Secondary Weathering Products Research Articles

The role of vegetation in setting strontium stable isotope ratios in the Critical Zone

At Earth9s surface the stable isotope ratio of strontium (⁸⁸Sr/⁸⁶Sr) is predominantly set by biological uptake of Sr and its storage in plant litter. This conclusion was reached from a stable isotope mass balance that was independently validated by direct determination of elemental fluxes between the Critical Zone compartments (rock, soil, vegetation, and stream water) of three field sites located in the Swiss Alps, the US Sierra Nevada, and the tropical highlands of Sri Lanka. These sites cover a gradient in erosion rates, which is inversely related to the residence time of solids in the Critical Zone thereby constituting an “erodosequence”. For eroding landscapes, previous stable isotope models predicted that isotope ratios are set by the rate at which secondary solids form during the conversion of rock to regolith. Counter to this expectation we found that, after release from primary minerals, Sr is partitioned into one fraction taken up by plants and the remainder into dissolved Sr flux. The formation of secondary weathering products such as clays and oxides plays a subordinate role in determining the Sr budget. A Sr isotope fractionation factor for biological uptake was determined for each of the three ecosystems from the average Sr stable isotope composition in bulk plants and its dissolved counterpart in stream water. This fractionation factors range from <i>ca</i>. −0.3 ‰ for the Alps and Sierra Nevada to ∼0 ‰ for the tropical Sri Lanka site. That these isotope fingerprints caused by biologic uptake are preserved means that more Sr was physically removed in plant litter than recycled. Such Sr removal in plant litter appears to be strongest at the slowly-eroding site, whereas the dissolved Sr export by streams is highest at the site with the fastest erosion rate. There, all Sr taken up by plants is returned from litter back into solution. The site with short residence time of solids is the only one at which parent material and dissolved export differ in their Sr isotope composition. Our study shows that the behavior of Sr in the Critical Zone is in stark contrast to that of metals of which the isotope fractionation is not affected by biological uptake (for example lithium, mostly set by formation of secondary solids) or affected by both secondary solid formation and biological uptake (for example silicon). Strontium stable isotope signatures offer the new opportunity to quantify nutrient cycling in the Critical Zone as a function of environmental and ecological parameters.

The trajectory of soil development and its relationship to soil carbon dynamics

It has been postulated that the amount of soil organic carbon (SOC) associated with soil minerals exhibits a threshold relationship in response to effective soil moisture (estimated as precipitation less evapotranspiration). To better characterize the role of moisture in influencing mechanisms of SOC storage during pedogenesis, we compare soils from two different chronosequence sites: the Santa Cruz and Mattole River marine terraces that together form a soil age-by-climate gradient (i.e., climo-chronosequence). Our results demonstrate how variation in the effective soil moisture may drive soil development along divergent pedogenic trajectories, resulting in variations in the form and depth distribution of secondary weathering products. In particular, the residual metals Fe and Al are directly related to the type of secondary minerals that accumulate during weathering, and these variations are coupled to differences in the storage and long-term preservation of SOC both within and between soils. Over time, these differences in soil development may lead to ‘pedogenic thresholds’ that further differentiate soil characteristics and influence SOC dynamics. In this case, the pedogenic threshold takes the form of clay-rich argillic horizons that once formed, inhibit aqueous transport, decouple shallow and deep soil environments, and potentially limit SOC inputs and increase microbial recycling in deep soils. Our data suggest argillic horizon development is favorable in the drier Santa Cruz soils, where kaolinite is the dominant secondary weathering product. In contrast, greater available moisture in soils of the Mattole chronosequence drive a different weathering trajectory characterized by the accumulation of more amorphous secondary minerals. As a result, the Mattole soils and do not exhibit argillic horizon development but are instead characterized by greater accumulation of SOC across all depths sampled. Overall, our results illustrate how the interaction of climate (i.e., moisture) and time may shape the trajectory of soil development and the dynamics of SOC storage and preservation.

