Lead Isotope Research Articles

Relative sea‐level changes in southeastern Australia during the 19th and 20th centuries

ABSTRACTRates of global and regional sea‐level rise between ~1850 and 1950 were high compared to those in preceding centuries. The cause of this sea‐level acceleration remains uncertain, but it appears to be pronounced in a small set of relative sea‐level proxy records from the Southern Hemisphere. Here we generate three new proxy‐based relative sea‐level reconstructions for southeastern Australia to investigate spatial patterns and causes of historical sea‐level changes in the Tasman Sea. Palaeo sea‐level estimates were determined using salt‐marsh foraminifera as sea‐level indicators. Records are underpinned by chronologies based on accelerator mass spectrometry 14C, radiogenic lead (210Pb), stable lead isotopes and palynological analyses. Our reconstructions show that relative sea level rose by ~0.2–0.3 m over the last 200 years in southeastern Australia, and rates of sea‐level rise were especially high over the first half of the 20th century. Based on modelled estimates of the contributing components to sea‐level rise, we suggest that the episode of rapid sea‐level rise was driven by barystatic contributions, but sterodynamic contributions were dominant by the mid‐20th century. Significant spatial variability in relative sea level indicates that local to sub‐regional drivers of sea level are also prominent. Our reconstructions significantly enhance our understanding of the spatiotemporal pattern of early 20th century sea‐level rise in the region.

Albany K‐Feldspar: A New Pb Isotope Reference Material

Lead isotopes are a powerful and versatile tool to elucidate fundamental geological problems related to the formation and evolution of continental crust. K‐feldspar is a popular target for Pb isotope measurement as it is prevalent in many rock types and tends to capture the initial Pb isotope composition of its parental magma. We present data for a new Pb isotope reference material: Albany K‐feldspar; as well as updated data for Shap K‐feldspar. Results of Pb double‐spike TIMS for Albany K‐feldspar are 206Pb/204Pb = 16.7872 ± 0.0062, 207Pb/204Pb = 15.5640 ± 0.0056, and 208Pb/204Pb = 36.6600 ± 0.0168 (2s). TIMS measurement results for Shap K‐feldspar indicate two isotopically distinct Pb populations. LA‐MC‐ICP‐MS, with a spatial resolution as high as 15 μm, indicates a homogeneous Pb isotopic composition in Albany K‐feldspar. In accord with previous studies, our results show that scatter in the measured Pb isotope ratios, related to the low natural isotopic abundance of 204Pb, along with the effect of isobaric 204Hg‐204Pb interference, increases at lower count rates. However, the mean Pb isotope ratios measured via LA‐MC‐ICP‐MS using a range of spot sizes are in excellent agreement with TIMS results thus highlighting the feasibility of Pb isotope determination via LA‐MC‐ICP‐MS to access geological information preserved in small crystals, including mineral inclusions.

Effects of atmospheric deposition on heavy metals accumulation in agricultural soils: Evidence from field monitoring and Pb isotope analysis

Atmospheric deposition is an essential pathway of heavy metals (HMs) from the atmosphere to soils, while few studies assess the effects and contributions of atmospheric deposition on HMs accumulations in agricultural soils from the field and regional scales. In this study, eleven representative field monitoring sites from industrial areas, agricultural areas, and reference site in a typical rapid industrial development region were selected to determine the effects of atmospheric deposition on soil HMs accumulation. Industrial activities significantly increased the deposited particles flux from atmospheric deposition, with annual particles fluxes in industrial areas being 1.83 and 1.90 times higher than in agricultural areas and reference site, respectively. Although the HMs deposition fluxes had decreased significantly with time by literature comparison, the deposition fluxes of Cd and Pb were still at high levels in this study area. Precipitation was the key factor affecting seasonal variations of atmospheric HMs deposition. Lead isotope analysis indicated that atmospheric Pb originated from coal combustion, and atmospheric deposition was the primary source of Pb contamination in agricultural soil adjacent to industries. This study provided insight into the effects of atmospheric deposition on agricultural soil HMs accumulations at the regional scale and an important theoretical basis for source-preventing soil HMs contamination in industrial developed and other similar areas.

