Fumarolic alteration products at Sousaki (Greece) : occurrence and environmental impact

Fumarolic alteration crusts and efflorescences have been sampled at the Sousaki solfataric field. Samples have been analysed for mineralogical (XRD) and chemical composition (HNO3 digestion and leaching with distilled water). Results show that mineralogical and chemical compositions (major, minor and trace metals) are controlled by microenvironmental conditions. The sample collected in the anoxic part of a cave is composed almost exclusively by native sulfur. The samples collected in the oxidizing part of the cave and outside in relatively sheltered position are mainly composed by very soluble sulfates. Chemical composition evidence strong enrichments in Al, Ca, Cr, Fe, Mg and Ni which are present in highly soluble form and derive from the fumarolic alteration of the outcropping rocks (Marls and peridotites). One sample collected outside the cave, well exposed to atmospheric agents, is composed almost exclusively of gypsum and the chemical composition reveals, with respect to the previous samples, a relative enrichment of elements (Ba, Ca, K, Pb and Sr) forming less soluble sulfates. The presence of toxic metals like Al, Cr and Ni in high concentrations and highly soluble form evidences the potential impact of the fumarolic activity on the local environment.