Arsenian Pyrite and Cinnabar from Active Submarine Nearshore Vents, Paleochori Bay, Milos Island, Greece

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