Using dual-isotope data to trace the origin and processes of dissolved sulphate: a case study in Calders stream (Llobregat basin,Spain)

Whereas most of the reported δ³⁴S values of dissolved sulphate are positive in the Llobregat basin, Calders stream, which is a tributary of the Llobregat River, is characterised by negative values. Stream waters, sampled monthly between 1997 and 1998, and quarterly in 1999, show an overall increase in δ³⁴S from −10‰ to 0‰, coupled with an increase in Na and Cl concentration. On the other hand, the oxygen isotopic composition of dissolved sulphate, δ¹⁸O, displayed an opposite trend with a slight decrease, from +9‰ to +6‰. Detailed sampling up stream in November 2000 indicated that, contrary to most of the surficial waters of the Llobregat basin with a δ³⁴S_SO4 mainly controlled by evaporites, in Calders stream, sulphate is derived from pyrite oxidation. The dual-isotope approach, coupled with chemical data, allowed us to identify the contribution of ³⁴S-rich sulphate effluents from anthropogenic sources, while mixing models, calculated between natural and anthropogenic sources, enabled us to estimate their contribution. Sudden increases of δ³⁴S and δ¹⁸O of dissolved sulphate in stream waters are believed to be caused by a sulphate reduction process related to oil spillage. The long-term enrichment in δ³⁴S, coupled with a decrease in δ¹⁸O_SO4, from Jan-97 to Aug-99, is interpreted as a progressive increase in the contribution of pig manure.     

Geological controls on the sulphur content of coal seams in the Northumberland Coalfield, Northeast England

The sulphur content of coal is an important consideration when developing reserves for exploitation, driven by emission limits from power stations becoming more stringent. Variations in the sulphur content of Westphalian A and B coals from the predominantly freshwater Northumberland Coalfield, Northeast England, were studied according to their regional, stratigraphic and in-seam location. The observed variation in sulphur content spatially increases towards the source area away from more marine influenced areas, with increased sulphur content through time linked to changes in the general depositional environment as conditions became more marine-influenced. A model of basinal surface water and groundwater flow driven by post-depositional source area tectonism is thought to have played only a minor role in contributing secondary sulphur to the coal. However, the isotopic composition of coal pyrite shows a similar range in composition to that of pyrite and other sulphides from the North Pennine Orefield along the southern margin of the coalfield, suggesting an additional potential source of secondary sulphur, as sulphur-rich fluids were expelled northwards through the coal measures during early Permian Variscan transpression from the south. The Westphalian A and B are interpreted as third-order depositional sequences, defined by third-order maximum flooding surfaces. Each sequence is made up of several coal-bearing fourth-order parasequences, which tend to be more brackish to marine in character, on either side of the third-order maximum flooding surfaces when base level was relatively high. The lowest sulphur coals are confined to the lower to middle, relative low stand part of the Westphalian A third-order base level curve and the lowest part of the Westphalian B third-order base level curve. This difference is attributed to a more rapid rise of base level in the Westphalian B. The stratigraphic and spatial distribution of coal sulphur has been used as a guide to prediction of reserve identification for surface mining operations.     

Supergene sulphides and related minerals in the supergene profiles of VHMS deposits from the South Urals

The mineralogy and structure of the supergene profile in recently-exploited volcaniс hosted massive sulphide (VHMS) deposits of Cyprus, Uralian and Kuroko type in the South Urals, Russia, have been studied. Specific subzones enriched in secondary sulphides and associated minerals have been distinguished in residual pyrite and quartz–pyrite sands at the Gayskoye, Zapadno-Ozernoye, Dzhusinskoye and Alexandrinskoye deposits. Besides minerals which are common to the cementation subzones (covellite, chalcocite and acanthite), non-stoichiometric colloform and framboidal pyrite, pyrite–dzharkenite, pyrrhotite-like and jordanite-like minerals, metacinnabar, sphalerite, selenium-enriched tetrahedrite and unidentified As-, Sb sulphosalts of Pb or Hg and Ag, sulphur-bearing clausthalite, naumannite and tiemannite were also found. Secondary sulphide minerals in VHMS deposits of the South Urals region are characterized by light sulphur isotope compositions (− 8.1 to − 17.2‰). Superposition of the advanced oxidation of colloform pyrite, an enrichment in impurities (sphalerite, galena, and tennantite) from the primary ores, stagnant water conditions, an elevation of the water table during oxidation, and bacterial activity led to supergene concentrations of the base metals as sulphide, selenides or sulphosalts.     

