Lead Isotope Values Research Articles

Lead isotopes in New England (USA) volcanogenic massive sulfide deposits: implications for metal sources and pre-accretionary tectonostratigraphic terranes

Lead isotope values for volcanogenic massive sulfide (VMS) deposits provide important insights into metal sources and the nature of pre-accretionary tectonostratigraphic terranes and underlying basements. Deposits of this type in New England formed in diverse tectonic settings including volcanic arcs and backarcs, a supra–subduction zone arc, a rifted forearc foreland basin, and a rifted continental margin. Following VMS mineralization on or near the seafloor, components of the tectonostratigraphic assemblages—volcanic ± sedimentary rocks, coeval intrusions, sulfide deposits, and underlying basements—were diachronously accreted to the Laurentian margin during the Paleozoic. Lead isotope data for galena show relatively large ranges for206Pb/204Pb,207Pb/204Pb, and208Pb/204Pb. Evaluation of potential lead sources, using for comparison Pb-isotope data from modern and ancient settings, suggests that principal sources include the mantle, volcanic ± sedimentary rocks, and deeper basement rocks. Integration of the Pb-isotope values with published data such as Nd isotopes for the volcanic rocks and from deep seismic reflection profiles points to the involvement of several basements, including those of Grenvillian, Ganderian, Avalonian, and West African (and (or) Amazonian) affinity. Clustering of Pb-isotope data for VMS deposits within individual Cambrian and Ordovician volcanic and volcanosedimentary settings, delineated by differences in206Pb/204Pb and µ (238U/204Pb) values, are consistent with lead derivation from at least four and possibly five different tectonostratigraphic assemblages with isotopically distinct basements. Collectively, our Pb-isotope data for New England VMS deposits provide a novel window into the nature of subarc basement rocks during pre-accretionary sulfide mineralization outboard of Laurentia during early Paleozoic time.

Miocene Volcanism of the Baikal Rift Across the Boundary of the Siberian Craton: Evidence for Lithospheric Mantle Melting

Abstract Continental rifting is usually viewed in terms of two contrasting models of active and passive extension. The origin of the Baikal Rift, adjacent to the southern part of the Siberian Craton, has been described by both models in the past. It is expected that basaltic magmatism in an active model scenario should be primarily sourced from a mantle plume or plume-fed asthenosphere, whereas melting of the lithospheric mantle is expected to be a predominant source for magmatism in the passive model. In this paper, we focus on the Miocene volcanic rocks sampled along two 60-km-long profiles that cross the boundary between the Neoproterozoic Tuva-Mongolian massif and the Archean-Paleoproterozoic Siberian Craton. Most of the samples studied are trachybasalts. In terms of trace element concentrations normalised to primitive mantle, the lavas mimic oceanic island basalt-like patterns with troughs at Rb, Th–U, Pb, and Y, and peaks at Ba, Nb, Ta, K, and Sr. Moreover, similar trace element patterns to the studied samples are also observed for Miocene and Quaternary lavas located in the southwestern of the Baikal Rift, and adjacent regions of non-rifted Mongolia. According to the ratio of CaO to MgO, and TiO2/Al2O3 to SiO2, the compositions of the studied lavas coincide with experimental melts derived from mafic lithologies. Trace element data of samples suggest that garnet was a residual phase during partial melting. The Sr-Nd isotopic characteristics of the studied lavas are 87Sr/86Sr 0.70427–0.70469 and 143Nd/144Nd 0.51267–0.51284. They are identical to the coeval Miocene lavas of neighbouring volcanic fields, but they differ from the Quaternary lavas that extend to lower 87Sr/86Sr (0.7038–0.7044) with near identical 143Nd/144Nd. Isotopes of Hf for studied samples show values εHf = 6.0–7.7, except for the two samples taken within the boundary between two lithospheric blocks with εHf 4.6 and 4.8. The δ18O of olivine from lava samples is everywhere higher than that of the asthenospheric mantle and ranges from 5.5 to 6.4‰. Variations of δ18O versus Mg#, 87Sr/86Sr and εHf in the studied samples do not correlate, but do unequivocally rule out crustal assimilation. The isotopic variations are consistent with recycling of mafic crustal lithologies at mantle depths. Lavas from the Tuva-Mongolian massif and the Siberian Craton differ in lead isotopes by lower values of 206Pb/204Pb (< 17.785) and higher values of Δ8/4Pb (61–75) for on-cratonic samples and the reverse relationship for off-cratonic lava (> 17.785 and 55–61), respectively. The equation for Δ8/4Pb = [208Pb/204Pb-(1.209*(206Pb/204Pb) +15.627)] *100 is from Hart (Nature, 309, 753–757, 1984). The correlation of lead isotopes with the mafic recycled component, the sharp change of lead isotopic values at the cratonic boundary and decoupling of lead isotope ratios from other isotopic ratios lead us to suggest that the values of 206Pb/204Pb and Δ8/4Pb are associated with an ancient accessory mineral phase such as sulphide confined within the lithospheric mantle. The predominant role of the lithospheric sources in the formation of the Miocene volcanic rocks indicate that the volcanism of the Baikal Rift was caused by a passive tectonic process, rather than active rifting.

