Lead Isotopic Compositions Research Articles

Combining lead isotopes and cluster analysis to distinguish the Guarani and Serra Geral Aquifer Systems and contaminated waters in a highly industrialized area in Southern Brazil

The Rio dos Sinos Watershed area is located at the Middle-West region of the Rio Grande do Sul State, Southern Brazil, along thirty two municipalities and affecting 1.5 million inhabitants and many important industrial centers. Three main aquifers are recognized in the study area: the unconfined-fractured Serra Geral Aquifer System, the porous Guarani Aquifer System, and the Permian Aquitard. This study aims to understand groundwater, surface water and human activity interactions in the Rio dos Sinos Watershed, evaluating the application of stable lead isotopic ratios analyzed for this propose. Thirty six groundwater samples, 8 surface water samples and 5 liquid effluents of tanneries and landfills samples were measured using a Thermal Ionization Mass Spectrometer Thermo-Finnigan and a Neptune Multi-Collector Inductively Coupled Plasma Mass Spectrometer. Groundwater isotopic ratios have a wider range compared to the surface water, with less radiogenic averages 208Pb/204Pb = 38.1837 vs 38.4050 (standard deviation = 0.2921 vs 0.1343) and 206Pb/204Pb = 18.2947 vs 18.4766 (standard deviation = 0.2215 vs 0.1059), respectively. Industrial liquid effluents (tanneries and industrial landfill) have averages 208Pb/204Pb = 38.1956 and 206Pb/204Pb = 18.3169, distinct from effluent samples of domestic sanitary landfill (averages 208Pb/204Pb = 38.2353 and 206Pb/204Pb = 18.6607). Hierarchical cluster analysis led to distinguish six groups of groundwater, representing the three aquifers that occur in the area, two clusters suggesting groundwater mixtures and one demonstrating a highly contaminated groundwater. By analyzing the cluster results and wells’ stratigraphic profiles it was possible to distinguish the different aquifers in the area. The Serra Geral Aquifer System has 206Pb/204Pb ratios between 18.4718 and 18.7089; 207Pb/204Pb between 15.6692 and 15.6777; 208Pb/204Pb between 38.6826 and 38.7616; 207Pb/206Pb between 0.8372 and 0.8623; 208Pb/206Pb between 2.0671 and 2.0964 and the Guarani Aquifer System has a wider range (208Pb/204Pb ranged from 37.9393 to 38.1279 and 206Pb/204Pb ranged from 18.0892 to 18.3217). Water mixing of these two aquifer systems is reflected by transitional results. The results confirm that the hierarchical cluster analysis of lead isotopes is a useful tool to discriminate different aquifer conditions, reflecting mostly the influence of the natural lead isotopic composition of the aquifers instead of the anthropogenic activities (urban and industrial), except when the groundwater is highly contaminated by human activity.

Accurate and precise determination of lead isotope composition in selected geochemical reference materials

Lead (Pb) isotopes have been extensively employed in tracing sources of Pb and its transport pathways through the environment. However, Pb isotopic ratios in related geochemical reference materials are scarce. Here, we report high-precision Pb isotopic ratios measured by Nu Plasma II MC-ICP-MS using calibrated 205Tl/203Tl = 2.38865 (NIST SRM 997) for mass discrimination correction. The long-term external precision (2SD) for NIST SRM 981 of Pb, BCR-2, and BHVO-2 are 0.31‰ (n = 105), 0.42‰ (n = 11), and 0.25‰ (n = 5) for 208Pb/206Pb and 0.16‰, 0.53‰, and 0.07‰ for 206Pb/207Pb, both respectively, and their Pb isotopic ratios are in excellent agreement with the recommended values. Using this method, we report for the first time Pb isotopic compositions in shale SGR-1b (USGS); coal CLB-1 (USGS); stream sediments GSD-17, -21, and -23 (IGGE); soils GSS-12, -13, -14, -15, and -16 (IGGE); plants GSV-1, -2, and -3 (IGGE); and human hair GSH-1(IGGE).

