Bacteriohopanepolyols in tropical soils and sediments from the Congo River catchment area

The Congo River basin drains the second largest area of tropical rainforest in the world, including a large proportion of pristine wetlands. We present the bacteriohopanepolyol (BHP) inventory of a suite of tropical soils and, from comparison with published data, propose some initial ideas on BHP distribution controls. Strong taxonomic controls on BHP production are evident in wetland sediments. Dominant within the suite were 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol) and 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), indicating aerobic methanotrophy. A narrow range and low mean relative abundance of 30-(5′-adenosyl)hopane (adenosylhopane) and related compounds, collectively termed “soil marker” BHPs, were observed in Congo soils (mean 17%, range 7.9–36% of total BHPs, n = 22) compared with literature data from temperate surface soils and Arctic surface soils (mean 36%, range 0–66% of total BHPs, n = 28) suggesting a greater rate of conversion of these BHP precursors to other structures.     

The nature and distribution of Cu,Zn, Hg,and Pb in urban soils of a regional city: Lithgow,Australia

This study investigates the concentration and spatial distribution of Cu, Zn, Hg and Pb in the surface (0–2 cm) soils of a regional city in Australia. Surface soils were collected from road sides and analysed for their total Cu, Zn, Hg and Pb concentrations in the <180 μm and <2 mm grain size fractions. The average metal concentration of surface soils, relative to local background soils at 40–50 cm depth, are twice as enriched in Hg, more than three times enriched in Cu and Zn, and nearly six times as enriched in Pb. Median surface soil metal concentration values were Cu – 39 mg/kg (682 mg/kg max), Zn – 120 mg/kg (4950 mg/kg max), Hg – 44 μg/kg (14,900 μg/kg max) and Pb – 46 mg/kg (3490 mg/kg max). Five sites exceeded the Australian NEPC (1999) 300 mg/kg guideline for Pb in residential soils. Strong positive correlations between Cu, Zn and Pb, coupled with the spatial distribution of elevated soil concentrations towards the city centre and main roads suggest traffic and older housing as major sources of contamination. No spatial relationships were identified between elevated metal loadings and locations of past or present industries.     

Arsenic in the water–soil–plant system and the potential health risks in the coastal part of Chianan Plain,Southwestern Taiwan

The present study investigates the bioavailability, soil to plant transfer and health risks of arsenic (As) in the coastal part of Chianan Plain in southwestern Taiwan. Groundwater used for irrigation, surface soils from agricultural lands and locally grown foodstuffs were collected from eight locations and analyzed for As to assess the risks associated with consuming these items. The concentration of As in groundwater ranged from 13.8 to 881 μg/L, whereas surface soil showed total As content in the range of 7.92–12.7 mg/kg. The available As content in surface soil accounted for 0.06–6.71% of the total As content, and was significantly correlated with it (R² = 0.65, p < 0.05). Among the leachable fraction, the organic matter (3.23–54.8%) and exchangeable portions of oxides (6.03–38.4%) appear to be the major binding phases of As. The average As content in fourteen studied crops and vegetables varied from 10.3 to 151 μg/kg with maximum in mustard and minimum in radish. All the plants showed considerably higher As content (21.5 ± 3.64–262 ± 36.2 μg/kg) in their roots compared to the edible parts (9.15 ± 1.44–75.8 ± 22.9 μg/kg). The bioaccumulation factor (BAF) based on total As (ranging from 0.0009 to 0.144) and available As in soil (ranging from 0.039 to 0.571) indicate that mustard, rice, amaranth and spinach are the highest accumulators of As. Although the health risk index (HRI) of the studied crops and vegetables ranged from only 0.0068–0.454, with the maximum in rice, the combined HRI indicates an alarming value of 0.88. Therefore, the possible health risks due to long-term consumption of rice and other As-rich foodstuffs could be overcome by controlling the contamination pathways in the water–soil–plant system.     