Analyses of queen Hetepheres’ bracelets from her celebrated tomb in Giza reveals new information on silver, metallurgy and trade in Old Kingdom Egypt, c. 2600 BC

Egypt has no domestic silver ore sources and silver is rarely found in the Egyptian archaeological record until the Middle Bronze Age. Bracelets found in the tomb of queen Hetepheres I, mother of pyramid builder king Khufu (date of reign c. 2589–2566 BC), form the largest and most famous collection of silver artefacts from early Egypt, but they have not been analysed for decades. We analysed samples from the collection in the Museum of Fine Arts, Boston using bulk XRF, micro-XRF, SEM-EDS, X-ray diffractometry and MC-ICP-MS to obtain elemental and mineralogical compositions and lead isotope ratios, to understand the nature and metallurgical treatment of the metal and identify the possible ore source. We found that the pieces consist of silver with trace copper, gold, lead and other elements. The minerals are silver, silver chloride and a possible trace of copper chloride. Surprisingly, the lead isotope ratios are consistent with ores from the Cyclades (Aegean islands, Greece), and to a lesser extent from Lavrion (Attica, Greece), and not partitioned from gold or electrum as previously surmised. Sources in Anatolia (Western Asia) can be excluded with a high degree of confidence. Imaging of a cross-section of a bracelet fragment reveals that the metal was repeatedly annealed and cold-hammered during creation of the artefacts. The results provide new information about silver ore sources, commodity exchange networks and metallurgy in Egypt during the Early Bronze Age.

Sulfide Trace Element Signatures and S- and Pb-Isotope Geochemistry of Porphyry Copper and Epithermal Gold-Base Metal Mineralization in the Elatsite–Chelopech Ore Field (Bulgaria)

The Elatsite–Chelopech ore field in the northern part of the Panagyurishte district in Central Bulgaria comprises numerous spatially associated porphyry copper and epithermal gold deposits and prospects. In addition to the mineralization and alteration features, trace elements, lead and sulfur isotope signatures of sulfide minerals from porphyry copper, base metal and gold-base metal deposits/prospects have been studied. LA-ICP-MS analyses of pyrite, arsenopyrite and sulfosalt minerals validate them as major carriers for Au, Ag, Sb, Se and Co. Pyrite from the three types of mineralization has specific geochemical characteristics. Pyrite from the porphyry copper deposits/prospects has generally lower total trace element content compared to pyrite from the epithermal prospects, except for Se, Co and Ni. Pyrite from the base metal and gold-base metal veins is enriched in As, Au, Ag, Sb and Pb. In pyrite from the base metal deposits, Co and Ni have contents comparable to the pyrite from the porphyry copper deposits, while pyrite from the gold-base metal veins shows lower Co and Ni. Arsenopyrite from these deposits shows similar features. Similarly, sphalerite from the gold-base metal veins also has lower Co content compared to sphalerite from the base metal veins but higher In and Cu contents. In addition to the close spatial relationships between the Elatsite and Gorna Kamenitsa porphyry Cu deposits and Negarstitsa-West and Dolna Kamenitsa base metal prospects, as well as similarities in the mineralization and alteration styles, the lead isotopic (206Pb/204Pb = 18.61–18.68, 207Pb/204Pb = 15.64–15.65 for porphyry and 206Pb/204Pb = 18.55–18.67, 207Pb/204Pb = 15.64–15.68 for base metal) and sulfur isotopic (δ34S values of −3 to +1‰ for porphyry and δ34S values of −1.7 to +3.5‰ for base metal) signatures of sulfides support the idea of a genetic link between these two types of deposits. The porphyry and base-metal mineralization result from a common major ore-forming event during the Late Cretaceous, corresponding to deep/higher-temperature and shallower/distal/lower-temperature environments, respectively. In particular, more radiogenic lead (206Pb/204Pb = 18.41–18.47, 207Pb/204Pb = 15.67–15.76) and slightly different sulfur isotopic compositions (δ34S values of +3.5 to +10.6‰) of sulfides from the distal gold-base metal veins of Kordunsko Dere, Svishti Plaz and Shipkite might be a consequence of the interaction of the ore-forming fluids with an external older crustal and isotopically positive S source. Alternatively, a different fluid source/event for the formation of these gold-base metal veins may be suggested.