Remobilisation of industrial lead depositions in ash during Australian wildfires

This study examined the recycling of lead (Pb) in ash from wildfires, its source and potential contribution to environmental contamination. Ash from wildfires was collected from four Australian sites following uncontrolled fires during 2012 to 2013 close to major urban populations in Sydney (New South Wales), Hobart (Tasmania) and Adelaide (South Australia). The samples were analysed for their total Pb concentration and Pb isotopic composition to determine the sources of Pb and the extent, if any, of industrial contamination and its recycling into the ecosystem. Median ash concentrations (23mg/kg) released from a wildfire close to Australia's largest city, Sydney, exceeded the median ash Pb concentrations from wildfires from the less populated locations of Hobart, Adelaide and NSW Central Coast. Lead isotopic compositions of Duffys Forest wildfire ash demonstrate that anthropogenic inputs from legacy leaded petrol depositions were the predominant source of contamination. Despite the cessation of leaded petrol use in Australia in 2002, historic petrol Pb deposits continue to be a substantial source of contamination in ash: petrol Pb contributed 35% of the Pb in the Woy Woy ash, 73% in Duffys Forest ash, 39% in Forcett ash and 5% in Cherryville ash. The remobilisation of legacy industrial Pb depositions by wildfires in ash results in it being a persistent and problematic contaminant in contemporary environmental systems because of its known toxicity.

Lead isotopic evidence for interaction between plume and lower crust during emplacement of peralkaline Lovozero rocks and related rare-metal deposits, East Fennoscandia, Kola Peninsula, Russia

The Lovozero alkaline massif—an agpaitic nepheline syenite layered intrusion—is located in the central part of the Kola Peninsula, Russia, and belongs to the Kola ultramafic alkaline and carbonatitic province (KACP) of Devonian age. Associated loparite and eudialyte deposits, which contain immense resources of REE, Nb, Ta, and Zr, constitute a world class mineral district. Previous Sr, Nd, and Hf isotope investigations demonstrated that these rocks and mineral deposits were derived from a depleted mantle source. However, because the Sr, Nd, and Hf abundances in the Kola alkaline rocks are significantly elevated, their isotopic compositions were relatively insensitive to contamination by the underlying crustal rocks through which the intruding magmas passed. Pb occurring in relatively lower abundance in the KACP rocks, by contrast, would have been a more sensitive indicator of an acquired crustal component. Here, we investigate the lead isotopic signature of representative types of Lovozero rocks in order to further characterize their sources. The measured Pb isotopic composition was corrected using the determined U and Th concentrations to the age of the crystallization of the intrusion (376 ± 28 Ma, based on a 206Pb/204Pb versus 238U/204Pb isochron and 373 ± 9 Ma, from a 208Pb/204Pb versus 232Th/204Pb isochron). Unlike the previously investigated Sr, Nd, and Hf isotopes, the lead isotopic composition plot was well outside the FOZO field. The 206Pb/204Pb values fall within the depleted MORB field, with some rocks having lower 207Pb/204Pb but higher 208Pb/204Pb values. Together with other related carbonatites having both lower and higher 206Pb/204Pb values, the combined KACP rocks form an extended linear array defining either a ~2.5-Ga secondary isochron or a mixing line. The projection of this isotopic array toward the very unradiogenic composition of underlying 2.4–2.5-Ga basaltic rocks of the Matachewan superplume and associated Archean granulite facies country rock provides strong evidence that this old lower crust was the contaminant responsible for the deviation of the Lovozero rocks from a presumed original FOZO lead isotopic composition. Evaluating the presence of such a lower crustal component in the Lovozero rock samples suggests a 5–10% contamination by such rocks. Contamination by upper crustal rock is limited to only a negligible amount.

Assessment of Heavy Metal Pollution and Tracing Sources by Pb & Sr Isotope in the Soil Profile of Woodland in Quanzhou

The contents of 8 heavy metal elements (Sr, Ni, Fe, Cr, Cu, Mn, Pb, Zn) and the lead & strontium isotope composition of soil profile of woodland in Quanzhou city were analyzed by AAS and ICP-MS, respectively. A modified BCR four-step sequential extraction procedure was carried out to obtain the speciation fractionation of heavy metals in the soil profile from 4 stations. The results of the heavy metal elements and the speciation fractionation of heavy metals in the soil profile showed that the heavy metal pollution in the woodland in Quanzhou was relatively light, and the main pollution factor was Sr. The non-residue state of Pb was the highest, leading to the highest activity. The result of Nemero comprehensive pollution index showed that Sr in the depth of 0-60 cm was at heavy pollution level. The results of the RSP showed that the activity of Pb was the highest. The results of EF showed that Pb, Sr, Mn and Zn had exogenous sources. Factor analysis showed that the main sources of heavy metals were the compound pollution of agricultural activities, natural resources, and the vehicle exhaust. Composition of Pb isotopic ratios showed that, Pb in soil profile of woodland in Quanzhou was from vehicle exhaust and parent material. The contribution rates of the two sources in the soil profile were calculated by using the two-mixed model. The contribution rates of parent material and vehicle exhaust were 85.14%(62.53%-98.36%) and 14.86%(1.640%-37.47%) on average, respectively. Strontium isotope tracing results showed that the main sources of strontium were also vehicle exhaust and parent material. Coupling both Pb and Sr isotope ratios agreed with the above mentioned results.