Organic geochemistry of the Vindhyan sediments: Implications for hydrocarbons

The organic geochemical methods of hydrocarbon prospecting involve the characterization of sedimentary organic matter in terms of its abundance, source and thermal maturity, which are essential prerequisites for a hydrocarbon source rock. In the present study, evaluation of organic matter in the outcrop shale samples from the Semri and Kaimur Groups of Vindhyan basin was carried out using Rock Eval pyrolysis. Also, the adsorbed low molecular weight hydrocarbons, methane, ethane, propane and butane, were investigated in the near surface soils to infer the generation of hydrocarbons in the Vindhyan basin. The Total Organic Carbon (TOC) content in shales ranges between 0.04% and 1.43%. The S₁ (thermally liberated free hydrocarbons) values range between 0.01–0.09 mgHC/gRock (milligram hydrocarbon per gram of rock sample), whereas the S₂ (hydrocarbons from cracking of kerogen) show the values between 0.01 and 0.14 mgHC/gRock. Based on the T_max (temperature at highest yield of S₂) and the hydrogen index (HI) correlations, the organic matter is characterized by Type III kerogen. The adsorbed soil gas, CH₄ (C₁), C₂H₆ (C₂), C₃H₈ (C₃) and nC₄H₁₀, (nC4), concentrations measured in the soil samples from the eastern part of Vindhyan basin (Son Valley) vary from 0 to 186 ppb, 0 to 4 ppb, 0 to 5 ppb, and 0 to 1 ppb, respectively. The stable carbon isotope values for the desorbed methane (δ¹³C₁) and ethane (δ¹³C₂) range between −45.7‰ to −25.2‰ and −35.3‰ to −20.19‰ (VPDB), respectively suggesting a thermogenic source for these hydrocarbons. High concentrations of thermogenic hydrocarbons are characteristic of areas around Sagar, Narsinghpur, Katni and Satna in the Son Valley. The light hydrocarbon concentrations (C₁–C₄) in near surface soils of the western Vindhyan basin around Chambal Valley have been reported to vary between 1–2547 ppb, 1–558 ppb, 1–181 ppb, 1–37 ppb and 1–32 ppb, respectively with high concentrations around Baran-Jhalawar-Bhanpur-Garot regions (Kumar et al., 2006). The light gaseous hydrocarbon anomalies are coincident with the wrench faults (Kota – Dholpur, Ratlam – Shivpuri, Kannod – Damoh, Son Banspur – Rewa wrench) in the Vindhyan basin, which may provide conducive pathways for the migration of the hydrocarbons towards the near surface soils.     

Constraints on the application of the MBT/CBT palaeothermometer at high latitude environments (Svalbard,Norway)

Branched glycerol dialkyl glycerol tetraethers (GDGTs) are membrane lipids of unknown bacteria that are ubiquitous in soil and peat. Two indices based on the distribution of these lipids in soils, the Cyclization of Branched Tetraethers (CBT) and the Methylation of Branched Tetraethers (MBT) indices have been shown to correlate with soil pH, and mean annual air temperature (MAT) and soil pH, respectively, and can be used to reconstruct MAT in palaeoenvironments. To verify the extent to which branched GDGTs in marine sediments reflect the distribution pattern on land and whether these proxies are applicable for palaeoclimate reconstruction in high latitude environments with a MAT of <0 °C, we compared the branched GDGT distribution in Svalbard soils and nearby fjord sediments. Although branched GDGT concentrations in the soil are relatively low (0.02–0.95 μg/g dry weight (dw)) because of the cold climate and the short growing season, reconstructed MATs based on the MBT/CBT proxy are ca. ?4 °C, close to the measured MAT (ca. ?6 °C). Concentrations of branched GDGTs (0.01–0.20 μg/g dw) in fjord sediments increased towards the open ocean and the distribution was strikingly different from that in soil, i.e. dominated by GDGTs with one cyclopentane moiety. This resulted in MBT/CBT-reconstructed MAT values of 11–19 °C, well above measured MAT. The results suggest that at least part of the branched GDGTs in marine sediments in settings with a low soil organic matter (OM) input may be produced in situ. In these cases, the application of the MBT/CBT palaeothermometer will generate unrealistic MAT reconstructions. The MBT/CBT proxy should therefore only be used at sites with a substantial input of soil OM relative to the amount of marine OM, i.e. at sites close to the mouth of rivers with a catchment area where sufficient soil formation takes place and the soil thus contains substantial amounts of branched GDGTs.     