A search for life in Palaeoproterozoic marine sediments using Zn isotopes and geochemistry

Sediments from the 2.1- to 1.9-billion-year-old Francevillian Group in southeastern Gabon include centimeter-sized pyritized structures suggestive of colonial organisms (El Albani et al., 2010), some of which may have been motile (El Albani et al., 2019). However, these interpretations were largely based on morphological and geochemical characteristics that lack metabolic clues and/or can be explained by abiotic processes. To move this work forward, we describe other centimeter-sized specimens, loosely referred to as lenticular forms (LF), from the same area and apply a more holistic approach including morphology, mineralogy, and geochemistry. The objects are 0.2–4 cm in diameter, and most of them are endowed with a regular brim that scales proportionally to external diameter reminiscent of biological order, hence rendering the LF putative biogenic traces. The LF are perfectly delineated in every direction and deflect the sedimentary layers on which they rest. X-ray microtomography further demonstrates that the LF are syn-depositional features and not concretions, while lead isotope systematics indicate that the geochemical imprint of diagenesis is inconsequential. Low sulfur content is largely concentrated in the organic matrix, and scarcity of pyrite and its persistence as micron-sized crystals show that the role of sulfate reduction is minor. Most interestingly, the fillings of the LF cavities show large and correlated excesses of organic carbon and zinc, with the latter being distinctly enriched in its light isotopes. The geochemical anomalies of the fillings relative to the host rock, notably those associated with Zn, clearly were buried with the LF, and further imply biogenicity. In this regard, a ten-fold increase in LF size towards the top of the black shale series hosting the LF might be related to increasing Zn (nutrient) availability. Although we cannot conclude with any certainty what these remnant organisms were, their features all taken together are evocative of very large agglutinate protists that grazed on bacterial biomass either in the water column or as benthic mats.

Risk Evaluation of Pollutants Emission from Coal and Coal Waste Combustion Plants and Environmental Impact of Fly Ash Landfilling.

Emission factors (EFs) of gaseous pollutants, particulate matter, certain harmful trace elements, and polycyclic aromatic hydrocarbons (PAHs) from three thermal power plants (TPPs) and semi-industrial fluidized bed boiler (FBB) were compared. EFs of particulate matter, trace elements (except Cd and Pb), benzo[a]pyrene, and benzo[b]fluoranthene exceed the upper limits specified in the EMEP inventory guidebook for all combustion facilities. The comparison of trace elements and PAHs content in fly ashes (FAs) from lignite and coal waste combustion in TPPs and FBB, respectively, as well as the potential environmental impact of FAs disposal, was performed by employing a set of ecological indicators such as crustal enrichment factor, risk assessment code, risk indices for trace elements, and benzo[a]pyrene equivalent concentration for PAHs. Sequential analysis shows that the trace elements portion is the lowest for water-soluble and exchangeable fractions. The highest enrichment levels in FAs are noticed for As and Hg. Based on toxic trace elements content, FAs from TPPs represent a very high ecological risk, whereas fly ash from FBB poses a moderate ecological risk but has the highest benzo[a]pyrene equivalent concentration, indicating its increased carcinogenic potential. Lead isotope ratios for Serbian coals and FAs can contribute to a lead pollution global database.

Decryption analysis of antimony pollution sources in PM2.5 through a multi-source isotope mixing model based on lead isotopes

Antimony (Sb) in PM2.5 has attracted close attention as a new air pollutant due to its extensive use in daily life. The identification of antimony sources in PM2.5 by scientific methods is important to control its pollution. In this study, the Sb and other elements concentrations and Pb isotopic compositions in PM2.5 and possible pollution sources (soil, road dust, traffic emission, coal-fired fly ash, local factory emission dust and cement dust) were analyzed. The results showed that the Sb in the PM2.5 samples had seasonal change. The enrichment factors of Sb in PM2.5 samples were all above 100 in four seasons, which indicated anthropogenic pollution. The average value of potential ecological risk index was at extremely high-risk level greater than 320. Based on Pearson correlation coefficient and hierarchical cluster analysis results, the pollution sources of antimony and lead in PM2.5 samples were highly consistent which means that Pb isotopes might be a new and feasible tracer for Sb pollution in air. The sources analysis results based on Pb isotopes indicated that the proportion of Pb and Sb from coal-fired fly ash was the highest in winter (47.7%) and inclined to road dust in spring (34.5%), but it was mainly from traffic emissions in summer and autumn (34.2% and 32.8%). This study showed that Pb isotope tracing can be applied to predict the potential pollution sources, and it was also a feasible substitute for tracing Sb pollution in PM2.5.

