Rare Earth Elements in Mud Volcanic Water of the North-Western Caucasus

Abstract

The distribution and abundance of rare earth elements in mud volcanic waters of the North-Western Caucasus were studied. Waters are represented by two types: Na-Cl and Na-HCO3-Cl. All waters are characterized by high TDS (8.1-29.5 g/l), neutral to alkaline pH (7.2–8.9), reduced conditions (Eh from -280 to +92 mV), and methane as the main associated gas. It is established that concentrations of REE vary from 0.18 to 7.02 ppb. Based on REE content and pH mud volcanic waters were subdivided into three groups. In each group the concentration of ∑REE roughly increases as pH decreases. Due to geological conditions the highest concentrations of REE are observed in mud volcanoes located within the oldest Cretaceous sediments within the flexural-fault zones of the North-Western Caucasus and the Taman region. Mud volcanoes connected with the Maikop series (₽3-N1), have lower REE concentrations. For the first time the geochemical and geological data suggest different sources of matter for mud volcanoes of the studied area.