Genesis and prospecting significance of the Buziwannan gold-polymetallic ore deposit in the West Kunlun Orogen Belt, China: Constraints from mineral geochemistry and in situ S–Pb isotope analyses of sulfides

The Buziwannan gold-polymetallic deposit is located in Northwest China's West Kunlun Orogen Belt (WKOB). There are two metallogenic stages that have been identified: skarn and hydrothermal. In this research study, in situ mineral geochemistry and sulfur–lead isotopes are used to precisely constrain the genesis and ore-forming process.Pyrite is the most dominant sulfide, and four types have been identified. Py0 is a sedimentary euhedral crystal; Py1 is a subhedral grain occurring in skarn ores, and coexists with Po1, Apy1, Ccp1 and Gn1; Py2, which coexists with Apy2, Po2 and Ccp2, is a subhedral to irregular crystal; and Py3 is a colloform crystal. Gn2 is the most recent sulfide. Magnetite and Ccp1 LA–ICMPS analyses indicate a skarn origin. Py0 and Py1 have the highest Co/Ni ratios and Ni contents, respectively, and Au has positive correlations with Pb, Ag and As, according to the trace element compositions of pyrite (LA–ICPMS). With the exception of four spots, most pyrites have Au (0.01–30.23 ppm) and As (1.47–15,709 ppm) concentrations below the Au saturation line, indicating that the majority of gold is present as lattice bound Au+. Py3 has clearly higher Sb contents indicating that Sb-rich fluids were added.The δ34S values of sulfides show that the sedimentary Py0 and skarn sulfides have the highest and lowest δ34S values of +13.30 to +14.67 ‰ and +4.48 to +7.77 ‰, respectively, and other sulfides possess δ34S values that fall between the two members, indicating a mixed source of magmatic and sedimentary. The lead isotope values also indicate that the sulfides from the hydrothermal stage have a mixed Pb source of magmatic and sedimentary.The skarn ores are spatially and genetically related to the Triassic granodiorite, indicating a Triassic age for ore formation. The Triassic magmatic intrusions hold the potential for future gold deposit exploration in the WKOB.

Non-Local Enemies or Local Subjects of Violence?: Using Strontium (87Sr/86Sr) and Lead (206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) Isobiographies to Reconstruct Geographic Origins and Early Childhood Mobility of Decapitated Male Heads from the Majes Valley, Peru

Throughout much of the pre-Hispanic Andes, bioarchaeological and iconographic evidence shows that the decapitation, dismemberment, and display of human heads were important aspects of ritual practices. Researchers have debated about the social identities of these decapitated heads—were they revered local ancestors, non-local enemies captured in raids or war, or locals injured in distant combat partially repatriated for home burial—answers which have distinct implications for understanding the motivations and social contexts of this practice. We describe trophy-taking and trophy-making from the Uraca cemetery in pre-Hispanic Arequipa, Peru. To determine whether these trophies were locals, we employ radiogenic isotope analyses (87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb) of tooth enamel from 37 individuals (25 non-trophies and 12 adult male trophies). To understand the degree of childhood mobility that occurred and whether that differed between individuals who became trophies and those who did not, we also examine 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb in paired teeth from infancy/early childhood and middle childhood of 18 individuals (8 non-trophies and 10 trophies). Results show that 20% of the non-trophies and 75% of the trophies were non-local relative to modeled local 87Sr/86Sr and mean (± 2 SD) of lead isotope values. Intra-childhood differences show that the individuals who became trophies experienced more childhood mobility than non-trophy individuals. This suggests Uraca’s external interactions and mobility were structured by violent intergroup raids and warfare throughout the region. Ongoing analyses will extend Uraca’s residential isobiographies to adolescence and late-life, refine the expected range of isotope ratios in the region, and clarify the extent of Majes Valley mobility during the mid-first millennium CE.

Modern isotopic signatures of Plata River sediments and changes in sediment supply to the western subtropical South Atlantic during the last 30 kyr

Sediments transported in rivers reflect the geology of the catchment area and its radiogenic isotopic composition. These isotopic signatures are not significantly altered by weathering, transport or deposition and hence can document variations in sediment supply. Here we present strontium (Sr), neodymium (Nd) and lead (Pb) isotope values from suspended and riverbed sediments of the Plata River drainage basin, the second largest on the South American continent, and from two marine sediment cores collected off the mouth of the Plata River in the western subtropical South Atlantic. Our modern riverine data suggest that the basin has three main sediment source areas, namely the upper Paraná River, the Uruguay River and the Andean draining rivers. Sediments from the Andean draining rivers (Salado and Bermejo Rivers) have the most radiogenic Pb (i.e. >18.5 for 206Pb/204Pb) and Sr (average of 0.726 ± 0.031; 2SD) isotopic signatures, and least radiogenic εNd values (average of −10.5 ± 3.1; 2SD). The upper Paraná and Uruguay Rivers have less radiogenic Pb (i.e. <18.5 for 206Pb/204Pb) and Sr (average of 0.715 ± 0.003; 2SD) isotopic signatures. While the upper Paraná River has average εNd values of −7.8 ± 1.1 (2SD), the Uruguay River has average εNd values of −5.9 ± 0.2 (2SD). The modern isotopic signature at the mouth of the Plata River is largely dominated by the Andean draining rivers. To reconstruct changes in sediment supply to the western subtropical South Atlantic, we used this new riverine dataset together with literature values from the Argentine continental margin to interpret the data from two marine sediment cores. The downcore records cover the last ∼30 kyr and show two short-lived excursions (i.e. Heinrich Stadial 1 and the Younger Dryas) and two long-term trends (i.e. late Pleistocene (i.e. ∼29 to 11 cal ka BP for Sr and ∼29 to 25 cal ka BP for Nd), and early and mid-Holocene). We suggest that the short-lived excursions result from increased precipitation in the headlands of the Andean draining rivers during Heinrich Stadial 1 and the Younger Dryas. The late Pleistocene long-term change showed an increase in the contribution of material from the Plata River drainage basin in relation to material from the Argentine continental margin most probably due to low sea-level. The early and mid-Holocene long-term trend showed the opposite change in sediment input and was related to decreased precipitation over most of the Plata River drainage basin.

