Ra-partitioning between phlogopite and silicate melt and 226Ra/Ba–230Th/Ba isochrons

In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~ 0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~ 1 ppb). D_Ra^{phlogopite/melt} was determined to 2.28 ± 0.44 and 2.84 ± 0.47 in two experiments, the ratio D_Ra/D_Ba is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of D_Ra and D_Ra/D_Ba for magmatic minerals containing appreciable Ra, yields D_Ra^mineral/melt ranging from ~ 2.6 for phlogopite down to 2–3 ? 10^? 5 for pyroxenes, and D_Ra/D_Ba^mineral/melt from ~ 4 for leucite to 2 ? 10^? 2 for orthopyroxene. The influence of melt composition on D_Ra/D_Ba is less than 10%. All investigated minerals have different D_Ra/D_Ba, strongly fractionating Ra from Ba. Thus, for magmatic systems, (²²⁶Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the (²²⁶Ra)/Ba–(²³⁰Th)/Ba system at the time of crystallization and thus, there is no (²²⁶Ra)/Ba–(²³⁰Th)/Ba isochron at t₀. ²²⁶Ra–²³⁰Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known D_Ra.     

Evaluation of radiation dose due to naturally occurring radionuclides in rock samples of different origins collected from Azad Kashmir

The state of Azad Kashmir is rich in three types of rocks, namely, sedimentary, metamorphic, and igneous rocks. These rocks contain extensive deposits of graphite, marble, limestone, quartzite, granite, dolerite, and sandstone, which are widely used for the construction of dwellings in Azad Kashmir and Pakistan. Therefore, knowledge about the presence of natural radioactivity in these materials is desirable to assess the radiological hazards associated with it. In this context, 30 rock samples were collected from different geologic formations of the Muzaffarabad Division, Azad Kashmir. After processing the samples, the specific activities of ²²⁶Ra, ²³²Th, and ⁴⁰ K in them were measured using a P-type coaxial high-purity germanium detector. The observed highest dose rate values for sedimentary, metamorphic, and igneous rocks have been found to be 83.16 ± 1.08, 135.87 ± 1.18, and 115.98 ± 1 nGy ⋅ h^–1, respectively. The radium equivalent activity (Ra_eq) varied from 23.76 ± 1.15 for dolerite sample (igneous rock) to 293.69 ± 2.60 Bq ⋅ kg^–1 for marble (metamorphic rock). The Ra_eq values of all rock samples are lower than the limit mentioned in the Organization for Economic Cooperation and Development (OECD, 1979) report (370 Bq ⋅ kg^–1, equivalent to γ-dose of 1.5 mSv ⋅ y^–1). The values of external (H_ex) and internal hazard indices (H_in) are less than unity. The mean outdoor and indoor annual effective dose equivalents are 0.073 mSv ⋅ y^–1 and 0.29 mSv ⋅ y^–1, respectively. The mean (over all types of rock samples) annual effective dose equivalent is reported as 0.36 mSv ⋅ y^–1.     

Soil pH governs production rate of calcium carbonate secreted by the earthworm Lumbricus terrestris

Lumbricus terrestris earthworms exposed to 11 soils of contrasting properties produced, on average, 0.8 ± 0.1 mg_CaCO3 earthworm^?1 day^?1 in the form of granules up to 2 mm in diameter. Production rate increased with soil pH (r² = 0.68, p < 0.01). Earthworms could be a significant source of calcite in soils.     

Spatial variability of initial 230Th/232Th in modern Porites from the inshore region of the Great Barrier Reef