Barium stable isotopes as a fingerprint of biological cycling in the Amazon River basin

Abstract. The biological cycle of rock-derived nutrients on the continents is a major component of element transfer between the Earth's surface compartments, but its magnitude currently remains elusive. The use of the stable isotope composition of rock-derived nutrients, which can be fractionated during biological uptake, provides a promising path forward with respect to quantifying biological cycling and its overall contribution to global element cycling. In this paper, we rely on the nutrient-like behaviour of the trace element barium (Ba) and use its elemental and stable isotope compositions in dissolved and sediment load river samples to investigate biological cycling in the Amazon Basin. From these measurements, we show that dissolved Ba mainly derives from silicate rocks, and a correlation between dissolved Ba and K abundances suggests that biological cycling plays a role in the Ba river budget. Furthermore, the isotope composition of Ba (δ138Ba) in the dissolved load was found to be significantly different from that of the parent silicate rocks, implying that dissolved Ba isotopic signatures are affected by (i) the precipitation of soil-forming secondary phases as well as (ii) biological uptake and release from dead organic matter. Results from an isotope mass balance method applied to the river dissolved load data indicate that, after its release to solution by rock weathering, Ba is partitioned between the river dissolved load, secondary weathering products (such as those found in soils and river sediments), and the biota. In most sub-catchments of the Amazon, river Ba abundances and isotope compositions are significantly affected by biological cycling. Relationships between estimates of Ba cycled through biota and independent metrics of ecosystem dynamics (such as gross primary production and terrestrial ecosystem respiration) allow us to discuss the role of environmental parameters such as climate or erosion rates on the biological cycling of Ba and, by extension, the role of major rock-derived nutrients. In addition, catchment-scale mass and isotope budgets of Ba show that the measured riverine export of Ba is lower than the estimated delivery of Ba to the Earth surface through rock alteration. This indicates the existence of a missing Ba component, which we attribute to the formation of Ba-bearing particulate organics (possibly accumulating as soil organic matter or currently growing biomass within the catchments) and to organic-bound Ba exported as “unsampled” river particulate organic matter. Given our findings on the trace element Ba, we explore whether the river fluxes of most major rock-derived nutrients (K, Mg, Ca) might also be significantly affected by biological uptake or release. A first-order correction of river-derived silicate weathering fluxes from biological cycling shows that the carbon dioxide (CO2) consumption by silicate weathering at the mouth of the Amazon could be several times higher than the previously reported value of 13 × 109 mol CO2 yr−1 (Gaillardet et al., 1997). Overall, our study clearly shows that the chemical and isotope compositions of rivers in the Amazon – and most likely in other large river basins – bear a biological imprint, thereby challenging common assumptions made in weathering studies.

Unraveling sedimentary processes in fluvial sediments from two basalt dominated watersheds in northern Idaho, USA

Basaltic sediments generated from the breakdown of the Columbia River Basalts (CRB) in the Lawyer Creek and Lapwai Creek watersheds of northern Idaho demonstrate that sediment composition in these fluvial systems is impacted by a number of processes, including, chemical weathering, sediment mixing, fluvial sorting, and diagenesis. Chemical weathering is documented in the compositional transformations that occur from the parent material to fluvial detritus, specifically in the leaching of labile cations (i.e., Ca, Mg, Na, and K), an overall increase in weathering indices, and the generation of secondary weathering products (i.e., clay minerals and X-ray amorphous phases) in these sediments. While the two watersheds mainly downcut through the Columbia River Basalt, the incorporation of material derived from local, glacially-derived soil and/or second cycle detritus from interbedded sandstone units significantly modifies the chemical and mineralogical signatures that would normally be used to fingerprint a mafic provenance, highlighting a potential difficulty for provenance reconstruction in sedimentary rocks derived from mixed sources. However, the influence of this mixing is less pronounced in the clay size fraction, highlighting the potential of the <2 μm sediments to preserve the chemical weathering history of the provenance during sedimentation. In addition to weathering and mixing, fluvial sorting is also recorded in the sediment composition and results in the separation of weathering products as a function of grain size. This process is first recognized from the enrichment of secondary weathering phases as grain size decreases, thus resulting in the most chemically altered material sorted into the clay size fraction of sediment deposits downstream. Lastly, early diagenesis of fluvial sediments in the CRB watersheds results in a Ce-anomaly that also correlates with grain size, suggesting the preferential formation of oxide phases in the fine-grained fraction. Furthermore, the most positive Ce-anomaly is recorded in an ancient stream deposit, suggesting that authigenic oxide precipitation initiates during sediment accumulation and advances as the deposit is cut off from the active stream channel.

