Applied Geochemistry (v.68, #C)

Using total suspended solids (TSS) and turbidity as proxies for evaluation of metal transport in river water by T. Nasrabadi; H. Ruegner; Z.Z. Sirdari; M. Schwientek; P. Grathwohl (1-9).
The present study was carried out in Haraz basin (Iran) that is located in south of the Caspian Sea. The goal of this study was to establish correlations amongst total suspended solids concentration (TSS) and turbidity with total pollutant concentrations to evaluate the dissolved and particle-bound concentrations of major toxic metals. It also aimed to validate TSS and/or turbidity measurements as proxies to monitor pollutant fluxes. Eight metals, namely nickel, lead, cadmium, copper, zinc, cobalt, arsenic and strontium were analyzed for dissolved and total concentrations in water at ten locations within the catchment. TSS and turbidity were also measured. Sampling campaigns were designed to cover both the rainy (December) and the dry (May) season within the basin. The robust relationship between TSS (202–1212 mg/l) and turbidity (63–501 NTUs) in both seasons warranted their interchangeable potential as proxies within the observed ranges. Total element concentrations were plotted in separate attempts versus TSS and turbidity for all locations and both events. Very good linear correlations were attained where the slopes represent the metals concentration on suspended solids and the intercept the dissolved concentration in water. The results achieved by these linear regressions were in very good agreement with independently measured values for dissolved concentration and concentrations on river bed sediments taken at the same locations. This demonstrates that turbidity and/or TSS measurements may be used for monitoring of metal loads if once calibrated against total concentration of metals. The results also revealed that in the lower Haraz catchment metal concentrations on suspended and river bed sediment were homogeneously distributed along the investigated river stretch. This is assumed to be due to intensive gravel and sand mining activities in the upper and middle part of the catchment.Display Omitted
Keywords: Heavy metal; Dissolved concentration; Particle-bound; Regression; Proxy;

Deep groundwater circulation and associated methane leakage in the northern Canadian Rocky Mountains by S.E. Grasby; G. Ferguson; A. Brady; C. Sharp; P. Dunfield; M. McMechan (10-18).
Concern over potential impact of shale gas development on shallow groundwater systems requires greater understanding of crustal scale fluid movement. We examined natural deeply circulating groundwater systems in northeastern British Columbia adjacent to a region of shale gas development, in order to elucidate origin of waters, depths of circulation, and controls on fluid flow. These systems are expressed as thermal springs that occur in the deformed sedimentary rocks of the Liard Basin. Stable isotope data from these springs show that they originate as meteoric water. Although there are no thermal anomalies in the region, outlet temperatures range from 30 to 56 °C, reflecting depth of circulation. Based on aqueous geothermometry and geothermal gradients, circulation depths up to 3.8 km are estimated, demonstrating connection of deep groundwater systems to the surface. Springs are also characterised by leakage of thermogenic gas from deep strata that is partly attenuated by methanotrophic microbial communities in the spring waters. Springs are restricted to anomalous structural features, cross cutting faults, and crests of fault-cored anticlines. On a regional scale they are aligned with the major tectonic features of the Liard Line and Larsen Fault. This suggests that while connection of surface to deep reservoirs is possible, it is rare and restricted to highly deformed geologic units that produce permeable pathways from depth through otherwise thick intervening shale units. Results allow a better understanding of potential for communication between deep shale gas units and shallow aquifer systems.
Keywords: Shale gas; Thermal spring; Methane leakage;

