Lead Isotopic Compositions Research Articles

Recycled mantle source for porphyry mineralization: U[sbnd]Pb and Re[sbnd]Os geochronology, and S–Pb–Cu isotopic constraints from the Urumieh-Dokhtar magmatic arc, central Iran

The Urumieh−Dokhtar magmatic arc (UDMA) hosts some of the world-class porphyry copper deposits in Iran. Here, we present high-resolution geochronological and stable isotope data to gain insights into the timing and source of the metallogeny of Kahang porphyry Cu deposit. Zircon UPb data show crystallization age of ca. 15 Ma age for the host porphyry intrusion and ReOs geochronology yields 14.5 Ma from the molybdenite associated with the ores. Sulfur isotope values on the sulphide minerals range from −1.6 ‰ to + 2.1 ‰, indicating a magmatic source for sulfur. Lead isotopic compositions of the S-bearing minerals are akin to those of the intrusive rocks, suggesting that the metal was likely sourced from mantle reservoirs. We propose a model for the UDMA involving slab break-off during the maturity of arc magmatism from the syn- to post-collisional stages of orogenesis. The δ65Cu data trace a systematic change from the barren to the fertile magmas. We suggest that partial melting of the sub-continental lithospheric mantle that has previously been refertilized of Cu through time as the potential source for the formation of ore-bearing magmas.

Sources of lead in a Tibetan glacier since the Stone Age

The Tibetan Plateau glaciers, among the world’s most remote and pristine places, provide water to millions and play a vital environmental role. We measured the lead isotopic composition in a dusty ice core from the Guliya ice cap in northwest Tibet, from approximately 36 thousand years Before Present (Stone Age) to 2015, to determine the onset and sources of anthropogenic lead. Despite the dust-laden nature of the core, a clear change in the lead isotope signature to below Stone Age levels started in 1949 followed by a rapid decrease in 1960 and an even more rapid decrease in 1974 indicating the first emergence of anthropogenic lead. Accurate isotopic lead measurements allowed us to better, and more sensitively, quantify sources using a Bayesian mixing model. Chinese gasoline was the primary anthropogenic source surpassing natural contributions in the 2000s until 2007 when emissions from leaded gasoline decreased and those from coal and lead-zinc ores increased.

Mineralization characteristics of Lead-Zinc-Copper deposits in Akdağmadeni Region (Northern Central Anatolia, Türkiye): Integration of field study, geochemical, isotope, and geophysical data

The Akdağmadeni region is one of the important Pb-Zn-Cu metallogenic provinces in Türkiye. Most of the Pb-Zn-Cu deposits in the region are located near granitoid intrusions within metamorphic rocks, and they are typically classified as skarn-type ores associated with granitoids. However, no relationship has been determined between the Başçatak prospect and any granitoid outcrop. This raises the question of whether the Pb-Zn-Cu mineralization in the region is related to granitoids or if magmatic processes remobilized pre-existing mineralization. Observations from field studies suggest that mineralization in the Başçatak prospect is a stratiform type, metamorphosed occurrence that might have occurred earlier than the granitic intrusions. The geochemical data indicated that the granitoids have low-grade, subeconomic Cu potential and no Zn productivity potential, supporting these observations. Geophysical data also show that there is no intrusive body beneath this prospect. Granitoid-related deposits (Karapir - Ortaköy and Akçakışla) exhibit two distinct occurrences around the contact between the granite and the surrounding metamorphic rocks. The first type of occurrence (O-1) is formed at the contact and contains magnetite, pyrrhotite, and chalcopyrite. The second type of occurrence (O-2) is located outside the contact and is rich in sphalerite and galena. Both O-1 and O-2 contain skarn minerals along with ore minerals. The δ34S values of sulfide minerals from the deposits range from −0,7 to 7,5 ‰ (V-CDT). These values overlap with those of both magmatic sulfur and reduced sulfur from seawater-dissolved sulfate, making it difficult to suggest a sulfur source without additional data. Lead isotope compositions of the galenas from all deposits plot above the average crustal growth curve, suggesting an upper crustal and orogenic source similar to Western Mediterranean and Türkiye type materials described in the literature for the lead, source in different time intervals. Furthermore, Pb isotope geochemistry suggests a contemporaneous age with the host metamorphic rocks (Carboniferous – Lower Permian) for the Başçatak prospect. These results support observations indicating a syn-genetic formation for the Başçatak prospect. The age range of granite-related deposits forms two sub-groups:105–77 Ma and 61–50 Ma corresponding to the Upper Cretaceous and Paleocene transition. These data indicate that that the galenas were formed in two different stages in these mineralizations. Stratiform mineralization in the Başçatak prospect likely formed either through exhalative sedimentary processes by hydrothermal fluids or through chemical sedimentary processes under reductive conditions in a marine environment during metamorphism. O-1 appears to have been formed by hydrothermal fluids developed during granitic magmatism. A plausible formation process for O-2 involves the leaching of sulfur, lead and other metals from Başçatak type enrichments in metamorphics, with transportation and deposition within the epidotized calc-schist and marbles outside the granitoid contacts. The uplift of granitic intrusions prepared the channels and depositional environment for O-2 and caused heating of the hydrothermal fluids during this mineralization period.