Sediment geochemistry and mineralogy from a glacial terrain river system in southwest Iceland

Abstract The weathering of basalt has implications for the global carbon cycle on Earth as well as for understanding sedimentary processes on other terrestrial bodies dominated by a basaltic crust (e.g., Mars), but yet studies in mafic terrains are limited in comparison to their felsic counterpart. Our work details the compositional transformations resulting from the sedimentation process of first-cycle sediments generated in a basalt dominated watershed of southwest Iceland. By sampling multiple sites along the Hvita S river transport pathway and analyzing the sedimentology, geochemistry, and mineralogy, this work provides a geologically integrated approach to understanding a fluvial source-to-sink system in mafic terrains. Environmental conditions such as climate, hydrology, and transport distance all influence the overall sediment composition, and in response, chemical weathering, physical abrasion, sorting, transport, and mixing are all sedimentary processes unraveled in the geochemical and mineralogical relationships of individual grain size bins. Chemical weathering initiates in the upper reaches of the watershed with the alteration of primary mafic phases to form secondary weathering products. As sediment continues to move downstream, the entire sediment suite becomes more altered, and the extent of chemical weathering is intensified, as evidenced by a higher abundance of clay minerals and glassy material. Fluvial sorting separates detritus by particle size and differentiates them by compositional gradients in geochemistry and mineralogy. As grain size decreases, mafic minerals become less abundant and the finer grain sizes are preferentially enriched in immature weathering minerals and mineraloids (e.g., smectite clays and X-ray amorphous phases). This grain size trend is also correlated with elemental fractionation, illustrated most notably by the clay size fraction (

Germanium isotopes and Ge/Si fractionation under extreme tropical weathering of basalts from the Hainan Island, South China

Abstract Chemical weathering of silicate rocks controls the fluvial input of dissolved Ge and Si into the ocean, and has substantial influence on the global Ge and Si geochemical cycles. The heavier dissolved Ge isotope compositions in the rivers (relative to the bulk silicate earth) suggest preferential incorporation of light isotopes into secondary weathering products during rock weathering (Baronas et al., 2017a). In this paper, we present the Ge isotope and Ge/Si ratio variations in the solid weathering products (soil and saprolite) from a well-developed basalt weathering profile (>15 m thick, including soil, saprolite, semi-weathered rock and fresh basalt) on the tropical island of Hainan (South China). We discussed the elemental/isotopic fractionation mechanism and the possible influence of major oxide composition on Ge isotope fractionation during extreme weathering of basalts in tropical climate. The Ge content ([Ge] = 2.19–4.12 ppm, 2.93 ppm on average, n = 52) and Ge/Si ratios (5.55–13.7 μmol/mol, 7.42 μmol/mol on average, n = 52) of solid weathering products are distinctly higher than those of the fresh basalts (avg. [Ge] = 1.64 ppm, Ge/Si = 2.66 μmol/mol, n = 5). The δ74Ge values of solid weathering products range from −0.02 ± 0.10‰ (2σ) to 0.63 ± 0.10‰ (2σ), and exhibits complex stratigraphic variation across the weathering profile. There are no distinct correlations between the concentrations of Ge (or the Ge/Si ratio and δ74Ge values) and SiO2, Al2O3, Fe2O3 and MnO for most of the soil and saprolite samples. The distinct positive δ74Ge vs. Ge (or τGe value and Ge/Si ratio) correlations for most soil and saprolite samples indicate that the enrichment (or depletion) of Ge content, Ge isotopes and Ge/Si fractionation are controlled by a common sorption process of solid weathering products. The predicted opposite relationships between Ge/Si ratios and δ74Ge values for pore water and that for solid weathering products can be evidenced by the positive Ge/Si vs. δ74Ge correlation in the Wenchang basalt weathering profile and a negative one in the river water (Baronas et al., 2017a). Moreover, the estimated negative Δ74Gesolid-dissolved (1000 * Ln(α)) value (−1.38 ± 0.28‰ (2σ)) indicates that solid weathering products are a sink for light Ge isotopes, possibly balancing the isotopic budget with heavy Ge isotope compositions in global rivers and oceans.

Glacial–interglacial change in chlorite concentration from the Lingtai section in the Chinese Loess Plateau over the past 1.2 Ma and its possible forcing mechanisms

AbstractHigh-precision concentrations of chlorite minerals from the Lingtai section in the Chinese Loess Plateau and the surrounding deserts are presented through a mineral liberation analyzer technique. Variations in chlorite concentration over the last 0.5 Ma display a typical pattern of glacial–interglacial changes, with its bulk content in loess units approximately twice that in paleosol units. This climate-driven chlorite change is more pronounced in the fine-size fraction (5–20 μm) of the loess deposits. Evidence from changes in hornblende and muscovite along the same profile suggests that the glacial–interglacial oscillations were likely controlled by changes in atmospheric circulation and shifts in the dust provenance instead of postdepositional weathering. A relatively high chlorite content in several deserts near Mt. Qilian compared with the other desert basins suggests that a transport pathway in the west–east direction, associated with southward shifts of the winter monsoons, may play an important role in modulating the chlorite records. In addition, enhanced saltation and transportation of dust materials is thought to be a main driver of the pronounced changes in the fine-size fraction. Finally, we discuss a possible forcing mechanism behind different long-term trends between the chlorite and its secondary weathering products we observed here.