Processes and ore genesis at the Yaochong Mo deposit, Henan Province, China

The Yaochong Mo deposit in Henan Province is located in the Dabie orogen, and its orebodies primarily occur as numerous veinlets hosted in the contact zone of the Yaochong stock with the Dabie Complex. Based on vein crosscutting relationships, mineral assemblages, and paragenetic sequence, the mineralization is divided into four stages: a quartz–K-feldspar–magnetite–hematite stage, a quartz–K-feldspar–molybdenite stage, a quartz–polymetallic sulfide mineral stage, and a quartz–carbonate stage. Three types of fluid inclusions have been recognized in the quartz: CO2-bearing fluid inclusions, H2O-rich fluid inclusions, and solid-bearing fluid inclusions. Microthermometric analyses of the fluid inclusions suggest that the fluids evolved gradually during the ore-forming process. In stages 1, 2, 3, and 4, the homogenization temperatures varied in the ranges 264–400°C, 175–487°C, 171–433°C, and 119–172°C, respectively, and the salinities varied in the ranges 4.34–7.70wt% NaClequiv, 2.77–32.49wt% NaClequiv, 2.20–30.70wt% NaClequiv, and 1.06–7.73wt% NaClequiv, respectively. The calculated δ18OH2O values of stages 1, 2, 3, and 4 ranged from 2.2‰ to 3.9‰, 0.9‰ to 1.7‰, −0.8‰ to −0.1‰, and −1.3‰ to 0.6‰, respectively, and the δ18D values varied from −68‰ to −62‰, −73‰ to −64‰, −75‰ to −65‰, and −68‰ to −65‰, respectively. These results show that the ore-forming fluids of the Yaochong molybdenum deposit were mainly derived from magmatic water, which likely included a small component of meteoric water. The δ34S values of pyrite and molybdenite varied from −2.9‰ to −1.8‰, and −2.7‰ to −1.6‰, respectively, and the 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the sulfide minerals ranged from 16.193 to 16.818, 15.105 to 15.288, and 36.698 to 37.307, respectively. The sulfur and lead isotope compositions indicated that the ore-forming constituents were derived from a deep igneous source originating in the lower crust. The Yaochong porphyry Mo deposit may have formed in a post-collision extensional setting. The Mo mineralization in the Yaochong deposit occurred at depths of 0.87–1.68km, and phase separation and immiscibility of the ore-forming fluids were critical for the formation of the deposit.

Geochemical and isotopic evidence for a magmatic-hydrothermal origin of the polymetallic vein-type Zn-Pb deposits in the northwest margin of Jiangnan Orogen, South China

Polymetallic vein-type Zn-Pb deposits are located in the Xiangxi–Qiandong zinc-lead metallogenic belt (XQMB) of the northwestern margin of the Jiangnan Orogen, South China. Ores are mainly found in fault-bounded quartz veins hosted in the upper part of the Banxi Group that consists of low-grade metamorphic sandstone, siltstone with minor tuff interbeds. The Zn-Pb deposits primarily contain sphalerite, galena, chalcopyrite and pyrite, accompanied by quartz and minor calcite. Zinc, lead, copper, indium and gallium are enriched in these ores. Investigation of the ore fluid reveals low temperature (87–262°C) with scattered salinity (range from 2.73 to 26.64wt% NaCleqv.). Hydrogen and oxygen isotopic compositions of fluid inclusions in quartz indicate mixing of magmatic hydrothermal fluid and meteoric water (δ18OH2O SMOW=0.2‰ to 4.2‰; δDH2O SMOW=−126‰ to −80‰). Carbon and oxygen isotopic composition of carbonate samples indicate the magmatic hydrothermal origin of CO32− or CO2 in ore-forming fluid (δ13CPDB=−6.9‰ to −5.7‰, δ18OSMOW=11.3‰ to 12.7‰). Sulfur and lead isotopic compositions (δ34SVCDT=8.8–14.2‰ and 206Pb/204Pb=17.156–17.209, 207Pb/204Pb=15.532–15.508, 208Pb/204Pb=37.282–37.546) demonstrate that sulfur sources were relatively uniform, and low radiogenic lead isotopic compositions indicate that ore metals were derived from a relatively unradiogenic source, probably by mixing of mantle with crust. Therefore, polymetallic vein-type Zn-Pb mineralization in this area probably arose from a magmatic-related hydrothermal system, and the deposition of sulfides occurred in response to cooling and boiling of magmatic hydrothermal fluids (high salinity, high δ18OH2O and δDH2O and metal-bearing), and is mainly the result of emplacement into open space and mixing with meteoric water (low salinity, low δ18OH2O and δDH2O). This study provides direct evidence that magmatism was involved in the ore-forming processes of the low temperature metallogenic district, South China, and it raises awareness about the presence of polymetallic vein-type Zn-Pb deposits in the northwest margin of Jiangnan Orogen and their potential as a source of zinc, copper, indium and gallium.

