Mercuric (Hg) and silver-bearing (Ag) sphalerite was first detected in the Hellenic Volcanic Arc, in shallow seafloor hydrothermal vent buildings (~500 mbsl) (i.e. chimneys, mounds etc.) of the Kolumbo shallow - active hydrothermal vent system submarine arc volcano. At this point I would like to thank Marianne Ahlbom, operator of the Environmental Scanning Electron Microscope and Dr.
Introduction
Mean values of siliceous sediments of Methana (Huebner et al. 2004): thick red line and solid square;. Mean values of Methane carbonate sediments (Huebner et al. 2004): thick red-brown darker line and solid lozenges;.
Scope of thesis
Previous work
Sphalerite as a carrier of Hg and Ag
- Mercury(Hg)- and Silver(Ag)-rich sphalerite from the modern ocean-floor
Microanalysis of sphalerite often reveals heterogeneous distributions within individual data sets that reflect the importance of (micro)inclusions of Ag minerals ( Cook et al. 2009 ). Further recent studies of trace elements in smoker hydrothermal black sulphides (Wohlgemuth-Ueberwasser et al. 2015;
Hg in the geoenvironment: what we know and what we don’t know
- The international scene: Health concerns and related Hg-reduction policies
- Emissions of Hg to the atmosphere
- Hg in terrestrial ore deposits
- Hg bioaccumulation in the marine environment
The half-life of elemental Hg in the body is reported to be approximately 60 days (Broussard et al. 2002). Concentrations of Hg in hydrothermal fluids are found to be 1,000 times higher than those in ambient seawater (Vetriani et al. 2005).
Silver in the geoenvironment: what we know and what we don’t know
- Health effects caused by silver
- Silver in marine/submarine hydrothermal systems
- Silver occurrence in the environment
- Transport of silver in magmatic-hydrothermal systems
- Silver bioaccumulation
In both aquatic and coastal sediments, microbes and sulfate-reducing bacteria, respectively, are the main agents controlling methylmercury production (Gilmour et al. 1992, Compeau & Bartha 1985, King et al. 1999). Martin et al. 2001) reported that methylmercury in hydrothermal mussels (B. azoricus) was below the detection limit (<6 ng g-1) and the methylmercury concentration in hydrothermal molluscs from the Tonga Arc (Pacific Ocean) was extremely low (Lee et al. 2015). Hg could be reduced to a less toxic form of Hg0 by mercury reductase, a prominent detoxifying enzyme in the bacterial kingdom (Colaço et al. 2006, Lee et al. 2015).
Silver is listed on the 1977 US EPA (Environmental Protection Agency) Priority Pollutant List and on Schedule II of the 1976 EEC Hazardous Substances Directive (76/464/EEC), so releases of silver are subject to regulation (Fabrega et al. 2011 ). Another possible effect of silver is influencing the population size of certain types of bacteria living in the intestinal microflora (Sawosz et al. 2007, Fabrega et al. 2011). Silver accumulation in marine sediments is controlled by the flux of Ag into the sediments and by sediment conditions that may or may not contribute to authigenic accumulation (Morford et al. 2008).
Silver ions have such chemical properties that they can bioconcentrate in organisms (bacteria, fungi and plants), pass through their cell walls and reach the plasma membrane (Luoma 2008, Fabrega et al. 2011).
Hg and silver in the unique shallow–submarine volcano, Kolumbo (Santorini), Hellenic
Geodynamic and geological setting of the HVA
Hg and silver in the unique shallow submarine volcano, Kolumbo (Santorini), Hellenic Vulcanic Arc (HVA). The modern Aegean volcanic arc was developed behind the Hellenic Arc, the Peloponnese-Crete island arc and the Cretan back-arc basin. The African plate to the south subducts under the Eurasian plate to the north along the red lines just south of Crete.
Yellow arrows indicate GPS velocities (approximately 40 mm/y) from the Aegean Sea towards the African plate (considered stable) (adapted from Nomikou et al. 2013). Hellenic volcanic arc'', within the active continental margin, developed behind the molasses back-arc basin, hosted over the thinned continental crust. e) Swath bathymetry map of the Santorini-Kolumbo volcanic field (modified after ref.
