Applied Geochemistry (v.82, #C)

The Sr isotopic compositions (87Sr/86Sr) of varied organs (branches, leaves and olives) of olives trees (Olea europaea) and those of their growing environment (soils, waters, agricultural products) were determined in two distinct agricultural contexts to discuss the origin of Sr as a function of the irrigation and fertilization techniques. The two studied sites belong to the same geographic area and the same geological basement and soils, but were by subjected to different agricultural practices in terms of irrigation and supply of fertilizers and protection products. The conventional and biological agriculture modalities were defined and tested. Homogeneous 87Sr/86Sr ratios were measured in the various organs of the trees from a given site. However, the composition was significantly different at the two studied sites. When considering a biological agricultural modality, significant correlations are obtained between the Sr isotopic composition of the tree organs, the soils and the irrigation waters. The mobile and exchangeable fractions of the soils have identical 87Sr/86Sr ratios that were transferred to the trees. In case of a conventional agriculture with more intensive irrigation and spreading of plant-protection products, a clear impact of these products is visible in the soils. The 87Sr/86Sr ratio of the olive trees not only derives from soil sources, but also from added products with a clear role of the irrigation. A slight but noticeable foliar uptake of anthropogenic Sr is also observed. The disturbance of the soil and tree Sr isotope composition as a function of the agricultural practices is discussed in the context of using the Sr isotopic tool as a tracer of the geographic origin of olives and olive oil.
Keywords: Bioavailability; Strontium uptake; Strontium isotope tracing; Olive geographic discrimination; Agricultural practice;

Stable isotopes reveal human influences on southern New Zealand soils by K.M. Rogers; R.E. Turnbull; A.P. Martin; W.T. Baisden; M.S. Rattenbury (15-24).
A multi-isotopic soil study across a southern New Zealand transect has been undertaken as part of a geochemical baseline survey to identify human impacts on New Zealand's landscape and characterise different land uses and anthropogenic effects. Carbon, nitrogen and sulphur isotopes from two soil depths (0–30 and 50–70 cm) were acquired across a variety of land uses (including pristine national parks, urban centres, intensively farmed pastoral land), climates (dry <500 mm annual rainfall to wet >6000 mm annual rainfall), altitude (sea level to >2300 m above sea level) and soil parent material lithology (sandstone, schist, basalt). Detrital organic matter accumulated more in lowlands than at higher altitudes with higher carbon and nitrogen contents found in river valleys. Carbon isotopes clearly differentiated between drier higher altitude or open pastoral sites (more positive values) and wetter forested sites (more negative values). Nitrogen isotopes reflect anthropogenic human influence with elevated values around urban and intensively farmed sites, and lower values characterising indigenous forests and pristine sites. Sulphur isotopes either show more positive values, typical of fertilisers, rain or sea spray in open pastoral sites, or more negative values consistent with weathered geological sources such as metamorphic sulphides found in schist in some river valley sites. The study demonstrates that regional isotope studies are a potential tool to understand the long and short term impacts on landscapes, and may be useful for future mineral exploration, urban health studies, agricultural site remediation, and land use control and regulation.
Keywords: Stable isotopes; Carbon; Nitrogen; Sulphur; Anthropogenic impact; Regional survey; Soil; New Zealand;