Soot black carbon concentration and isotopic composition in soils from an arid urban ecosystem

Black carbon (BC) is a poorly understood type of organic carbon but it is present in almost all environmental systems (i.e., atmosphere, soil and water). This work focuses on soot BC in desert soils and, in particular, urban soils from the Phoenix, Arizona metropolitan area. Soot BC is that fraction of black carbon formed from the condensation of gas phase molecules produced during burning. Soot BC in Phoenix area soils exhibits a range in both concentration and isotopic composition. Soot BC concentration in 52 soils (desert, agricultural and urban) ranges from 0.02–0.54 wt% and comprises from < 1 to as much as 89% of the soil organic carbon (OC). Soot BC concentrations are higher in urban soils than in desert or agricultural soils. The average isotopic composition of soot BC is −18‰ ± 3‰; this is an enrichment of 5.5‰ relative to bulk soil organic carbon. The distribution in concentration and variation in isotopic composition across the study area suggests soot BC in this arid-land city has multiple sources, including a significant fossil fuel component.     

Investigation of bacterial hopanoid inputs to soils from Western Canada

Hopanoids have been widely used as characteristic biomarkers to study inputs of bacterial biomass to sediments because they are preserved in the geologic record. A limited number of studies have been performed on hopanoid biomarkers in soils. The present study examined the distribution and potential preservation of hopanoids in soils that are developed under different climatic conditions and varying vegetative inputs. Solvent extraction and sequential chemical degradation methods were employed to extract both “free” and “bound” hopanoids, from three grassland soils, a grassland–forest transition soil, and a forest soil from Western Canada. Identification and quantification of hopanoids in the soil samples were carried out by gas chromatography–mass spectrometry. Methylbishomohopanol, bishomohopanol and bishomohopanoic acid were detected in all solvent extracts. The base hydrolysis and ruthenium tetroxide extracts contained only bishomohopanoic acid at a concentration range of 0.8–8.8 μg/gC and 2.2–28.3 μg/gC, respectively. The acid hydrolysis procedure did not release detectable amounts of hopanoids. The solvent extraction yielded the greatest amounts of “free” hopanoids in two of the grassland soils (Dark Brown and Black Chernozems) and in the forest soil (Gray Luvisol). In contrast, the chemical degradation methods resulted in higher amounts of “bound” hopanoids in the third grassland soil (Brown Chernozem) and the transition soil (Dark Gray Chernozem), indicating that more hopanoids exist in the “bound” form in these soils. Overall, the forest and the transition soils contained more hopanoids than the grassland soils. This is hypothesized to be due to the greater degradation of hopanoids in the grassland soils and or sorption to clay minerals, as compared to the forest and transition soils.     

Geochemical challenges of diverse regolith-covered terrains for mineral exploration in China