Mixed lead sources in tin metal: Implications for using lead isotopes to study tin artifacts

Methods for provenancing copper, lead, and silver using the isotopic composition of lead are well-established. Lead isotope analysis holds promise for the study of tin metal as well, as long as one accounts for the U-Th-Pb systematics of cassiterite (SnO2) and chaîne opératoire of tin production. Although Precambrian cassiterite may contain 10s of ppm Pb or more (predominantly radiogenic 206Pb), Phanerozoic examples typically contain only a few parts per million Pb. However, all but one of the 133 raw tin ingots excavated from European Bronze Age shipwrecks contains more Pb than could have come from cassiterite alone, as do six of the twelve analyzed tin objects interpreted to have been derived from the ores of southern Africa. Accordingly, almost all tin objects must contain Pb from external cassiterite sources and interpretation of LIA must account for this contamination. The nature of the contaminant (sulfides, U-Th-bearing minerals, silicates) can be inferred from patterns in Pb concentration and LI values. The 3 major sources of Pb that can typically be identified in tin artifacts are original Pb from the tin ore, radiogenic Pb produced in-situ due to U decay, and external Pb added during the cassiterite smelting and ingot production. As cassiterite has high U/Pb but low Th/Pb, the 208Pb/204Pb may be representative of the initial Pb incorporated in the mineral. This is assuming either that no external Pb is added during the ore processing or that the added Pb is from coeval sulfides from the same Pb ore provenance. In such cases 208Pb/204 Pb can be used to estimate a Pb model age, which in turn can be used for provenance estimate of the ingots. If the addition of Pb is from U-Th-mineral contaminants to the ore concentrate, then this will also increase 208Pb/204Pb and point to erroneously young model Pb ages. In such cases, the problem would be evident in positively correlated values of 206Pb/204Pb and 208Pb/204Pb. If Pb concentrations are above a certain threshold (approximately 5 ppm). LIA typical common Pb isotope ratios will be clear indication that external, non-cassiterite Pb, is added to the tin artifact. This tin could be from impurities in the ore (e.g., inclusions in cassiterite, impurities in the ore concentrate, or added during ore smelting and/or metal processing. Overall, elevated Pb concentrations accompanied with non-radiogenic Pb isotopes typical for common Pb, is a clear indication that significant amount of external (contaminant) Pb is added to the tin artifact.

