- Arsenic Contamination in Ground Water, Stable Isotopes, Ore Geology, Geochemistry, Sedimentary Geochemistry, Meteorite Impacts, and 16 morePaleoclimatology, Carbonate Diagenesis and Stratigraphy, Environmental Geochemistry, Analytical Geochemistry, Pyrite Formation, Paleooceanograhy, Sedimentology, Sulphur Stable Isotopes, Stable Carbon and Oxygen Isotopes, Paleofloods, Hydrogeochemistry, Trace element Geochemistry, Multivariate Data Analysis, Geostatistics, Mineral exploration, and Age of Chixculub impactedit
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ABSTRACT The unusually high grade hypogene zinc ore at Angouran in northwestern Iran (40.4% Zn, 1.9% Pb in the sulfide ore, 28.1% Zn, 4.4% Pb in the carbonate ore, and 110 g/t Ag) formed from an initially highly saline, reduced,... more
ABSTRACT The unusually high grade hypogene zinc ore at Angouran in northwestern Iran (40.4% Zn, 1.9% Pb in the sulfide ore, 28.1% Zn, 4.4% Pb in the carbonate ore, and 110 g/t Ag) formed from an initially highly saline, reduced, relatively acid hydrothermal brine at two successive sulfide and carbonate ore stages. The early ore stage consists of multiple phases of sphalerite dominated sulfide ore breccia with subordinate amounts of galena (± Pb sulfosalts), minor pyrite, and abundant barite. Sphalerite precipitated at moderate temperatures (≥ 155 °C) because of pH increase in the presence of hangingwall marble. Smithsonite precipitated at a higher pH value (≥ 7) and at lower temperatures (≤ 120 °C) from dilute solutions (salinities close to zero) by mixing of the Zn bearing brines with cool, HCO3− bearing waters. The first melting points of the primary (LV) fluid inclusions in sphalerite and in hydrothermal quartz are unusually low (≤ − 60 °C), close to the eutectic point of the ZnCl2–H2O system (− 62 °C). Total salinities taken from the ZnCl2–H2O system as a best approximation correspond to 26–41 eq mass % ZnCl2. The initial brine evolved to a CaCl2–NaCl rich solution with 27 eq mass % salinity. Gas densities (≤ 0.1 g cm− 3 for water vapor and ≤ 0.18 g cm− 3 for CO2) in the fluid inclusions indicate low pressure (≤ 5 bar for water vapor, and ≤ 100 bar for CO2) at the entrapment temperatures.At the first carbonate ore stage sulfides continued to precipitate characteristically as arsenopyrite with minor amounts of galena and pyrite. The abrupt change of the fluid composition at the sulfide–carbonate boundary was accompanied by a change of the fluid temperature and pressure that produced brecciation of the sulfide ore matrix and an almost total dissolution of barite and replacement by the hypogene smithsonite. Alteration is restricted to ore deposition and consists of weak sericitization and silicification with local dolomitization at the sulfide ore stage, and pervasive dissolution of the hangingwall marble, in particular at the carbonate ore stage.The breccia orebody at Angouran is sited at the crestal portion of a domed antiform at the lithological and thrust boundary of Neoproterozoic–Lower Cambrian footwall schists and the hangingwall marble in rapidly uplifted and exhumated Angouran Block east of the Geynardjeh Thrust Fault. The footwall schists occupy a detachment fault zone above imbricated nappe sheets of the basement metamorphic complex of the Sanandaj–Sirjan zone. During the Pliocene, the nappe sheets were thrust toward the southwest onto the Miocene felsic volcanic rocks of the Urumieh Dokhtar Volcanic Belt that are intruded by 10 Ma late Miocene basalts. The 11.9 Ma and 18.4 Ma zircon ages of the felsic volcanic rocks indicate the lower age limit of the ore body emplacement.The associations with large scale, mid-late Miocene, felsic volcanism along the active Tethyan belt, as well as the ubiquitous presence of the volcanic rock clasts in the sphalerite ore matrix, provide strong evidence of the involvement of hydrothermal processes at Angouran. Ore fluids were successively and pulsatorily generated within the seismically active region. A following geothermal activity appears to have had a significant input in the formation of the carbonate ore of the hypogene, as well as the supergene stage. Stable isotope data suggest complex interaction of element sources and processes. Allowing a broad interpretation, the sulfur isotopic composition of the sulfides δ34S (3.9 to 7.4‰) suggests that the sulfur could be sourced from evolving, mixed magmatic–basinal brine. The isotopic composition of the hypogene smithsonites (δ13C: 2.72 to 5.51‰, δ18O: 18.4 to 22.8‰) broadly supports the local geology and field relationships, which comply with a marble wallrock source for the carbonate ores. They lend support to the assumption that smithsonite was deposited from solutions with isotopic composition similar to those involved in the hydrothermal dolomitization of the marbles. The excess of dissolved marble precipitated as large volumes of travertine and as late calcite veins (δ13C: 18.8 to 20.3‰, δ18O: 3.1 to 6.4‰) at the mineralization site. Isotope values of the travertine (δ13C: 4.5 to 6.6‰, δ18O: 20.1 to 21.1‰ V-SMOW) are consistent with the involvement of CO2 derived from thermogenic decarbonization of the host marble by waters of dominantly meteoric origin, most likely concomitantly with ore forming processes.The Angouran deposit is the only reported case of a two stage, hypogene zinc sulfide–zinc carbonate mineralization, and represents a new style of nonsulfide zinc mineralization.