An offline column extraction with Presep® PolyChelate resin and AG1‐X8 resin for the determination of the isotope compositions of low‐concentration lead in natural waters by the multi‐collector inductively coupled plasma mass spectrometry

AbstractA new high‐precision offline method for the determination of seawater lead (Pb) isotope ratios was developed, which simplifies and optimizes previously published protocols for the isotopic analysis of trace elements. The procedure involves initial separation of Pb from 250 to 500 mL of seawater by Presep® PolyChelate cation exchange resin and purification by AG1‐X8 anion exchange resin, and subsequently analyzed by Neptune multi‐collector ICP‐MS. For the extraction of Pb in seawater, the Presep® PolyChelate resin was characterized by a wide pH range and a faster adsorption rate, greatly reducing the volume of buffer solution required and significantly shortening the time required for the whole process. The total procedural Pb blank of this method is < 0.05% of the sample extract and the typical Pb recovery is ~ 100%. The method was evaluated by processing GEOTRACES intercalibration samples surface water (GSI, 206Pb/207Pb = 1.1744, 208Pb/206Pb = 2.0844) and GEOTRACES GP15 sample (14140#, 206Pb/207Pb = 1.1685, 208Pb/206Pb = 2.0960). Finally, this method was applied to riverine samples from the Changjiang and seawater samples from the East China Sea, and the in situ extraction was also applied in the Indian Ocean.

Lead isotope reveals the mineral source change of late Bronze Age bronze mirrors excavated in Hunan Province, Southern China

The late Bronze Age was the first golden period for bronze mirror production in ancient China. In this paper, scientific analysis and research were carried out on 28 late Bronze Age bronze mirrors excavated in Hunan Province, Southern China. All bronze mirrors are Cu-Sn-Pb materials, and their lead isotope data are in line with the characteristics of common lead. Among them, 4 bronze mirrors containing metal bodies all show bronze casting structures with high tin features, and there are some differences in the elemental composition distribution range between them and previously tested bronze mirrors. This paper significantly reveals that the lead mineral source of Hunan bronze mirrors underwent two obvious changes during the late Bronze Age. The Warring States bronze mirrors excavated in Hunan mainly used lead ore from the Nanling region and Northern Hunan region, and Changsha should be the center of mirror-production and mirror-circulation in Southern Chu Kingdom. However, the lead ore consumed by the Western Han bronze mirrors excavated in Hunan primarily came from the East Qinling region, which was close to the core region under the rule of the Western Han government. In the middle and late Eastern Han Dynasty, with the frequent metal production activities in the Nanling region and the prosperity of private mirror-casting industry in Southern China, lead ore from the Nanling region was re-introduced in the production of Hunan bronze mirrors.

A complex case of trade in metals: The origin of copper used for artefacts found in one hoard from a Late Bronze Age Lusatian Urnfield Culture in Poland

Metal artefacts from Bronze Age hoards have routinely been used to study interregional contacts. Their stylistic and typological features helped distinguish local products and imports by appearance. In the last 40 years, combined lead isotope and chemical analyses of metals have been widely applied to verify hypotheses based on style and typology. This paper is a comprehensive typological and analytical study of a metal item hoard discovered in Paszowice, SW Poland. In the Bronze Age, the area was inhabited by the Lusatian Urnfield culture (ca. 1350/1300–800/750 BC) communities. We expected that at least some of the artefacts would be local products fashioned according to foreign stylistic patterns. The research aimed to determine whether a ‘classical’ stylistic analysis combined with provenance studies of metals would allow more decisive conclusions. This combination of methods could also show how the metal reached the Lusatian Urnfield culture settlement zone. We conducted a detailed typological and chronological analysis to map the distribution of similar artefact types. It demonstrated that stylistic matches for the artefacts from Paszowice occur mainly in NE Hungary, S Czech Republic, Slovakia, and Romania. Selected metal artefacts (both tin bronze items and raw copper objects) from Paszowice were also analysed for their chemical (EPMA) and lead isotope (MC ICP MS) compositions. The study revealed many copper sources used for their production, ranging from the nearest copper mines in the Slovak Ore Mountains, through Eastern Alps and mines in Sardinia, to possibly the Iberian Peninsula. In this way, we identified the potential trade routes by which metal could get to SW Poland: the southwestern and southeastern routes and the Mediterranean-Danube route. The Iberian metal might have also reached the study area from the north – through its redistribution by Scandinavian traders. Our results show that metal from many sources circulated in central Europe during the Late Bronze Age. The Lusatian Urnfield communities were part of a pan-European exchange network and maintained extensive long-distance contacts, allowing metal acquisition from various sources.