Geochronological, geochemical and Pb isotopic compositions of Tasmanian granites (southeast Australia): Controls on petrogenesis, geodynamic evolution and tin mineralisation

Large volumes of Devonian-Carboniferous granites were emplaced across Tasmania in southeast Australia, which was along the easternmost boundary of mid-Palaeozoic Gondwana. Some of these granites are associated with world class Sn–W deposits. Previous studies have focused mainly on relationships between granite petrogenesis and source rocks, and rarely on geochemical controls on Sn mineralisation. New zircon U-Pb ages of 405 to 396Ma reveal that the George River Granodiorite, Grant Point Granite and Mt. Pearson Granite from eastern Tasmania intruded prior to the Tabberabberan Orogeny. The Coles Bay Granite has a U-Pb age of 388±7Ma, implying that it was emplaced simultaneously with the Tabberabberan Orogeny in Tasmania. The western Tasmanian granites mostly intruded from 374 to 360Ma, after the Tabberabberan Orogeny. Granites associated with Sn–W deposits are moderately to strongly fractionated, including the Housetop, Meredith, Pine Hill and Heemskirk granites. Lead isotopic compositions of K-feldspars from the analysed granites, combined with isotopic evidence from other studies, suggest that differentiated granites in Tasmania had been highly contaminated by a crustal (sedimentary) component, and that western Tasmanian granites had a crustal source with substantially different isotopic characteristics to that of eastern Tasmania, which has a character similar to the Lachlan Orogen in southeast Australia. Tin-mineralised granites in Tasmania formed in a post-collisional extensional margin, a favourable environment for the production of Sn-rich melts from the lower crust. Prolonged fractional crystallisation, low oxygen fugacity and enrichments of volatiles are crucial factors to promote Sn enrichment in magmatic-hydrothermal fluids exsolved from crystallised felsic magmas.

Pb‐isotope compositions of the Tasik Chini volcanic‐hosted massive sulfide deposit, Central Belt of Peninsular Malaysia: Implication for source region and tectonic setting

AbstractLead isotope data of sulfides and host volcanic rocks from the Bukit Botol and Bukit Ketaya deposits, the two representative deposits of the Tasik Chini volcanic‐hosted massive sulfide (VHMS) deposit, Central Belt of Peninsular Malaysia, are reported. Lead isotope compositions of the associated sulfide minerals and volcanic rocks from the Bukit Botol deposit exhibit homogeneous and less radiogenic values (206Pb/204Pb showing a range of composition from 18.14 to 18.20, 207Pb/204Pb between 15.52 and 15.59 and 208Pb/204Pb from 37.96 to 38.35). Similarly, the Pb isotopic compositions of the host volcanic rocks from the Bukit Ketaya deposit yielded a narrow range to those of the sulfide samples (206Pb/204Pb from 18.04 to 18.20, 207Pb/204Pb between 15.43 and 15.57 and 208Pb/204Pb of 37.96 to 38.30). The uniform Pb‐isotope compositions of the sulfides in the ore horizon and the host volcanic rocks from both deposits suggest a derivation from a similar source reservoir and mineralization processes. In the framework of the tectonic model for the Central Belt of Peninsular Malaysia, both deposits display a range of lead isotopic compositions originated from mixing of bulk crust/juvenile arc and minor mantle sources, which are typical for VHMS deposits in an island arc–back arc setting.