Sulphur atmospheric deposition in areas with different anthropogenic loads in Belarus

This article presents some results of an investigation of sulphur atmospheric deposition in areas with different anthropogenic loads in Belarus. Through sampling and chemical analysis of precipitation, new data about sulphate concentrations in precipitation and atmospheric deposition of sulphur in different conditions, including regional background conditions, a large industrial city and a zone affected by point source of sulphur emission, were obtained. Comparison of the chemical composition of precipitation at three sampling locations has shown that the local emission of sulphur compounds has a minor influence on local sulphur deposition. This data points to the dominant role of transboundary transfer of sulphur in contamination and acidification of the environment in Belarus.     

Magmatic mineralization and hydrothermal enrichment of the High Grade Zone at the Lac des Iles palladium mine, northern Ontario, Canada

The economic mineralization of Pd at the Lac des Iles mine occurs in the gabbroic rocks of the Mine Block Intrusion in the 2.69 Ga Lac des Iles Intrusive Complex. The complex intruded the tonalitic rocks of the Lac des Iles greenstone belt in the Wabigoon Subprovince of the Superior Province of Canada. We conducted a detailed study on the Pd mineralization in the southern Roby Zone and the Twilight Zone. Sulphide minerals commonly display exsolution textures where pentlandite and chalcopyrite are exsolved from pyrrhotite. Sulphur contents from these zones display positive correlations with the contents of platinum group elements (PGE), Se, and Te, suggesting a magmatic origin of the mineralization where PGE were concentrated in immiscible sulphide melt in the parental magmas. The average ratios of Se/S (703±192×10^–6) and Te/S (192±104×10^–6) in the two zones are higher than the primitive mantle values of ~300×10^–6 and ~48×10^–6, respectively. The high ratios are consistent with the derivation of their parental magmas from a depleted mantle source. The High Grade Zone forms a narrow northwest-trending zone in the margin of the Roby Zone, and is hosted by an intensely altered clinopyroxenite/melanogabbroic unit. It contains two mineral assemblages; millerite + siegenite ± chalcopyrite ± pyrite co-existing with hornblende + plagioclase ± quartz ± carbonate, and pyrite ± chalcopyrite with chlorite + actinolite ± albite ± quartz ± carbonate. The ore is high in Pd (mean Pd/Pt ratio of 16.5; up to 25) compared to the southern Roby Zone and Twilight Zone where the Pd/Pt ratios are ~8. It shows positive correlations between Se and Te and between Se and immobile metals, such as Ni and Co. The data suggest a primary magmatic origin of mineralization of the High Grade Zone, but there is substantial scatter on diagrams involving S, such as the plot between S and Se. The evidence suggests that the primary magmatic mineralization was followed by hydrothermal transport of mobile elements. Using the relationships between Se and metals, the ore most likely had 0.8–2 ppm Pt and 8–21 ppm Pd during the primary mineralization. The subsequent hydrothermal activity resulted in the enrichment of Pd by up to 40 ppm. The lack of fluid pathways in the High Grade Zone and the distribution of the zone are consistent with magmatic-hydrothermal activity by aqueous fluids exsolved from the parental magmas of the Roby Zone and High Grade Zone. Sulphide minerals from the southern Roby Zone, Twilight Zone, and High Grade Zone have similar ³⁴S values, ranging from 0.0 to +1.5. The data are consistent with the derivation of S from the mantle. In individual samples from the southern Roby Zone and High Grade Zone, pyrite shows lower ³⁴S than chalcopyrite, suggesting isotopic disequilibrium of S. This likely reflects the crystallization and re-crystallization of sulphide minerals over a wide range of temperatures.Editorial handling: B. Lehmann     

Optimization and modeling of boric acid extraction from colemanite in water saturated with carbon dioxide and sulphur dioxide gases

In this study, the boric acid extraction from colemanite ore in aqueous media saturated by CO₂ and SO₂ gases was studied and the effects of relevant parameters, namely; reaction temperature, solid-to-liquid ratio, mean particle size, stirring speed and reaction time have been investigated on the boric acid extraction from colemanite ore by using the fractional factorial design and central composite design methods. The chosen experimental parameter levels were as follows: reaction temperature, 11.4–58.6 °C; solid-to-liquid ratio, 0.0685–0.1315 g/mL; mean particle size, 0.2835–3 mm; stirring speed, 107–893 rpm; reaction time, 7.125–22.875 min. A model has been developed between the boric acid extraction efficiency from colemanite ore and relevant parameters by means of variance analysis by using the matlab computer software and the obtained model was used to determine optimum conditions. The optimum conditions were found to be as follows: reaction temperature, 41 °C; solid-to-liquid ratio, 0.0685 g/mL; mean particle size, 0.2835 mm; stirring speed, 266 rpm; reaction time, 7 min. The calculated boric acid extraction efficiency from colemanite ore was approximately 99.9% under the optimum conditions.     