In recent years mineral exploration has concentrated on concealed deposits in regolith-covered terrains. In China, the regolith-covered landscapes mainly include desert windblown sand basins, desert peneplains, semi-arid grassland, loess plateaus, forestry land, alluvial plains and laterite terrains. These diverse regolith-covered areas represent geochemical challenges for mineral exploration in China. This paper provides an overview of recent progress on mechanisms of metal dispersion from the buried ore deposits through the transported cover to the surface and penetrating geochemical methods to detect the anomalies. Case studies show that, in arid and semi-arid desert sand-covered terrains, sampling of fine-fraction (− 120 mesh, < 0.125 mm) clay-rich horizon soil is cost-effective for regional geochemical surveys for sandstone-type uranium, gold, and base metal deposits. Fine-fraction sampling, selective-leaching and overburden drilling geochemical methods can effectively indicate the 210 gold ore body at Jinwozi goldfield. In alluvium-covered terrains, fine-grained soil sampling (− 200 mesh, < 0.074 mm) combined with selective leaching geochemistry shows clear ring-shaped anomalies of Cu and Ni over the Zhouan concealed Cu–Ni deposit. In laterite-covered terrains, the anomalies determined by the fine-fraction soils and selective leaching of absorbed metals on coatings of Fe–Mn oxides coincide well with the concealed deposit over the Yueyang ore deposits at the Zijin Au–Cu–Ag field. Nanoparticles of hexagonal crystals mainly native copper, gold and alloys of Cu–Fe, Cu–Fe–Mn, Cu–Ti, and Cu–Au were observed in gases, soils and ores using a transmission electron microscope (TEM). The findings imply that nanoparticles of gold and copper may migrate through the transported cover to the surface. Uranium is converted to uranyl ions [UO₂^2 +] under oxidizing conditions when migrating from ore bodies to the surface. The uranyl ions are absorbed on clay minerals, because clay layers have a net negative charge, which needs to be balanced by interlayer cations. Nanoparticles of Au and Cu and ion complexes of U are more readily absorbed onto fine fractions of soils containing clays, colloids, oxides and organic matters. Thus, fine-grained soils enriched with clays, oxides and colloids are useful media for regional geochemical surveys in regolith-covered terrains and in sedimentary basins. Fine-fraction soil sampling combined with selective leaching geochemistry is effective for finding concealed ore bodies in detailed surveys. Penetrating geochemistry at surface sampling provides cost-effective mineral exploration methods for delineation of regional and local targets in transported cover terrains.     

Assessing soil erosion and control factors by radiometric technique in the source region of the Yellow River,Tibetan Plateau

Measurements of ¹³⁷Cs concentration in soils were made in a representative catchment to quantify erosion rates and identify the main factors involved in the erosion in the source region of the Yellow River in the Tibetan Plateau. In order to estimate erosion rates in terms of the main factors affecting soil loss, samples were collected taking into account the slope and vegetation cover along six selected transects within the Dari County catchment. The reference inventory for the area was established at a stable, well-preserved, site of small thickness (value of 2324 Bq·m^− 2). All the sampling sites had been eroded and ¹³⁷Cs inventories varied widely in the topsoil (14.87–25.56 Bq·kg^− 1). The effective soil loss values were also highly variable (11.03–28.35 t·km^− 1·yr^− 1) in line with the vegetation cover change. The radiometric approach was useful in quantifying soil erosion rates and examining patterns of soil movement.     

Are burnt sediments reliable recorders of geomagnetic field strength?

This study tests if burnt soils and sediments can provide reliable records of geomagnetic field strength at the time of burning by carrying out an experiment to reproduce the prehistoric use of fire on a clayish soil substratum. Rock magnetic experiments showed that in the upper 0–1 cm of the central part of the burnt surface, remanence is a thermoremanent magnetization carried by single-domain magnetite and that samples are thermally stable. Fourteen specimens from that area were subjected to paleointensity experiments with the Coe method (1967). An intensity of 42.9 ± 5.7 μT was estimated below 440°C, whereas at higher temperatures magneto-mineralogical alterations were observed. Corresponding successful microwave intensity determinations from two specimens gave a mean value of 47.6 μT. Both results are in reasonable agreement with the expected field value of 45.2 μT. Burnt soils of archeological fires thus have the potential to record accurately the paleofield strength and may be useful targets for archeointensity investigations. Coincident results obtained from two different paleointensity determination methods support this conclusion.     

Is silt the most influential soil grain size fraction?

The contribution of individual grain size fractions (2000–500, 500–250, 250–63, 63–2 and < 2 μm) to bulk soil surface area and reactivity is discussed with reference to mineralogical and oxalate and dithionite extractions data. The 63–2 μm fraction contributed up to 56% and 67% of bulk soil volume and BET surface area, respectively. Consideration of these observations and the mineralogy of this fraction suggest that the 63–2 μm fraction may be the most influential for the release of elements via mineral dissolution in the bulk soil.     