Genesis of the Changba–Lijiagou Giant Pb‐Zn Deposit, West Qinling, Central China: Constraints from S‐Pb‐C‐O isotopes

AbstractThe extensive Changba‐Lijiagou Pb‐Zn deposit is located in the north of the Xihe–Chengxian ore cluster in West Qinling. The ore bodies are mainly hosted in the marble, dolomitic marble and biotite‐calcite‐quartz schist of the Middle Devonian Anjiacha Formation, and are structurally controlled by the fault and anticline. The ore‐forming process can be divided into three main stages, based on field geological features and mineral assemblages. The mineral assemblages of hydrothermal stage I are pale‐yellow coarse grain, low Fe sphalerite, pyrite with pits, barite and biotite. The mineral assemblages of hydrothermal stage II are black‐brown cryptocrystalline, high Fe shalerite, pyrite without pits, marcasite or arsenopyrite replace the pyrite with pits, K‐feldspar. The features of hydrothermal stage III are calcite‐quartz‐sulfide vein cutting the laminated, banded ore body. Forty‐two sulfur isotope analyses, twenty‐five lead isotope analyses and nineteen carbon and oxygen isotope analyses were determined on sphalerite, pyrite, galena and calcite. The δ34S values of stage I (20.3 to 29.0‰) are consistent with the δ34S of sulfate (barite) in the stratum. Combined with geological feature, inclusion characteristics and EPMA data, we propose that TSR has played a key role in the formation of the sulfides in stage I. The δ34S values of stage II sphalerite and pyrite (15.1 to 23.0‰) are between sulfides in the host rock, magmatic sulfur and the sulfate (barite) in the stratum. This result suggests that multiple S reservoirs were the sources for S2– in stage II. The δ34S values of stage III (13.1 to 22‰) combined with the structure of the geological and mineral features suggest a magmatic hydrothermal origin of the mineralization. The lead isotope compositions of the sulfides have 206Pb/204Pb ranging from 17.9480 to 17.9782, 207Pb/204Pb ranging from 15.611 to 15.622, and 208Pb/204Pb ranging from 38.1368 to 38.1691 in the three ore‐forming stages. The narrow and symmetric distributions of the lead isotope values reflect homogenization of granite and mantle sources before the Pb‐Zn mineralization. The δ13CPDB and δ18OSMOW values of stage I range from –0.1 to 2.4‰ and from 18.8 to 21.7‰. The values and inclusion data indicate that the source of fluids in stage I was the dissolution of marine carbonate. The δ13CPDB and δ18OSMOW values of stage II range from –4 to 1‰ and from 12.3 to 20.3‰, suggesting multiple C‐O reservoirs in the Changba deposit and the addition of mantle‐source fluid to the system. The values in stage III are –3.1‰ and 19.7‰, respectively. We infer that the process of mineralization involved evaporitic salt and sedimentary organic‐bearing units interacting through thermochemical sulfate reduction through the isotopic, mineralogy and inclusion evidences. Subsequently, the geology feature, mineral assemblages, EPMA data and isotopic values support the conclusion that the ore‐forming hydrothermal fluids were mixed with magmatic hydrothermal fluids and forming the massive dark sphalerite, then yielding the calcite‐quartz‐sulfide vein ore type at the last stage. The genesis of this ore deposit was epigenetic rather than the previously‐proposed sedimentary‐exhalative (SEDEX) type.

Trace elemental and sulfur-lead isotopic variations in metamorphosed volcanogenic massive sulfide (VMS) mineralization systems: An example from the Keketale Pb-Zn(-Ag) deposit, NW China

The effects of post-VMS (volcanogenic massive sulfide) deformation/metamorphism on sulfide trace element and sulfur-lead isotopic compositions remain unclear. The greenschist to lower amphibolite facies metamorphosed Keketale VMS Pb-Zn(-Ag) deposit, located in the Devonian Maizi volcanic-sedimentary basin in the Chinese Altay, NW China, provides an opportunity to resolve the abovementioned issue. Two mineralization stages are recognized at Keketale, including (1) primary banded, massive and disseminated ores derived from sea-floor hydrothermal mineralization and (2) ore remobilization, as represented by intensively-deformed ores and quartz-polymetallic sulfide ore veins that crosscut the primary ores. Sulfide trace elements data suggest that Stage II pyrite and pyrrhotite have higher contents of Cu, Zn, Ag, Sb and Pb, whereas contents of these elements are higher in Stage I sphalerite and galena than their Stage II counterparts. Such elemental remobilization was probably caused by the rapid intragrain diffusion and subsequent fluid-mediated liberation with trace elements re-precipitated as particles within the same grain and nearby minerals, respectively. The δ34SCDT values in both stages show a trimodal distribution (−25.9 to −22.7‰, −17.0 to −10.6‰ and 0.6 to 2.1‰). Sulfide mineral pairs formed during primary VMS mineralization are not in sulfur isotopic equilibrium, and only localized re-equilibration occurs during deformation and metamorphism. In addition, the lead isotopic values of galena from remobilized sulfide veins overlap with those of the Stage I galena and pyrite. These data indicate that regional deformation and metamorphism of the Keketale deposit can be approximated as a closed system in terms of sulfur-lead isotopes. Whilst the presence of the anomalously low δ34S values (minimum −25.9‰) and the distinct lead isotopic ratios of sulfides from the calcite-quartz veins argue for that in the late part of the metamorphic event, some exotic lead and light sulfur were sourced from outside the ore field. In situ δ34S values of Stage I sulfides vary widely (−17.0 to +2.1‰), suggesting that the sulfur was originated from bacterial sulfate reduction (BSR) of marine sulfates with probably some magmatic input. Lead isotopes of the sulfides and mineralized meta-sedimentary-volcanic rocks display a linear distribution between the mantle and upper crust line in the 206Pb/204Pb vs. 207Pb/204Pb diagram. The lead source may be derived from both felsic volcanic rocks and mafic igneous rocks (and/or magmatic volatiles), and the sulfur-lead isotopes may result from a shallow-level seawater circulating process. An additional group of lead isotopic compositions of the meta-volcanic rocks show elevated present-day 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values, probably due to decay of Th and U carried by deeply-penetrative circulation (~13 km) of CO2-F-Cl-rich hydrothermal (metamorphic) fluids. Both syn-VMS shallow (seawater) and post-VMS deep (metamorphic fluids) circulation processes are critical for the metal concentration at Keketale.