The main limiting factor in obtaining precise and accurate uranium-series (U-series) ages of corals that lived during the last few hundred years is the ability to constrain and correct for initial thorium-230 (²³⁰Th₀), which is proportionally much higher in younger samples. This is becoming particularly important in palaeoecological research where accurate chronologies, based on the ²³⁰Th chronometer, are required to pinpoint changes in coral community structure and the timing of mortality events in recent time (e.g. since European settlement of northern Australia in the 1850s). In this study, thermal ionisation mass spectrometry (TIMS) U-series dating of 43 samples of known ages collected from living Porites spp. from the far northern, central and southern inshore regions of the Great Barrier Reef (GBR) was performed to spatially constrain initial ²³⁰Th/²³²Th (²³⁰Th/²³²Th₀) variability. In these living Porites corals, the majority of ²³⁰Th/²³²Th₀ values fell within error of the conservative bulk Earth ²³⁰Th/²³²Th atomic value of 4.3 ± 4.3 × 10^?6 (2σ) generally assumed for ²³⁰Th₀ corrections where the primary source is terrestrially derived. However, the results of this study demonstrate that the accuracy of ²³⁰Th ages can be further improved by using locally determined ²³⁰Th/²³²Th₀ values for correction, supporting the conclusion made by Shen et al. (2008) for the Western Pacific. Despite samples being taken from regions adjacent to contrasting levels of land modification, no significant differences were found in ²³⁰Th/²³²Th₀ between regions exposed to varying levels of sediment during river runoff events. Overall, 39 of the total 43 ²³⁰Th/²³²Th₀ atomic values measured in samples from inshore reefs across the entire region show a normal distribution ranging from 3.5 ± 1.1 to 8.1 ± 1.1 × 10^?6, with a weighted mean of 5.76 ± 0.34 × 10^?6 (2σ, MSWD = 8.1). Considering the scatter of the data, the weighted mean value with a more conservative assigned error of 25% (i.e. 5.8 ± 1.4 × 10^?6) that encompasses the full variation of the 39 ²³⁰Th/²³²Th₀ measurements is recommended as a more appropriate value for initial ²³⁰Th corrections for U-series dating of most Porites samples from inshore regions of the GBR. This will result in significant improvement in both the precision and accuracy of the corrected ²³⁰Th ages related to those based on the assumed bulk Earth ²³⁰Th/²³²Th₀ value of 4.3 ± 4.3 × 10^?6. However, several anomalously high ²³⁰Th/²³²Th₀ values reaching up to 28.0 ± 1.6 × 10^?6 occasionally found in some coral annual bands coinciding with El Niño years imply high ²³⁰Th/²³²Th₀ sources and highlight the complexities of understanding ²³⁰Th/²³²Th₀ variability. For U-series dating of young coral samples from such sites where anomalous ²³⁰Th/²³²Th₀ values occur, we suggest replicate dating of multiple growth bands with known age difference to verify age accuracy.     

High cadmium concentration in soil in the Three Gorges region: Geogenic source and potential bioavailability

This study investigated the distribution and sources of Cd in soils from a Cd-rich area in the Three Gorges region, China. The results showed that in the study area arable soils contain 0.42–42 mg kg⁻¹ Cd with 0.12–8.5 mg kg⁻¹ in the natural soils, corresponding to high amounts of Cd (0.22–42 mg kg⁻¹) in outcropping sedimentary rocks in the area. Both lognormal distribution and enrichment factor (EF) plots were applied in an attempt to distinguish between geogenic and anthropogenic origins of Cd in the local soils. The lognormal distribution plots illustrated that geogenic sources dominated in soils with low and moderate Cd concentrations (<8.5 mg kg⁻¹), whereas anthropogenic sources (agricultural activities, coal mining) significantly elevated Cd contents in some arable soils (>8.5 mg kg⁻¹). The enrichment factor plots illustrated that the majority of the soil samples had EF values of <5, pointing to a geogenic origin of Cd in the soils, whereas some arable soils had EF values >5, pointing to an additional anthropogenic input of Cd to the soils. Sequential extraction results showed that Cd soluble in water and weak acid (water-soluble, exchangeable and carbonate fraction of the soil) accounts for an average of 31% of the total soil Cd, which indicates high potential for Cd mobility and bioavailability. The findings point to a potential health risk from Cd in areas with high geogenic background concentrations of this metal.     

Total concentration,speciation and mobility of potentially toxic elements in soils around a mining area in central Iran

The current study was designed to investigate the extent and severity of contamination as well as the fractionation of potentially toxic elements (As, Cd, Cr, Cu, Pb, Zn, Ni) in minesoils and agricultural soils around a Pb–Zn mine in central Iran. For this purpose, 20 agricultural soils and eight minesoils were geochemically characterized. Results showed that minesoils contained elevated concentrations of As (12.9–254 mg kg⁻¹), Cd (1.2–55.1 mg kg⁻¹), Pb (137–6239 mg kg⁻¹) and Zn (516–48,889 mg kg⁻¹). The agricultural soils were also polluted by As (5.5–57.1 mg kg⁻¹), Cd (0.2–8.5 mg kg⁻¹), Pb (22–3451 mg kg⁻¹) and Zn (94–9907 mg kg⁻¹). The highest recorded concentrations for these elements were in soils influenced directly by tailing ponds. Chromium, Cu and Ni content in agricultural soils (with average value of 74.1, 34.6 and 50.7 mg kg⁻¹, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4 mg kg⁻¹, respectively). Sequential extraction data indicated that there were some differences between the speciation of PTEs in soil samples. In the agricultural soils, Zn and Cd were mainly associated with carbonate bound fraction, As and Pb with reducible fraction, Cu with oxidisable fraction and Cr and Ni with residual phase. With respect to mobility factor values, Zn and Cd in the agricultural soils have been found to be the most mobile while As mobility is negligible. Also, the mobility factor of As, Cd and Pb in agricultural soils adjoining tailing ponds was high. In minesoil sample Cd was most abundant in the carbonate form, whereas other studied elements were mainly present in the reducible and residual fractions; therefore, despite the high total concentrations of As, Pb and Zn in the minesoils, the environmental risk of these elements was low. Based on the obtained data, a portion of Cu, Cr and Ni input was from agricultural activities.     