North American origin of “pink–white” layers at the Mendeleev Ridge (Arctic Ocean): New insights from lead and neodymium isotope composition of detrital sediment component

Dolomite–rich layers of distinct pinkish colour are used as lithostratigraphic markers in the Amerasian Basin of the Arctic Ocean. However, origin of dolomite in these sediment units has not been studied in detail. In this study, lead (Pb) and neodymium (Nd) isotope composition of detrital clay–size fraction from different lithofacies were investigated in core PS72/340-5 recovered at the eastern flank of the Mendeleev Ridge. Prior to the geochemical analyses, grain–size distribution was analyzed in order to minimize the grain–size effect on the provenance signature. For provenance discrimination, results of isotope measurements were compared with marine surface sediment data and values for the circum–Arctic subaerial provinces. Late Quaternary sediment supply variability was analyzed using the mixing model constrained by two tracers: 207Pb/206Pb and εNd. Variations of sediment isotopic composition are inferred to result from mixing of volcanic and plutonic components. Usage of Pb isotopic ratios alone does not allow distinction between these two types of sources. Results confirm that over the last estimated ca. 200ka dolomite–rich pink layers at the Mendeleev Ridge were deposited during events probably associated with intensified iceberg transport from North America. In general, however, sedimentation was mostly controlled by terrigenous input from the Chukchi and East Siberian Seas, whereas sediment supply from the Laptev Sea area remained less important and relatively constant at the studied location.

Source apportionment of lead in the blood of women of reproductive age living near tailings in Taxco, Guerrero, Mexico: An isotopic study.

The concentration and isotopic composition of lead in the blood of forty seven women of reproductive age (15-45y) exposed to multiple sources in two rural communities of the mining region of Taxco, Guerrero in southern Mexico were determined in order to identify specific contributing sources and their apportionment and to trace probable ingestion pathways. Our data indicate that >36% of the studied women have blood lead concentrations above 10μgdL-1 and up to 87% above 5μgdL-1. Tailings contain between 2128 and 5988mgkg-1 of lead and represent the most conspicuous source in the area. Lead contents in indoor dust are largely variable (21.7-987mgkg-1) but only 15% of samples are above the Mexican Regulatory Guideline for urban soils (400mgkg-1). By contrast, 85% of glazed containers (range: 0.026-68.6mgkg-1) used for cooking and food storage are above the maximum 2mgL-1 of soluble lead established in the Mexican Guideline. The isotopic composition indicates that lead in the blood of 95% of the studied women can be modeled in terms of a mixing system between local ores (and derivatives), glazed pottery and Morelos bedrock, end-members, with the two former being largely the most important contributors. Only one sample shows influence of indoor paints. Indoor dust is dominated by ores and derivatives but some samples show evidence of contribution from a less radiogenic source very likely represented by interior paints. This study supports the application of lead isotopic ratios to identify potential sources and their apportionment in humans exposed to multiple sources of lead from both, natural and anthropogenic origin.

Abnormal mortality of octopus after a storm water event: Accumulated lead and lead isotopes as fingerprints.

Octopus vulgaris is a sedentary organism that inhabits coastal waters being exposed to anthropogenic compounds. Lead concentration in coastal environments reflects many processes and activities namely weathering, industrial and domestic discharges, and atmospheric deposition. Since lead isotopic composition is little affected by kinetic processes occurring between source and sink, its signature has been used to identify different Pb sources. After a short-term heavy rainfall, hundreds of octopus appeared dead in two Portuguese coastal areas. Histopathology and Pb levels and its stable isotopes were determined in tissues, such as digestive gland, of stranded octopus and compared to alive specimens, sediments and runoff material from the same areas. Histology results showed severe damage in stranded octopus tissues suggesting that death was probably associated to multiple organ failure linked to hypertrophy and exudates input. In addition, Pb in stranded specimens reach concentrations up to one order of magnitude above the levels reported for alive octopus. Pb isotopic signatures in stranded organisms were closer to runoff material pointing to a similar origin of Pb. In summary, the results in this study showed that a short-term runoff event might change abruptly the salinity leading to the disruption of the osmoregulation function of octopus and consequently leading to its death. The analyses of stable isotopic Pb signature in octopus tissues corroborate these results and points to a change in the Pb source due to runoff after the storm water event. Pb stable isotopes in octopus proved to be an adequate tool to confirm the cause of death and linking it to the environment conditions.