Mississippi Valley-Type (MVT) lead-zinc deposits, which account for 24% of the global resources of Pb and Zn, are found throughout the world with the largest deposits occurring in North America. The Tri-State Mining district, located at the intersection of Oklahoma, Kansas, and Missouri, was one of the most productive Pb and Zn districts during the turn of the 20th century.The current geochemical study of ore samples from the Tri-State district and of stream-sediment samples collected from selected sites from the lower Arkansas River drainage basin (the Neosho River, Tar Creek, and Spring River) show that the effect of past mining activity and leaded gasoline on Pb concentrations in the river sediment can be readily documented. Lead isotopic ratios of leachates of stream sediments from the Tar Creek area collected downstream from Picher, OK, correlate well with those of ore samples from the Tri-State Mining District, suggesting that most of the Pb adsorbed onto the stream sediments was sourced by the ores. Lead isotope measurements of leachates delimit the extent of high Pb concentrations in the Tar Creek region caused by mineralization and mining at Picher, OK. The effects of mining are noticed to a lesser extent in the Spring and Neosho rivers, with increasing distance from Picher. The influence of the leaded gasoline is more pronounced with increasing distance from the superfund site, contributing between around 52% and 68% extractable Pb to the stream sediments 14 km from the Picher mining area. This discovery can have major implications in how to evaluate the risk to human and animal health, as well as guide remediation efforts in this region.Leachates from stream-sediment samples collected from the Spring and Neosho rivers show lower Pb isotopic ratios than the Tar Creek leachates and plot outside the field defined by ore samples from the Tri-State Mining District. They fall along an array defined by a binary mixture of Pb from the leaded gasoline and the Pb sourced from the Tri-State mining district, indicative of two distinct Pb sources.There is a gradual decrease in the Zn, Pb, As, and other heavy-metal concentrations in the stream sediment leachates with distance from the mines. The Zn concentration reaches a maximum of 1592 ppm in the Picher area, more than 29 times the average natural background levels in the Tri-State region (41 ppm). About 24 km downstream from Picher, the Zn concentrations decrease substantially to values lower than both, normal crustal abundance and background levels. Similarly, the Pb concentration is highest in the Picher area (326 ppm), about 14 times the natural background levels in the Tri-State region (16 ppm), and it drops to much lower values downstream. Even though the highest Cu and As concentrations are seen in the Picher area (10 ppm and 1.44 ppm, respectively), they are lower compared to the natural background levels for the region (11 ppm and 6 ppm, respectively).Display Omitted

Study of particles in the ascending gas of ruptures caused by the 2008 Wenchuan earthquake by Jianjin Cao; Shuting Cheng; Songying Luo; Chang Liu (38-46).
Ascending gas is a global phenomenon. It can move upwards along faults or fissures from the interior of the Earth to the surface of the Earth. Seismically active regions near continental plate boundaries are active regions of ascending gas. Based on the results of previous research, abnormal concentrations of SO2, CO2, Rn, He, H2, O2, Ar, N2, and CH4 in ascending gas may be applied to earthquake prediction. In our study, particles carried by ascending gas in ruptures caused by the Wenchuan earthquake have been discovered using a transmission electron microscope. It can be seen that there are far more particles in the ascending gas of ruptures caused by the 2008 earthquake than there are in the ascending gas of the non-seismic Fengguanshan fault or the ascending gas of the soil in Wufeng Town of Jintang County or Yuhe Village of Pengshan County (which represent background areas). The abnormal characteristics of the particles carried by the ascending gas of ruptures also include Cu-, Hg-, and Os-enriched particles. The typical elemental associations are Fe-Mn-Ni-Cr and Pb-Cr. SiO2 particles contain abnormally high contents of impure elements in the form of particles that have been encapsulated by SiO2. This is the first study to report the presence of particles carried by ascending gas in earthquake ruptures. This study represents a new method of earthquake prediction. These particles can provide us with abundant and direct information about earthquake activity, which can be applied to earthquake prediction. Characteristics of the particles in the ascending gas, combined with the concentrations of Hg, SO2, CO2, Rn, He, H2, O2, Ar, N2, and CH4, can be used to develop a more efficient method of earthquake prediction.
Keywords: Particles; Ascending gas; Ruptures; Wenchuan earthquake;