Stable isotopic signatures of the modern land snail Eremina desertorum from a low-latitude (hot) dry desert—A study from the Petrified Forest,New Cairo,Egypt

This study was conducted on recent desert samples—including (1) soils, (2) plants, (3) the shell, and (4) organic matter from modern specimens of the land snail Eremina desertorum—which were collected at several altitudes (316–360 m above sea level) from a site in the New Cairo Petrified Forest. The soils and shell_{E. desertorum} were analyzed for carbonate composition and isotopic composition (δ¹⁸O, δ¹³C). The plants and organic matter_{E. desertorum} were analyzed for organic carbon content and δ¹³C. The soil carbonate, consisting of calcite plus minor dolomite, has δ¹⁸O values from −3.19 to −1.78‰ and δ¹³C values −1.79 to −0.27‰; covariance between the two values accords with arid climatic conditions. The local plants include C3 and C4 types, with the latter being dominant. Each type has distinctive bulk organic carbon δ¹³C values: −26.51 to −25.36‰ for C3-type, and −13.74 to −12.43‰ for C4-type plants.The carbonate of the shell_{E. desertorum} is composed of aragonite plus minor calcite, with relatively homogenous isotopic compositions (δ¹⁸O_mean = −0.28 ± 0.22‰; δ¹³C_mean = −4.46 ± 0.58‰). Most of the δ¹⁸O values (based on a model for oxygen isotope fractionation in an aragonite-water system) are consistent with evaporated water signatures. The organic matter_{E. desertorum} varies only slightly in bulk organic carbon δ¹³C values (−21.78 ± 1.20‰) and these values suggest that the snail consumed more of C3-type than C4-type plants. The overall offset in δ¹³C values (−17.32‰) observed between shell_{E. desertorum} carbonate and organic matter_{E. desertorum} exceeds the value expected for vegetation input, and implies that 30% of carbon in the shell_{E. desertorum} carbonate comes from the consumption of limestone material.     

Autocompaction of shallow silty salt marsh clay

Empirically derived algorithms are suggested by means of which it is possible to evaluate relations between physical properties in silty salt marsh clay. A relation between loss on ignition, sand content and bulk dry density in the topmost 5 cm was found to explain 84% of the variation of the latter. The bulk dry density in the topmost ≈ 0.5 m was found to vary as a logarithmic function of depth below the surface controlled by two constants directly dependent on the bulk dry density in the topmost 5 cm. Integration of this function illustrates that mass depth (MSD_z) down core can be directly related to the bulk dry density of the surface layer. For sediments with a surface bulk dry density between 400 kg m^? 3 and 800 kg m^? 3 the porosity was found to vary (+/?10%) with MSD_z as another logarithmic function. The results allow for an evaluation of the use of marker horizons in the topmost layers. Right after such a layer has been spread on the surface, sedimentation measured in length per time (accretion), will be significantly larger than for subsequent periods. Using marker horizons, it is therefore not trivial to know the level of the marker, as deeper located markers will indicate successively smaller accretion rates with the same sediment input.     

Assessment of trace metal and rare earth elements contamination in rivers around abandoned and active mine areas. The case of Lubumbashi River and Tshamilemba Canal,Katanga, Democratic Republic of the Congo