A global Ge isotope budget

We present measurements of Ge isotope composition and ancillary data for samples of river water, low- and high-temperature hydrothermal fluids, and seawater. The dissolved δ74Ge composition of analyzed rivers ranges from 2.0 to 5.6‰, which is significantly heavier than previously determined values for silicate rocks (δ74Ge=0.4–0.7‰, Escoube et al., Geostand. Geoanal. Res., 36(2), 2012) from which dissolved Ge is primarily derived. An observed negative correlation between riverine Ge/Si and δ74Ge signatures suggests that the primary δ74Ge fractionation mechanism during rock weathering is the preferential incorporation of light isotopes into secondary weathering products. High temperature (>150°C) hydrothermal fluids analyzed in this study have δ74Ge of 0.7–1.6‰, most likely fractionated during fluid equilibration with quartz in the reaction zone. Low temperature (25–63°C) hydrothermal fluids are heavier (δ74Ge between 2.9‰ and 4.1‰) and most likely fractionated during Ge precipitation with hydrothermal clays. Seawater from the open ocean has a δ74Gesw value of 3.2±0.4‰, and is indistinguishable among the different ocean basins at the current level of precision. This value should be regulated over time by the isotopic balance of Ge sources and sinks, and a new compilation of these fluxes is presented, along with their estimated isotopic compositions. Assuming steady-state, non-opal Ge sequestration during sediment authigenesis likely involves isotopic fractionation Δ74Gesolid-solution that is −0.6±1.8‰.

Long-term controls on soil organic carbon with depth and time: A case study from the Cowlitz River Chronosequence, WA USA

Over timescales of soil development (millennia), the capacity of soils to stabilize soil organic carbon (SOC) is linked to soil development through changes in soil mineralogy and other soil properties. In this study, an extensive dataset of soil profile chemistry and mineralogy is compiled from the Cowlitz River Chronosequence (CRC), WA USA. The CRC soils range in age from 0.25 to 1200kyr, spanning a developmental gradient encompassing clear changes in soil mineralogy, chemistry, and surface area. Comparison of these and other metrics of soil development with SOC properties reveal several relationships that may be diagnostic of the long-term coupling of soil development and C cycling. Specifically, SOC content was significantly correlated with sodium pyrophosphate extractable metals emphasizing the relevance of organo-metal complexes in volcanic soils. The depth distributions of organo-metals and other secondary weathering products, including the kaolin and short-range order (SRO) minerals, support the so-called “binary composition” of volcanic soils. The formation of organo-metal complexes limits the accumulation of secondary minerals in shallow soils, whereas in deep soils with lower SOC content, secondary minerals accumulate. In the CRC soils, secondary minerals formed in deep soils (below 50cm) including smectite, allophane, Fe-oxides and dominated by the kaolin mineral halloysite. The abundance of halloysite was significantly correlated with bulk soil surface area and 14C content (a proxy for the mean age of SOC), implying enhanced stability of C in deep soils. Allophane, an SRO mineral commonly associated with SOC storage, was not correlated with SOC content or 14C values in CRC soils. We propose conceptual framework to describe these observations based on a general understanding of pedogenesis in volcanic soils, where SOC cycling is coupled with soil development through the formation of and fate of organo-metal or other mobile weathering products. This framework highlights interactions between SOC and soil development, which may be applicable to other soils where organic inputs interact with the products of chemical weathering.

Chemical and morphological characteristics of solid metal-bearing phases deposited in snow and stream sediment as indicators of their origin.

Detailed scanning electron microscopy/energy dispersive spectroscopy of metal-bearing particles in snow deposits and stream sediment from a steelworks area was performed. Identified metal-bearing phases were apportioned according to their chemical and morphological characteristics to anthropogenic phases and secondary weathering products. Anthropogenic metal-bearing phases are the most abundant in both media and are represented by various irregular ferrous oxides, ferrous alloys, spherical ferrous oxides, and ferrous silicates with variable contents of Cr, Mn, Ni, V, W, and Mo. Secondary weathering products are Al silicates, Fe oxy-hydroxides, and Fe oxy-hydroxy sulfates with minor contents of transition metals, resulting from weathering of anthropogenic phases and Pb-Zn ore minerals from a closed Pb-Zn mine located upstream from the study area. Comparison of anthropogenic metal-bearing phases in both media showed agreement in their compositions and morphologies and indicated their sources are high-temperature processes in steel production. It also showed that spherical metal-bearing phases were transported by the same transport medium, which is the atmosphere, while other phases were transported into stream sediment mostly by other pathways, such as precipitation runoff over contaminated surfaces.