Lead concentrations and isotopic compositions in the Western Philippine Sea

Dissolved lead (Pb) concentrations and isotope ratios in seawater of the Western Philippine Sea (WPS) were determined to investigate sources of Pb in the region. Surface seawater concentrations at seven sampling stations ranged from 36.2 to 68.1pmolkg−1. Isotopic composition of surface water, with 206Pb/207Pb ranging from 1.162 to 1.170, 208Pb/207Pb ranging from 2.445 to 2.451, and 206Pb/204Pb ranging from 18.14 to 18.27, reflects Asian anthropogenic aerosols input to the WPS. Shallow water Pb concentrations within the Kuroshio Current domain are about 15pmol kg−1 lower than at other sites and, together with a distinct isotopic signature (206Pb/207Pb=1.167–1.170, 208Pb/207Pb=2.447–2.451 and 206Pb/204Pb=18.22–18.27), reflect water originating from the Equatorial Pacific that is relatively less impacted by contamination from anthropogenic inputs. An isotopically distinct sub-surface Pb maximum at about 100 to 250m, representing water originating from the Western North Pacific where anthropogenic Pb deposition is high, was seen at all seven sites. Lead concentrations in deep water in the stations further from shore are typically lower than in the surface layer and ranged from 11.2 to 51.6pmolkg−1. Lead isotopic signatures in deep water at these sites (206Pb/207Pb=1.162–1.184; 208Pb/207Pb=2.448–2.471; 206Pb/204Pb=18.13–18.51) are offset from pre-anthropogenic values and suggest that anthropogenic sources have penetrated the deep water column. Elevated concentrations and isotopic signatures observed in the deep water at stations closer to shore, where sediment transport is prevalent, indicate that sedimentary input is a major source of dissolved Pb at these sites. Differences in Pb concentrations and isotopic signatures between samples collected from the Pacific Deep Water (PDW) water-mass during this study and those collected a decade ago suggest that Pb inputs even in deep water change on decadal scales.

Magmatic-hydrothermal origin of the early Triassic Laodou lode gold deposit in the Xiahe-Hezuo district, West Qinling orogen, China: implications for gold metallogeny

The Xiahe-Hezuo district in the West Qinling orogen contains numerous Au-(As-Sb) and Cu-Au-(W) deposits. The district is divided into eastern and western zones by the Xiahe-Hezuo Fault. The western zone is exposed at a shallow level and contains sediment-hosted disseminated Au-(As-Sb) deposits, whereas the eastern zone is exposed at a deeper level and contains Cu-Au-(W) skarn and lode gold deposits within or close to granitic intrusions. The Laodou gold deposit in the eastern zone consists of auriferous quartz-sulfide-tourmaline and minor quartz-stibnite veins that are structurally controlled by fault zones transecting the Laodou quartz diorite porphyry stock and enveloped by potassic and phyllic alteration. Both the veins and alteration halos commonly contain quartz, sericite, tourmaline, pyrite, and arsenopyrite, with minor galena, sphalerite, chalcopyrite, tetrahedrite, and enargite. Gold occurs mainly as invisible gold in pyrite or arsenopyrite and locally as inclusions less than 50 μm in diameter. The zircon U-Pb age of 247.6 ± 1.3 Ma (2σ) on the host quartz diorite porphyry and the sericite 40Ar/39Ar plateau ages of 249.1 ± 1.6 and 249.0 ± 1.5 Ma (2σ) on two ore-related hydrothermal sericite samples are within analytical errors of one another. At the formation temperature (275 °C) inferred from microthermometric measurements of fluid inclusion, sericite and tourmaline yield calculated δDH2O values of −70 to −45‰ and δ 18OH2O of 5.8 to 9.7‰, while quartz yields calculated δ 18OH2O values of 5.1∼5.7‰. Hydrothermal tourmaline in quartz-sulfide-tourmaline veins has δ 11B of −11.2 to −0.9‰ (mean of −6.3‰) that are similar to the values of magmatic tourmaline (−8.9 to −5.5‰ with a mean of −6.8‰) in the host quartz diorite porphyry. The δ 34S values of sulfide minerals range from −5.9 to +5.8‰ with a mean of −0.6‰ that is typical of magmatic sulfur. Pyrite from hydrothermally altered quartz diorite porphyry and quartz-sulfide-tourmaline veins have relatively homogeneous lead isotopic compositions, compatible with granitic intrusions in the district. The geochronological and isotopic data combined support a magmatic origin for the Laodou gold deposit, most likely formed from fluids exsolved from the Laodou quartz diorite porphyry or associated intrusive phases at deeper levels beneath the stock. Orogenic and Carlin-like gold deposits in the West Qinling orogen have been commonly thought to have formed from metamorphic fluids. This study, however, highlights the role of magmatic-derived fluids in the formation of lode gold deposits. Synthesis of geochronological, geological, and geochemical data on magmatic rocks and ore deposits in and surrounding the Xiahe-Hezuo district indicates that gold mineralization predominantly occurred within a subduction-related magmatic arc prior to collision between the Yangtze and North China cratons that produced the West Qinling orogen.