Significance of weathering and regolith/landscape evolution for mineral exploration in the NE Albany-Fraser Orogen,Western Australia

The Albany-Fraser Orogen (AFO), southeast Western Australia, is an underexplored, deeply weathered regolith-dominated terrain that has undergone complex weathering associated with various superimposed climatic events. For effective geochemical exploration in the AFO, integrating landscape evolution with mineralogical and geochemical variations of regolith and bedrock provides fundamental understanding of mechanical and hydromorphic dispersion of ore and pathfinder elements associated with the different weathering processes.In the Neale tenement, northeast of the AFO, a residual weathering profile that is 20-55 m thick was developed under warm and humid climatic conditions over undulating Proterozoic sheared granitoids, gneisses, schists and Au-bearing mafic rocks. From the base, the typical weathering profile consists of saprock, lower ferruginous saprolite, upper kaolinitic saprolite and discontinuous silcrete duricrust or its laterally coeval lateritic residuum. These types of duricrusts change laterally into areas of poorly-cemented kaolinitic grits or loose lateritic pisoliths and nodules.Lateritic residuum probably formed on remnant plateaus and was transported mechanically under arid climatic conditions over short distances, filling valleys to the southeast. Erosion of lateritic residuum exposes the underlying saprolite and, together with dilution by aeolian sands, constitutes the transported overburden (2-25 m thick). The reworked lateritic materials cover the preserved silcrete duricrusts in valleys. The lower ferruginous saprolite and lateritic residuum are well developed over mafic and sulphide-bearing bedrocks, where weathering of ferromagnesian minerals and sulphides led to enrichment of Fe, Cu, Ni, Cr, Co, V and Zn in these units. Kaolinitic saprolite and the overlying pedogenic silcrete are best developed over alkali granites and quartzofeldspathic gneisses, which are barren in Au and transition elements, and enriched in silica, alumina, rare earth and high field strength elements.A residual Au anomaly is formed in the lower ferruginous saprolite above a Au -bearing mafic intrusion at the Hercules prospect, south of the Neale tenement, without any expression in the overlying soil (< 20 cm). Conversely, a Au anomaly is recorded in the transported cover, particularly in the uppermost 3 m at the Atlantis prospect, 5 km southwest of the Hercules prospect. No anomalies have been detected in soils using five different size fractions (> 2,000 μm, 2,000-250 μm, 250-53 μm, 53-2 μm and < 2 μm). Therefore, soil cannot be efficiently applied as a reliable sampling medium to target mineralization at the Neale tenement. This is because mechanical weathering was interrupted by seasonal periods of intensive leaching under the present-day surface conditions and/or dilution by recently deposited aeolian sediments which obscure any signature of a potential Au anomaly in soils. Therefore, surface soil sampling should extend deeper than 20 cm to avoid dilution by aeolian sands and seasonal leaching processes. Regolith mapping and the distinction between the residual and transported weathering products are extremely significant to follow the distal or proximal mineralization.     

Effects of acid-sulfate weathering and cyanide-containing gold tailings on the transport and fate of mercury and other metals in Gossan Creek: Murray Brook mine,New Brunswick,Canada

Gossan Creek, a headwater stream in the SE Upsalquitch River watershed in New Brunswick, Canada, contains elevated concentrations of total Hg (Hg_T up to 60 μg/L). Aqueous geochemical investigations of the shallow groundwater at the headwaters of the creek confirm that the source of Hg is a contaminated groundwater plume (neutral pH with Hg and Cl concentrations up to 150 μg/L and 20 mg/L, respectively), originating from the Murray Brook mine tailings, that discharges at the headwaters of the creek. The discharge area of the contaminant plume was partially delineated based on elevated pH and Cl concentrations in the groundwater. The local groundwater outside of the plume contains much lower concentrations of Hg and Cl (<0.1 μg/L and 3.8 mg/L, respectively) and displays the chemical characteristics of an acid-sulfate weathering system, with low pH (4.1–5.5) and elevated concentrations of Cu, Zn, Pb and SO₄ (up to 5400 μg Cu/L, 8700 μg Zn/L, 70 μg Pb/L and 330 mg SO₄/L), derived from oxidation of sulfide minerals in the Murray Brook volcanogenic massive sulfide deposit and surrounding bedrock. The Hg_T mass loads measured at various hydrologic control points along the stream system indicate that 95–99% of the dissolved Hg_T is attenuated in the first 3–4 km from the source. Analyses of creek bed sediments for Au, Ag, Cu, Zn, Pb and Hg indicate that these metals have partitioned strongly to the sediments. Mineralogical investigations of the contaminated sediments using analytical scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM), reveal discrete particles (<1–2 μm) of metacinnabar (HgS), mixed Au–Ag–Hg amalgam, Cu sulfide and Ag sulfide.     