Heterogeneous arsenic enrichment in meta-sedimentary rocks in central Maine, United States

Arsenic is enriched up to 28 times the average crustal abundance of 4.8mgkg−1 for meta-sedimentary rocks of two adjacent formations in central Maine, USA where groundwater in the bedrock aquifer frequently contains elevated As levels. The Waterville Formation contains higher arsenic concentrations (mean As 32.9mgkg−1, median 12.1mgkg−1, n=38) than the neighboring Vassalboro Group (mean As 19.1mgkg−1, median 6.0mgkg−1, n=38). The Waterville Formation is a pelitic meta-sedimentary unit with abundant pyrite either visible or observed by scanning electron microprobe. Concentrations of As and S are strongly correlated (r=0.88, p<0.05) in the low grade phyllite rocks, and arsenic is detected up to 1944mgkg−1 in pyrite measured by electron microprobe. In contrast, statistically significant (p<0.05) correlations between concentrations of As and S are absent in the calcareous meta-sediments of the Vassalboro Group, consistent with the absence of arsenic-rich pyrite in the protolith. Metamorphism converts the arsenic-rich pyrite to arsenic-poor pyrrhotite (mean As 1mgkg−1, n=15) during de-sulfidation reactions: the resulting metamorphic rocks contain arsenic but little or no sulfur indicating that the arsenic is now in new mineral hosts. Secondary weathering products such as iron oxides may host As, yet the geochemical methods employed (oxidative and reductive leaching) do not conclusively indicate that arsenic is associated only with these. Instead, silicate minerals such as biotite and garnet are present in metamorphic zones where arsenic is enriched (up to 130.8mgkg−1 As) where S is 0%. Redistribution of already variable As in the protolith during metamorphism and contemporary water–rock interaction in the aquifers, all combine to contribute to a spatially heterogeneous groundwater arsenic distribution in bedrock aquifers.

Testing the limits of micro-scale analyses of Si stable isotopes by femtosecond laser ablation multicollector inductively coupled plasma mass spectrometry with application to rock weathering

An analytical protocol for accurate in-situ Si stable isotope analysis has been established on a new second-generation custom-built femtosecond laser ablation system. The laser was coupled to a multicollector inductively coupled plasma mass spectrometer (fsLA-MC-ICP-MS). We investigated the influence of laser parameters such as spot size, laser focussing, energy density and repetition rate, and ICP-MS operating conditions such as ICP mass load, spectral and non-spectral matrix effects, signal intensities, and data processing on precision and accuracy of Si isotope ratios. We found that stable and reproducible ICP conditions were obtained by using He as aerosol carrier gas mixed with Ar/H2O before entering the plasma. Precise δ29Si and δ30Si values (better than ±0.23‰, 2SD) can be obtained if the area ablated is at least 50×50μm; or, alternatively, for the analysis of geometric features down to the width of the laser spot (about 20μm) if an equivalent area is covered. Larger areas can be analysed by rastering the laser beam, whereas small single spot analyses reduce the attainable precision of δ30Si to ca. ±0.6‰, 2SD, for <30μm diameter spots. It was found that focussing the laser beam beneath the sample surface with energy densities between 1 and 3.8J/cm2 yields optimal analytical conditions for all materials investigated here. Using pure quartz (NIST 8546 aka. NBS-28) as measurement standard for calibration (standard-sample-bracketing) did result in accurate and precise data of international reference materials and samples covering a wide range in chemical compositions (Si single crystal IRMM-017, basaltic glasses KL2-G, BHVO-2G and BHVO-2, andesitic glass ML3B-G, rhyolitic glass ATHO-G, diopside glass JER, soda-lime glasses NIST SRM 612 and 610, San Carlos olivine). No composition-dependent matrix effect was discernible within uncertainties of the method.The method was applied to investigate the Si isotope signature of rock weathering at the micro-scale in a corestone sampled from a highly weathered roadcut profile in the tropical Highlands of Sri Lanka. The results show that secondary weathering products accumulated in cracks and grain boundaries are isotopically lighter than their unweathered plagioclase host, consistent with isotopically heavy dissolved Si found in rivers.

