Distribution of trace elements in soils surrounding the El Teniente porphyry copper deposit,Chile: the influence of smelter emissions and a tailings deposit

In the area surrounding the El Teniente giant porphyry copper deposit, eight soil sites were sampled at three depth levels in the summer 2004. The sites were selected for their theoretical potential of being influenced by past SO₂ emissions from the smelter and/or seepage from a now idle tailings impoundment. The soil mineralogy, grain size distribution, total organic matter contents, major element composition, cation exchange capacity, and Cu, Mo, Pb, Zn, As and SO₄ ²⁻ concentrations were determined for all samples after nitric acid extraction and separate leaches by ammonium acetate (pH 7) and sodium acetate (pH 5). For water rinses, only Cu could be determined with the analytical set-up used. Cu and SO₄ ²⁻ enrichment in topsoils was found at six sites either downwind from the smelter or within the combined influence of the smelter and the tailings impoundment. Both elements were released partially by ammonium and sodium acetate extractions. Due to the scarce background trace element concentrations of soil and rock outside the immediate mine area, assessment of trace element mobility for Mo, Zn, Pb and As was difficult. Arsenic was found to be concentrated in soil horizons with high smectite and/or organic matter contents. Mo appears to be linked to the presence of windblown tailings sediment in the soils. Mobilization of Mo, Zn, and As for the acetate extractions was minimal or below the detection limits for the AAS technique used. The presence of windblown tailings is considered to be an additional impact on the soils in the foothills of the El Teniente compound, together with the potential of acidity surges and Cu mobilization in topsoils after rainfalls. Two sites located at the western limit of the former SO₂ saturated zone with strongly zeolitized soils and underlying rock did not show any Cu or SO₄ ²⁻ enrichment in the topsoils, and remaining total trace element concentrations were below the known regional background levels.     

The Use of Rock Mass Classification Systems to Estimate the Modulus and Strength of Jointed Rock

Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the measured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confidence in the use of classification schemes to estimate the deformation and stability in jointed rock.     

Morphological and geochemical analysis of the Laguna Blanca/Zapaleri obsidian source in the Atacama Puna

This paper describes a large obsidian deposit located along the southern banks of Laguna Blanca, on the eastern slope of the Jarellón volcanic caldera near the Chilean–Bolivian border. The obsidian at this site occurs in flows or sheets of deflated black or reddish to brown pebbles, redeposited on the shores of a lake. Blocks of obsidian are only found around the caldera rim. Here we analyze the shape of the obsidian pebbles and their geochemistry, comparing them with previously published data. The results indicate that the geochemical composition of the samples strongly matches previous analyses of obsidian from cultural contexts. This obsidian source was one of the most important sites of obsidian procurement since at least the Formative Period in the Atacama Puna region. © 2010 Wiley Periodicals, Inc.     

Fluid pathways and high‐P metasomatism in a subducted continental slice (Mt. Emilius klippe,W. Alps)

The Mt. Emilius klippe (Western Alps, Italy) corresponds to a segment of the stretched Adriatic continental margin metamorphosed at granulite facies during Permian. This slice was subducted during the early Cenozoic Alpine subduction with the underlying eclogite facies remnants of the Tethyan seafloor (Zermatt‐Saas zone). Near the base of the Mt. Emilius massif, there is a shear zone with eclogite facies hydrofracture systems associated with deformation‐induced re‐equilibration of granulites during high‐P metamorphism. In the basal part of the massif, a pluri‐hectometre domain of sheared mafic boudins is hosted in the granulitic paragneiss. In these mafic boudins, there are garnetites, garnet veins and clinopyroxenites, as well as clinozoisite and calcite veins. These features record multiple events of fracture opening, brecciation, boudinage and parallelization of structures coevally with fluid–rock interaction, metasomatism and volume change. This integrated petrological, micro‐textural and geochemical investigation illustrates the multiplicity and the chemical variability of fluid sources during prograde to peak metamorphic evolution in the lawsonite–eclogite‐facies field (at ~2.15–2.4 GPa, 500–550 °C) during subduction of the Mt. Emilius slice. The calcite veins crosscutting the garnetites have relatively low δ¹⁸O_VSMOW values (～+6.5‰) near those for marble layers (and nearby calcsilicates) embedded within the metasomatized granulites (+8 to +10‰). It is proposed that infiltration of externally‐derived H₂O‐rich fluids derived from the plate interface flushed the marbles, promoting decarbonation followed by short‐distance transport and re‐precipitation along garnetite fractures. This study highlights the importance of inherited structural heterogeneities (such as mafic bodies or sills) in localizing deformation, draining fluids from the downgoing plate and creating long‐lasting mechanical instabilities during subduction zone deformation.     