The Kolumbo submarine volcano and hydrothermal system
- Kolumbo volcanic field
- Kolumbo hydrothermal field
Furthermore, the size and height of the volcanic domes generally decrease toward the northeast, indicating that volcanic activity decreases as the distance from Columbus increases (Nomikou et al. 2013). Small pot-like craters from the Fe microbial mat emit clear, low-temperature (≤70°C) fluids and CO2 gases (Kilias et al. 2013). Seismic profiles provide evidence that Columbo formed due to at least four eruptive cycles (Fig. 14) (Hübscher et al. 2015).
This interpretation has been verified by repeated ROV dives in the Kolumbo crater and in different locations of the inner crater walls (Nomikou et al. 2013). "Diffuser Spires" emit clear, nearly particle-free fluids from which sulfide minerals have precipitated prior to discharge (Fig. 15b) (Hannington et al. 2005, Kilias et al. 2013). Hanging gray filamentous microbial biofilms cover the exterior of Politeia pins (Kilias et al. 2013).
At the northern crater slope, the largest hydrothermal chimney (height ~4 m) covered by Fe microbial mat ("Poet's Candle") was observed (Fig. 15d) (Kilias et al. 2013).
Materials and methods
Sampling
The studied samples are characterized by four mineralogical zones according to the classification of Kilias et al. 2013): (a) a coarse porous “sulfide-sulfate inner core” (ISSC), (b) a thin orange-yellow As-sulfide-dominated outer shell (OAsL), (c) a Fe- orange to brown-( Hydrated microbial surface)-oxyhydroxide, Fe crust (SFeC) and (d) internal networks of hydrothermal vents are coated with unidentified Sb-Zn-S (IPCN) phases.
Sample preparation
Analytical methods
The standards for each element are included in the software, so the instrument is automatically calibrated to the standard during the EDS procedure. The Hg standard for WDS was a sphalerite also produced by Oxford, but it was manually introduced into the instrument. A few supplementary PXRD analyzes were performed to verify the ESEM results by identifying the atomic and molecular crystal structure.
The PXRD method is performed using a PANalytical X'pert PRO automated diffractometer, located at the Swedish Museum of Natural History in Stockholm. Raman spectra were recorded at the Department of Geological Sciences, Stockholm University, using a laser Raman confocal spectrometer (Horiba instrument LabRAM HR 800) and equipped with a multichannel air-cooled CCD detector. An Ar-ion laser (λ = 514 nm) with an output power at the sample of 8 mW was used as the excitation source.
The instrument was calibrated with a neon lamp and the Raman line (520.7 cm-1) of a silicon wafer.
Results
Mineralogy and sphalerite textures of the ‘Inner Sulfide-Sulfate Core’ (ISSC)
- Type 1: Microglobular and colloform zoned sphalerite
- Type 2: Zoned sphalerite with porous core and massive rim
- Type 3: Inclusion-rich and compositionally zoned massive sphalerite
Galena (PbS) occurs anhedrally, up to 10μm across (Fig. 24a, d), as rims surrounding concentrically laminated spheroids of pyrite/marcasite (Fig. 24b) or as inclusions in sphalerite grains (Fig. 24c). An unidentified non-stoichiometric Zn sulphide phase was found in a texture of parallel bundles (Fig. 27). The second form of this sphalerite type occurs as independent microglobules within massive sphalerite or in open space (Figs. 28, 29).
Raman analyzes were performed on the red and dark yellow areas of type 1 sphalerite, as shown in figure 30. In figure 34 the correlation between Zn and other detected trace elements (Fe, Sb, Cu, Cd, As and Ag ) in sphalerite type 1 is illustrated. Type 3 sphalerite is found either rich in randomly distributed inclusions (Fig. 48) or linear (Fig. 49), without inclusions (Fig. 50) or compositionally zoned (Fig. 51).