The Influence of Hydrothermal Activity on the Li Isotopic Signature of Rivers Draining Volcanic Areas

We explore the geochemistry and the isotopic composition of lithium (δ7Li) of rivers draining volcanic islands (Guadeloupe, Iceland, Java, Martinique and Sao Miguel) with a specific focus on continental hydrothermal activity. Our preliminary results reveal a global-scale trend between δ7Li and the elemental ratio Li/Na in rivers draining volcanic islands. We suggest that this trend results from a mixture between waters with low δ7Li and high Li/Na, inherited from high-temperature water rock interactions, and waters with low Li/Na and high δ7Li, in which Li is controlled by the neoformation of clays during low-temperature chemical weathering in basaltic soils. This latter process can be described by a simple isotope fractionation model, consistent with reported values for isotopic fractionation factors between secondary weathering products and water.These data highlight the important potential role of continental high-temperature weathering processes on the oceanic budget of lithium.

Surprisingly contrasting metal distribution and fractionation patterns in copper smelter-affected tropical soils in forested and grassland areas (Mufulira, Zambian Copperbelt)

Six soil profiles located near Mufulira (Zambian Copperbelt) were studied to evaluate and compare the extent of environmental pollution of Cu-ore mining and smelting in both forested and grassland areas. The highest metal concentrations were detected in the uppermost soil layers with the following maxima: Co 45.8mgkg−1, Cu 8980mgkg−1, Pb 41.6mgkg−1, and Zn 97.0mgkg−1. Numerous anthropogenic metal-bearing particles were detected in the most polluted soil layers. The spherical smelter-derived particles were mainly composed of covellite (CuS) and chalcocite (Cu2S), while the angular mining-derived particles were mostly composed of chalcopyrite (CuFeS2). Additionally, Fe–Cu oxide particles predominantly corresponding to tenorite (CuO) and delafossite (Cu1+Fe3+O2), along with hydrated Fe-oxides corresponding to secondary weathering products, were detected. In contrast to smelter-affected soils in temperate climates, where forest soils are significantly more enriched in metals than tilled soils due to high canopy interception, our data indicate a higher proportion of metal-bearing anthropogenic particles and higher metal concentrations in soils from unforested sites. This phenomenon is probably related to the more frequent and intense bushfires in forested areas, leading to the mobilization of pollutants contained in the biomass-rich surface soils back into the atmosphere.

Assessment of Metal Pollution Sources by SEM/EDS Analysis of Solid Particles in Snow: A Case Study of Žerjav, Slovenia

Solid particles in snow deposits, sampled in mining and Pb-processing area of Žerjav, Slovenia, have been investigated using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS). Identified particles were classified as geogenic-anthropogenic, anthropogenic, and secondary weathering products. Geogenic-anthropogenic particles were represented by scarce Zn- and Pb-bearing ore minerals, originating from mine waste deposit. The most important anthropogenic metal-bearing particles in snow were Pb-, Sb- and Sn-bearing oxides and sulphides. The morphology of these particles showed that they formed at temperatures above their melting points. They were most abundant in snow sampled closest to the Pb-processing plant and least abundant in snow taken farthest from the plant, thus indicating that Pb processing was their predominant source between the last snowfall and the time of sampling. SEM/EDS analysis showed that Sb and Sn contents in these anthropogenic phases were higher and more variable than in natural Pb-bearing ore minerals. The most important secondary weathering products were Pb- and Zn-containing Fe-oxy-hydroxides whose elemental composition and morphology indicated that they mostly resulted from oxidation of metal-bearing sulphides emitted from the Pb-processing plant. This study demonstrated the importance of single particle analysis using SEM/EDS for differentiation between various sources of metals in the environment.

Origin, mineral speciation and geochemical baseline mapping of Ni and Cr in agricultural topsoils of Thiva Valley (central Greece)

Lithogenic Ni and Cr enrichment in agricultural topsoils of Thiva Valley (central Greece) is the result of transport of weathered parent rock fragments from upslope ultramafic sources. Chemical and mineralogical evolution of these potentially toxic elements between the trace metal bearing bedrock and the overlying soil horizon along two weathering profiles located in an area where the ultramafic rocks are exposed was accomplished to unravel the source and mineral speciation dynamics of Ni and Cr in the soil system of Thiva Valley. Within the soil horizons, Ni primarily occurs in serpentine (average 0.5wt.% of NiO) and secondary weathering products like smectites (average 0.5wt.% of NiO) and goethite (average 1.1wt.% of NiO). Significant amounts of this element are also hosted in less abundant Mn (hydr)oxides. On the contrary, Cr is mainly bounded with inherited chromite (average 54.7wt.% of Cr2O3) and to a lesser extent with Cr-magnetite (average 12.2wt.% of Cr2O3) and Cr silicates like enstatite (average 0.8wt.% of Cr2O3). As a result of the solid speciation and the applied decomposition method (aqua regia digestion), the soil geochemical anomalies within the valley are more pronounced with respect to Ni (up to 2640mg/kg) compared to Cr (up to 856mg/kg). The geochemical baseline maps produced by the ordinary kriging interpolation method reveal a strong tendency for large Ni and Cr amounts in the southern part of the area warning about the potential occurrence of high metal values in soils of Thiva town with an approximate number of 25,000 exposed population. Based on the mineralogical residence of Ni and Cr differences in their potential bioavailability and leaching to groundwater are anticipated.