Active and abandoned mine activities constitute the sources of deterioration of water and soil quality in many parts of the world, particularly in the African Copperbelt regions. The accumulation in soils and the release of toxic substances into the aquatic ecosystem can lead to water resources pollution and may place aquatic organisms and human health at risk. In this study, the impact of past mining activity (i.e., abandoned mine) on aquatic ecosystems has been studied using ICP-MS analysis for trace metals and Rare Earth Elements (REE) in sediment samples from Lubumbashi River (RL) and Tshamilemba Canal (CT), Katanga, Democratic Republic of the Congo (DRC). Soil samples from surrounding CT were collected to evaluate trace metal and REE concentrations and their spatial distribution. The extent of trace metal contamination compared to the background area was assessed by Enrichment Factor (EF) and Geoaccumulation Index (I_geo). Additionally, the trace metal concentrations probable effect levels (PELs) for their potential environmental impact was achieved by comparing the trace metal concentrations in the sediment/soil samples with the Sediment Quality Guidelines (SQGs). Spearman's Rank-order correlation was used to identify the source and origin of contaminants. The results highlighted high concentrations of trace metals in surface sediments of CT reaching the values of 40152, 15586, 610, 10322, 60704 and 15152 mg kg⁻¹ for Cu, Co, Zn, Pb, Fe and Mn, respectively. In the RL, the concentrations reached the values of 24093, 2046, 5463, 3340, 68290 and 769 mg kg⁻¹ for Cu, Co, Zn, Pb, Fe and Mn, respectively. The ΣREE varied from 66 to 218 and 142–331 mg kg⁻¹ for CT and RL, respectively. The soil samples are characterized by variable levels of trace metals. The EF analysis showed “extremely severe enrichment” for Cu and Co. However, no enrichment was observed for REE. Except for Mo, Th, U, Eu, Mo, Ho and Tm for which Igeo is classified as “moderately polluted and/or unpolluted”, all elements in different sites are classified in the class 6, “extremely polluted”. The trace metal concentrations in all sampling sites largely exceeded the SQGs and the PELs for the Protection of Aquatic Life recommendation. Cu and Co had positive correlation coefficient values (r = 0.741, P < 0.05, n = 14). This research presents useful tools for the evaluation of water contamination in abandoned and active mining areas.     

Mercury and methylmercury in riparian soil,sediments, mine-waste calcines,and moss from abandoned Hg mines in east Guizhou province,southwestern China

Concentrations of total Hg and methylmercury (MMHg) in riparian soil, mine-waste calcine, sediment, and moss samples collected from abandoned Hg mines in Wanshan district, Guizhou province, China, were measured to show regional dispersion of Hg-contamination. High total Hg and MMHg concentrations obtained in riparian soils from mined areas, ranged from 5.1 to 790 mg kg⁻¹ and 0.13 to 15 ng g⁻¹, respectively. However, total Hg and MMHg concentrations in the soils collected from control sites were significantly lower varying from 0.1 to 1.2 mg kg⁻¹ and 0.10 to 1.6 ng g⁻¹, respectively. Total Hg and MMHg concentrations in sediments varied from 90 to 930 mg kg⁻¹ and 3.0 to 20 ng g⁻¹, respectively. Total Hg concentrations in mine-waste calcines were highly elevated ranging from 5.7 to 4400 mg kg⁻¹, but MMHg concentrations were generally low ranging from 0.17 to 1.1 ng g⁻¹. Similar to the high Hg concentrations in soil and sediments, moss samples collected from rocks ranged from 1.0 to 95 mg kg⁻¹ in total Hg and from 0.21 to 20 ng g⁻¹ in MMHg. Elevated Hg concentrations in mosses suggest that atmospheric deposition might be an important pathway of Hg to the local terrestrial system. Moreover, the spatial distribution patterns of Hg contamination in the local environment suggest derivation from historic Hg mining sites in the Wanshan area.     

Late-glacial to Holocene transition in northern Spain deduced from land-snail shelly accumulations

Shells of the helicid Cepaea nemoralis were studied using taphonomic, isotopic and morphometric measurements to estimate late glacial–Holocene (~ 12.1–6.3 cal ka BP) environmental conditions in northern Spain. Higher taphonomic alteration among Holocene shells suggests lower sedimentation rates or higher shell-destruction rates than during glacial conditions. Shells preserved the aragonitic composition despite differing degree of skeleton damage. Shell δ¹³C values were ? 10.3 ± 1.1‰, ? 8.2 ± 2.3‰, and ? 7.3 ± 1.6‰ for modern, Holocene and late-glacial individuals, respectively. Higher δ¹³C values during the late-glacial and some Holocene periods imply higher water stress of C₃ plants and/or higher limestone contribution than today. Intrashell δ¹³C values were higher during juvenile stages suggesting higher limestone ingestion to promote shell growth. Shell δ¹⁸O values were ? 1.1 ± 0.7‰, ? 0.9 ± 0.8‰ and ? 0.1 ± 0.7‰ for modern, Holocene and late-glacial specimens, respectively. A snail flux-balance model suggests that during ~ 12.1 ? 10.9 cal ka BP conditions were drier and became wetter at ~ 8.4 ? 6.3 cal ka BP and today. Intrashell δ¹⁸O profiles reveal that glacial individuals experienced more extreme seasonality than interglacial shells, despite possible larger hibernation periods. Shell size correlated positively with δ¹⁸O values, suggesting that growth rates and ultimate adult size of C. nemoralis may respond to climate fluctuation in northern Spain.     

