The Lavrion area corresponds to the western part of the Attic-Cycladic metamorphic belt, in the back-arc region of the active Hellenic subduction zone. Between the Eocene and the Miocene, metamorphic rocks (mainly marbles and schists) underwent several stages of metamorphism and deformation due to collision and collapse of the Cycladic belt. Exhumation during the Miocene was accommodated by the movement of a large-scale detachment fault system, which also enhanced emplacement of magmatic rocks, leading to the formation of the famous Lavrion silver deposits. The area around the mines shows the stacking of nappes, with ore deposition mainly localized within the marbles, at marble-schist contacts, below, within, or above the detachment. The Lavrion deposit comprises five genetically-related but different styles of mineralization, a feature never observed in another ore deposit elsewhere, containing the highest number of different elements of any known mining district. The local geology, tectonic, and magmatic activity were fundamental factors in determining how and when the mineralization formed. Other key factors, such as the rise and the fall of sea level, which resulted from climate change over the last million years, were also of major importance for the subsequent surface oxidation at Lavrion that created an unmatched diversity of secondary minerals. As a result, the Lavrion deposit contains 638 minerals of which Lavrion is type-locality for 23 of them, which is nearly 12% of all known species. Apart from being famous for its silver exploitation, this mining district contains more minerals than any other district on Earth. The unique geological, mineralogical, and educational (mining, archaeological, and environmental) features suggest that it is highly suitable to be developed as a future UNESCO Global Geopark.

Active, shallow-water (2–10 m below sea level) and low temperature (up to 115 °C) hydrothermal venting at Paleochori Bay, nearshore Milos Island, Greece, discharges CO₂ and H₂S rich vapors (e.g., low-Cl fluid) and high-salinity liquids, which leads to a diverse assemblage of sulfide and alteration phases in an area of approximately 1 km². Volcaniclastic detritus recovered from the seafloor is cemented by hydrothermal pyrite and marcasite, while semi-massive to massive pyrite-marcasite constitute mounds and chimney-like edifices. Paragenetic relationships indicate deposition of two distinct mineralogical assemblages related to the venting of high-Cl and low-Cl fluids, respectively: (1) colloform As- and Hg-bearing pyrite (Py I), associated with marcasite, calcite, and apatite, as well as (2) porous and/or massive As-rich pyrite (Py II), associated with barite, alunite/jarosite, and late-stage hydrous ferric oxides. Mercury, in the form of cinnabar, occurs within the As-rich pyrite (Py I) layers, usually forming distinct cinnabar-enriched micro-layers. Arsenic in colloform pyrite I shows a negative correlation with S indicating that As¹⁻ dominates in the pyrite structure suggesting formation from a relatively reducing As-rich fluid at conditions similar to low-sulfidation epithermal systems. On the contrary, As³⁺ dominates in the structure of porous to massive pyrite II suggesting deposition from a sulfate-dominated fluid with lower pH and higher fO₂. Bulk sulfide data of pyrite-bearing hydrothermal precipitates also show elevated As (up to 2587 ppm) together with various epithermal-type elements, such as Sb (up to 274 ppm), Tl (up to 513 ppm), and Hg (up to 34 ppm) suggesting an epithermal nature for the hydrothermal activity at Paleochori Bay. Textural relationships indicate a contemporaneous deposition of As and Hg, which is suggested to be the result of venting from both high-salinity, liquid-dominated, as well as CO₂- and H₂S-rich vapor-dominated fluids that formed during fluid boiling. The CO₂- and H₂S-rich vapor that physically separated during fluid boiling from the high-salinity liquid led to calcite formation upon condensation in seawater together with the precipitation of As- and Hg-bearing pyrite I. This also led to the formation of sulfuric acid, thereby causing leaching and dissolution of primary iron-rich minerals in the volcaniclastic sediments, finally resulting in pyrite II precipitation in association with alunite/jarosite. The Paleochori vents contain the first documented occurrence of cinnabar on the seafloor in the Mediterranean area and provide an important link between offshore hydrothermal activity and the onshore mercury and arsenic mineralizing system on Milos Island. The results of this study therefore demonstrate that metal and metalloid precipitation in shallow-water continental arc environments is controlled by epithermal processes known from their subaerial analogues.

Amethyst occurrences in Tertiary volcanic rocks of Greece: mineralogical and genetic implications

Skyros Island, the largest island of the Sporades Complex (NW Aegean Sea, Greece), preserves a geologically diverse record spanning from the Upper Permian to the Quaternary, including crystalline and non-metamorphosed carbonate rocks, ophiolitic rocks and mélanges, medium-grade metamorphic units, rare Miocene volcanic rocks, and impressive fossil-bearing sediments and tufa deposits, together with historically significant quarry and mining landscapes. Through a comprehensive evaluation of the geological heritage of Skyros, this study proposes a transferable, results-based framework for geoconservation, geoeducation, and tourism space management within a geopark context. A systematic inventory of twenty (20) geosites, including six (6) flagship case studies, was established based on scientific value, dominant geodiversity type, risk of degradation, accessibility, educational and tourism potential. The assessment integrates the Scientific Value and Risk of Degradation criteria with complementary management and sustainability indicators. The results demonstrate consistently high scientific value across the selected geosites, with several reaching maximum or near-maximum scores due to their rarity, integrity, and reference character at a regional to international scale. Although some geosites exhibit elevated degradation risk, overall vulnerability is considered manageable through targeted conservation measures and spatially explicit visitor management. Based on the assessment results, a network of thematic georoutes was developed and evaluated using route-level indicators, including number of geosites, route length, educational potential, tourism suitability, accessibility, and contribution to responsible geotourism. The study demonstrates how integrated geosite and georoute assessment can support sustainable land management and confirms that Skyros Island meets key criteria for inclusion in the Hellenic Geoparks Network, providing a robust scientific basis for future UNESCO Global Geopark designation.

Vein-type zeolites in Kizari area, (western Thrace) are found within fresh to zeolitic altered volcanic rocks of andesitic to dacitic composition. The zeolites stilbite-Ca, Sr-bearing heulandite-Ca and laumontite occur in epithermal-style crustiform quartz/chalcedony-calcite veins crosscuting lavas and volcanic breccias. Open-space filling is common and well-shaped crystals (up to 3cm) were observed. Smectite, feldspar, magnetite, pyrite and rutile occur in minor amounts in the veins. Halite and barite grains are included in stilbite-Ca. SEM EDS data indicate high Sr (up to 4.4 wt. % SrO) and Ba (up to 2.9 wt. % BaO) contents for heulandite-Ca. It is suggested that the studied zeolites are intergral parts of the porphyry-epithermal mineralizing systems which operated in the area during the Oligocene. Their formation took place in the outmost transitional propylitic to fresh zones of the porphyry-epithermal systems and in a submarine environment as indicated by the geological and mineralogical evidence.