Geological, geochemical and microthermometric characteristics of the Hakkari region Zn-Pb deposits, SE Turkey

The Hakkari region in SE Turkey contains large Zn-Pb deposits, primarily of non-sulfide ore in Upper Triassic passive margin carbonates. In the Karakaya, Meskantepe and Üzümcü Zn-Pb deposit, the 3 main and >15 ore layers alternate with a thick-bedded limestone. The feeder in the region veins are well defined, containing both non-sulfide and sulfide ore. Primary sulfide ore contains between 1 and 37 % Zn, has transformed to “non-sulfide” ore containing Zn > 10%. Both non-sulfide and sulfide ore is associated with As, Se, Hg, Tl, Mn and Sb, which is similar to other SEDEX deposits. The average δ34S of the stratiform and feeder zone sulfides are 2.1‰ and 1.67‰, respectively. Sulfur isotope data of sphalerite, galena and pyrite (from −3.4 to 8.8‰) indicates that sulfur came from a homogeneous large source. Sulfate was reduced by the process of thermochemical sulfate reduction (TSR) rather than bacterial sulfate reduction (BSR). Lead isotope values (206Pb/204Pb ≈ 18.49, 207Pb/204Pb ≈ 15.66 and 208Pb/204Pb ≈ 38.69) reflect an evolved upper crustal source. The homogenisation temperature (Th) and salinity of fluid inclusions is from 165 to 289 °C, and from 1 to 22% equiv. NaCl salinity. Such a wide range of Th and salinity, and Cl/Br ratio (409 from sphalerite and galena; 662 from barite) of fluid inclusions may indicate mixing of basinal brines and seawater.Successive ore levels, laminated with shale-carbonate rich in organic matter, formed on the seafloor as banded and replacement ore. Trace element associations, fluid inclusion and isotope data indicate that the Zn-Pb deposits were formed as synsedimentary processes associated with feeder systems during the initiation of the Triassic rifting as a vent-proximal SEDEX-type. The metals (Pb, Zn, Fe) were leached from Palaeozoic and older clastic rocks in the Arabian platform by seawater sourced fluids, and ascended through deep fractures. The metalliferous fluids should have formed vein type mineralization in feeder zone, sub-seafloor replacement type ore under the ocean floor, and stratiform ore on the seafloor.

Genesis of the Bagenheigeqier Pb–Zn skarn deposit in Inner Mongolia, NE China: constraints from fluid inclusions, isotope systematics and geochronology

AbstractMost skarns are found near the pluton or in lithologies containing at least some limestone. However, recent research has shown that neither a pluton nor limestone is necessarily required to form a skarn deposit. The newly discovered Bagenheigeqier Pb–Zn skarn deposit is located in NE China. The skarn and Pb–Zn orebodies occur in volcanic lithologies of the Baiyin’gaolao Formation and are controlled by NE–SW-trending faults. The nearest pluton is a granite porphyry, at a distance of 20–250 m from the orebodies. Five paragenetic stages at Bagenheigeqier are recognized: (I) skarn; (II) oxide; (III) early sulphide; (IV) late sulphide; and (V) late quartz–calcite. The fluid inclusions from stages II to V homogenized at temperatures of 402–452, 360–408, 274–319 and 167–212°C, respectively. The hydrogen and oxygen isotope compositions (δ18OH2O, –12.4‰ to +9.3‰; δDH2O, –156.5‰ to –99.1‰) indicate that the ore-fluids were primarily of magmatic origin, with the proportion of meteoric water increasing during the progression of ore formation. Sulphur isotope values (δ34SVCDT, 1.4–5.5‰), lead isotope values (206Pb/204Pb, 18.184–18.717; 207Pb/204Pb, 15.520–15.875; 208Pb/204Pb, 37.991–38.379) and the initial 187Os/188Os ratios of the pyrite (0.307 ± 0.06) suggest that the ore metals were derived from the granite porphyry and Baiyin’gaolao Formation. Re–Os dating of pyrite intergrown with galena and sphalerite yielded a well-constrained isochron age of 151.2 ± 4.7 Ma, which is coeval with the laser ablation – inductively coupled plasma – mass spectrometry zircon U–Pb age of 154 ± 1 Ma for the granite porphyry. The deposit was therefore formed during Late Jurassic time.

Geology, fluid inclusion, and H–O–S–Pb isotopic study of the Shenshan skarn Fe–Cu deposit, Southern Great Xing'an Range, Northeast China

