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Tunnel drilling provides a unique opportunity to sample and study deep groundwaters that are otherwise difficult to access. Understanding deep groundwater flow is of primary importance in assessing the possible impacts of tunnelling on hydrogeological systems. During this study, water was sampled for noble-gas analysis from tunnel inflows in the AlpTransit Ceneri Base Tunnel (Canton Ticino, southern Switzerland), which passes through an area mainly characterized by metamorphic rocks (gneiss). Furthermore, water was sampled from springs located in the same geological environment. Based on the measurement of noble-gas concentrations and isotope ratios, tritium concentrations, the stable isotope composition of hydrogen ( δ 2 H) and oxygen ( δ 18 O), and the concentrations of major ions in the water, a conceptual hydrogeological model was established for this case study that allowed the most probable origin of the groundwaters sampled at different locations to be determined. The measured abundances of 3 He, 4 He, and 20 Ne allow the geochemical characterization of old groundwaters strongly enriched in terrigenic helium of crustal origin and the identification of mixing with water that circulates preferentially through cataclastic structures. Noble-gas concentrations and isotope ratios as well as tritium are useful proxies for the characterization of faults that may be critical for tunnel drilling because of their active hydrogeological role and their influence on the mechanics of the rocks.

The application of organic amendments on soils poor in organic matter (OM) can improve long-term soil fertility, but may also enhance the mineralization of native soil organic matter. Three organic amendments, compost, sewage sludge and horse manure, used by urban market gardeners in Dakar, Senegal were analyzed for their OM maturity. Their fate was evaluated in a 45-d agronomic trial in a sandy Arenosol with lettuce. In each case, water-extractable organic matter (WEOM) and humic-like substances (HLS) were isolated from raw amendments and amended soils, and characterized using ultraviolet-visible (UV/Vis) spectroscopy. Results highlighted the general more aromatic character of HLS and WEOM fractions extracted from compost compared to the other two amendments. When applied to soils, however, these differences were not clearly observed. The aromaticity and humification degree of the labile fraction (WEOM) increased with depth in the first 30 cm for all amendments. This indicated the high lixiviation rates that fresh OM underwent in the studied sandy soil. Finally, a statistical analysis of the results was able to discriminate between surface and deeper horizons and between amended- and non-amended soil samples. Spectroscopic indices showed indeed strong increase/decrease with depth linked with the mineralization/humification processes that the fresh OM from amendments underwent during the 45 d of the agronomic trial. This study highlights the potential of spectroscopic techniques to study agricultural amendment organic matter fractions and their fate in soils.