Element release and reaction-induced porosity alteration during shale-hydraulic fracturing fluid interactions by Anna L. Harrison; Adam D. Jew; Megan K. Dustin; Dana L. Thomas; Claresta M. Joe-Wong; John R. Bargar; Natalie Johnson; Gordon E. Brown; Katharine Maher (47-62).
The use of hydraulic fracturing techniques to extract oil and gas from low permeability shale reservoirs has increased significantly in recent years. During hydraulic fracturing, large volumes of water, often acidic and oxic, are injected into shale formations. This drives fluid-rock interaction that can release metal contaminants (e.g., U, Pb) and alter the permeability of the rock, impacting the transport and recovery of water, hydrocarbons, and contaminants. To identify the key geochemical processes that occur upon exposure of shales to hydraulic fracturing fluid, we investigated the chemical interaction of hydraulic fracturing fluids with a variety of shales of different mineralogical texture and composition. Batch reactor experiments revealed that the dissolution of both pyrite and carbonate minerals occurred rapidly, releasing metal contaminants and generating porosity. Oxidation of pyrite and aqueous Fe drove precipitation of Fe(III)-(oxy)hydroxides that attenuated the release of these contaminants via co-precipitation and/or adsorption. The precipitation of these (oxy)hydroxides appeared to limit the extent of pyrite reaction. Enhanced removal of metals and contaminants in reactors with higher fluid pH was inferred to reflect increased Fe-(oxy)hydroxide precipitation associated with more rapid aqueous Fe(II) oxidation. The precipitation of both Al- and Fe-bearing phases revealed the potential for the occlusion of pores and fracture apertures, whereas the selective dissolution of calcite generated porosity. These pore-scale alterations of shale texture and the cycling of contaminants indicate that chemical interactions between shales and hydraulic fracturing fluids may exert an important control on the efficiency of hydraulic fracturing operations and the quality of water recovered at the surface.

In Canada's Northwest Territories, mining for base metals and diamonds are vital economic activities which carry risks of adverse environmental impacts. To gather baseline geochemical data against which the impact of future mining activities may be measured, a survey of trace metal concentrations in snow was carried out in 2012 along a 285-km stretch of winter mining road crossing the taiga-tundra ecotone between latitudes 62.8 and 65.5° N. The distribution of 17 elements, including mercury (Hg), was measured and mapped. Results indicate that road traffic along the winter road has only a modest impact on the metal content of the nearby tundra-taiga snowpack, and that this impact is largely due to the mobilization of soil dust and associated elements. However, some enrichment of As, Pb, Sr and Zn in snow was detected near former gold mine sites, likely reflecting the windborne dispersion of contaminated soils. The Hg concentrations in snow across the study area were generally low (≤3.01 ng L−1), and did not covary with any other metals, which suggests atmospheric deposition from distant/diffuse sources. An analysis of air back-trajectories pointed to the most likely distant (>103 km) anthropogenic source regions being eastern Asia or Russia. Using Hg data from the present survey and another source, in combination with gridded maps of snowpack water equivalent, we calculated the potential flux of atmospherically-derived Hg that could be released by spring snowmelt into the Mackenzie River to be in the order of ∼195–404 kg a−1, which may represent a substantial fraction of the estimated total Hg discharge to the Beaufort Sea.
Keywords: Snow; Trace metals; Mercury; Aerosols; Canada; Subarctic; Mackenzie river;

The solubility of fluorite in Na-K-Cl solutions at temperatures up to 260 °C and ionic strengths up to 4 mol/kg H2O by Wei Zhang; Li Zhou; Hongfeng Tang; Heping Li; Wenlei Song; Gang Xie (79-88).
The solubility of fluorite in hydrothermal conditions is important in ore forming and geothermal processes and groundwater utilization. However, a quantitative description of the geochemical behavior of fluorite under hydrothermal conditions has not been previously reported. In this work, the solubility of fluorite in Na-K-Cl solutions at temperatures up to 260 °C and ionic strengths up to 4 M was determined by experiments and modeling. The solubility products obtained in this work at 30 and 50 °C under ambient pressure and those from literature were used to regress the density model parameters for fluorite solubility product calculation at high temperature. The Pitzer interaction model was adopted to calculate the activity coefficient. The fluorite solubility determined in KCl solution at 250 °C under vapor saturated pressure and that from the literature were combined with the low-temperature thermodynamic properties of heat capacity and osmotic coefficient to obtain the binary parameters of NaF and KF at temperatures up to 260 °C. A thermodynamic model was then developed for calculating the fluorite solubility in Na-K-Cl solution at temperatures up to 260 °C, under vapor saturated pressure and ionic strengths up to 4 M. As calculated from this model, fluorite solubility measured at 200 °C and 0.1 M NaCl was well predicted. Both temperature and ionic strength had significant effects on fluorite solubility, and fluorite exhibited a similar dissolution pattern in both NaCl and KCl solution. When the concentration was lower than 2 M, the solubility of fluorite first increased with temperature, reached a maximum at approximately 100 °C, and then decreased. When the concentration was higher than 2 M, the solubility of fluorite increased monotonically with temperature.
Keywords: Fluorite solubility; Hydrothermal condition; High temperature; Pitzer model;