Partitioning and mobility of trace metals in the Blesbokspruit: Impact assessment of dewatering of mine waters in the East Rand,South Africa

A suite of trace metals was analyzed in water and sediment samples from the Blesbokspruit, a Ramsar certified riparian wetland, to assess the impact of mining on the sediment quality and the fate of trace metals in the environment. Limited mobility of trace metals was observed primarily because of their high partition coefficient in alkaline waters. Nickel was most mobile with a mean K_d of 10^3.28 L kg⁻¹ whereas Zr was least mobile with a mean K_d of 10^5.47 L kg⁻¹. The overall trace metal mobility sequence, derived for the Blesbokspruit, in increasing order, is: Zr < Cr < Pb < Ba < V < Cu < Zn < Sr < Mn < U < Mo < Co < Ni. Once removed from the solution, most trace metals were preferentially associated with the carbonate and Fe–Mn oxide fraction followed by the exchangeable fraction of the sediments. Organic C played a limited role in trace metal uptake. Only Cu was primarily associated with the organic fraction whereas Ti and Zr were mostly found in the residual fraction. Compared to their regional background, Au and Ag were most enriched, at times by a factor of 20–400, in the sediments. Significant enrichment of U, Hg, V, Cr, Co, Cu and Zn was also observed in the sediments.The calculated geoaccumulation indices suggest that the sediments are very lightly to lightly polluted with respect to most trace metals and highly polluted with respect to Au and Ag. The metal pollution index (MPI) for the 20 sampled sites varied between 2.9 and 45.7. The highest MPI values were found at sites that were close to tailings dams. Sediment eco-toxicity was quantified by calculating the sediment quality guideline index (SQG-I). The calculated SQG-I values (0.09–0.69) suggest that the sediments at the study area have low to moderate potential for eco-toxicity.     

Hydrosulfide/sulfide complexes of zinc to 250 °C and the thermodynamic properties of sphalerite

The solubility of synthetic ZnS_(cr) was measured at 25–250 °C and P = 150 bars as a function of pH in aqueous sulfide solutions (~ 0.015–0.15 m of total reduced sulfur). The solubility determinations were performed using a Ti flow-through hydrothermal reactor. The solubility of ZnS_(cr) was found to increase slowly with temperature over the whole pH range from 2 to ~ 10. The values of the Zn–S–HS complex stability constant, β, were determined for Zn(HS)₂⁰_(aq), Zn(HS)₃^?, Zn(HS)₄^2?, and ZnS(HS)^?. Based on the experimental values the Ryzhenko–Bryzgalin electrostatic model parameters for these stability constants were calculated, and the ZnS_(cr) solubility and the speciation of Zn in sulfide-containing hydrothermal solutions were evaluated. The most pronounced solubility increase, about 3 log units at m(S_total) = 0.1 for the temperatures from 25 to 250 °C, was found in acidic solutions (pH ~ 3 to 4) in the Zn(HS)₂⁰_(aq) predominance field. In weakly alkaline solutions, where Zn(HS)₃^? and Zn(HS)₄^2? are the dominant Zn–S–HS complexes, the ZnS_(cr) solubility increases by 1 log unit at the same conditions. It was found that ZnS(HS)^? and especially Zn(HS)₄^2? become less important in high temperature solutions. At 25 °C and m(S_total) = 0.1, these species dominate Zn speciation at pH > 7. At 100 °C and m(S_total) = 0.1, the maximum fraction of Zn(HS)₄^2? is only 20% of the total Zn concentration (i.e. at pH_t ~ 7.5), whereas at 350 °C and 3 <pH_t <10, the fraction of Zn(HS)₄^2? and ZnS(HS)^? is less than 0.05% and 2.5% respectively, of the total Zn concentration and Zn(HS)₂⁰ and Zn(HS)₃^? predominate. The measured equilibrium formation constants were combined with the literature data on the stability of Zn–Cl complexes in order to evaluate the concentration and speciation of Zn in chloride solutions. It was found that at acidic pH, and in more saline fluids having total chloride > 0.05 m, Zn–Cl complexes are responsible for hydrothermal Zn transport with no significant contribution of Zn–S–HS complexes. The hydrosulfide/sulfide complexes will play a more important role in lower salinity (< 0.05 m chloride) hydrothermal solutions which are characteristic of many epithermal ore depositing environments. The value of Δ_fG° (β-ZnS_(cr)) = ? 198.6 ± 0.2 kJ/mol at 25 °C was determined via solubility measurements of natural low-iron Santander (Spain) sphalerite.     