Among the various inclusions found in sphalerite type 3, inclusions of Hg-Cd sulfosalts (Fig. 52) were also analyzed (Table 7).
Quantitative EPMA analysis, compositional mapping and element distribution and
EPMA analyzes performed massive sphalerite of type 3, where concentrations of ten elements (S, Zn, Fe, Cu, Cd, Sb, As, Ag, Hg and Pb) were determined using the EDS mode. Furthermore, for the compositionally zoned type 3 massive sphalerite, the concentrations of seven elements (S, Zn, Fe, Sb, Cu, Cd, and Ag) were determined using the EDS mode. Massive sphalerite is the type that contains a large amount of inclusions, including galena, Sb-Pb and Hg-Cd sulfosalts (Fig.
To investigate potential chemical variations across Type 3 massive sphalerite grains, systematic trace element concentration profiles were performed by ESEM-EDS, as shown in Figure 59. To investigate potential chemical variations within the inclusion-rich Type 3 massive sphalerite, trace element mapping was performed by ΕSEM -EDS (Fig. In the figures, the correlation between Zn and the other detected trace elements (Fe, Sb and Cd) in massive sphalerite of type 3 is illustrated.
The correlation between Zn and the other trace elements (Fe, Sb and Cd) in zoned, massive sphalerite of type 3 is depicted respectively in Figures, while for the correlation between Zn with Cu and Ag it is not possible to reach any conclusion, because of the scarcity in the number of analyzes for it (Fig. 71, 72).
Discussion
- Structural and chemical variation of sphalerite crystals and control of trace element
- Trace elements in sphalerite: element substitution versus micro-, and/or nano-
- Genetic considerations
- Mechanisms of sphalerite precipitation
- Effects of phase separation and metal complexation on sphalerite composition
- Environmental considerations
This can be explained by variable fluid conditions during sphalerite growth from porous to massive and/or fractionation of the studied trace metals due to physicochemical changes in the parent fluids during sphalerite 2 precipitation (Keith et al. 2016; Wohlgemuth-Ueberwasser et al. 2015). More specifically, these variations in trace element chemistry likely reflect a decreasing solubility of Sb, Ag and Cu, and increasing solubility of Fe and Cd, during sphalerite growth due to changes in the physicochemical parameters of the discharge fluids (cf. Maslennikov et al. 2009 ), Revan et al. 2014, Wohlgemuth-Ueberwasser et al. This is supported by Cook et al. 2009) who noted that a common linked substitution mechanism would.
Consequently, phase separation of CO2-rich hydrothermal fluids occurs in the Columbus seafloor (see Kilias et al. 2013) because the hydrostatic pressure is ambient. In addition, the results of Wohlgemuth-Ueberwasser et al. 2014) also show that the composition of hydrothermal sulfides is influenced by phase separation below the seafloor. Systematic variations of trace elements along growth zones within sphalerite crystals (Fig. 33) are probably similar to such variations in a geochemical manner (Wohlgemuth-Ueberwasser et al. 2015).
If this were to happen, living organisms would accumulate methylmercury, which biomagnifies through the food chain (Monteiro et al. 1996).
Conclusions
Microbial transformations of Hg: potential, challenges and achievements in controlling Hg toxicity in the environment. Advances in Applied Microbiology 57 (SUPPL. A):1–52. The role of Hg-organic interactions in the hydrothermal transport of Hg. Chemoautotrophic and methanotrophic symbiosis in marine invertebrates. Probable modern analogue of Kuroko-type massive sulphide deposits in the Okinawa Trough back-arc basin.
New insights into hydrothermal vent processes at a unique shallow submarine arc volcano, Kolumbo (Santorini), Greece. Sulfosalt melts: evidence for high-temperature metal vapor transport in the formation of high-sulfidation gold deposits. Soil Hg distribution and evolution of soil Hg anomalies in the Yellowstone geothermal area, Wyoming Econ.
Elemental Hg in submarine hydrothermal vents in the Bay of Plenty, Taupo Volcanic Range, New Zealand.