Geochemical signatures and processes in a stream contaminated by heavy mineral processing near Ipoh city, Malaysia by Akane Ito; Tsubasa Otake; Ki-Cheol Shin; Kamar Shah Ariffin; Fei-Yee Yeoh; Tsutomu Sato (89-101).
The environmental impacts of a heavy mineral processing involving rare earth elements (REEs) in the Kinta River and its tributaries near Ipoh city in Malaysia is investigated using geochemical and isotopic signatures and geochemical modeling. Analysis of water, sediment, suspended particulate matter, and rock samples reveals that stream waters close to the heavy mineral processing plant site are anthropogenically influenced, as indicated by slightly low pH (4.98–6.24) and elevated concentrations of Fe (up to 129 mg/L), Cl (1540 mg/L), total REEs (1580 μg/L), U (17.2 μg/L), and Th (0.33 μg/L). REE patterns and Pb isotope ratios of waters and sediments from a tributary are similar to those of tailings pond seepage and sediments, suggesting that not only these elements but also U and Th are derived from heavy mineral processing. The δ56Fe values of water in the tributary decrease downstream, accompanied by a decrease in Fe concentration, which is likely due to isotope fractionation via oxidative precipitation of Fe hydroxides. The concentrations of REEs, U, and Th decrease downstream, accompanied by an increase in pH, with different removal factors (Th > U > REEs). The influence of contamination is confined to within ∼1.5 km downstream of the source. Tamm's acid oxalate extraction (to dissolve only low crystalline phases) showed that Th and Al concentrations were lower while U and Fe concentrations were higher in downstream suspended particulate samples, suggesting that Th and U may be removed by different mechanisms from stream water. The results of geochemical modeling suggest that Th precipitated as a solid phase, such as an intermediate between ThO2 and Th(OH)4, with increasing stream water pH. In contrast, U may have been removed by adsorption onto Fe hydroxides, as supported by surface complexation modeling. The geochemical signatures and processes discussed in this study may be applicable for environmental assessment of REE processing.Display Omitted
Keywords: Rare earth elements; Pb isotope; Fe isotope; Radioactive elements; Natural attenuation; Geochemical modeling;

The characterization, mobility, and persistence of roaster-derived arsenic in soils at Giant Mine, NWT by Mackenzie J. Bromstad; Lori A. Wrye; Heather E. Jamieson (102-118).
Approximately 20,000 tonnes of arsenic (As)-bearing emissions from roasting gold (Au)-bearing arsenopyrite ore were aerially released from 1949 to 1999 at Giant Mine, near Yellowknife, Canada. Soil samples collected within 4 km of the former roaster from sites undisturbed by mining or other human activity contain up to 7700 mg/kg total As. Total As concentrations are highest within a few cm of the surface, and particularly enriched in soil pockets on rock outcrops. Scanning electron microscopy and synchrotron microanalysis show that roaster-derived arsenic trioxide (As2O3) has persisted in shallow soils in the area. Roaster-generated maghemite and hematite are also present. These anthropogenic forms of As are much more common in near-surface soils than natural As-bearing minerals. Comparison of the proportions of As, Sb, and Au concentrations in outcrop soil samples and historic As2O3-rich dust captured by emission controls suggest most of the roaster-derived As in soils at Giant was likely deposited before 1964. Topographic restriction by rock outcrops and a dry, cold climate likely contribute to the persistence of As2O3 in outcrop soils.Limited post-depositional mobility of roaster-generated As is evident from textural relationships in thin section, the presence of As in weathering products, the variation of As:Sb with depth, and the elevated As concentrations in soil pore waters sampled by suction lysimeters. Synthetic gastric and lung fluids extracted an average of 34% and 18% of the total As in three adjacent soil samples. Given that As2O3 is one of the most toxic and bioaccessible forms of As, the persistence of roaster-generated As in shallow soils may be a human health risk at this site.
Keywords: Arsenic trioxide; Arsenic; Soils; Arsenic speciation; Giant Mine; Synchrotron;