Reconstructing the geological provenance and long-distance movement of rectangular, fishtail, and croisette copper ingots in Iron Age Zambia and Zimbabwe.

The southern third of Africa is unusually rich in copper ore deposits. These were exploited by precolonial populations to manufacture wound-wire bangles, other forms of jewelry, and large copper ingots that were used as stores of copper or as forms of prestige. Rectangular, fishtail, and croisette ingots dating between the 5th and 20th centuries CE have been found in many locations in the Democratic Republic of the Congo (DRC), Zambia, and Zimbabwe, with isolated finds in Malawi and Mozambique. Molds for casting these ingots have been found mostly in the Central African Copperbelt, but also around the Magondi Belt copper deposits in northern Zimbabwe. For years, scholars have debated whether these ingots were exclusively made in the Copperbelt or if the molds found in Zimbabwe indicate that local copies were produced from Magondi Belt copper ore (Garlake 1970; Bisson 1976). Before the recent application of lead isotopic and chemical methods to provenance copper in central and southern Africa, there was no way to discern between these hypotheses. Rademakers et al. (2019) and Stephens et al. (2020) showed that copper artifacts from southern DRC (mostly from Upemba) and from northwestern Botswana (Tsodilo Hills) match the lead isotope ratios of ores from the Copperbelt. Building upon these previous studies, we present here the first results from a copper provenance project across the southern third of Africa, from the Copperbelt to northern South Africa. We apply lead isotopic analysis (LIA) and chemical analyses to establish the provenance of 29 croisette ingots recovered in Zimbabwe, 2 fishtail and 1 rectangular ingot recovered from sites in Zambia, and an "X" shaped ingot smelted in an experiment in Zambia in the 1970's. Our chemistry and lead isotopic results indicate that 16 of these objects were smelted with copper from the Copperbelt, 16 objects source more specifically to the Kipushi deposit within this geological district, and only one HXR ingot sources to the Magondi Belt in Zimbabwe. Taken together, we clearly illustrate that croisette ingots were traveling significant distances to reach their eventual sites of deposition, and that there was also local production of these objects in Zimbabwe.

Assessing the Impact of Holocene Climate Change on Bioavailable Strontium Within the Nile River Valley

The impact of the climate drying during the Holocene within the Nile River Valley System (NRVS) has been the focus of recent debate in the archaeological community. It is argued that the increased contribution of aeolian material from the neighboring Sahara Desert during the last ~7,000 years has changed the isotope compositions of bioavailable Sr relative to the geological background and thus hinders provenance investigations of human remains within the NRVS. This study reports new trace element and strontium (Sr), neodymium (Nd), and lead (Pb) isotope compositions for a combined total of 125 samples consisting of human tooth enamel and various faunal samples from different time periods, and present-day botanical samples from 11 archaeological sites along the NRVS. The new isotope data combined with published data do not support a time-dependent increase in a Saharan aeolian bioavailable Sr component during the Holocene within the NRVS; in general, Sr isotope compositions for human enamel samples match those of their corresponding faunal matrices, and these define a similar range of isotope compositions over the various time periods. The Nd and Pb isotope compositions for human tooth enamel reported here also support the limited contribution of Saharan aeolian dust within the NVRS.

A study to characterize the lead isotopic fingerprint in PM2.5 emitted from incense stick and cigarette burning.