Research Interests: Geology and Geochemistry
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Zusammenfassung Reifen-, Ruß-, Motorenöl-, Asphalt-, Plastik- und Lackproben aus dem Straßenverkehr wurden auf ihre Kohlenstoff- und Schwefel-isotopenverhältnisse mit dem Ziel untersucht, die Frage zu beant-worten, ob diese... more
Zusammenfassung Reifen-, Ruß-, Motorenöl-, Asphalt-, Plastik- und Lackproben aus dem Straßenverkehr wurden auf ihre Kohlenstoff- und Schwefel-isotopenverhältnisse mit dem Ziel untersucht, die Frage zu beant-worten, ob diese Isotopenverhältnisse als Indikatoren für die Belastungssituation und die Schadstoffquellen bei der Untersuchung von straßennahen Böden eingesetzt werden können. Die δ11C-Werte der technischen Substrate lagen zwischen-30‰ und-18‰ relativ zum PDB-Standard, Dabei zeigte sich aufgrund der
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The TEX86 paleotemperature proxy, based on tetraether membrane lipids derived from aquatic Crenarchaeota has been applied in a variety of marine and lacustrine systems. A recent study analyzing a suite of 50 globally distributed lakes for... more
The TEX86 paleotemperature proxy, based on tetraether membrane lipids derived from aquatic Crenarchaeota has been applied in a variety of marine and lacustrine systems. A recent study analyzing a suite of 50 globally distributed lakes for TEX86 discovered that this proxy does not appear to work in all lake systems and that the TEX86 correlates well with both annual and
Research Interests: Climate Change, Sea Level, Clay Minerals, Stratification, Environmental Change, and 19 moreGlobal change, Seasonality, Sea level rise, Land Surface Temperature, Surface Water, Upper Cretaceous, Mass Extinction, Water Temperature, Sediment Traps, Lake superior, Deep water, Dinoflagellate cysts, Marine Environment, Annual Cycle, Particulate Matter, Nutrient Loading, Organic Matter, Suspended Particulate Matter, and Planktic Foraminifera
In the wake of the idea that surface derived dissolved organic carbon (DOC) plays an important role in the mobilization of arsenic (As) from sediments to groundwater and may provide a vital tool in understanding the mechanism of As... more
In the wake of the idea that surface derived dissolved organic carbon (DOC) plays an important role in the mobilization of arsenic (As) from sediments to groundwater and may provide a vital tool in understanding the mechanism of As contamination (mobilization/fixation) in Bengal delta; a study has been carried out. Agricultural fields that mainly cultivate rice (paddy fields) leave significantly large quantities of organic matter/organic carbon on the surface of Bengal delta which during monsoon starts decomposing and produces DOC. The DOC thus produced percolates down with rain water and mobilizes As from the sediments. Investigations on sediment samples collected from a paddy field clearly indicate that As coming on to the surface along with the irrigation water accumulates itself in the top few meters of sediment profile. The column experiments carried out on a 9 m deep sediment profile demonstrates that DOC has a strong potential to mobilize As from the paddy fields and the water recharging the aquifer through such agricultural fields contain As well above the WHO limit thus contaminating the shallow groundwater. Experiment also demonstrates that decay of organic matter induces reducing condition in the sediments. Progressively increasing reducing conditions not only prevent the adsorption of As on mineral surfaces but also cause mobilization of previously sorbed arsenic. There seems to be a cyclic pattern where As from deeper levels comes to the surface with irrigational water, accumulates itself in the sediments, and ultimately moves down to the shallow groundwater. The extensive and continual exploitation of intermediate/deep groundwater accelerates this cyclic process and helps in the movement of shallow contaminated groundwater to the deeper levels.
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High concentrations of As in groundwater frequently occur throughout the world. The dissolved concentration, however, is not necessarily determined by the amount of As in the ambient sediment but rather by the partitioning of As between... more
High concentrations of As in groundwater frequently occur throughout the world. The dissolved concentration, however, is not necessarily determined by the amount of As in the ambient sediment but rather by the partitioning of As between different minerals and the type of fixation. Sequential extractions are commonly applied to determine associations and binding forms of As in sediments. Due to the operational nature of the extracted fractions, however, the results do not provide insight into how and where precisely As is bound within mineral grains and no information about elemental associations or involved mineral phases can be gained. Furthermore, little is known about possible geochemical alterations that actually occur within a single grain during sequential extraction. Therefore, micro-synchrotron X-ray fluorescence analysis was applied to study the micro-scale distribution of As and other elements in single sediment grains. Arsenic was found to be mainly enriched in Fe oxy-hydroxide coatings along with other heavy metals resulting in high correlations. Phosphate leached 34-66% of As from the studied grains. The release of As in this leaching step was accompanied by the disappearance of correlations between As and Fe as well as by a higher Fe/As ratio compared to untreated samples. During the Fe-leaching step the coatings were largely dissolved leading to much lower concentrations of As and Fe. The correlation between As and Fe was preserved only in association with K, indicating the presence of both elements in silicate structures. Several distinctive features were observed such as the release of Fe, Mn and Cr during phosphate leaching as well as the lowering of mean K concentrations due to the Fe-leaching which indicates that not only target mineral phases were dissolved in these extraction steps. The importance of re-precipitation processes during sequential extraction was indicated by a consistently observed increase of the Fe/As ratio from the untreated to the Fe-leached samples.