In an active tailings impoundment, we studied the evolution of freshly deposited tailings from alkaline, unoxidized to acidic, oxidized tailings tracing changes in pore water quality, mineralogy, and element pathways. The tailings originate from the giant porphyry copper deposit Chuquicamata (Chile), and were deposited in different basins with varying times of surface exposure (0 to five years) to the hyper-arid climate in the Atacama desert. Fresh alkaline tailings (pH 9.1) had high concentrations of dissolved Na (1773 mg/L), Ca (556 mg/L), SO 4 (2496 mg/L) and Cl (1678 mg/L) due to dissolution of primary gypsum, and high dissolved element concentrations in the flotation process water due to recycling of water from the tailings impoundment. High As and Mo concentrations resulted from desorption processes during the flotation, with minor contributions from As-rich river water and recycled tailings water. After draining of free water in freshly deposited tailings, evaporation-driven capillary rise was the dominant water transport in the vadose zone. In younger tailings (up to three years), the pH decreased due to sulfide oxidation to circumneutral values (6.4–8.6). The capillary fringe reached 1 m depth, where ongoing evaporation enriched Na (up to 5483 mg/L), K (742 mg/L), and Cl (6892 mg/L). In the vadose zone above 1 m, the high daily temperature amplitude resulted in condensation of pore water in the uppermost 80 cm of sedimented tailings. Subsequent capillary rise depleted uppermost tailings in soluble phases and increase superficial salt precipitation (halite, gypsum and Na–K–Ca–Mg sulfates). After four years, a 13 cm thick oxidation zone with acidic pH (4.7) evolved. After five years, a well-defined oxidation zone (28 cm thickness) with low pH (3.8) and high mobility of heavy metals was found (e.g., 247 mg/L Fe, 177 mg/L Cu, 61.8 mg/L Zn). This mobility allowed transport and enrichment in the efflorescent salt crust (e.g., as Cu sulfates devilline, krohnkite and Cu-chlorides eriochalcite and atacamite), with SO 4 dominantly from sulfide oxidation (− 1.0 to 5.9‰ δ 34 S, − 1.0 to 4.4‰ δ 18 O sulfates ). Stable isotope data suggest that capillary rise from the water table reached the surface, most probably due to the reduction of pore size by precipitating secondary minerals, decreased water loss by clogging of pores and heat isolation by the efflorescent salt crust. The cycles of surface exposure and new tailings deposition in the last decades resulted in buried former oxidation zones, which showed lesser K and Cu concentrations in Fe oxides than recent oxidized tailings, most probably due to the transformation of jarosite and schwertmannite to Fe(3 +) oxyhydroxides and dissolution of Cu sulfates. Pore water in the saturated deep tailings was highly dynamic and displayed influences of local groundwater, and mixing with acid rock drainage (ARD) and fresh tailings water, both infiltrating from the surface. At the tailings dam, seepage water varied in time between neutralized ARD and fresh tailings water with groundwater influence, due to the periodic shift of the deposition zone and the resulting shallow groundwater changes. Adjacent efflorescent salts include typical minerals found in the secondary porphyry copper deposits in northern Chile (e.g., atacamite), displaying the similarity between geochemical processes in weathered tailings impoundments and secondary enrichment zones of ore bodies, like Exotica from the Chuquicamata mine.

Between the cities of Domodossola and Locarno, the complex “Centovalli Line” tectonic zone of the Central Alps outlines deformation phases over a long period of time (probably starting ~ 30 Ma ago) and under variable P–T conditions. The last deformation phases developed gouge-bearing faults with a general E–W trend that crosscuts the roots of the Alpine Canavese zone and the Finero ultramafic body. Kinematic indicators show that the general motion was mainly dextral associated with back thrusting towards the S. The On the basis of the K–Ar ages and with a thermal gradient of 25–30 °C/km, the studied fault zones were located at a depth of 4–7 km. If they were active until now as observed in field, the exhumation was approximately 2.5–3.0 km for the last 12 Ma with a mean velocity of 0.4 mm/y. Comparison with available models on the recent Alpine evolution shows that the tectonic activity in the area relates to a continuum of the back-thrusting movements of the Canavese Line, and/or to several late-extensional phases of the Rhone–Simplon Line. The Centovalli–Val Vigezzo zone therefore represents a major tectonic zone of the Central–Western Alps resulting from different interacting tectonic events.

Artificial radionuclides ( 137 Cs, 90 Sr, Pu, and 241 Am) are present in soils because of Nuclear Weapon Tests and accidents in nuclear facilities. Their distribution in soil depth varies according to soil characteristics, their own chemical properties, and their deposition history. For this project, we studied the atmospheric deposition of 137 Cs, 90 Sr, Pu, 241 Am, 210 Pb, and stable Pb. We compared the distribution of these elements in soil profiles from different soil types from an alpine Valley (Val Piora, Switzerland) with the distribution of selected major and trace elements in the same soils. Our goals were to explain the distribution of the radioisotopes as a function of soil parameters and to identify stable elements with analogous behaviors. We found that Pu and 241 Am are relatively immobile and accumulate in the topsoil. In all soils, 90 Sr is more mobile and shows some accumulations at depth into Fe–Al rich horizons. This behavior is also observed for Cu and Zn, indicating that these elements may be used as chemical analogues for the migration of 90 Sr into the soil.