Gas and particle emissions from Soufrière Hills Volcano, Montserrat, West Indies: characterization and health hazard assessment

 The Soufrière Hills Volcano, Montserrat, erupting since 18 July 1995, intensified its degassing in early 1996 with the continuing growth of the lava dome inside the summit crater. During this period of increased activity, between 11 and 18 March 1996, we measured gases and particles within the visible plume to determine whether at that time it posed a health risk to the population of Plymouth, the capital town, which is 5 km southwest (downwind) and was then still occupied. Gravimetric measurements were made of total suspended particles (TSP) and particles having an aerodynamic diameter of less than 10 μm (PM₁₀). Measurements were made of sulphur dioxide (SO₂), hydrochloric acid (HCl), hydrofluoric acid (HF), nitric acid (HNO₃), acetic acid (CH₃COOH), formic acid (HCOOH), and particulate sulphate (SO₄ ^2–), chloride (Cl^–), nitrate (NO₃ ^–), fluoride (F^–), methanesulphonate (CH₃SO₃ ^–), acetate (CH₃COO^–), formate (HCOO^–), ammonium (NH₄ ⁺), sodium (Na⁺) and acidity (H⁺). Trace metals having human health implications [chromium (Cr), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), tin (Sn), mercury (Hg) and lead (Pb)] were also determined. Mean concentrations of HCl, SO₂ and HF obtained in the town of Plymouth were 14.0, 5.9 and 0.8 ppbv, respectively. Corresponding concentrations in the mixed plume on the crater edge were 533, 168 and 22 ppbv. There were no direct emissions of HNO₃, although nitrate was detected in coarse particles at the source. Higher concentrations of CH₃COOH and HCOOH were measured close to the crater. Mean TSP and PM₁₀ were 64 and 15 μg m^–3 in Plymouth, and 455 and 47 μg m^–3 on the upper volcano slope. Aerosols were highly acidic at the source but rapidly neutralised during transport. Trace metals were enriched in the aerosol relative to crater surface material. The concentrations of the acid gases, sulphur dioxide in particular, and particles were found to be too small to pose a health hazard at the time of these measurements, when relatively modest volcanic activity was occurring. Received: 9 September 1998 / Accepted: 29 August 1999     

The genesis of the west shropshire orefield: Evidence from fluid inclusions,sphalerite chemistry,and sulphur isotopic ratios

The Pb + Zn + Ba veins of West Shropshire, England, occupy fractures in Ordovician and Precambrian rocks of the Shelve Inlier. Precipitation of sphaleritic ores was succeeded by galena + baryte mineralization, with chalcopyrite also occurring late in the mineralizing episode. Three generations of sphalerite are recognized, and second being chemically zoned with distinct Fe + Cd-rich growth zones. Associated with these iron-rich bands are smaller (∼ 10 μm) zones rich in indium (>1.0 wt%) and copper, electron electron probe microanalyses suggesting coupled substitution of Cu⁺ + In⁺³ in the ZnS. Based on the sequence of growth zones and their chemistry a sphalerite stratigraphy can be recognized within the orefield. Fluid inclusions studies reveal the mineralizing fluids to be highly saline (18–30 wt% CaCl₂ equivalent) Na + Ca-richbrines, with mineralizing temperatures in the range 200–120°C. A trend from higher temperature-low salinity to low temperature-high salinity fluids with time is recognized. Sulphide sulphur isotopic ratios are consistent and suggest a ΔS³⁴S_H2S of the mineralizing fluid of 10%, while ³⁴S_baryte values are in the range + 14 to + 19%, indicating separate sulphate and sulphide sulphur sources. The mineralogical, fluid inclusion, and isotopic data suggest the saline fluids rose into an open plumbing system where mineral precipitation was mainly controlled by fluid cooling. The baryte however, formed due to mixing with oan overlying sulphate-bearing reservioir. Theree possible fluid sources are considered, namely: Lower Carboniferous seawater, basinal brines, and metamorphic fluids. However, the information available does not allow the source to be positively identified.