Provenance changes of the holocene deposits of Oga and Tsivolki bays (Novaya Zemlya archipelago) according to SR, ND, PB isotope data

The paper is devoted to the Sr-, Nd-, Pb-isotope data obtained for two cores of bottom sediments taken in the Oga and Tsivolki bays of the Severny Island of the Novaya Zemlya archipelago. The studied sequence of sediments from Oga Bay has been accumulated over the last thousand years. The 87Sr/86Sr ratio decreases from top to bottom down the section from 0.72225 to 0.71995, the value of εNd varies from –6.1 to –5.5. The Pb isotopic composition varies within narrow limits: the 206Pb/204Pb ratio from 19.107 to 19.139, the 207Pb/204Pb ratio from 15.632 to 15.635, and the 208Pb/204Pb ratio from 38.568 to 38.635. A rapid decrease in the 87Sr/86Sr ratio at a relatively stable neodymium and lead isotope composition indicates a change in the source of the clastogenic material. This can be explained by the fact that the material of the destruction of Permian clay shales, and then the Devonian-Silurian sedimentary carbonates, first entered the area of glacier abrasion and further, respectively, into the sedimentation zone. The sediment column from the Tsivolki Bay was formed over a little more than 10 thousand years. Based on the Sr, Nd, and Pb isotope ratios, these bottom sediments are divided into lower and upper parts: before and after 150 cm (or ~3500 years). In the lower part of the column, the 87Sr/86Sr ratio increases from 0.72055 to 0.72580, the value of εNd remains approximately the same and varies around –8.2. In the upper part, the 87Sr/86Sr ratio drops to 0.72049 in the near-surface layer; at the same time, the value of εNd increases to –6.4. At the boundary of these two units, the 206Pb/204Pb ratio abruptly changes from about 18.0 in the lower part to 19.3 in the upper part and 208Pb/204Pb from about 36.5 in the lower part to 38.7 in the upper part of the section. The change in the Sr, Nd, and Pb isotope characteristics is likely a reflection of changes in the composition of the rocks in the area where the basin was removed, which is now being eroded by the glacier. Comparison with modern sources supplying clastic material to the Kara Sea showed that the material inputs the Oga and Tsivolki bays only from Novaya Zemlya.

Copper for the early oxhide ingots traced to the South Urals

Oxhide ingots are flat, rectangular slabs of metal, most commonly of copper, with protruding corners of varying styles. These Late Bronze Age artifacts were widespread across the Mediterranean for approximately half a millennium between the 16th and 11th centuries BC. Although they are generally known as essentially a Cypriot “commodity brand” by the late 15th century BCE, the origin of this ingot’s distinct shape has remained unknown. With the expansion of the lead-isotope database of Eurasian copper ores, the origin of the oldest chemically characterized oxide ingots may now be defined. The bimodal lead isotope compositions of 15 early, pillow-shaped oxhide ingots excavated in Crete are consistent with those of copper ores from the Southern Urals, which are known to have been actively mined in the Bronze Age. Together, Pb isotope and trace element compositions indicate that the majority of the ingots were cast from copper derived from Ural-type Cu-Zn volcanogenic massive sulfide deposits. However, two ingots enriched in Ni, As, and Co match Main Ural Fault-type ores that are hosted by ultramafic rocks.The characteristic design of the pillow-shaped ingot was likely related to the particulars of overland transport, facilitating their long-distance conveyance on pack animals. There is further support of a non-Cypriot origin of this form in the possible association between the words for “ingot”, “copper” and “hide” across languages of Western Asia and the Mediterranean. Thus, an eastern origin of the oxhide form for ingots is likely.

Relationship between Pb-Zn and Au mineralization in the Laoyachao deposit, South China: Constraints from geology and S-Pb-He-Ar isotopes