Rare earth elements (REE) and stable isotope compositions (?13C and ?18O) of shark teeth and phosphatic coprolites were analyzed from the Lower Maastrichtian layers of the El Haria Formation and two sequences of the Paleocene–Eocene (P/E) Chouabine Formation in the Gafsa Basin (south western of Tunisia) in order to trace the sedimentological, climatic and oceanographic conditions. The REE chemistry and their distribution in the two archives are the same for each of the studied layers indicating that the coprolites and shark teeth experienced the same early diagenetic environments. However major differences occur between the Maastrichtian and the P/E reflecting changes in the depositional conditions. The Early Maastrichtian burial environment tended to be more anoxic with REE derived from reduced FeO. While in the P/E the REE patterns mimic the modern oxic–suboxic seawater, the REE source from remineralisation of organic coating could have more significance. The oxygen isotope compositions of the structural phosphates (?18OPO4) indicate a stable and warm climate during both studied time intervals. A small offset ( 0.4‰) in the ?18O value between the coprolites and shark teeth show minor thermal gradient between bottom and surface water. The pronounced negative shift of 3–4‰ in ?13C values recorded in the upper part of the Chouabine Formation was ascribed to the Paleocene–Eocene boundary. At the same time the lack of negative change in the ?18O is explained by the semi-closed situation of the Gafsa Basin, which situation also played an important role in the evolution of the organic matters in the sediment resulting in the exceptional low ?13C values.

Prevention of acid mine drainage (AMD) in sulfide-containing tailings requires the identification of the geochemical processes and element pathways in the early stages of tailing deposition. However, analyses of recently deposited tailings in active tailings impoundments are scarce because mineralogical changes occur near the detection limits of many assays. This study shows that a detailed geochemical study which includes stable isotopes of water (δ2H, δ18O), dissolved sulfates (δ34S, δ18O) and hydrochemical parameter (pH, Eh, DOC, major and trace elements) from tailings samples taken at different depths in rainy and dry seasons allows the understanding of weathering (oxidation, dissolution, sorption, and desorption), water and element pathways, and mixing processes in active tailings impoundments. Fresh alkaline tailings (pH 9.2–10.2) from the Cu–Mo porphyry deposit in El Teniente, Chile had low carbonate (0.8–1.1 wt.% CaCO3 equivalent) and sulfide concentrations (0.8–1.3 wt.%, mainly as pyrite). In the alkaline tailings water, Mo and Cu (up to 3.9 mg/L Mo and 0.016 mg/L Cu) were mobile as MoO42− and Cu(OH)20. During the flotation, tailings water reached equilibrium with gypsum (up to 738 mg/L Ca and 1765 mg/L SO4). The δ34S vs. δ18O covariations of dissolved sulfate (2.3 to 4.5‰ δ34S and 4.1 to 6.0 ‰ δ18O) revealed the sulfate sources: the dissolution of primary sulfates (12.0 to 13.2‰ δ34S, 7.4 to 10.9‰ δ18O) and oxidation of primary sulfides (− 6.7 to 1.7‰ δ34S). Sedimented tailings in the tailings impoundment can be divided into three layers with different water sources, element pathways, and geochemical processes. The deeper sediments (> 1 m depth) were infiltrated by catchment water, which partly replaced the original tailings water, especially during the winter season. This may have resulted in the change from alkaline to near-neutral pH and towards lower concentrations of most dissolved elements. The neutral pH and high DOC (up to 99.4 mg/L C) of the catchment water mobilized Cu (up to 0.25 mg/L) due to formation of organic Cu complexes; and Zn (up to 130 mg/L) due to dissolution of Zn oxides and desorption). At 1 m depth, tailings pore water obtained during the winter season was chemically and isotopically similar to fresh tailings water (pH 9.8–10.6, 26.7–35.5 mg/L Cl, 2.3–6.0 mg/L Mo). During the summer, a vadose zone evolved locally and temporarily up to 1.2 m depth, resulting in a higher concentration of dissolved solids in the pore water due to evaporation. During periodical new deposition of fresh tailings, the geochemistry of the surface layer was geochemically similar to fresh tailings. In periods without deposition, sulfide oxidation was suggested by decreasing pH (7.7–9.5), enrichment of MoO42− and SO42−, and changes in the isotopic composition of dissolved sulfates. Further enrichment for Na, K, Cl, SO4, Mg, Cu, and Mo (up to 23.8 mg/L Mo) resulted from capillary transport towards the surface followed by evaporation and the precipitation of highly soluble efflorescent salts (e.g., mirabilite, syngenite) at the tailing surface during summer.

