Mercury in the Clay Pulp of Mud Volcanoes of the West Kuban Trough (Crimean–Caucasian Region)

The bulk mercury concentrations were determined in samples of fresh mud volcanic clays from 31 mud volcanoes of the Kerch‒Taman mud volcanic province. Its concentration ranged from 20 to 640 μg/kg. It is shown that the mercury concentrations do not depend on the size of the mud volcanic edifice or its activity. At the same time, it was noted that mud volcanic clays with higher density are characterized by higher Hg concentrations, which may reflect an increase in the concentration of mercury-bearing sulfides. Correlations were established between mercury concentrations in the clays and estimated formation temperatures obtained using hydrochemical geothermometers, Tmax values for clay kerogen, concentrations of HCO3, Li, B, Si in water, as well as δ18O(H2O) and δ13C(CH4). These relationships show that the observed [Hg] variations in the clays can be explained by different depths of the volcanic “roots.”. A hypothesis is put forward that the observed variability in mercury concentrations may not only reflect differences in its concentrations in the vertical section of the Maikop deposits, as previously thought, but also be a consequence of the fluid enrichment with this element as a result of the lithogenesis of clay rocks. The latter can be provided by smectite illitization, which is activated at temperatures >80–100°C and, due to desorption from the clay material, enriches mud volcanic fluids with a complex of chemical elements, including mercury.