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.     

Detrital zircon provenance of early Palaeozoic sediments at the southwestern margin of the Siberian Craton: Insights from U–Pb geochronology

Detrital zircons from the Ordovician and Devonian sedimentary cover of the Siberian Craton were analyzed for U/Pb geochronology to understand their sediment provenances. Five main age-peaks were identified in the zircon U/Pb age-spectra: (1) Neoarchaean – early Palaeoproterozoic (2.7–2.4 Ga); (2) late Palaeoproterozoic (2.0–1.65 Ga); (3) minor early Neoproterozoic (1.0–0.75 Ga); (4) Ediacaran (0.65–0.60 Ga) and (5) Cambrian – Early Ordovician (0.54–0.47 Ga), reflecting the main magmatic events in the sediment source regions. The oldest zircons (groups 1 and 2) are derived from the Siberian Craton which amalgamated during the Neoarchean – Palaeoproterozoic. The Neoproterozoic zircons (groups 3 and 4) likely sourced from southwestern basement uplifts and Neoproterozoic belts of the Siberian margin such as the Yenisey Ridge and Baikal-Muya region. The provenance of the youngest zircons (group 5) can be traced to the Altai–Sayan fold-belt, where peri-Gondwanan microcontinents and island-arcs accreted to Siberia during late Neoproterozoic – early Palaeozoic progressive consumption of the Palaeo-Asian Ocean.     

Soil evidence for historical human-induced land degradation in West Iceland

Human impacts have been severe on Icelandic soils and vegetation. In order to assess human impact on soils soil quality, soil organic C (SOC), soil bulk density (BD), soil moisture content (SMC), soil mass, and SOC sequestration were measured from two Histosol cores in West Iceland. The cores cover a period from around 665 BC to present, capturing the initial human settlement of Iceland in AD 871. Tephrochronology allowed for a reliable correlation and comparison between the two cores. The initial settlement had profound impacts on the soil quality, causing decreased SOC concentration and SMC, and increased vegetation degradation, soil exposure, eolian deposition, and BD. The total SOC pool was 34.6 kg C m² at one of the sites, of which 60.1% was formed during historic times, driven by increased soil mass deposition from surrounding eroded areas. The SOC pool was 43.7 kg C m² at the other site, of which 31.4% was formed during historic time, constrained by water cycling and decomposition.     

Arsenic in agricultural and grazing land soils of Europe

Arsenic concentrations are reported for the <2 mm fraction of ca. 2200 soil samples each from agricultural (Ap horizon, 0–20 cm) and grazing land (Gr, 0–10 cm), covering western Europe at a sample density of 1 site/2500 km². Median As concentrations in an aqua regia extraction determined by inductively coupled plasma emission mass spectrometer (ICP-MS) were 5.7 mg/kg for the Ap samples and 5.8 mg/kg for the Gr samples. The median for the total As concentration as determined by X-ray fluorescence spectrometry (XRF) was 7 mg/kg in both soil materials. Maps of the As distribution for both land-use types (Ap and Gr) show a very similar geographical distribution. The dominant feature in both maps is the southern margin of the former glacial cover seen in the form of a sharp boundary between northern and southern European As concentrations. In fact, the median As concentration in the agricultural soils of southern Europe was found to be more than 3-fold higher than in those of northern Europe (Ap: aqua regia: 2.5 vs. 8.0 mg/kg; total: 3 vs. 10 mg/kg). Most of the As anomalies on the maps can be directly linked to geology (ore occurrences, As-rich rock types). However, some features have an anthropogenic origin. The new data define the geochemical background of As in agricultural soils at the European scale.     