Lead isotope analysis in magic artefacts from the Berlin museums

A set of 59 ancient magical artefacts, mainly made of lead, was selected from the collections of the Staatliche Museen zu Berlin in order to unravel their origins. All the selected artefacts have been studied for their Pb isotope compositions, which covered the whole range of the Mediterranean ore deposits. However, the majority (≈86%) were made of lead matching the small compositional range of the Laurion ore deposits. Only eight out of the 59 artefacts were made of recycled lead or lead from other ore deposits. Additionally, all but two were approximately dated based on their inscriptions. The lead isotopic composition together with information obtained from the inscriptions, the resulting dating, the context of the find and the known history of each item allowed us to gain more detailed information about the origins of these magical artefacts. The Attic provenance of 36 curse tablets was confirmed, whereas for 11 curse tablets previously classified as non-Attic, the provenance was either confirmed and specified (six artefacts) or changed to Attic (five artefacts). Surprisingly, the majority (six out of eight) of the analysed curse tablets from the Egyptian collection showed a lead isotopic composition closely matching that of Laurion. A Laurion-like lead isotopic composition was also observed for three of the four analysed oracular tablets from Dodona. Together with the dating information, this points to Laurion as the major and dominant lead source in the Aegean, at least during the fourth–third century B.C. The few curse tablets from earlier than the fourth–third century B.C. point to the use of multiple and thus isotopically more variable lead sources compared with the Roman times.

Staurolite as an isotopic U–Pb geochronometer

A new approach is suggested for measuring the real U–Pb and Pb–Pb ages of rock-forming metamorphic staurolite. Previously, two approaches have been used for this purpose: (1) measurement of the lead isotopic compositions, uranium and lead contents in leach substance as a product of the step-leaching technique; age is calculated by plotting the Pb–Pb leaching isochron; and (2) lead and uranium isotopic compositions are measured in completely dissolved mineral material without leaching. In both cases, it is assumed a priori that inclusions, overgrowths, secondary phases, and the host mineral are cogenetic. This assumption may lead to errors in the measured age. The technique suggested in this paper uses various reagents (acids) to purify staurolite from the above-mentioned secondary phases while obtaining a staurolite “pure culture,” its subsequent disolution, introduction of the mixed spike, separation of lead and uranium compounds, and, finally, estimation of a real staurolite age using several samples to plot the monomineralic Pb–Pb isochron or by plotting measured Pb/U ratios in the diagram with concordia. The data can be used then to reconstruct the P–T–t evolution of metamorphism.

Thallium-rich pyrite ores from the Apuan Alps, Tuscany, Italy:constraints for their origin and environmental concerns

The southern sector of the Apuan Alps (AA) massif, Tuscany, Italy, is characterized by the occurrence of a series of baryte–pyrite–iron oxide orebodies whose Tl-rich nature was recognized only recently. The geochemistry of the pyrite ore was investigated through inductively coupled plasma mass spectrometry. In addition, lead isotope data for selected pyrite ores from AA were collected. Pyrite ores are characterized by a complex geochemistry, with high concentrations of Tl (up to 1100 μg/g) coupled with high As and Sb contents; the Co/Ni ratio is always <1. Geochemical data of pyrite and marcasite ore samples from other mining districts of Tuscany have been collected in order to compare them with those from the AA. These samples usually have very low Tl content (less than 2 μg/g) and high to very high Co/Ni and As/Sb ratios. Only some samples from the Sb–Hg ore deposits showed very high Tl concentrations (up to ~3900 μg/g). Another difference is related to the lead isotope composition, with pyrite ores from AA markedly less radiogenic than those from the other deposits from Tuscany. Geochemical data of pyrite ores from AA give new insights on the genesis of the baryte–pyrite–iron oxide orebodies, relating their formation to low-temperature hydrothermal systems active during early Paleozoic; in addition, these data play a fundamental role in assessing the environmental impact of these deposits.

An isotopic study of atmospheric lead in a megacity after phasing out of leaded gasoline

Atmospheric lead (Pb) concentrations in São Paulo city, Brazil, remain significant, despite the fact that leaded gasoline was phased out. The use of its isotope signature allows tracing emissions to the increasing number of cars, urban construction, and industrial emissions in this densely populated area. High-precision and accurate stable isotope ratio determinations using isotope dilution thermal ionization mass spectrometry (ID-TIMS) combined with particle induced X-ray emission (PIXE) and multivariate analysis were used to identify the main sources of lead present in São Paulo atmospheric particulates. Throughout a period of sixty days, aerosol samples were collected every 12 h during the summer of 2005 at the University of São Paulo (USP) and simultaneously during one week in an industrial area (Cubatão) and in two more remote areas (São Lourenço da Serra and Juquitiba). The data suggests that aerosols from São Paulo are mainly derived from vehicular exhaust (mostly gasoline) and traffic dust resuspension, with the admixture of industrial emissions, including cement. Lead isotopic compositions (expressed as 206Pb/207Pb ratios) measured in São Paulo aerosols range from 1.1491 to 1.2527 and are similar to those determined from tunnel dust, fuels, and vehicular exhaust; therefore, those are likely to be the main lead sources in the atmosphere of São Paulo. Vehicular traffic (fuel combustion, dust from vehicular components, and road dust) remains an important source of lead in the atmosphere. The maximum concentration occurring during the summer was 0.055 μg m−3 in fine particles, which is detrimental for human health and may lead to exceedances of the Air Quality Standard for lead of 0.15 μg m−3 (3-month average) during other seasons when the dispersion of pollutants is less favourable.

