into account, we write a balance equation for 238 U atoms, assuming that, in expression (6), N 1rock is the total amount of 238 U atoms passing into water and remaining in it by the moment per one decay of 238 U. Accordingly, γ DD is the initial activity ratio of 234 U and 238 U isotopes entering water and remaining in it at the current moment; p is the probability for a 234 U atom to pass into water at 238 U decay.…”

“…Studies of uranium isotope composition of groundwater in Mezen syneclise have established that the maximal separation of odd U isotopes is typical of groundwater in the aquifer system of sandstones and aleurolites of the Padunskaya suite of Vend [6]. A char acteristic area is the Northern Dvina Depression, where the latter is overlain from the surface by a stra tum of clay deposits of moskovskaya and valdaiskaya moraines, as well as mikulinskoe interglacial period.…”

“…Thus, its mean value in the Belomoro Kuloiskoe Plateau (BKP) (the area of Lomonosov Diamond Deposit) by 42 determinations was ~5 [6].…”