Abstract
We characterize the mineralogy and geochemistry of Fe, Zn, Pb, Sb, As, Hg, Ag sulfide assemblages from mud masses currently extruded by the onshore South Sakhalin and Pugachev mud volcanoes (Sakhalin Island, Russia). Abundant Tl-rich pyrite in sulfide concentrate samples from the mud volcanoes coexists with common Hg- and Ge-rich sphalerite, as well as with sporadic boulangerite, robinsonite, bournonite, galena, realgar, metacinnabar, cinnabar, acanthite, and chalcopyrite. Sphalerites are remarkably enriched in Hg (locally reaching 27 wt%) and coupled zwith permanent abnormal enrichment in Ge (3008–3408 ppm). According to single-crystal XRD analyses and Raman spectroscopy, both Hg-poor and Hg-rich sphalerites are single-phase (Zn,Hg)Scub compounds. Pyrite is of diagenetic origin, judging by its trace-element chemistry, particular morphology, and heavy S isotope composition. Another assemblage, composed of Pb-Sb-(Hg) sulfide minerals and lesser As, Cu, Ag, and Bi compounds, results from hydrothermal alteration and is genetically related to Neogene volcano-sedimentary rocks found among the ejecta of the mud volcanoes. The composition of impurities in sphalerite from mud masses indicates crystallization at temperatures lower than ~100 °C, under the leaching effect of mud volcano waters.
Highlights
South Sakhalin and Pugachev mud volcanoes (MVs) differ in the relative percentages of emitted gases: more carbon dioxide in the former and more methane in the latter (50% to 85% CH4 against 40% CO2 ), with minor amounts of oxygen and nitrogen [61,62]
The MV waters of South Sakhalin volcano have HCO3 -Cl/Na-Mg chemistry and low salinity (TDS, total dissolved solids), which is common to waters of this kind in the Pacific active belt [21,42,62,63,64]
Ag sulfide assemblages from mud masses extruded by large South Sakhalin and Pugachev
Summary
Sphalerite commonly contains a few wt% of Fe or Mn, and smaller amounts of Cd, Hg, and/or Se, which occur as impurities and rarely reach high concentrations [1]. Cenozoic sediments and is bounded by the West-Sakhalin and Tym-Poronay fault systems, which generated many large earthquakes in the Sea of Japan and in Sakhalin Island. Sakhalin Island belongs to a relict zone of Late Mesozoic-mid-Miocene subduction of the Okhotsk plate beneath the eastern Eurasian margin [17,22]. Several Paleozoic blocks may be remnant islands accreted during the subduction [25]. One such block in the southern part of Sakhalin within
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