The timing of mantle−derived CO2 charging in sedimentary basins is the basis for studying CO2-sandstone interactions and CO2-oil interactions. In general, the time of the volcanic eruption near the CO2 gas reservoir is considered to be the time of mantle-derived CO2 charging. However, this approach is not suitable for hydrocarbon-bearing basins that have experienced multiple volcanic events. In this paper, using dawsonite-bearing sandstones contained in an oil-bearing CO2 gas and oil reservoir in the southern Songliao Basin as the object of the study on the basis of paragenetic sequence and fluid inclusions, we establish a mineral dating method for determining the time of mantle-derived CO2 charging. In this method, the mineral used for dating is dawsonite, which is formed under a high CO2 partial pressure and records the migration and aggregation of mantle-derived CO2 in geologic history. By interpreting the dawsonite-bearing sandstone in the southern Songliao Basin, we find two hydrocarbon charges and one CO2 charge and that the mantle-derived CO2 charging occurred slightly later than or quasi-simultaneously with the second hydrocarbon filling. Combining the currently known time of hydrocarbon reservoir formation and the time of tectonic fracture development, we deduce that the mantle-derived CO2 formed the dawsonite in the southern Songliao Basin at the end of the Cretaceous (end of the Mingshui period) and the beginning of the Paleogene.
Keywords: Mantle−derived CO2; Dawsonite; The time of CO2 charging; Southern Songliao Basin;

In Belgium, compatibility studies are performed in view of the final disposal of nitrate-containing bituminised intermediate-level radioactive waste in Boom Clay, which is considered as a potential host formation. Due to the presence of large amounts of nitrate in the waste, a slow release of nitrate (and to a smaller extent also nitrite) into the Boom Clay is expected. Nitrate and/or nitrite reduction by redox-active components of the host rock may cause a geochemical perturbation of the clay and subsequently might affect its barrier function against the migration of radionuclides. This paper therefore addresses the possible oxidation of one of the main redox-active components of the Boom Clay, i.e. dissolved organic matter, by nitrate and nitrite. For this, abiotic and microbially mediated nitrate and nitrite reduction was studied during long-term batch tests (2–2.5 years) in Boom Clay pore water, containing 155 ± 15 mg C/l present as humic and fulvic acids. Changes in the reducing capacity of the DOM due to oxidation were assessed successfully using two oxidants, namely ferricyanide and ferric citrate. The results of these experiments indicate that an abiotic reaction between DOM and nitrate does not occur or is characterised by very slow kinetics. On the other hand, a slow microbial nitrate reduction to nitrite was observed and the associated oxidation of DOM was confirmed by a decrease in the (partial) reducing capacity of DOM for ferric citrate. In contrast to nitrate, nitrite was shown to oxidise DOM both abiotically and mediated by microbes through (chemo)denitrification, although these reactions also seem to occur only at a rather slow rate. No significant change in the maximally obtainable reducing capacity of DOM (using ferricyanide) was detected during any of the observed reactions, suggesting that the impact of such a slow heterotrophic nitrate reduction is very limited.
Keywords: Nitrate; Nitrite; Oxidation; Dissolved organic matter; Bituminised waste;

Comparison of Cu, Zn and Fe bioleaching from Cu-metallurgical slags in the presence of Pseudomonas fluorescens and Acidithiobacillus thiooxidans by Anna Potysz; Piet N.L. Lens; Jack van de Vossenberg; Eldon R. Rene; Malgorzata Grybos; Gilles Guibaud; Jakub Kierczak; Eric D. van Hullebusch (39-52).
Metal leaching from metallurgical wastes (slags) by means of environmentally friendly approaches is promising for practical applications. The goal of this study was to compare the feasibility of metal bioleaching from Cu slags by means of Pseudomonas fluorescens and Acidithiobacillus thiooxidans. Two size particles (<0.3 mm and 1–2 mm) of two types of Cu slags (massive crystalline slag and granulated amorphous slag) were used to study metal (Cu, Zn and Fe) bioleaching. The 40-days bioleaching experiments with P. fluorescens began at circumneutral pH (7.0), whereas the experiments with A. thiooxidans were started under acidic (pH 2.5) conditions. The results demonstrated that A. thiooxidans catalyzes metal leaching from both slag types investigated. After 21 days of incubation, optimal leaching was achieved and up to 79% Cu, 76% Zn and 45% Fe could be extracted from crystalline slag under conditions of 1 wt.% pulp density and particle size <0.3 mm. The optimal efficiency achieved with amorphous slag was 81% Cu, 79% Zn and 22% Fe when 1% pulp density and 1–2 mm particle size were used. The use of P. fluorescens resulted in poor leaching efficiencies as compared to the performance of A. thiooxidans, presumably due to the higher pH conditions maintained during the P. fluorescens incubations. The maximum metal leaching efficiencies with P. fluorescens were achieved at 1% pulp density and particle size <0.3 mm and did not exceed 10% Cu, 4% Zn, 0.3% Fe for crystalline slag and 4% Cu, 3% Zn, 0.7% Fe for amorphous slag. Both slags exhibited a good potential for bioleaching with A. thiooxidans, however; further optimization of the process parameters (e.g. pulp density, particle size and pH) is needed to improve the efficiency.Display Omitted
Keywords: Cu slags; Metals (Cu, Zn, Fe); Bioleaching; Pseudomonas fluorescens; Acidithiobacillus thiooxidans;

