Environmental availability of ultramafic rock derived trace elements in the fumarolic - geothermal field of Soussaki area, Greece

Abstract

The geothermal degassing and fumarolic alteration occurring at Soussaki, an area in SE mainland Greece, facilitated a strongly acidic environment which resulted in the serpentinized ultramafic parent rock's severe weathering and a large increase of mobility of trace elements, which may be incorporated in newly formed fumarolic alteration products and secondary clays (Cr – bearing clays). We hypothesized that the fumarolic – hydrothermal alteration of ultramafic parent rock would increase the mobility and availability and would cause the distribution of Cr, Ni, Mn and Co in stream sediments and soils in labile fractions. Stream sediment and surface soil samples were collected from 46 sampling sites and the <1.8 mm grain size fraction was analyzed by Flame Atomic Absorption spectroscopy for the above mentioned elements. Evaluation of geochemical abundance and leachability of the above mentioned elements in each operationally defined geochemical fraction, was conducted by applying multi - acid digestion, single and selective sequential extraction, respectively. Mineralogical composition of the parent rock was determined by means of X – ray diffraction. The stream sediment and soil samples show significant levels of Cr: 1237 mg/kg and 1448 mg/kg, Ni: 1789 mg/kg and 1879 mg/kg, Mn: 875 mg/kg and 904 mg/kg and Co: 114 mg/kg 115 mg/kg content, respectively, in agreement with the high geochemical background of these elements in Soussaki. Our results also indicate that there is a high risk of immediate Ni, Mn and Co mobilization, reaching percentages of 17.8% and 11.3%, 67.7% and 45.2%, 44.2% and 17.6% in the surface adsorbed fraction, in stream sediments and soils, respectively. The stability of significant percentage of all trace elements found in Fe – Mn oxide fractions (Ni > Co > Mn > Cr) is controlled primarily by the Eh/pH system.