Sulfur and lead isotopic compositions of massive sulfides from deep-sea hydrothermal systems: Implications for ore genesis and fluid circulation

Studies of sulfur and lead isotopic compositions in hydrothermal deposits are an important tool to determine the source and processes of both sulfur and lead, and to understand the origin of hydrothermal ore deposits. Here, the sulfur and lead isotopic compositions of sulfide minerals have been studied for different hydrothermal fields in the East Pacific Rise (EPR), Mid-Atlantic Ridge (MAR), Central Indian Ridge (CIR), Southwest Indian Ridge (SWIR), and North Fiji Basin (NFB). The sulfur isotopic compositions of the studied sulfide samples are variable (δ34S 0.0 to 9.6‰, avg. δ34S 4.7‰; n=60), being close to the associated igneous rocks (~0‰ for, e.g., basalt, serpentinized peridotite), which may reflect the S in the sulfide samples is derived mainly from the associated igneous rocks, and a relatively small proportion (<36%) of seawater sulfur incorporated into these sulfides during mixing between seawater (δ34S 21‰) and hydrothermal fluid. In contrast for a mixed origin for the source of S, the majority of the lead isotopic compositions (206Pb/204Pb 17.541±0.004 to 19.268±0.001, 207Pb/204Pb 15.451±0.001 to 15.684±0.001, 208Pb/204Pb 37.557±0.008 to 38.988±0.002, n=21) of the sulfides possess a basaltic Pb isotopic composition, suggesting that the lead in the massive sulfide is mainly leached from local basaltic rocks that host the sub-seafloor hydrothermal systems in sediment-free mid-ocean ridges and mature back-arc basins. Furthermore, sulfide minerals in the super-fast and fast spreading mid-ocean ridges (MORs) exhibit less spread in their the δ34S values compared to sulfides from super-slow, and slow spreading MORs, which is most easily explained as a lesser degree of fluid-rock interaction and hydrothermal fluid-seawater mixing during hydrothermal ore-forming process. Additionally, the S and Pb isotope compositions of sulfides are controlled by the fluid processes for forming seafloor massive sulfide deposits. We demonstrate that the variable sulfur and lead isotopic compositions exhibit a relationship with the sulfur and lead sources, fluid–rock interaction, and fluid–seawater mixing.

Early Cretaceous tungsten mineralization in Southeastern China: the Wuning example

ABSTRACTThe Wuning tungsten deposits in northwestern Jiangxi are located in the Middle-Lower Yangtze River metallogenic belt of SE China. This article decodes the large tungsten-mineralized ore field by analysing three typical deposits: Shimensi, Dahutang, and Shiwendong. The Shimensi deposit shows three mineralization styles, and the associated hydrothermal alteration mainly includes K-feldspathization, greisenization, chloritization, silicification, and carbonatization. The sulphur isotopic compositions of sulphides in the Dahutang deposit indicate that the sulphur source was homogeneous and closely related to magmatic sulphur. The lead isotopic compositions of sulphides suggest multiple sources that were also closely related to magmatism. The carbon isotopic compositions of calcite indicate that hydrothermal fluids were derived from the granitic magma. Hydrogen and oxygen isotopic compositions of quartz veins indicate that the ore-forming fluids had a magmatic-hydrothermal origin, but mixed with meteoric water. Fluid inclusions from the Shiweidong deposit are low density, indicating medium-high T and low-medium salinity, further suggesting that it was a shallow magmatic-hydrothermal deposit, and the metallogenic hydrotherm mingled with the surface water late in the evolution of the system. Mineralization was related to Early Cretaceous magmatism in eastern China. The subduction of the palaeo-Pacific plate and the subsequent lithospheric delamination reflected transition from a compressional to extensional tectonic regime. The upwelling of the hot asthenosphere triggered partial melting of the Neoproterozoic Shuangqiaoshan Group, with high W background concentrations. The ascent of the magma resulted in the exsolution of the ore-bearing magmatic hydrothermal fluid.