The southern Great Xing'an Range (SGXR) is one of the most important metallogenic belts in Northeast China, containing numerous deposits of Cu, Fe, Pb, Zn, Au, etc. The newly discovered Shenshan Fe–Cu skarn deposit, located in the northern segment of the SGXR, is spatially and temporally associated with Mesozoic granodiorites that were emplaced into the Zhesi Formation. Based on field investigations and petrographic observations, four main paragenesis stages of skarn formation and ore deposition have been distinguished: garnet–diopside (Stage I), magnetite–quartz (Stage II), pyrite–chalcopyrite–molybdenite–quartz (Stage III), and barren sulphide–quartz–carbonate (Stage IV). Stage I is characterized by the formation of garnet and diopside and high-temperature (365–495 °C) hypersaline (37.56–49.8 wt% NaCl equiv.) hydrothermal fluids with a fluid inclusion (FI) assemblage of daughter-mineral-bearing three-phase (SL-type), liquid-rich (VL-type), and vapour-rich (LV-type) FIs. These fluids were most likely generated directly from a silicate melt due to the boiling of primary magmatic fluids at a depth of ~1 km, at a lithostatic pressure of 300 bars. Stage II coincides with the replacement of garnet and diopside by tremolite, quartz and magnetite. Associated hydrothermal fluids are preserved in coexisting VL- and LV-type FIs and are characterized by δD and δ18OH2O values in a narrow range (−87.2‰ to −85.3‰ and 7.6‰ to 8‰, respectively) and lower fluid salinity and temperature than Stage I. This suggests that the Fe-mineralization-related fluids also evolved by the boiling of magmatic brine. Stage III is characterized by the growth of pyrite, chalcopyrite, and molybdenite. The hydrothermal fluids of this stage are also represented by VL- and LV-type FIs that yield low temperatures (223–350 °C) and low salinities (0.7–13.4 wt%). These fluids yield lower δD values (−113.6‰ to −108.7‰) that indicate the Stage III fluids originated from the mixing of magmatic brine with meteoric water. Stages II and III are the main ore-forming stages in the Shenshan deposit. The sulfur isotope (δ34S) concentrations of Stage III sulphides cover a narrow range of −5.54‰ to +0.1‰ (mean = −1.75‰), indicating a magmatic source. Based on the fluid inclusion and stable isotopic data, it is concluded that the fluids of the main ore-forming stage evolved by the boiling of magmatic fluids at a depth of ~1 km and hydrostatic pressure of ~100 bars. Only VL-type FIs are observed in Stage IV; these fluids yield the lowest homogenization temperatures (120–217 °C) and lowest salinities (5.7–9.9 wt%). The results of fluid inclusion and H–O isotopic analyses indicate that the ore-forming fluids evolved from a magmatic fluid in Stages I and II to a lower-temperature and lower-salinity meteoric water during Stages III and IV. Boiling is considered an important mechanism of extensive metal precipitation in the Shenshan Fe–Cu deposit. Lead isotope values (206Pb/204Pb = 18.195–18.352, 207Pb/204Pb = 15.519–15.532, 208Pb/204Pb = 38.072–38.11) also suggest that the ore materials in the hydrothermal fluids were derived from magmas. Taken together, the geology, mineralogy, fluid inclusion, and H–O–S–Pb isotopic characteristics of the Shenshan deposit confirm that it is a typical contact metasomatic skarn deposit.

Circulation Patterns of Copper-Based Alloys in the Late Iron Age Oppidum of Třísov in Central Europe

This article presents an insight into the sourcing and circulation of copper alloys during the Late La Tène period in Central Europe where the specialised production of metals is regarded as complex and conducted chiefly within the bounds of the oppida. Contrary to the logical, though not necessarily data-based, assumption that local raw materials for the production of bronze were mostly used from the local primary deposits, we argue that an advanced and complex economy of Late Iron Age allowed for the steady and consistent material supply even from distant areas and that such pattern was possibly commonly practised by the oppida sites. Concurrently, we do not argue against the possibility of the exploitation and processing of the locally mined metal, we only point out that in provenance studies the evidence for that is yet difficult to find. We back our hypothesis by archaeometric analysis of the assemblage of bronze objects from the oppidum of Třísov (Czech Republic) collected during the long-term investigations of this site. The selection of objects for analyses covers the spectrum from the local products to potentially imported items. A provenancestudy based on the analysis of lead isotopes and chemical composition has shown rather homogeneous pattern of lead isotopic values and, on the contrary, quite a variability among the chemical composition of the individual artefact groups suggesting thus 1) standardised technological procedures for individual types of objects, 2) common recycling of the materials used and/or 3) contamination of low-leaded alloys from highly leaded bronzes.

Lead exposure in an urban, free-ranging parrot: Investigating prevalence, effect and source attribution using stable isotope analysis

Anthropogenic lead use has resulted in widespread environmental lead contamination known to affect wildlife populations worldwide. Ecotoxicological investigations in wild birds have thus far prioritised waterfowl and raptor species and primarily addressed contamination in natural ecosystems. Urban areas are increasingly associated with high levels of heavy metal contamination, however the risk of lead exposure in urban wildlife is less well known. This study investigates lead exposure in an urban population of North Island Kaka (Nestor meridionalis septentrionalis), an endemic New Zealand parrot. The inquisitive nature of these birds, an expanding urban population and increased availability of food in the urban environment are the primary factors implicated in their dispersal into urban areas where there is increased exposure to anthropogenic sources of lead. Blood lead concentrations were assessed in free-ranging birds to quantify the prevalence and magnitude of lead exposure. The impact of lead on physiological and neurological function was assessed using behavioural and clinical examinations. Finally, lead stable isotope analysis was employed to investigate lead in roofing material as a potential source of exposure in the urban environment. Results indicate a significant prevalence of lead exposure in this population (43.2%) with a maximum recorded plasma concentration of 50.7μg/dL. Although no mortality was observed during this study, lead exposure was associated with reduced body condition in kaka. Behavioural changes were present in one individual with the highest recorded blood lead concentration. Lead isotope values of roof-collected rainwater overlapped with kaka blood lead isotope values, suggesting this to be an important source of exposure in this population. The prevalence of lead exposure observed in this study suggests that lead is a toxin of importance to kaka in this urban area. Wildlife intoxications largely result from anthropogenic lead sources and this study identifies a previously undescribed urban source of lead for wildlife.

Genesis of the Wurinitu W-Mo deposit, Inner Mongolia, northeast China: Constraints from geology, fluid inclusions and isotope systematics