Arsenic concentration variability in public water system wells in Minnesota,USA

There is significant random and systematic variability in As concentrations in numerous public water system wells in Minnesota. Arsenic concentrations fluctuate above and below the USA’s As drinking water Maximum Contaminant Level (MCL) of 10 μg/L. The average As concentration is commonly within one standard deviation of the MCL. Results of intensive sampling conducted over the course of approximately 1 year at 3 public water system wells is consistent with the analysis of historic As measurements. In some cases, significant As concentration variability was noted over a short period of time. In these wells, the As concentration was less than 10 μg/L shortly after pumping started, but the As concentration increased over time to a level exceeding 10 μg/L. In these wells, the As concentration decreased to below 10 μg/L again when pumping was briefly restarted after being stopped for 4 h. The As concentration variability is likely due to As adsorption reactions between Fe oxides in the well borehole and in the aquifer near the well borehole during periods when the pump is not in operation. When it is crucial to accurately determine true average As concentrations – for example, at one of the many wells that fluctuate above and below the regulatory As limit of 10 μg/L – it is worthwhile collecting samples frequently during pumping to more accurately determine the average As concentration. Determining a reliable average depends on the standard deviation (SD) of the measurements, with more measurements required if the SD is larger.     

Rutile geochemistry and thermometry of eclogites and associated garnet-mica schists in the Biga Peninsula,NW Turkey

In northwest Turkey, high-pressure metamorphic rocks occur as exotic blocks within the Çetmi mélange located on the south of the Biga Peninsula. Rutile chemistry and rutile thermometry obtained from the eclogite and associated garnet-mica schist in the Çetmi mélange indicate significant trace element behaviour of subducted oceanic crust and source-rock lithology of detrital rutiles. Cr and Nb contents in detrital rutile from garnet-mica schist vary from 355 to 1026 μg/g and 323 and 3319 μg/g, respectively. According to the Cr-Nb discrimination diagram, the results show that 85% of the detrital rutiles derived from metapelitic and 15% from metamafic rocks. Temperatures calculated for detrital rutiles and rutiles in eclogite range from 540 °C to 624 °C with an average of 586 °C and 611 °C to 659 °C with an average of 630 °C at P = 2.3 GPa, respectively. The calculated formation temperatures suggest that detrital rutiles are derived from amphibolite- and eclogite-facies metamorphic rocks. Amphibolite-facies rocks of the Kazdağ Massif could be the primary source rocks for the rutiles in the garnet-mica schist from the Çetmi mélange. Nb/Ta ratios of metapelitic and metamafic rutiles fall between 7–24 and 11–25, respectively. Nb/Ta characteristics in detrital rutiles may reflect a change in source-rock lithology. However, Nb/Ta ratios of rutiles in eclogite vary from 9 to 22. The rutile grains from eclogites are dominated by subchondritic Nb/Ta ratios. It can be noted that subchondritic Nb/Ta may record rutile growth from local sinks of aqueous fluids from metamorphic dehydration.     

Re–Os and U–Pb geochronology of the Duobaoshan porphyry Cu–Mo–(Au) deposit,northeast China,and its geological significance

The large-scale Duobaoshan porphyry Cu–Mo–(Au) deposit is located at the north segment of the Da Hinggan Mountains, northeast China. Six molybdenite samples from the Duobaoshan deposit were selected for Re–Os isotope measurement to define the mineralization age of the deposit, yieldings a Re–Os isochron age of 475.9 ± 7.9 Ma (2σ), which is accordant with the Re–Os model ages of 476.6 ± 6.9–480.2 ± 6.9 Ma. This age is consistent with the age of the related granodiorite porphyry, which was dated as 477.2 ± 4 Ma by zircon U–Pb analysis using LA-ICP-MS. These ages disagree with the previous K–Ar age determinations that suggest a correlation of intrusive rocks of the Duobaoshan area with the Hercynian intrusive rocks of Carboniferous–Permian age. These ages demonstrate that the Duobaoshan granodiorite porphyry and related Cu–Mo deposit occurred in the Early Ordovician. The rhenium content of molybdenite varies from 290.9 to 728.2 μg/g, with an average content of 634.8 μg/g. The high rhenium content in molybdenite of the Duobaoshan deposit suggests that the ore-forming materials may be mainly of mantle source.