Metallogenesis at the Carris W–Mo–Sn deposit (Gerês,Portugal): Constraints from fluid inclusions,mineral geochemistry,Re–Os and He–Ar isotopes

The Carris orebody consists of two partially exploited W–Mo–Sn quartz veins formed during successive shear stages and multipulse fluid fillings. They cut the Variscan post-D3 Gerês I-type granite. The most important ore minerals are wolframite, scheelite, molybdenite and cassiterite. There are two generations of wolframite. The earlier generation of wolframite is rare and has the highest WO₄Mn content (91 mol%) and the most common wolframite contains 26–57 mol% WO₄Mn. Re–Os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 ± 1.2 Ma and 280.3 ± 1.2 Ma, respectively which are in very good agreement with the previous ID-TIMS U–Pb zircon age for the Carris granite (280 ± 5 Ma).³He/⁴He ratio of pyrite ranging between 0.73 and 2.71 Ra (1 Ra = 1.39 × 10^− 6) and high ³He/³⁶Ar (0.8–5 × 10^− 3) indicate a mixture of a crustal radiogenic helium fluid with a mantle derived-fluid.The fluid inclusion studies on quartz intergrown with wolframite and scheelite, beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit. The first was a low to medium salinity aqueous carbonic fluid (CO₂ between 4 and 14 mol%) with less than 1.95 mol% N₂, which was only found in quartz associated with wolframite. The other was a low salinity aqueous fluid found in all the four minerals. The homogenization temperatures indicate minimum entrapment temperatures of 226–310 °C (average 280 °C) for the H₂O–CO₂–N₂–NaCl fluid and average temperatures of 266 °C for scheelite and 242 °C, 190 °C and 160 °C for the last generations of beryl, fluorite and quartz, respectively. It was estimated that wolframite was deposited ~ 7 km depth, assuming a lithostatic pressure, probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event. Precipitation of scheelite and sulphides took place later, at the same depth, but under a hydrostatic or suprahydrostatic pressure regime, and probably caused by mixing between the magmatic–hydrothermal fluid and meteoric waters that deeply penetrated the basement during post-Variscan decompression.     

Geochemistry and U–Pb zircon geochronology of the Alvand plutonic complex in Sanandaj–Sirjan Zone (Iran): New evidence for Jurassic magmatism

This paper presents geochemical, Sr–Nd isotopic, and U–Pb zircon geochronological data on the Alvand plutonic complex in Sanandaj–Sirjan zone (SSZ), Western Iran. The gabbroic rocks show a trend of a calc-alkaline magma suite and are characterized by low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7023–0.7037) and positive εNd(t) values (2.9–3.3), which suggest derivation from a moderately depleted mantle source. Geochemical features of the granites illustrate a high-K calc-alkaline magma series, whereas the leucocratic granitoids form part of a low-K series. Granites have intermediate ⁸⁷Sr/⁸⁶Sr ratios (0.707–0.719) and negative εNd_(t) values (−1.0 to −3.4), while leucocratic granitoids have higher initial ⁸⁷Sr/⁸⁶Sr ratio (0.713–0.714) and more negative εNd_(t) values (−3.5 to −4.5). Potential basement source lithologies for the granites are Proterozoic granites and orthogneisses, and those for the leucocratic granites are plagioclase-rich sources such as meta-arkoses or tonalites. The U–Pb dating results demonstrate that all granitoids were exclusively emplaced during the Jurassic instead of being Cretaceous or younger in age as suggested previously. The pluton was assembled incrementally over c. 10 Ma. Gabbros formed at 166.5 ± 1.8 Ma, granites between 163.9 ± 0.9 Ma and 161.7 ± 0.6 Ma, and leucocratic granitoids between 154.4 ± 1.3 and 153.3 ± 2.7 Ma. Granites and leucocratic granitoids show some A-type affinity. It is concluded that the Alvand plutonic complex was generated in a continental-arc-related extensional regime during subduction of Neo-Tethyan oceanic crust beneath the SSZ. The U/Pb zircon age data, recently corroborated by similar results in the central and southern SSZ, indicate that Jurassic granitoids are more areally extensive in this belt than previously thought.     

Solubility of Fe2(OH)3Cl (pure-iron end-member of hibbingite) in NaCl and Na2SO4 brines

Pure-iron end-member hibbingite, Fe₂(OH)₃Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe₂(OH)₃Cl(s), the pure-iron end-member of hibbingite (Fe^II, Mg)₂(OH)₃Cl(s), and Fe(OH)₂(s) in 0.04 m to 6 m NaCl brines has been determined. For the reactionFe₂(OH)₃Cl(s) + 3H⁺ ? 3 H₂O + 2 Fe²⁺ + Cl^?,the solubility constant of Fe₂(OH)₃Cl(s) at infinite dilution and 25 °C has been found to be log₁₀ K = 17.12 ± 0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionFe(OH)₂(s) + 2H⁺ ? 2 H₂O + Fe²⁺,the solubility constant of Fe(OH)₂ at infinite dilution and 25 °C has been found to be log₁₀ K = 12.95 ± 0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe₂(OH)₃Cl(s) and Fe(OH)₂(s), the Na⁺–Fe²⁺ pair Pitzer interaction parameter θ_{Na⁺/Fe²⁺} has been found to be 0.08 ± 0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)₂(s) to Fe₂(OH)₃Cl(s). Additionally, when Fe₂(OH)₃Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations.     