Iodine budget in surface waters from Atacama: Natural and anthropogenic iodine sources revealed by halogen geochemistry and iodine-129 isotopes by Fernanda Álvarez; Martin Reich; Glen Snyder; Alida Pérez-Fodich; Yasuyuki Muramatsu; Linda Daniele; Udo Fehn (53-63).
Iodine enrichment in the Atacama Desert of northern Chile is widespread and varies significantly between reservoirs, including nitrate-rich “caliche” soils, supergene Cu deposits and marine sedimentary rocks. Recent studies have suggested that groundwater has played a key role in the remobilization, transport and deposition of iodine in Atacama over scales of millions-of-years. However, and considering that natural waters are also anomalously enriched in iodine in the region, the relative source contributions of iodine in the waters and its extent of mixing remain unconstrained. In this study we provide new halogen data and isotopic ratios of iodine (129I/I) in shallow seawater, rivers, salt lakes, cold and thermal spring water, rainwater and groundwater that help to constrain the relative influence of meteoric, marine and crustal sources in the Atacama waters. Iodine concentrations in surface and ground waters range between 0.35 μM and 26 μM in the Tarapacá region and between 0.25 μM and 48 μM in the Antofagasta region, and show strong enrichment when compared with seawater concentrations (I = ∼0.4 μM). In contrast, no bromine enrichment is detected (1.3–45.7 μM for Tarapacá and 1.7–87.4 μM for Antofagasta) relative to seawater (Br = ∼600 μM). These data, coupled to the high I/Cl and low Br/Cl ratios are indicative of an organic-rich sedimentary source (related with an “initial” fluid) that interacted with meteoric water to produce a mixed fluid, and preclude an exclusively seawater origin for iodine in Atacama natural waters. Iodine isotopic ratios (129I/I) are consistent with halogen chemistry and confirm that most of the iodine present in natural waters derives from a deep initial fluid source (i.e., groundwater which has interacted with Jurassic marine basement), with variable influence of at least one atmospheric or meteoric source. Samples with the lowest isotopic ratios (129I/I from ∼215 to ∼1000 × 10−15) strongly suggest mixing between the groundwater and iodine storage in organic-rich rocks (with variable influence of volcanic fluids) and pre-anthropogenic meteoric water, while samples with higher values (∼2000–93,700 × 10−15) indicate the input of anthropogenic meteoric fluid. Taking into account the geological, hydrologic and climatic features of the Atacama region, we propose that the mean contribution of anthropogenic 129I is associated with 129I releases during nuclear weapon tests carried out in the central Pacific Ocean until the mid 1990's (129I/I = ∼12,000 × 10−15). This source reflects rapid redistribution of this radioisotope on a global scale. Our results support the notion of a long-lived continental iodine cycle in the hyperarid margin of western South America, which is driven by local hydrological and climate conditions, and confirm that groundwater was a key agent for iodine remobilization and formation of the extensive iodine-rich soils of Atacama.
Keywords: Iodine; natural waters; iodine isotopic ratios; anthropogenic sources;