Both Pb-Zn and Au mineralization can simultaneously occur at the deposit, camp or regional scale, but their spatial-temporal and genetic relationships have received less attention so far. Here we present detailed field investigations and S-Pb-He-Ar isotope data for the Laoyachao deposit, South China, to interpret the intrinsic associations between Pb-Zn and Au mineralization. Both Pb-Zn and Au ores in the studied area are distributed independently but spatially associated with the same granodiorite. Field and microscopic observations, together with previous dating, show that the Au mineralization postdated the Pb-Zn mineralization. The relatively restricted range and lower δ34S values for the Au ores (−0.72 to +0.94 ‰) and the Pb-Zn ores (−1.98 to +2.36 ‰) indicate that both metal mineralization types are attributed to a homogeneous magmatic sulfur source. Lead isotope compositions for the ores and the feldspars from the granodiorites define a well-defined linear array, with the Au ores displaying less radiogenic Pb. In addition, the Pb-Zn ores exhibit lower 3He/4He and 40Ar/36Ar ratios (0.01–0.26 Ra, 298–313) than the Au ores (0.16–2.93 Ra, 341–382). All evidence demonstrated that, besides the granodiorite end-member, an end-member with high-radiogenic Pb and lower 3He/4He values participated in the early Pb-Zn mineralization, in contrast, the other end-member with less radiogenic Pb and higher 3He/4He values was involved in the late Au mineralization. Considering that both Pb-Zn and Au mineralization in the studied deposit are spatially, temporally and genetically related to the same granodiorite, the Pb-Zn mineralization associated with granodiorite can provide an indicator for gold exploration.

Rb–Sr Pyrite Dating and S–Pb Isotopes in the Fang’an Gold Deposit, Wuhe Area, Eastern Anhui Province

The Fang’an gold deposit in the Wuhe area, Anhui Province, is located in the area adjacent to the Bengbu Uplift and Wuhe Platform Depression in the southeastern part of North China. This study aimed to determine the deposit’s mineralization age and the source of its metallogenic materials and mineralization processes through investigations into its geological characteristics, Rb–Sr isotopes, and S–Pb isotopes. The orebodies of the Fang’an gold deposit in the Neoarchean Xigudui Formation primarily exhibit a vein-type structure. The ore-forming process can be divided into four stages: (i) the quartz stage (Py1); (ii) the quartz–pyrite stage (Py2); (iii) the polymetallic sulfide stage (Py3); and (iv) the carbonate stage. Of these, the main mineralization stage is also the main period in which gold mineralization occurs. In situ sulfur isotope results of pyrite (Py1 to Py3) in the first three mineralization stages, suggesting a contribution of sulfur from crust–mantle magmatic fluids. The δ34S values for Py2 (average 5.51‰) are higher than Py1 (average 4.45‰) and showed that the magmatic fluids mixed with meteoric waters. The δ34S values for Py3 (average 5.18‰) are lower than Py2 (average 5.51‰), revealing that it related fluid immiscibility. The lead isotopic compositions of sulfides within the ores possessed 206Pb/204Pb ratios ranging from 16.759 to 16.93, 207Pb/204Pb ratios ranging from 15.311 to 15.402, and 208Pb/204Pb ratios ranging from 37.158 to 37.548. These lead data were plotted close to the Xigudui Formation, relatively distant from the Mesozoic granites, indicating that the Xigudui Formation was the source of lead for the Late Mesozoic ores of the deposit. Taken together, due to the degassing of mantle-derived magma in the shallow parts of the crust, it can be determined that the sources of ore-forming sulfur and lead were crust–mantle magmatic activities in the Wuhe area. Rb–Sr dating of pyrite from Fang’an gold deposit reveals that the mineralization occurred at 126.89 ± 0.58 Ma. Considering the previous research into the dating of magmatic rocks in the Wuhe area, we propose that the genesis of the Fang’an gold deposit is closely associated with magmatic activities in the area at around 130 Ma.

Lead isotopic compositions of sulfides in the Taoxikeng tungsten deposit, southern Jiangxi and their geological significance

Lead isotopic compositions of sulfides in the Taoxikeng tungsten deposit, southern Jiangxi and their geological significance

Tracing the lead source of maiolica: a pilot isotopic study on artefacts from the area of Florence, Italy (fifteenth–nineteenth century)