Zircon U-Pb geochronology,Lu-Hf isotope systematics,and geochemistry of bimodal volcanic rocks and associated granitoids from Kotri Belt,Central India: Implications for Neoarchean–Paleoproterozoic crustal growth

The Bastar Craton of Central India has a thick sequence of volcano–sedimentary rocks preserved in Kotri–Dongargarh belt that developed on a tonalite-trondhjemite-granodiorite (TTG) basement followed upwards by the Amgaon, Bengpal, Bailadila, and Nandgaon Groups of rocks. Here, we report the U-Pb geochronology and Lu-Hf isotope systematics and whole rock geochemistry of volcanic rocks and associated granitoids belonging to the Pitepani basalts, Bijli rhyolites, and Dongargarh granite in the Nandgaon Group of the Kotri belt. The volcanic rocks of the Nandgaon Group are bimodal in nature in which the basalts exhibit intergranular, porphyritic to spherulitic texture composed of pyroxenes, plagioclase, tremolite, actinolite, and chlorite ± Fe oxides. The rhyolites display porphyritic texture consisting of K-feldspar, quartz, and plagioclase as phenocrysts. The associated porphyritic granitoids have K-feldspar, microcline, plagioclase, and biotite phenocrysts within a groundmass of similar composition. The bimodal suite displays LILE, LREE enrichment, and HFSE depletion with significant negative Nb-Ta anomalies combined with slightly fractionated REE patterns in the basalts and highly fractionated patterns and prominent negative Eu anomalies in the rhyolites endorsing their generation in an island-arc/back-arc tectonic setting. The geochemical features of the associated granitoids indicate that these are potassic and classify as within-plate A-type granites. Zircons from the basalts show clear oscillatory zoning in their CL images. They cluster as a coherent group with ²⁰⁷Pb/²⁰⁶Pb spot ages ranging from 2446 to 2522 Ma and weighted mean age of 2471 ± 7 Ma. Zircons from the rhyolite samples are subhedral to euhedral and show simple oscillatory zoning with some heterogeneous fractured domains. The data from two samples define upper intercept ages of 2479 ± 13 Ma and 2463 ± 14 Ma. Zircon grains in the granite show clear oscillatory zoning and their U-Pb data define an upper intercept age of 2506 ± 50 Ma. The Lu-Hf isotopic data on the zircons from the basalts show initial ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.280925 to 0.281018. Their ε_Hf(t) values are in the range of − 10.0 to − 6.7. The Hf-depleted model ages (T_DM) are between 3038 Ma and 3171 Ma, and Hf crustal model ages (T_DM^C) vary from 3387–3589 Ma. The zircons from the rhyolites show initial ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.280919 to 0.281020 and from 0.281000 to 0.281103, respectively, with ε_Hf(t) values varying from − 10 to − 6.4 and from − 7.5 to − 3.9. Among these, one sample shows T_DM between 3038 Ma and 3182 Ma, and T_DM^C varies from 3377 to 3596 Ma, whereas the other sample shows ages of 2925 Ma and 3072 Ma with T_DM^C varying from 3208 to 3432 Ma. The initial ¹⁷⁶Hf/¹⁷⁷Hf ratios of the granites range from 0.280937 to 0.281062 with ε_Hf(t) values of − 8.8 to − 4.3. The T_DM shows a range of 2979 Ma and 3170 Ma, and T_DM^C varies from 3269 to 3541 Ma. The predominant negative ε_Hf(t) values of zircons from these rocks suggest that the source material was evolved from the Paleoarchean crust. The geological, geochemical, and geochronological evidence suggests coeval tectonic and magmatic episodes of volcanic and plutonic activity in an island-arc setting where the arc migrated toward the continental margin and played a significant role in the Neoarchean–Paleoproterozoic crustal growth of the Kotri belt of Central India.     