The Wurinitu W–Mo deposit is located in the Erlian-East Ujimqin metallogenic belt in the Great Xing’an Range, NE China. Tungsten and molybdenum mineralization generally occurs as veins in quartz hosted by the Middle to Lower Ordovician wall rocks or as disseminations in the Early Cretaceous monzogranite intrusions. Fluid inclusion studies and multiple isotope analyses, provide systematic evidence to determine the evolution of the hydrothermal fluids, the source of metals and fluids, as well as mineral precipitation mechanisms, which are significant for the magmatic-hydrothermal system but are poorly understood. Three types of fluid inclusion assemblages (FIAs), including L (liquid-rich two-phase FIAs), V (vapor-rich two-phase FIAs), and L-V (liquid–vapor two-phase FIAs), have been identified in quartz veins from the W-mineralization (I), Mo-mineralization (II), and quartz – carbonate (III) stages at Wurinitu. The ore-forming fluids evolved from a high- to moderate-temperature and moderate- to low-salinity H2O–NaCl ± CO2 system in the W- and Mo- mineralization stages to a low-temperature and low-salinity H2O–NaCl system in the quartz-carbonate stage; they were trapped at temperatures of ∼365 °C, ∼266 °C, and ∼198 °C. The results of hydrogen and oxygen isotope analyses (δ18OH2O = −4.0 to +7.7‰; δDH2O = −116 to −92‰) indicate that the stage I fluids dominantly originated from magmatic water, and the stages II and III show addition of meteoric water. Sulfur (δ34SVCDT = 1.9–4.0‰) and lead isotope values (206Pb/204Pb = 18.099–18.728, 207Pb/204Pb = 15.527–15.616, and 208Pb/204Pb = 38.019–38.465) suggest that the ore metals in the hydrothermal fluids were derived from the granitic magma. All these observations reveal that (1) the Wurinitu W–Mo deposit is a magmatic-hydrothermal ore system, (2) W- and Mo- mineralization occurred under lithostatic pressure of 203–294 bars, and hydrostatic pressure of ∼102 bars, respectively, and (3) fluid boiling and mixing with meteoric water might be the key factors controlling the large-scale ore deposition at Wurinitu.

Genesis of the Pb−Zn deposits of the Qingchengzi ore field, eastern Liaoning, China: Constraints from carbonate LA−ICPMS trace element analysis and C–O–S–Pb isotopes

The Qingchengzi ore field is an important Pb–Zn polymetallic ore district located in northeastern China, where more than ten Pb–Zn deposits and several Au-Ag deposits occur. The Pb–Zn mineralization is mainly hosted in the marble of the Dashiqiao Formation. Three distinct mineralization styles (strata-bound, open-space-filling and transitional type) are recognized. Two genetic models have been proposed to explain the Pb–Zn mineralization in this district: the sedimentary-exhalative model and the superimposed multi-stage model, in which syn-sedimentary deposition is overprinted by metamorphic and magmatic hydrothermal modification. Based on these three mineralization styles, this study provides new C–O–S–Pb isotopic data and LA–ICPMS trace element analyses of carbonates in order to place more constraints on the genesis of the Pb–Zn deposits.The δ13CPDB values of the syn-ore carbonates range from −5.11‰ to −1.06‰, and their δ18OSMOW values range from 3.30‰ to 13.2‰; these values are distinctively lower than those of barren meta-sedimentary rocks (δ13C=−1.98‰–−0.55‰, δ18O=19.69‰−22.76‰). The depleted C–O isotopic values of syn-ore carbonates are inferred to result from fluid-rock interactions combined with the impact of graphite. In situ LA–ICPMS trace element analyses show that syn-ore carbonates record enriched REE contents, pronounced positive Eu anomalies and lower Y/Ho ratios compared to barren carbonates. The depleted C–O isotopic signatures and distinctive REE characteristics of syn-ore carbonates indicate that the hydrothermal fluid is likely magmatic in origin and has mixed with low δ18O fluids, such as meteoric or formation water. Sulfide minerals have δ34S values ranging from 3.16‰ to 9.14‰ and display a gradually increasing trend from open-space-filling to transitional type to strata-bound mineralization styles, which reflect different mixing proportions of the two end-members of magmatic sulfur and sedimentary sulfur. The Pb isotopic compositions of sulfide minerals are relatively uniform (206Pb/204Pb=17.511–17.883, 207Pb/204Pb=15.549–15.64 and 208Pb/204Pb=37.670–38.178) for different mineralization styles; however, the open-space-filling mineralization records relatively lower lead isotope values. The linear correlation of ore lead isotopes between schist and Triassic intrusions indicates that lead may have originated from a mixture of magmatic and sedimentary end-members. The relatively lower Pb isotopes of the open-space-filling mineralization suggest the presence of higher proportions from a magmatic source. Mineralization styles respond to diverse ore-controlling structures and their proximity to the mineralizing source: open-space-filling mineralization shows the least stratigraphic control, with more pronounced “magmatic marks” (i.e., lower S–Pb isotopic values and more depleted C–O values), compared to strata-bound mineralization.These mineralization styles, combined with C–O–S–Pb isotopic geochemistry, consistently preclude a SEDEX origin for the Pb–Zn deposits in the Qingchengzi district, but suggest that they represent a distal hydrothermal mineralization type related to Triassic magmatic activity.

Insights into past atmospheric lead emissions using lead concentrations and isotopic compositions in historic lichens and fungi (1852–2008) from central and southern Victoria, Australia

Lead concentrations and lead isotopic compositions were determined in historic central and southern Victoria, Australia lichen (Cladonia and Usnea) and fungi (Trametes) samples collected between 1852 and 2008 to evaluate long-term atmospheric lead contamination sources. The data are grouped into four time intervals of 1850–1931, 1932–1984, 1985–2001 and 2002–2008 corresponding to the history of leaded petrol use in Australia. Elevated lichen and fungi lead concentrations and relatively high isotopic compositions from the period 1850–1931 are attributed to lithogenic sources, gold mining activities and early industrialisation. Significant increases in lichen and fungi lead concentrations and concomitant lower lead isotopic compositions correspond to the marked increase in lead emissions from leaded petrol use after 1932. Following the end of leaded petrol use in 2002 lead isotopic composition values ‘recover’ toward more lithogenic values. However, the lead isotopic composition data indicate that the environmental impact from leaded petrol emissions persists in contemporary samples dated to 2002–2008. Overall, the data reveal that herbarium lichens and fungi from central and southern Victoria can be used as proxies for environmental lead emissions over the past 150 years.