The incense sticks and cigarettes burning are key sources of particulate matter with a diameter of ≤ 2.5μm (PM2.5) in indoor and outdoor air. While lead (Pb) isotope ratios provide valuable insights into the origin of particle pollution, their applicability for investigating these source remains unclear. The Pb isotope ratios in the PM2.5 emitted from these two sources were analyzed, and effects of brands or nicotine contents on the ratios were assessed. In addition, As, Cr, and Pb were analyzed to investigate whether Pb isotope ratios can serve as an indicator for the source investigation of these metals. We found that average ratios of 206Pb/204Pb, 206Pb/207Pb, and 208Pb/207Pb in cigarettes were heavier than those in incense sticks. Scatter plots of Pb isotope ratios indicated an overlap of values for incense sticks or cigarettes linked to different brands, in that ratios for cigarettes with high nicotine content were heavier than for those with low nicotine content. Scatter plots of As, Cr, or Pb concentration against Pb isotope ratios clearly distinguished the effects of cigarette burning versus incense sticks with respect to PM2.5 of these metals. Results indicate that brand differences did not affect the determination of PM2.5 in these two sources. We suggest that Pb isotope ratios can be a useful tool in investigating the influenceof incense sticks and of cigarettes (with high or low nicotine content) burning to PM2.5 and associated metals.

Molybdenum mineralization genetically linked with magmatism at the Shipingchuan deposit, SE China

Most molybdenum (Mo) deposits are considered to be associated with magmatic systems; however, their genetic link is not clearly resolved when using, for example, bulk sulfur (S) and lead (Pb) isotopes of sulfides dominated by pyrite separates. Here, we present microtextures and in situ trace-element results of pyrite, in situ S isotopic compositions of molybdenite and pyrite, and Pb isotopes of pyrite and K-feldspar determined by laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) and multicollector (MC) LA-ICP-MS. Combined with geochronologic data for both the magmatism and Mo mineralization, these in situ methods allowed the genetic link between Mo mineralization and magmatism to be unraveled at Shipingchuan, SE China. The Shipingchuan deposit is characterized by molybdenite-quartz veins hosted by faults or fractures around a biotite K-feldspar granite. Zircon LA-ICP-MS U-Pb and molybdenite Re-Os dating results confirm that the biotite K-feldspar granite and mineralization were coeval and formed during the end of the Early Cretaceous (ca. 105 Ma), whereas postmineralization monzogranite porphyry dikes formed at 93.7 Ma. Pyrite shows a close mutual relationship with molybdenite and is characterized by Co-Ni-As-Te-Cu-Pb-Ag-Bi−rich cores (PyI) revealed by LA-ICP-MS data. Co/Ni and calculated (Se/S)fluid ratios for both cores (PyI) and rims (PyII) indicate a magmatic-hydrothermal origin. The in situ S isotopic compositions (δ34S) of molybdenite are 2.1‰ to 6.8‰, which are identical to those of molybdenite separates. PyI has δ34S values of −6.9‰ to 0.8‰, whereas PyII exhibits slightly more negative values of −7.5‰ to −0.2‰. These analyses indicate reliable results for in situ S isotopes in molybdenite, which could be more appropriate to constrain the origin of sulfur in hydrothermal fluids than results from pyrite analysis. The in situ S isotopic compositions of sulfides confirm a magmatic source for sulfur. The in situ Pb isotopic compositions of pyrite are consistent with those of K-feldspar from the biotite K-feldspar granite, indicating a common source. The heterogeneous As/Ni, As/Sb, and As/Bi values, as well as the variations of δ34S values of both PyI and PyII, indicate progressive oxidization of the hydrothermal fluids. These results illustrate that the metal-rich fluids were released from the granite and migrated along faults and fractures around the granite in an extensional setting. The precipitation of molybdenite-quartz veins at Shipingchuan was triggered by changes in temperatures and redox conditions, which were caused by mixing of magmatic fluids and meteoric water. Results in this study provide an example of tracing the link between Mo mineralization and magmatism using in situ S isotopic compositions of molybdenite and Pb isotopes of pyrite and K-feldspar.