Environmental assessment of abandoned mine tailings in Adak,Västerbotten district (northern Sweden)

Sulfide-rich mine tailings in Adak that are exposed to weathering cause acid mine drainage characterized by low pH (2–4) and high SO₄ (up to 800 mg L⁻¹). Surface water, sediment and soil samples collected in this study contain higher concentrations of As, Cu, Fe and Zn, compared to the target and/or intervention limits set by international regulatory agencies. In particular, high As concentrations in water (up to 2900 μg L⁻¹) and sediment (up to 900 mg kg⁻¹) are of concern. There is large variability in trace element concentrations, implying that both physical (grain size) and chemical factors (pH, secondary phases as sulfides, Al-oxides or clay minerals) play an important role in their distribution. The low pH keeps the trace elements dissolved, and they are transported farther downstream. Trace element partition coefficients are low (log K_d = 0.3–4.3), and saturation indices calculated with PHREEQC are <0 for common oxide and sulfidic minerals. The sediment and soil samples indicate an enhanced pollution index (up to 17), and high enrichment factors for trace elements (As up to 38,300; Zn up to 800). Finally, leaves collected from different plant types indicate bioaccumulation of several elements (As, Al, Cu, Fe and Zn). However, some of the plants growing in this area (e.g., Salix, Equisétum) are generally resistant to metal toxicity, and hence, liming and phytoremediation could be considered as potential on-site remediation methods.     

Elemental sulfur in drain sediments associated with acid sulfate soils

This paper reports the abundance of elemental S in drain sediments associated with acid sulfate soils. The sediments exhibited near-neutral pH (5.97–7.27), high concentrations of pore-water Fe²⁺ (1.37–15.9 mM) and abundant oxalate-extractable Fe (up to 4300 μmol g⁻¹). Maximum acid-volatile sulfide (AVS) concentrations in each sediment profile were high (118–1019 μmol g⁻¹), with AVS often exceeding pyrite-S. Elemental S occurred at concentrations of 13–396 μmol g⁻¹, with the higher concentrations exceeding previous concentrations reported for other sedimentary systems. Up to 62% of reduced inorganic S near the sediment/water interface was present as elemental S, due to reaction between AVS and oxidants such as O₂ and Fe(III). Significant correlation (r = 0.74; P < 0.05) between elemental S and oxalate-extractable Fe(III) is indicative of elemental S formation by in situ oxidation of AVS. The results indicate that AVS oxidation in near-surface sediments is dynamic in acidified coastal floodplain drains, causing elemental S to be a quantitatively important intermediate S fraction. Transformations of elemental S may therefore strongly influence water quality in ASS landscapes.     

Intermediate sulfidation epithermal gold-base metal deposits in Tertiary subaerial volcanic rocks,Sahinli/Tespih Dere (Lapseki/Western Turkey)

Gold in the Sahinli and Tespih Dere intermediate sulfidation gold-base metal deposits in Western Turkey occurs in relatively deep epithermal quartz veins along with base metal minerals which have epithermal textures, including plumose quartz, vug infills, comb and cockade textures and matrix-supported milled breccias. The total sulfide content of the veins in the area is variable ranging from < 1% to 60% and is dominated by pyrite, galena, sphalerite and chalcopyrite. Sphalerite is Fe-poor (0.6 to 1.4 mol% FeS). Minor amounts of Ag-rich tetrahedrite are present. Primary hydrothermal alteration minerals include illite/muscovite, mixed-layer illite/smectite (11.6 Å) and clinochlore towards the east and, alunite, dickite/nacrite and pyrophyllite towards the west at Sahinli; major illite/muscovite and dickite occur at Tespih Dere and Sarioluk, respectively.Fluid inclusions in main-stage quartz at Sahinli are only liquid-rich, with homogenization temperatures ranging from 220 to 322 °C and the majority of T_h values between 250 and 300 °C. Salinity ranges from 4.3 to 6.9 wt.% NaCl equiv. First ice-melting temperatures (T_mf) between ?24.5 and ?19.0 °C indicate that the fluids were dominated by NaCl – H₂O during mineralization. The relatively higher average T_h at the Tespih Dere deposit (295 °C) is attributed to a relatively deeper level of exposure.Calculated δ¹⁸O values indicate that ore-forming hydrothermal fluids in the study area had δ¹⁸O_H2O ranging from + 1.1 to + 9.7‰ (average = 3.8‰), strongly ¹⁸O-enriched compared with present-day hydrothermal meteoric water in the area (δ¹⁸O = ?8.5‰). δD values of fluid inclusions in quartz range from ?58 to ?93‰ and δD values of clay minerals and alunite from ?40 to ?119‰. δD values from intermediate argillic alteration (average = ?68‰) in the study area are very similar to δD values of the present-day local geothermal system (average δD = ?54‰) whereas δD values from advanced-argillic alteration (average δD = ?33‰) are very different from the present-day local geothermal system.The δ³⁴S values in samples from the Sahinli and Tespih Dere deposits average ?2.9‰ for pyrite; ?3.3‰ for chalcopyrite; ?5.4‰ for sphalerite and ?7.6‰ for galena. These data are consistent with derivation of the sulfur from either igneous rocks or possibly from local wallrock.