Multiproxy summer and winter surface air temperature field reconstructions for southern South America covering the past centuries

We statistically reconstruct austral summer (winter) surface air temperature fields back to ad 900 (1706) using 22 (20) annually resolved predictors from natural and human archives from southern South America (SSA). This represents the first regional-scale climate field reconstruction for parts of the Southern Hemisphere at this high temporal resolution. We apply three different reconstruction techniques: multivariate principal component regression, composite plus scaling, and regularized expectation maximization. There is generally good agreement between the results of the three methods on interannual and decadal timescales. The field reconstructions allow us to describe differences and similarities in the temperature evolution of different sub-regions of SSA. The reconstructed SSA mean summer temperatures between 900 and 1350 are mostly above the 1901?C1995 climatology. After 1350, we reconstruct a sharp transition to colder conditions, which last until approximately 1700. The summers in the eighteenth century are relatively warm with a subsequent cold relapse peaking around 1850. In the twentieth century, summer temperatures reach conditions similar to earlier warm periods. The winter temperatures in the eighteenth and nineteenth centuries were mostly below the twentieth century average. The uncertainties of our reconstructions are generally largest in the eastern lowlands of SSA, where the coverage with proxy data is poorest. Verifications with independent summer temperature proxies and instrumental measurements suggest that the interannual and multi-decadal variations of SSA temperatures are well captured by our reconstructions. This new dataset can be used for data/model comparison and data assimilation as well as for detection and attribution studies at sub-continental scales.     

Bedload transport in shallow water models: Why splitting (may) fail, how hyperbolicity (can) help

In this paper, we are concerned with sediment transport models consisting of a shallow water system coupled with the so called Exner equation to describe the evolution of the topography. We show that, for some bedload transport models like the well-known Meyer-Peter and Müller model, the system is hyperbolic and, thus, linearly stable, only under some constraint on the velocity. In practical situations, this condition is hopefully fulfilled. Numerical approximations of such system are often based on a splitting method, solving first shallow water equation on a time step and, updating afterwards the topography. It is shown that this strategy can create spurious/unphysical oscillations which are related to the study of hyperbolicity. Using an upper bound of the largest eigenvector may improve the results although the instabilities cannot be always avoided, e.g. in supercritical regions.     

Spatial and temporal variability of Mehlich-1 extractable Fe, Mn and Zn over a rice field as a function of lime amendment

This study compares the effect of lime additions on the spatial variability of Fe, Mn and Zn extracted by Mehlich-1 during three different growth stages from an acid paddy soil, a Typic Plintacualf, in Corrientes, Argentina. Field trials were set up involving three treatments: control, without lime addition, plus two different dolomite doses of 625 and 1250 kg ha⁻¹. Soil was sampled first before sowing in aerobic conditions and then two more times in anaerobic conditions, i.e. by bunch formation and flowering. Ninety-six samples per plot were taken per lime treatment and sampling period, using a nested sampling strategy. Liming significantly increased extractable Fe and Mn, but decreased extractable Zn. The spatial variability of the studied soil properties was assessed using semivariogram analysis and examination of kriging maps. Models were fitted to experimental semivariograms for 27 data sets, i.e. three different soil properties, each of them sampled in three treatments and during three dates. Soil extractable and Fe, Mn and Zn exhibited a rather strong spatial dependence, as nugget variance was either null or a small proportion of the total variance, and this all over the three different study periods and for the three lime treatments. Geostatistical analysis provided insight into possible processes responsible of the observed spatial variability patterns within the rice soil. Kriging was useful in mapping soil micronutrient variability allowing identifying microrregions with high or low Fe, Mn and Zn concentrations, which showed the presence of small scale variability. These findings indicate the potential for applying the principles of precision agriculture to control spatiotemporal variability in rice fields.     

