On Nisyros island as a result of the volcanic activity and active tectonic, a hydrothermal system develops and it is expressed by 5 types of surface manifestations: i) thermal springs, ii) fumaroles iii) hydrothermal craters, iv) hot grounds

The Lapis Lacedaemonius (krokeatis lithos) is a well-known meta-volcanic rock of great historical importance. Petrographic observations, mineral chemistry data, as well as geochemical analysis of selected samples, reveal that these rocks are porphyritic metabasaltic rocks which have been significantly affected by saussuritization and also by restricted silicification processes. They represent subduction related calc-alkaline volcanic rocks which also appear in the adjacent Hellenic Triassic volcanic outcrops, and appear to be associated with the rift/drift phase within the Pindos oceanic realm. The unique features of the Lapis Lacedaemonius, when compared to geochemically similar volcanic rock outcrops, are mainly attributed to their distinct porphyritic textures, predominantly with microlithically textured groundmass along with the coarse grained plagioclase, and to saussuritization processes. The Lapis Lacedaemonius seems to have been formed in a sub-volcanic system closely associated with epidosites, suggesting that metasomatism occurred within hydrothermal upflow zones.

A hot spring at Ilia in the Greek Island of Euboea precipitates iron‐rich travertine at an ore‐grade concentration (up to 35.3 wt% Fe). This hydrothermal chemical sediment system deposits bands of iron oxyhydroxides (ferrihydrite), millimetres to centimetres thick, alternating with calcium carbonate‐dominated layers, creating “Banded Iron Travertine” (BIT). The ferrihydrite laminae display a dendritic texture formed of spherical nodules often covering filaments identified as bacterial stalks of Zetaproteobacteria. These microaerophilic iron‐oxidizing bacteria were identified by their 16S rRNA gene sequences in ferrihydrite‐enriched samples from areas under high water flow. They were missing in the aragonite/calcite‐dominated samples exhibiting features of aerial exposure and cyanobacteria instead. These characteristics, and the relative depletion in Fe‐rich layers of redox‐sensitive elements like Mn and Ce, as well as the presence of halite in Ca‐rich layers, suggest that the bands form by successive changes in hydrothermal flow. This allowed microaerophilic iron oxidation to form Fe‐rich layers, while Ca‐rich bands precipitated when the hydrothermal water had time to equilibrate with the atmosphere. This sea water‐dominated hydrothermal system is enriched in reduced iron and rapidly precipitating carbonates and ferrihydrite in the form of bands, having similarities to “Banded Iron Formation” (BIF). BIF represents archives of Earth's primitive biogeochemistry although the combined abiotic and biotic processes that have likely led to their formation are not fully resolved. Diagenesis and metamorphism have a strong imprint on BIF. Thus, continuous efforts are pursued to identify modern analogues that could help unravel their formation. Although carbonate is not a common feature of BIFs, Ilia system provides an interesting analogue for their depositional processes and potential microbial–mineral associations they may have hosted. It also presents pre‐diagenesis facies association and mineralogy that could bring new clues for unravelling BIF modes of formation and the salient biogeochemical conditions characteristic of their original depositional environment.

An extensive oceanographic survey was conducted in the marine area between Fe, Ti, Na, Mg, S, Cr, Cu, Ni, V, Zn; and (iii)

Pelotherapy is the application of thermal muds (peloids) for recovering muscle, bone and skin pathologies. Specific criteria were established for the evaluation of the therapeutic suitability of peloids. Critical factors ruling the quality of the solid phase of peloids include granulometry, mineralogy, and physical-chemical properties. The aim of the present study was to investigate the textural, mineralogical and geochemical characteristics of the Pikrolimni Lake sediments (PLS), Kilkis district (N. Greece) in order to assess their suitability for application as raw material into mud therapy technologies. Representative PLS samples were collected and analyzed by means of different techniques at the analytical laboratories of the Hellenic Survey of Geology and Mineral Exploration (HSGME). Results showed that, texturally, the PLS were classified as sandy loam sediments. X-ray diffraction (XRD) study revealed that the PLS consist mainly of quartz, clay minerals (kaolinite, montmorillonite, illite), and muscovite, with minor feldspar and calcite. X-ray fluorescence (XFR) analysis showed that PLS samples have higher SiO2 and lower Al2O3 contents compared to the average shale composition. Among the analyzed, by means of inductively coupled plasma mass spectrometry (ICP-MS) technique, potentially toxic elements only As and Pb contents were found significantly higher than those of the average shale. Based on the calculated mean values of enrichment factor (EF) and geo-accumulation index (Igeo) PLS displayed minor enrichment and moderate contamination by Pb and As, respectively. In conclusion, an improvement of the grain size composition of PLS by means of a sieving process is needed. Besides, the study of the concentration and behavior of toxic elements in peloids formed by the mixing of the processed PLS with salty thermo-mineral water is proposed.