Mineralogy and environmental geochemistry of historical iron slag, Hopewell Furnace National Historic Site, Pennsylvania, USA

The Hopewell Furnace National Historic Site in southeastern Pennsylvania, which features an Fe smelter that was operational in the 18th and 19th centuries, is dominated by three slag piles. Pile 1 slag, from the Hopewell Furnace, and pile 2 slag, likely from the nearby Cornwall Furnace, were both produced in cold-blast charcoal-fired smelters. In contrast, pile 3 slag was produced in an anthracite furnace. Ore samples from the nearby Jones and Hopewell mines that fed the smelter are mainly magnetite-rich with some sulfides (pyrite, chalcopyrite, sphalerite) and accessory silicates (quartz, garnet, feldspar, and clay minerals). Slag piles 1 and 2 are similar mineralogically containing predominantly skeletal and dendritic aluminian diopside and augite, skeletal forsteritic olivine, glass, rounded blebs of metallic Fe, and exotic quartz. Olivine is a major phase in all samples from pile 2, whereas it occurs in only a few samples from pile 1. Samples of the <2 mm-size fraction of surface composite slag material or crushed slag from at depth in piles 1 and 2 are mineralogically similar to the large surface slag fragments from those piles with the addition of phases such as feldspars, Fe oxides, and clay minerals that are either secondary weathering products or entrained from the underlying bedrock. Pile 3 slag contains mostly skeletal forsteritic olivine and Ti-bearing aluminian diopside, dendritic or fine-grained subhedral melilite, glass, euhedral spinel, metallic Fe, alabandite–oldhamite solid solution, as well as a sparse Ti carbonitride phase. The bulk chemistry of the slag is dominated by Al2O3 (8.5–16.2 wt.%), CaO (8.2–26.2 wt.%), MgO (4.2–24.7 wt.%), and SiO2 (36.4–59.8 wt.%), constituting between 81% and 97% of the mass of the samples. Piles 1 and 2 are chemically similar; pile 1 slag overall contains the highest Fe2O3, K2O and MnO, and the lowest MgO concentrations. Pile 3 slag is high in Al2O3, CaO and S, and low in Fe2O3, K2O and SiO2 compared to the other piles. In general, piles 1 and 2 are chemically similar to each other, whereas pile 3 is distinct – a conclusion that reflects their mineralogy. The similarities and differences among piles in terms of mineralogy and major element chemistry result from the different smelting conditions under which the slag formed and include the fuel source, the composition of the ore and flux, the type of blast (cold versus hot), which affects the furnace temperature, and other beneficiation methods. The three distinct slag piles at Hopewell are enriched in numerous trace elements, such as As (up to 12 mg/kg), Cd (up to 0.4 mg/kg), Co (up to 31.8 mg/kg), Cu (up to 647 mg/kg), Mn (up to 0.69 wt.%), Pb (up to 172 mg/kg) and Zn (up to 393 mg/kg), together with Fe (13.9 wt.%), when compared to the average for the continental crust, with the <2 mm-size fraction commonly containing the highest concentrations. Enrichments in various elements (e.g., Cd, Co, Cu, Pb, Zn) were also found in the ore samples. Despite these enrichments, comparison of bulk chemistry trace-element concentrations to the environmental guidelines suggests most elements are likely not problematic with the exception of As, Co, Fe and Mn. Leachate tests that simulate weathering indicate Fe (up to 973 μg/L) and Mn (up to 133 μg/L) are readily released in potentially harmful concentrations compared to secondary drinking water and some aquatic ecosystem toxicity criteria. Aluminum and Cu, although not high in the solid compared to environmental guidelines, also exceed relevant criteria in leachate extracts with maximum concentrations of 2700 μg/L and 17.7 μg/L, respectively. In contrast, As and Co, which are significant in the solids, are not leached in concentrations that exceed guidelines (i.e., 3 μg/L or less for both elements). The weathering rates of the Fe metal and Fe oxides, which host Cu and some Fe, are likely higher than the silicate glass, which hosts the majority of Al, Mn and some Fe, and the crystalline silicates and spinels affecting which elements and how much are released into the environment and surrounding aquatic ecosystem. The mineral assemblages and their chemical composition, the bulk sample chemistry, and leachability of trace elements are all important components in understanding the potential environmental impacts of the slag piles.