The mine wastes and their environmental impact described in this paper are related to a skarn-type ore deposit, located in the Variscan crystalline basement of the Aiguilles Rouges Massive, Western Switzerland. The main minerals of the deposit are arsenopyrite, lollingite, hematite, scheelite, magnetite, pyroxene, amphibole and dolomite. The ore has been mined for arsenic and gold between 1900 and 1928, producing about 700 t As and 55 kg Au, and leaving mine dumps of several hundred m 3 , situated on a relatively steep hill above the small Lake Ottans, at an altitude of 2200 m. This work was undertaken to determine the extent of the As-contamination, its environmental impact and to identify actual geochemical processes. Dump materials contain As and sulfur in the 10% range, contaminated soils contain between 50 mg/kg and several % As. Mine and dump percolating waters are weakly mineralized of the Ca–Mg–HCO 3 –SO 4 -type and have conductivities between 20 and 170 μS/cm, pH values around 8, and As contents varying from 60 to 4000 μg/l. Waters below the dump zone are of the same type and have slightly lower As-contents: in Lake Ottans, 200 m below the mine area, As is still between 100 and 160 μg/l. Our results indicate that: (1) the contaminated area is limited to about 500 m in radius (1.2 km 2 ) and that its environmental impact is rather limited, except for grazing cattle, (2) below the mine, the As decreases more rapidly in the soils than in the waters, (3) the distribution of the As seems to be determined by predominant alkaline pH in the surface and ground waters and by the distribution of the secondary solid phases (Fe-oxy-hydroxides, clays, carbonate minerals, especially in the lower part). Transport by gravity creep or as suspended particles in water seems to be of secondary importance.

In recent years, elevated arsenic concentrations have been found in waters and soils of many countries, often resulting in a health threat for the local population. Switzerland is not an exception and this paper deals with the release and subsequent fate of arsenic in a 200-km2 mountainous watershed, characterized by crystalline silicate rocks (gneisses, schists, amphibolites) that contain abundant As-bearing sulfide ore deposits, some of which have been mined for iron and gold in the past. Using analytical methods common for mineralogical, ground water and soil studies (XRD, XRF, XAS-XANES and -EXAFS, electron microprobe, extraction, ICP, AAS with hydride generator, ion chromatography), seven different field situations and related dispersion processes of natural arsenic have been studied: (1) release by rock weathering; (2) transport and deposition by water and ice; (3) release of As to the ground and surface water due to increasing pH; (4) accumulation in humic soil horizons; (5) remobilization by reduction in water-saturated soils and stagnant ground waters; (6) remobilization by using P-rich fertilizers or dung and (7) oxidation, precipitation and dilution in surface waters. Comparison of the results with experimental adsorption studies and speciation diagrams from the literature allows us to reconstruct and identify the typical behavior of arsenic in a natural environment under temperate climatic conditions. The main parameters identified are: (a) once liberated from the primary minerals, sorption processes on Fe-oxy-hydroxides dominate over Al-phases, such as Al-hydroxides or clay minerals and limit the As concentrations in the spring and well waters between 20 and 300 μg/l. (b) Precipitation as secondary minerals is limited to the weathering domain, where the As concentrations are still high and not yet too diluted by rain and soils waters. (c) Although neutral and alkaline pH conditions clearly increase the mobility of As, the main factor to mobilize As is a low redox potential (Eh close or below 0 mV), which favors the dissolution of the Fe-oxy-hydroxides on which the As is sorbed. (d) X-ray absorption spectroscopy (XAS) of As in water-logged humic forest soils indicates that the reduction to As III only occurs at the solid–water interface and that the solid contains As as As V. (e) A and Bh horizons of humic cambisols can effectively capture As when As-rich waters flow through them. Complex spatial and temporal variation of the various parameters in a watershed results in repeated mobilization and immobilization of As, which continuously transports As from the upper to the lower part of a watershed and ultimately to the ocean.