Impact of iron and magnesium on glass alteration: Characterization of the secondary phases and determination of their solubility constants by H. Aréna; N. Godon; D. Rébiscoul; P. Frugier; R. Podor; E. Garcès; M. Cabie; J.-P. Mestre (119-133).
In this study, the effects of iron and magnesium on International Simple Glass (ISG) alteration were studied throughout 511 days of aqueous leaching experiments. The aim was to determine by thorough characterization, the nature of the alteration products that control glass alteration. Iron and magnesium were added separately or together in solution as FeCl2 and MgCl2 salts, with monthly additions to compensate for their consumption. The alteration degree was determined by leachate analyses (ICP-AES) and the alteration products composition, morphology and microstructure were characterized (SEM, TEM-EDX and XRD).The results indicated that magnesium and iron increase glass alteration, forming tri-octahedral smectites with the same (Fe + Mg)/Si ratio. With iron, two kinds of silicates precipitate with the same composition but with a different morphology, whereas with magnesium alone, a single Mg-silicate forms. Moreover, it was found that the glass alteration rate drops when the pH stabilizes at a minimum value of 7.8 for Mg-silicates and 6.2 for Fe-silicates. At this point the secondary silicates stop precipitating. This result was confirmed by geochemical simulation and the solubility product of these silicates was estimated considering the presence or absence of aluminum in their structure.Finally, a two-step process was proposed to explain the location of the secondary phase precipitation: firstly in solution and at the solution/gel interface, and secondly in a highly porous upper zone of the gel.Display Omitted
Keywords: Glass; Alteration; Iron; Magnesium; Secondary phases; pH; Interface;

Understanding radionuclide transport processes deep underground is indispensable for safety assessments of the geological disposal of radioactive wastes. This study investigated the behavior of rare earth elements (REEs) associated with suspended particles in deep granitic groundwater and in a sealed drift at a depth of 500 m in the Mizunami Underground Research Laboratory (URL) in Japan, as an analogue study of radionuclide behavior around an underground waste disposal facility.Particles suspended in natural groundwater consist of silicate minerals including clays, and iron hydroxide, calcite, sulfide, and organic substances. Approximately 10%–60% of REEs in groundwater are associated with suspended particles. Furthermore, sequential chemical extraction analyses of the suspended materials trapped on membrane filters suggests that REEs are primarily sorbed onto carbonate particles in deep granitic groundwater. Carbonate particles in groundwater are most likely derived from in situ precipitation of supersaturated carbonate minerals such as calcite. The concentration of Lanthanum associated with suspended particles, as an example, is highest when the calcite saturation index shows equilibrium (SI = 0) and decreases as the calcite saturation index increase. Because deep granitic groundwater is generally in equilibrium with the saturated condition for calcite, the results of this study suggest that calcite particles inevitably exist in groundwater and preferentially sorb REEs.The REE concentrations in the water and suspended particles from the closed drift are significantly lower compared with concentrations in the surrounding groundwater. Thermodynamic calculations show that the dissolved REE carbonate complexes in the closed drift decreased in the drift closure period. These complexes may have been absorbed or co-precipitated within the shotcrete on the drift wall. In the closed drift, ZnS particles and large amounts of organic suspensions, as artificial suspended particles, were observed in addition to the particles observed in natural groundwater. A sequential chemical extraction analysis indicates that REEs are primarily sorbed onto the carbonate particles and not on the large quantity of organic particles. There may be little REE adsorption onto organic suspensions, or REEs may have preferentially adsorbed onto calcite particles or shotcrete rather than organic matter. The occurrence of calcite particles under the cementitious conditions of the closed drift changes from the large suspended particles to aggregates of relatively small particles with time. Precipitation of carbonate particle–borne REEs is probably one of reasons for the decrease in the suspended REEs concentrations. The usage of cement–based materials would generate environmental conditions in which REEs are fundamentally immobile in and around the underground facilities.
Keywords: Groundwater; Suspended particle; Rare earth element; Underground facility closure;