Mineral and chemical composition of the new iron meteorite Javorje from Slovenia

Abstract– The single‐piece iron meteorite Javorje, with a mass of 4920 g, is the heaviest and largest meteorite found in the territory of Slovenia. The meteorite Javorje is a medium octahedrite with kamacite bandwidth of 0.85 ± 0.26 mm. The bulk composition of Ni (7.83 wt%), Co (0.48 wt%) and trace elements Ga (25 μg/g), Ge (47 μg/g), Ir (7.6 μg/g), As (5.8 μg/g), Au (0.47 μg/g), and Pt (13.4 μg/g) indicates that the meteorite Javorje belongs to the chemical group IIIAB. Mineral and bulk chemical compositions are consistent with other reported group IIIAB meteorites. The presence of numerous rhabdites, carlsbergite, sparse troilite, and chromite and abundance of daubréelites are in accordance with low‐Ni and low‐P IIIAB iron meteorites. The severely weathered surface and secondary weathering products in the interior of the meteorite suggest its high terrestrial age.

Characteristics and potential environmental influences of mine waste in the area of the closed Mežica Pb–Zn mine (Slovenia)

About 19 million tons of Pb–Zn ore were excavated and processed during more than 300 years of mining and metallurgical activities in the Meža Valley, leaving behind large amounts of mine and ore processing wastes, which were deposited as spoil heaps in narrow valleys and on steep slopes of small streams and in abandoned mine shafts at about 30 locations. After the mine and processing facilities were closed in 1995, dumps of low-grade ore and ore processing wastes persisted as a source of potentially toxic elements in the environment. In the presented research, detailed chemical and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analyses of three of the most important mine waste deposits, the Štopar, Kavšak, and Fridrih waste deposits, were carried out with the purpose of determining the influence of mine waste deposits on high contents of potentially toxic elements in environmental media, determining modes of occurrence of metals in waste deposit material, and assessing the stability and mobility of toxic elements on the basis of solubility data of metal-bearing phases and minerals. Chemical analysis showed that the highest contents of Pb, Zn, and Cd occurred in the Štopar waste deposit and the highest contents of Mo, V, and As in the Fridrih waste deposit. SEM/EDS analysis revealed that Pb, Zn, V, and Mo in the waste deposit material occur mostly as primary ore minerals, such as cerussite, sphalerite, smithsonite, descloizite, and wulfenite. A considerable amount of Pb and Zn was found bound to secondary weathering products, such as Fe-oxy-hydroxides, Mn-oxides, Fe-oxy-hydroxy sulfates, and Al-silicates. Solubility of primary ore minerals is generally restricted to the pyrite weathering zones and consequently they are relatively stable in the carbonate environment of mine waste deposits. With the exception of Fe-oxy-hydroxy sulfates, which are considered unstable in high-pH environments, secondary weathering products are stable and thus represent sustainable trapping and stabilization media for Pb and Zn in the investigated mine waste deposits. However, mine waste material is being washed out into the nearby streams, where the changes in environmental conditions may cause leaching and mobilization of potentially toxic elements into water.

Mineralogy, chemistry, and irradiation record of Neuschwanstein (EL6) chondrite

Abstract– We present a detailed study of mineralogy, chemistry, and noble gases of the Neuschwanstein (EL6) chondrite that fell in 2002 in southern Germany. The meteorite has an unbrecciated texture and exhibits only minor shock features. Secondary weathering products are marginal. Neuschwanstein is an EL6 chondrite with heterogeneously distributed metal and sulfide grains. In terms of bulk chemistry, it has very high Fe concentrations, and siderophile and halogen element abundances higher than typical EL chondrites. However, like other ELs of higher petrologic type, it has low moderately volatile element abundances, e.g., Mn and Zn. We interpret these as indicators for loss of sulfide, probably through mobilization of ferroan alabandite and a Zn‐bearing sulfide, potentially sphalerite, during metamorphism. Trapped noble gases are dominated by a subsolar component with high Ar concentrations and are typical for EL chondrites. The shielding parameters indicate a small meteoroid (&lt;20 cm radius) with an exposure age of approximately 47 Ma, which is among the highest for enstatite chondrites.