b ´ Abstract Anthropogenic emissions of metals from sources such as smelters are an international problem, but there is limited published information on emissions from Australian smelters. The objective of this study was to investigate the regional distribution of heavy metals in soils in the vicinity of the industrial complex of Port Kembla, NSW, Australia, which comprises a copper smelter, steelworks and associated industries. Soil samples (ns25) were collected at the depths of 0-5 and 5-20 cm, air dried and sieved to -2 mm. Aqua regia extractable amounts of As, Cr, Cu, Pb and Zn were analysed by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Outliers were identified from background levels by statistical methods. Mean background levels at a depth of 0-5 cm were estimated at 3.2 mgykg As, 12 mgykg Cr, 49 mgykg Cu, 20 mgykg Pb and 42 mgykg Zn. Outliers for elevated As and Cu values were mainly present within 4 km from the Port Kembla industrial complex, but high Pb at two sites and high Zn concentrations were found at six sites up to 23 km from Port Kembla. Chromium concentrations were not anomalous close to the industrial complex. There was no significant difference of metal concentrations at depths of 0-5 and 5-20 cm, except for Pb and Zn. Copper and As concentrations in the soils are probably related to the concentrations in the parent rock. From this investigation, the extent of the contamination emanating from the Port Kembla industrial complex is limited to 1-13 km, but most likely -4 km, depending on the element; the contamination at the greater distance may not originate from the industrial complex. 2003 Elsevier B.V. All rights reserved.

Regions under tropical rainforest cover, such as central Africa and Brazil are characterised by degradation and dismantling of old ferricrete structures. In southern Cameroon, these processes are relayed by present-day ferruginous accumulation soil facies, situated on the middle and the lower part of hill slopes. These facies become progressively harder towards the surface, containing from bottom to top, mainly kaolinite, kaolinite–goethite and Al-rich goethite–hematite, and are discontinuous to the relictic hematite-dominated ferricrete that exist in the upper part of the hill slope. These features were investigated in terms of geochemical differentiation of trace elements. It appears that, in contrast to the old ferricrete facies, the current ferruginous accumulations are enriched in transitional trace elements (V, Cr, Co, Y, Sc) and Pb, while alkali-earth elements are less differentiated. This recent chemical accumulation is controlled both by intense weathering of the granodiorite bedrock and by mobilisation of elements previously accumulated in the old ferricrete. The observed processes are clearly linked to the present-day humid climate with rising groundwater tables. They slowly replace the old ferricretes formed during Cretaceous time under more seasonal climatic conditions, representing an instructive case of continuos global change.

Present downslope iron accumulations were investigated in the rainforest zone in southern Cameroon. Six clay and Fe-hydroxide dominated patterns have been identified and occur on the lower part of hill slopes. They can be subdivided in three different sequences, related to gentle, moderate or steep slopes. They are discontinuous with respect to the dismantling zone of the old ferricrete cap formed at Cretaceous period. They show a gradual development from a soft Fe-crust (carapace) to a vesicular facies that will, with time, cover the whole landscape again. To cite this article: E. Temgoua et al., C. R. Geoscience 334 (2002) 537–543.

The top soil of a 14.5 km 2 region at la Chaux-de-Fonds in the Swiss Jura is exceptionally rich in cadmium. It contains an average of 1.3 mg per kg of soil. The spatial distribution of the metal has no simple pattern that could be explained by atmospheric deposition or agricultural practices. Thin soil contained most of its Cd at the surface; in thicker soil Cd is mainly concentrated between 60 and 80 cm depth. No specific minerals or soil fractions could account for these accumulation, and the vertical distribution of Cd is best explained by leaching from the topsoil and further adsorption within layers of nearly neutral pH. The local Jurassic sedimentary rocks contained too little Cd to account for the Cd concentrations in the soil. Alpine gravels from glacial till were too sparse in soils to explain such a spreading of Cd. Moreover this origin is contradictory with the fact that Cd is concentrated in the sand fraction of soils. The respective distributions of Fe and Cd in soils, and soil fractions, suggested that the spreading of iron nodules accumulated during the siderolithic period (Eocene) was not the main source of Cd. Atmospheric deposition, and spreading of fertiliser or waste from septic tanks seem the only plausible explanation for the Cd concentrations, but at present few factors allow us to differentiate between them.