Reactivation of metal-fertilized lower continental crust: Origin of intrusion-related Asiha gold deposit in Eastern Kunlun orogenic Belt, China

Gold deposits in the East Kunlun Orogen Belt (EKOB) are generally identified as orogenic gold deposits. However, recently, a new magmatic-hydrothermal model has been proposed to explain the genesis of these deposits that show intimate spatial and temporal relationships with abundant Triassic granitic intrusions, implying an intrusion-related gold system. The petrogenesis of these granites and their relation to gold mineralization are still unclear, owing to the lack of direct evidence of the connection between gold mineralization and granitic rocks. The gold-bearing Asiha intrusions (GBAI) from the Gouli area of the eastern segment of the EKOB are not only contemporary and located with mineralization but also have abnormally high gold content and sulfide accessory mineral. The GBAI are mainly composed of quartz diorite and granite porphyry. An integrated investigation involving mineral composition, zircon U-Pb dating and Hf isotopes, whole-rock elemental (including Au) and Sr-Nd-Pb isotopic geochemistry of the GBAI, as well as the in-situ Pb isotopic geochemistry of pyrites from the Asiha gold deposit, was conducted to constrain magmatic sources and petrogenesis of the GBAI, and gold mineralization mechanism. Zircon U-Pb dating reveals that the Asiha quartz diorite was formed at 230 Ma. The mineralized granite porphyries with high SiO2 contents (71.7–74.3 wt%) are peraluminous high-K calc-alkalic rocks, while the unmineralized quartz diorite with low SiO2 contents (58.1–60.0 wt%) are metaluminous high-K calc-alkalic rocks. Both rocks are potassic, strongly enriched in LILEs and LREEs with high LILE/HFSE ratios, depleted in Nb, Ta, Ba and Sr, and have weakly negative Eu anomalies and high zircon saturation temperature. Petrographic and geochemical features suggest that the quartz diorite is typical of I-type, while the granite porphyry is highly fractionated I-type granite. Their variable concentrations of major and trace elements are due to fractional crystallization of plagioclase, hornblende, and accessory minerals (apatite, zircon and monazite). Notably, the Asiha intrusions all contain high Au contents (Au = 0.02–0.05 ppm) compared to the primitive mantle estimated from chondrite values (0.88 ppb), indicating the existence of gold enrichment. All these granites are characterized by limited ranges of initial 87Sr/86Sr (0.7087–0.7133), εNd(t) (−6.0 to −5.0), 206Pb/204Pb (18.1–19.0),207Pb/204Pb (15.6–15.7), and 208Pb/204Pb (38.2–38.9), as well as zircon εHf(t) with values of −4.4 to −1.7. Their lead isotopes are consistent with that of pyrite in the ores (206Pb/204Pb = 18.41–18.45, 207Pb/204Pb = 15.61–15.65, 208Pb/204Pb = 38.47–38.56). Based on our results, we suggest that the GBAI were originally generated by partially melting of a previously Au-fertilized juvenile lower crust, which had been formed by metasomatized SCLM-derived alkaline basaltic underplating, and underwent AFC processes during emplacement. Subsequently, the post-magmatic fluids concentrated and precipitated Au to form the Au-bearing quartz veins.

Sedimentation on the Siberian Arctic Shelf as an indicator of the arctic hydrological cycle

Siberia occupies a significant part of the Eurasian continent and environmental changes in this region can have an important impact on the climate system of the Northern Hemisphere. The sediment flux of Siberian rivers is sensitive to changes in physical, chemical, and biological processes taking place on the continent, and these changes can be recorded in marine sediments on the Siberian Arctic Shelf. This paper presents data on grain-size distribution of the sediments, the sedimentation rates, and the mass accumulation rates on the shelf over the past 100 years. Age models are based on the decay rate of excess lead isotope 210Pb, taking into account the sorption capacity of the marine sediments, and the presence of cesium isotope 137Cs peaks in the sediment cores. The highest sedimentation and mass accumulation rates were observed prior to the 1920–40 and coincide with larger particle sizes, indicate a period of active sediment-laden sea ice and iceberg melt. Systematic decrease in the sedimentation and mass accumulation rates against the background of an increase in the proportion of silt fractions in the shelf sediments in the second half of the 20th century can be explained by an acceleration of the arctic hydrological cycle.