Hydrologic Dynamics of a Subtropical Estuary Using Geochemical Tracers,Celestún,Yucatan, Mexico

Oxygen isotopes and strontium concentrations were used as geochemical tracers to discern the sources of water to Celestún Lagoon, a small subtropical estuary on the western side of the Yucatán Peninsula of Mexico. Celestún Lagoon is underlain by karstified limestone with numerous locations where groundwater is observed discharging directly to the lagoon. In this study, samples of groundwater, lagoon surface water, and seawater (SW) were collected in April 2008 and June 2009 and analyzed for salinity, stable isotopes of oxygen, and strontium (Sr²⁺) concentrations. These geochemical tracers were used in two tertiary mixing models to calculate the relative ratio inputs of fresh groundwater, brackish groundwater, and SW to the lagoon. Two sources of groundwater were found to contribute to the surface water in the lagoon; one fresh and the other brackish with an average salinity of 19 psu. The fresh groundwater had an oxygen isotopic signature (δ¹⁸O) and strontium concentration (Sr²⁺) of δ¹⁸O?=?-3.30‰ and Sr²⁺?=?0.03 mmol/l, respectively. The brackish groundwater observed in the northern end of the lagoon add a dissimilar oxygen isotopic signature and Sr²⁺ concentration of δ¹⁸O?=?3.01‰ and Sr²⁺?=?0.12 mmol/l, respectively. Local SW had an isotopic oxygen signature and Sr²⁺ concentration between the two fresher sources (δ¹⁸O?=?1.40‰, Sr²⁺?=?0.09 mmol/l). The lagoonwide results of the two tracer mixing models (δ¹⁸O and Sr²⁺) agreed well (within 5 %) and indicated a ratio of brackish groundwater–fresh groundwater– SW of 31 %–26 %–43 % (±5 %) for the Sr²⁺ model and 35 %–25 %–40 % (± 5 %) for the δ¹⁸O model. Brackish groundwater is dominant in the northern portion of the lagoon, while SW dominates the southern portion. Fresh groundwater discharge is a significant contributor of water along the entire eastern boundary of the lagoon where mangrove forests are the dominant vegetation.     

A study of water-soluble inorganic ions in size-segregated aerosols in atmospheric pollution episode

Particulate matter, the main pollutant in the atmospheric environment of the Santiago city in winter, was analyzed by means of the major water-soluble ionic species obtained under critical episodes of pollution in 2003. The particulate matter samples were collected using the Micro-Orifice uniform deposit impactors, with eight impactor stages connected in series, and the ionic species in particulate matter samples at each stage was analyzed by ion chromatography. While sulfate ion and nitrate ion showed bi-modal distributions, peaking in the fine and coarse mode, ammonium ion displayed a bi-modal size distribution, peaking in the fine and ultra fine mode. The equivalent concentration ratio of ammonium to sulfate was 2.03 ± 0.09, indicating the complete neutralization of sulfuric acid by ammonia. The excess ammonium ion was associated to nitrate ion. The study of the size distribution of water-soluble inorganic ions in particulate matter supports the notion that secondary aerosols play a significant role in the urban atmosphere.     

Reaction kinetics of dolomite rim growth

Reaction rims of dolomite (CaMg[CO₃]₂) were produced by solid-state reactions at the contacts of oriented calcite (CaCO₃) and magnesite (MgCO₃) single crystals at 400 MPa pressure, 750–850 °C temperature, and 3–146 h annealing time to determine the reaction kinetics. The dolomite reaction rims show two different microstructural domains. Elongated palisades of dolomite grew perpendicular into the MgCO₃ interface with length ranging from about 6 to 41 µm. At the same time, a 5–71 µm wide rim of equiaxed granular dolomite grew at the contact with CaCO₃. Platinum markers showed that the original interface is located at the boundary between the granular and palisade-forming dolomite. In addition to dolomite, a 12–80 µm thick magnesio-calcite layer formed between the dolomite reaction rims and the calcite single crystals. All reaction products show at least an axiotactic crystallographic relationship with respect to calcite reactant, while full topotaxy to calcite prevails within the granular dolomite and magnesio-calcite. Dolomite grains frequently exhibit growth twins characterized by a rotation of 180° around one of the $[11\bar{2}0]$ equivalent axis. From mass balance considerations, it is inferred that the reaction rim of dolomite grew by counter diffusion of MgO and CaO. Assuming an Arrhenius-type temperature dependence, activation energies for diffusion of CaO and MgO are E _a (CaO) = 192 ± 54 kJ/mol and E _a (MgO) = 198 ± 44 kJ/mol, respectively.