Methodology for determining the thermodynamic properties of smectite hydration by Hélène Gailhanou; Philippe Vieillard; Philippe Blanc; Arnault Lassin; Renaud Denoyel; Emily Bloch; Guy De Weireld; Stéphane Gaboreau; Claire I. Fialips; Benoit Madé; Eric Giffaut (146-163).
This study proposes an improved methodology for extracting the thermodynamic hydration properties of clay minerals from adsorption isotherms performed at two temperatures, by removing the capillary water contribution. The work focuses on Na-smectite. Its thermodynamic hydration properties were extracted as follows: (i) experimental measurement of water vapor adsorption isotherms at two temperatures (25 °C and 45 °C); (ii) removal of the capillary water contribution; (iii) calculation of the thermodynamic properties. The values obtained from the adsorption branch compare favorably with calorimetric measurements. We parameterized a strict regular solid solution model similar to that developed by Ransom and Helgeson (1994). From this we see how the thermodynamic properties of hydration evolve, so we can explain and sort the values obtained by previous authors. The calculation process, based on structural constraints from the literature, considers only half of the total adsorbed water as structurally related to the mineral, when relative humidity conditions are close to 100%. The approach proposed in this work enables generalization to other types of clay minerals and implementation of thermodynamic databases with thermodynamic properties that are intrinsic to each clay mineral and independent from contextual constraints.
Keywords: Water vapor; Smectite; Adsorption; Thermodynamic properties;

Rare earth elements in tributaries of Lake Baikal (Siberia, Russia) by O.A. Sklyarova; E.V. Sklyarov; L. Och; M.V. Pastukhov; N.A. Zagorulko (164-176).
REE dissolved in waters from sixty five sampled tributaries of Lake Baikal show diversity in abundances (∑REE = 0.02–2.16 μg/L) and distribution patterns ([La/Yb]N = 0.20–5.58; [La/Tb]N = 0.30–2.59). Total REE contents vary seasonally and yearly, while REE patterns remain generally similar. The REE patterns in stream waters correlate with those in the drained rocks and hence, seem to be predominantly controlled by watershed lithology. Rivers having small watersheds around Lake Baikal belong to six lithological provinces with different stream-water REE patterns: the Olkha plateau and the ranges of Primorsky, Baikalsky, Barguzin, Ulan-Burgassy, and Khamar-Daban. The Khamar-Daban province, in turn, is lithologically heterogeneous and comprises four subprovinces with different respective patterns of dissolved REE. Rock-water interaction in subsurface aquifers that feed the Baikal inlets provides much stronger lithological control of REE than the weak interaction of short and rapid streams with rocks on the surface. REE fractionation in stream waters show negative Ce anomalies in almost all samples (Ceanom = 0.12–0.97), except for those of large rivers (Selenga, Turka, Barguzin, Upper Angara, and Kichera). The reason is that the great length, relatively slow current, and the presence of streambed fine alluvium make the water chemistry more uniform and the REE patterns less dependent on local variations in watershed lithology. The sampled tributaries represent a range of physico-chemical and geomorphological conditions which can be used as reference for calibrations in future studies of sediment sources and, possibly, as a valuable tool for mineral exploration.
Keywords: Rare earth elements (REE); Stream waters chemistry; Watershed lithology; Lake Baikal; Siberia; Russia;

This study investigates the influence of temperature on the dissolution of MW25, a non-radioactive simulant of UK Magnox glass. A single-pass flow-through (SPFT) system was used to measure the forward dissolution rate of MW25 at 40 and 90 °C and circum-neutral pH. The forward dissolution rate was found to be approximately one order of magnitude higher at 90 °C than at 40 °C. A similar release was observed for Si, Mg and Al at 40 °C and 90 °C, whereas the B, Cs, Na, Li and Mo showed an order of magnitude increase when the temperature was increased from 40 to 90 °C for low q/S values. The temperature dependence of the dissolution rates was determined using the Arrhenius rate law and the resultant activation energy (Ea) shows that the dissolution process is a surface phenomenon. At 90 °C, the net effect of the processes governing MW25 dissolution led to preferential release of boron and alkali metals relative to the release of Si during the transient dissolution stage, accompanied by an increase in the concentration of silicic acid. This suggests that the solution activity of silicic acid at higher temperature has a weak influence on the release of the mobile elements. This study features a new method for estimating the surface area of reacted glass powder more accurately than the geometric surface area estimate, which is the preferred standard method among researchers.
Keywords: Dissolution; Forward rate; Temperature; Flow rate; Borosilicate glass; MW25;