A salt diapir-related Mississippi Valley-type deposit: the Bou Jaber Pb-Zn-Ba-F deposit, Tunisia: fluid inclusion and isotope study

The Bou Jaber Ba-F-Pb-Zn deposit is located at the edge of the Bou Jaber Triassic salt diapir in the Tunisia Salt Diapir Province. The ores are unconformity and fault-controlled and occur as subvertical column-shaped bodies developed in dissolution-collapse breccias and in cavities within the Late Aptian platform carbonate rocks, which are covered unconformably by impermeable shales and marls of the Fahdene Formation (Late Albian–Cenomanian age). The host rock is hydrothermally altered to ankerite proximal to and within the ore bodies. Quartz, as fine-grained bipyramidal crystals, formed during hydrothermal alteration of the host rocks. The ore mineral assemblage is composed of barite, fluorite, sphalerite, and galena in decreasing abundance. The ore zones outline distinct depositional events: sphalerite-galena, barite-ankerite, and fluorite. Fluid inclusions, commonly oil-rich, have distinct fluid salinities and homogenization temperatures for each of these events: sphalerite-galena (17 to 24 wt% NaCl eq., and Th from 112 to 136 °C); ankerite-barite (11 to 17 wt% NaCl eq., and Th from 100 to 130 °C); fluorite (19 to 21 wt% NaCl eq., Th from 140 to 165 °C). The mean temperature of the ore fluids decreased from sphalerite (125 °C) to barite (115 °C) and increased during fluorite deposition (152 °C); then decreased to ∼110 °C during late calcite precipitation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of fluid inclusions in fluorite are metal rich (hundreds to thousands ppm Pb, Zn, Cu, Fe) but the inclusions in barite are deficient in Pb, Zn, Cu, Fe. Inclusions in fluorite have Cl/Br and Na/Br ratios of several thousand, consistent with dissolution of halite while the inclusions analysed in barite have values lower than seawater which are indicative of a Br-enriched brine derived from evaporation plus a component of halite dissolution. The salinity of the barite-hosted fluid inclusions is less than obtained simply by the evaporation of seawater to halite saturation and requires a dilution of more than two times by meteoric water. The higher K/Na values in fluid inclusions from barite suggest that the brines interacted with K-rich rocks in the basement or siliciclastic sediments in the basin. Carbonate gangue minerals (ankerite and calcite) have δ13C and δ18O values that are close to the carbonate host rock and indicate fluid equilibrium between carbonate host rocks and hydrothermal brines. The δ34S values for sphalerite and galena fall within a narrow range (1 to 10 ‰) with a bulk value of 7.5 ‰, indicating a homogeneous source of sulfur. The δ34S values of barite are also relatively homogeneous (22 ‰), with 6 ‰ higher than the δ34S of local and regional Triassic evaporites (15 ‰). The latter are believed to be the source of sulfate. Temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of Triassic sulfate via hydrocarbons produced probably from Late Cretaceous source rocks. The 87Sr/86Sr ratio in the Bou Jaber barite (0.709821 to 0.711408) together with the lead isotope values of Bou Jaber galena (206Pb/204Pb = 18.699 to 18.737; 207Pb/204Pb = 15.635 to 15.708 and 208Pb/204Pb = 38.321 to 38.947) show that metals were extracted from homogeneous crustal source(s). The tectonic setting of the Bou Jaber ore deposit, the carbonate nature of the host rocks, the epigenetic style of the mineralization and the mineral associations, together with sulfur and oxygen isotope data and fluid inclusion data show that the Bou Jaber lead-zinc mineralization has the major characteristics of a salt diapir-related Mississippi Valley-type (MVT) deposit with superimposed events of fluorite and of barite deposition. Field relations are consistent with mineral deposition during the Eocene–Miocene Alpine orogeny from multiple hydrothermal events: (1) Zn-Pb sulfides formed by mixing of two fluids: one fluid metal-rich but reduced sulfur-poor and a second fluid reduced sulfur-rich; (2) barite precipitation involved the influx of a meteoric water component that mixed with a barium-rich fluid; and (3) fluorite precipitated from a highly saline fluid with higher temperatures.

Miocene andesitic lavas of Sierra de Angangueo: a petrological, geochemical, and geochronological approach to arc magmatism in Central Mexico

ABSTRACTThe early and middle Miocene andesitic lavas of the Sierra de Angangueo (MALSA) represent one of the most prominent landforms of intermediate magmatism in Central Mexico. In this paper, we present new petrological, geochemical, thermobarometric, and geochronological data in order to discuss the conditions of MALSA’s emplacement in the lithosphere.MALSA comprises a voluminous eroded early Miocene andesitic structure, emplaced on a Mesozoic basement. MALSA shows a wide variety of textures, from glassy and aphanitic to porphyritic, mainly composed of plagioclase (An10-55), clinopyroxene (Wo60-65; En35-40), amphibole (Mg-hornblende/edenite), and rarely olivine (Fo75–86) or orthopyroxene (En72-80). Major and trace elements plots follow a typical calc-alkaline trend with relatively increasing fractionation.The 87Sr/86Sr isotopic signatures range between 0.703343 and 0.704459 and εNd values from +1.37 to +4.84; apparently without a significant contribution of an old, thick, or highly radiogenic continental crust. Lead isotope values 206Pb/204Pb vary between 18.68 and 18.83, 207Pb/204Pb from 15.57 to 15.65, and 208Pb/204Pb from 38.39 to 38.67, suggesting contamination of magmas by juvenile crust. Thermodynamic calculations indicate equilibrium conditions at ≤900°C and ~2 kbar and an average log ƒO2 ≈ −10.Ar–Ar and K–Ar dating carried out on whole rock, matrix, amphibole, and plagioclase phenocrysts yielded ages between 13.0 ± 0.5 and 23.9 ± 0.3 Ma. These dates indicate a series of pulses with maximum magmatic activity between 24 and 18 Ma.The geochemical and petrologic data suggest partial melting processes in the lower or middle crust associated with possible magma mixing during its ascent; such a mechanism could explain a hybrid mantle-lower crust origin of this large volume of andesites. The MALSA, as well as the early to middle Miocene magmatism from Western Mexico, could represent two coeval and independent magmatic arcs prior to the present Trans-Mexican Volcanic Belt (TMVB) in Central Mexico.