S, Pb, and Fe isotope compositions of sulfides in middle and southern Okinawa Trough: Implying the complicated hydrothermal systems in back-arc spreading centers

Sulfur, lead, and iron isotopic systematics of sulfides from the Iheya North hydrothermal field in middle Okinawa Trough and the Yonaguni Knoll IV hydrothermal field in southern Okinawa Trough were investigated to understand the origin of ore-forming material and isotope fractionation during sulfide precipitation in back-arc spreading centers. The δ34S values (from 8.60‰ to 9.68‰) of sulfide minerals in Iheya North field suggest sulfur was derived from the leaching of basement rocks and the reduction of seawater sulfate. But an additional light sulfur source from the dissolution of biogenic sulfides in sediments is indispensable for the observed low δ34S values (between 4.78‰ and 4.97‰) of Yonaguni Knoll IV sulfides. Lead isotope compositions of all sulfides vary in a relatively wide range (206Pb/204Pb = 18.432 to 18.563, 207Pb/204Pb = 15.579 to 15.671, and 208Pb/204Pb = 38.539 to 38.979, respectively) which involves the mixing of mantle-derived and sediment-derived lead in varying proportions. Unusually high radiogenic lead isotope ratios of Yonaguni Knoll IV sulfides (207Pb/204Pb = 15.628 to 15.671, and 208Pb/204Pb = 38.854 to 38.979) imply the presence of old crustal fragments beneath southern OT. The hydrothermal fluids in OT are characterized by extremely low calculated δ56Fe values (−1.00‰ to −1.32‰) which is attributed to reducing sediments. The paired Fe-isotope compositions of pyrite and chalcopyrite revealed significantly different iron isotope compositions of hydrothermal fluids in study areas and extremely complicated ore-forming processes. Rapid precipitation of pyrite from FeS precursors accompanying iron isotopic disequilibrium moves from FeS-fluid equilibrium to pyrite-fluid equilibrium during pyrite recrystallization. The combination of sulfur, lead, and iron isotopic data suggests that hydrothermal systems in back-arc spreading centers related to plate subduction are generally affected by mantle, overlying sediments as well as potential old continental crust fragments, which results in various hydrothermal fluids and complicated mineralization processes.

A long‐distance copper alloy trade to the North Eastern Baltic during the late pre‐Roman and Roman Iron Age (250 BCE–450 CE) explored with lead isotope MC‐ICP‐MS

AbstractThe North Eastern Baltic has no copper resources of its own, meaning that Cu alloy was imported either as raw material or as finished objects. The north‐eastern coastline of Estonia during the late pre‐Roman and Roman Iron Age was connected to the south by sea to the long‐distance ‘amber’ trade route and to the east by Russian river systems. This study quantitatively assesses the direction of the Cu alloy supply in the region before and after brass enters circulation at the beginning of the Roman Iron Age. After an initial portable X‐ray fluorescence (pXRF) survey, 18 objects were chosen for Pb isotope analysis. This isotope analysis resolved a group of nine brass artefacts from the Roman Iron Age amongst a ‘melting pot’ of other Cu alloys. The similarity between the isotope ratios found in the Roman world suggests the presence of the same ‘melting pot’ in the North Eastern Baltic, possibly created by a large amount of Roman Cu alloy being traded north. No evidence for Cu alloy from Scandinavia or the Ural Mountains could be found. The hypothesis from this small study is that the Cu alloy entering Estonia was dominated by metal from Southern Europe from the late pre‐Roman Iron Age and the Roman period.

Analysis of Lead Smelting Technology in the Early Bronze Age Based on Smelting Slag from the Central Plains of China

To explore the source of Pb in Bronze Age artefacts from the Central Plains (Zhongyuan) in China, we investigated non-ferrous minerals from the Qingyuan archaeological site in Yuanqu County near the Zhongtiao Mountains. Fragments of smelting slag from the Erlitou cultural layer were collected. The smelting slag was investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and lead isotope analysis. The SEM and EDS results confirmed that the slag contained Pb, Pb–As, and Cu–Pb–Sn inclusions and non-metal impurities such as low-Zn spinels. The XRD results signified that the bulk of the slag comprised Fe–Mn–Si phases. The chemical state of Pb was mainly Pb–O with some metallic Pb, as identified by XPS. The theoretical melting point was calculated using FactSage7.1 based on the composition and phase characterisation. The calculated temperature was 1100–1200 °C, which agreed well with the actual melting point of 1114–1354 °C. The slag composition and inclusion phases indicated that Pb–Zn–O ores with Mn and As were added during reduction smelting in Qingyuan. The raw materials of smelting included crude Pb with minor amounts of Cu, As, and Sn. Lead isotope analysis revealed that the lead materials produced in Qingyuan were likely transferred to Yanshi City in the Shang Dynasty. The findings of this study provide significant clues for exploring lead mineral production in the Central Plains during the Early Bronze Age.