Establishing a shallow water cover over tailings deposited in a designated storage facility is one option to limit oxygen diffusion and retard oxidation of sulfides which have the potential to form acid mine drainage (AMD). The Old Tailings Dam (OTD) located at the Savage River mine, western Tasmania contains 38 million tonnes of pyritic tailings deposited from 1967 to 1982, and is actively generating AMD. The OTD was constructed on a natural gradient, resulting in sub-aerial exposure of the southern area, with the northern area under a natural water cover. This physical contrast allowed for the examination of tailings mineralogy and geochemistry as a function of water cover depth across the OTD. Tailings samples (n = 144, depth: ≤ 1.5 m) were collected and subjected to a range of geochemical and mineralogical evaluations. Tailings from the southern and northern extents of the OTD showed similar AMD potential based on geochemical (NAG pH range: 2.1 to 4.2) and bulk mineralogical parameters, particularly at depth. However, sulfide alteration index (SAI) assessments highlighted the microscale contrast in oxidation. In the sub-aerial zone pyrite grains are moderately oxidized to a depth of 0.3 m (maximum SAI of 6/10), under both gravel fill and oxidized covers, with secondary minerals (e.g., ferrihydrite and goethite) developed along rims and fractures. Beneath this, mildly oxidized pyrite is seen in fresh tailings (SAI = 2.9/10 to 5.8/10). In the sub-aqueous zone, the degree of pyrite oxidation demonstrates a direct relationship with cover depth, with unoxidized, potentially reactive tailings identified from 2.5 m, directly beneath an organic-rich sediment layer (SAI = 0 to 1/10). These findings are broadly similar to other tailings storage facilities e.g., Fox Lake, Sherritt-Gordon Zn―Cu mine, Canada and Stekenjokk mine, Sweden where water covers up to 2 m have successfully reduced AMD. Whilst geotechnical properties of the OTD restrict the extension of the water cover, pyrite is enriched in cobalt (up to 2.6 wt%) indicating reprocessing of tailings as an alternative management option. Through adoption of an integrated mineralogical and geochemical characterization approach for tailings assessment robust management strategies after mine closure can be developed.Display Omitted
Keywords: Tasmania; Sulfide alteration index; Automated mineralogy; Acid drainage; Pyrite;

In order to understand and mitigate the deterioration of water quality in the aquifer system underlying Guadalajara metropolitan area, an investigation was performed developing geochemical evolution models for assessment of groundwater chemical processes. The models helped not only to conceptualize the groundwater geochemistry, but also to evaluate the relative influence of anthropogenic inputs and natural sources of salinity to the groundwater. Mixing processes, ion exchange, water–rock–water interactions and nitrate pollution and denitrification were identified and confirmed using mass-balance models constraint by information on hydrogeology, groundwater chemistry, lithology and stability of geochemical phases. The water–rock interactions in the volcanic setting produced a dominant Na―HCO3 water type, followed by Na―Mg―Ca―HCO3 and Na―Ca―HCO3. For geochemical evolution modeling, flow sections were selected representing recharge and non-recharge processes and a variety of mixing conditions. Recharge processes are dominated by dissolution of soil CO2 gas, calcite, gypsum, albite and biotite, and Ca/Na exchange. Non-recharge processes show that the production of carbonic acid and Ca/Na exchange are decreasing, while other minerals such as halite and amorphous SiO2 are precipitated. The origin of nitrate pollution in groundwater are fertilizers in rural plots and wastewater and waste disposal in the urban area. This investigation may help water authorities to adequately address and manage groundwater contamination.Display Omitted
Keywords: Inverse geochemical modeling; PHREEQC; Water–rock interaction; La Primavera caldera; Nitrate; Groundwater mixing; Guadalajara; Mexico;