S, O and Pb isotopic evidence on the origin of the İnkaya (Simav-Kütahya) Cu–Pb–Zn–(Ag) Prospect, NW Turkey

The İnkaya Cu–Pb–Zn–(Ag) prospect is a typical example of the hydrothermal mineralization occurring in the Menderes Massif, which crop out in Western Anatolia. The prospect located approximately 20km west of Simav (Kütahya-Turkey) in northern part of the Menderes Massif have been characterized through the detailed examinations involving geological, mineralogical, whole-rock geochemistry, fluid inclusion, stable isotope and lead isotope.The İnkaya Cu–Pb–Zn–(Ag) prospect is located along an E–W-trending fault in the Cambrian Simav Metamorphics, which consist of quartz–muscovite schist, quartz–biotite schist, muscovite schist, biotite schist and the Arıkayası Formation, which is composed of marbles. Galena, sphalerite, chalcopyrite, pyrite and fahlore are the main minerals, and they are accompanied by small amounts of cerussite, anglesite, digenite, enargite, chalcocite, covellite, bornite, and Fe-oxides with gangue quartz. In addition to Pb, Zn, Cu, Ag, the ore samples contain substantial quantities of As, Cd and Bi and small amount of Au. Average contents of Cu, Pb, Zn and Ag are 77,400ppm, 102,600ppm, 6843ppm and 203ppm, respectively.The δ34S values for galena, chalcopyrite and pyrite formed in the same stage vary in the range from −1.7 to −2.1‰ (average −2.0), 0.1 to 0.3‰ (average 0.2) and −1.5 to 2.6‰ (average +1.5), respectively.δ34S values for H2S, representing the composition of the fluids responsible for the sulfide mineral formations and calculated from the δ34S value are between −2.77 and 1.33‰; it is consistent with the sulfur in sulfide minerals. δ18Oquartz values range from 11.3 to 16.4‰ and estimated δ18Ofluid values range from 5.4 to 10.6‰.Pyrite–galena and pyrite–chalcopyrite pairs calculated to determine equilibrium isotope temperatures based on δ34S values are between 254.6 and 277.4°C for pyrite–galena and 274.7°C for pyrite–chalcopyrite. Sulfur and oxygen isotope values similar to the values for fluid equilibrated with an felsic magmatic source.Fluid inclusion studies on quartz of the same silicification stage coexisting with galena, sphalerite and chalcopyrite collected from the mineralized vein indicate that the temperature range of the fluids is 235°C to 340°C and that the salinities are 0.7 to 4.49wt.% NaCl equivalent. The wide range of homogenization temperatures and relatively lower salinities of the fluid inclusions indicate that at least two different fluid generations were trapped in the quartz from only one fluid type. Also, lower salinities of fluid inclusion probably indicate mixing of meteoric water and magmatic fluid.The galena has 206Pb/204Pb values of 18.862–18.865, 207Pb/204Pb values of 15.707–15.711, and 208Pb/204Pb values of 39.033–39.042. The lead isotope values show a similarity with upper crustal values.

Sourcing copper ores for production of bronzes excavated at Shuangyantang, a Western Zhou (1046–771 bc) site in Chongqing (Southwest China): evidence from lead isotope analysis

Energy-dispersive X-ray fluorescence (EDXRF) and lead isotope analyses were applied to 12 Western Zhou (1046–771 bc) bronzes unearthed from the Shuangyantang site in Wushan County, Chongqing (southwest China), to investigate their chemical compositions and possible mineral source(s). The results showed that (1) the investigated bronzes were mostly bronzes with low, common lead and (2) their lead isotopic values almost all fall into a relatively narrow range, suggesting possibly the use of raw materials from a common copper mine. The comparison between lead isotopic values for Shuangyantang bronzes and those already published for copper mines and other bronzes produced and used about at the same times leads us to believe that the Shuangyantang bronzes probably used the same copper ores as used in bronzes from the Peng and Jin states in Shanxi Province. However, it would not be possible at this point to come up with a clear idea of where exactly these copper ores may come from. Candidate copper mines might be the Tonglvshan mines in Hubei Province, the Zhongtiaoshan mines in Shanxi Province, or the Dajing copper mines in Inner Mongolia.

Syncollisional tholeiitic magmatism induced by asthenosphere upwelling owing to slab detachment at the southern margin of the Central Asian Orogenic Belt

The mafic–ultramafic complexes containing magmatic sulphides at the southern margins of the Central Asian Orogenic Belt have been recently proposed to result from an Early Permian mantle plume. However, in this study we show that the plume model cannot account for the observed geological characteristics of the Huangshan–Jingerquan mafic–ultramafic belt in the Northern Tianshan. Low K 2 O contents and positive correlation between TiO 2 and (Fe 2 O 3 ) T /MgO of the mafic–ultramafic complexes of this belt demonstrate a tholeiitic affinity. Enrichment of large ion lithophile elements and depletion of high field strength elements (in particular Nb and Ta) relative to mid-ocean ridge basalt indicate a subduction-modified mantle source. Lead isotope values and compositions of chromite indicate a significant contribution from the melting of asthenosphere. The absence of Late Carboniferous strata in the Huangshan–Jingerquan belt and Early Permian exhumation of blueschist and eclogite along the Aqikkuduk suture at the southern boundary of the belt indicate that an arc–continent collision occurred in the Late Carboniferous to Early Permian. We propose that the detachment of oceanic lithosphere from continental lithosphere during the collision induced asthenospheric upwelling, which resulted in melting of both the asthenosphere and the overlying metasomatized mantle wedge, and the formation of the mafic–ultramafic complexes with ages of 270–285 Ma along the Huangshan–Jingerquan belt. Supplementary materials: Zircon SHRIMP U–Pb ages of the Tudun and Huangshannan intrusions, major oxide and trace element compositions of the discussed intrusions, and clinopyroxene and chromite compositions of the selected intrusions are available at www.geolsoc.org.uk/SUP18656 .