The manufacturing of Italian maiolica (tin-glazed pottery) was extremely appreciated during the Middle Ages and Renaissance, leading to the production and collection of a rich cultural heritage. This pilot study aims to characterize the production technique and the origin of the lead used as a flux in a set of samples of maiolica glazes made in the area of Florence over a wide time span, ranging from the fifteenth to the nineteenth century. In particular, this is the first study that applies provenance analysis, using lead isotopes, to tin-glazed artefacts made in the site of Montelupo Fiorentino and by the Ginori manufactory in Doccia (Florence, Italy), both important production centres of ceramics in Italy. The samples were first analysed by scanning electron microscopy to characterize their layer structure and chemical composition. Lead isotope analysis was then performed by thermal ionization mass spectrometry and showed that the samples tend to be distributed into distinct groups according to their period of production. Moreover, the comparison with the lead isotope composition of the deposits of the European and circum-Mediterranean area from which lead was historically extracted showed that the isotopic composition of the samples differs from that of the Italian deposits, suggesting that lead was imported from abroad. The isotopic composition of all the investigated maiolica glazes is compatible with German ore deposits, in agreement with what is reported by the historical sources relating to the lead supply areas.

The enrichment mechanism of indium in Fe-enriched sphalerite from the Bainiuchang Zn-Sn polymetallic deposit, SW China

Dispersed metals, such as indium and cadmium, are widely used in certain high-tech applications and are important resources for world economies. Sphalerite is an important host mineral for indium, cadmium and other trace elements which can record genetic information in hydrothermal systems. The Bainiuchang Zn-Sn polymetallic deposit, located in the southwest margin of the Yangtze Block, has substantial zinc concentrates with indium and cadmium mineralization. In this study, we examined different sphalerite grains from this deposit with elemental mapping, in-situ trace element geochemistry and S-Pb isotopic composition. The discrepancy of indium and Zn/Cd ratio suggest that there are at least two generations of sphalerite. The mineralization of indium is mainly enriched in marmatite [(Zn,Fe)S)] from cassiterite-bearing ore, rather than in that from cassiterite-poor ore. The mineralization of cadmium occurred in all types of ore. The relevance of trace elements suggests that indium can be incorporated into sphalerite by a couple substitution of (In, Ga)3+ + (Cu, Ag)+ ↔ 3(Zn, Fe)2+, whereas Fe, Cd can be incorporated into sphalerite by substitutions of Fe2+ ↔ Zn2+ and Cd2+ ↔ Fe2+. Sulfur (δ34SV-CDT =+2.43 to +3.88 ‰) and lead (206Pb/204Pb = 18.346–18.396, 207Pb/204Pb = 15.675–15.691) isotopic compositions indirectly suggest that indium and cadmium in the Bainiuchang Zn-Sn polymetallic deposit may be sourced from magmatic-hydrothermal fluids associated with Late-Cretaceous magmatic activities in this district.

Lead isotopic compositions link copper axes from Kietrz (Poland, 3500–3350 BC) to Slovak and Balkan copper mines

AbstractChemical and lead isotope analyses aided by metallographic examination of copper axes found at the Late Neolithic settlement of Kietrz in southwestern Poland provide new evidence for the origin of copper and metal trade routes in the region. Our results indicate that metal used for the axes could be sourced from copper mines in modern Slovakia, Bulgaria and perhaps Serbia. The evidence from this study confirms that the Funnel Beaker people from Poland became parties to a metal trading network that connected much of continental Europe in the mid‐4th millennium bce and provides a better understanding of how these contacts provided the background for the technological and socio‐economic developments of the Baden era.

Lead isotope compositions and modern sediments sources in the radial sand ridges from the Jiangsu coast, East China

The formation of the Jiangsu radial sand ridges (RSRs) in East China has received extensive attention. However, the provenance of the Jiangsu RSRs sediments is still controversial. In this study, the Pb isotopic compositions of residual fractions were used to elucidate the provenance of the Jiangsu RSRs sediments. The results showed that Pb isotopic compositions of sediments in onshore RSRs were not significantly different with those of the landward offshore RSRs, indicating the shoreward transport of sediments from the landward offshore RSRs. The combination of Pb–Nd isotopic compositions revealed that the seaward offshore sediments mainly originated from the Yangtze River Mouth, while the onshore and landward offshore sediments were dominantly supplied by the Old Yellow River Delta through the southward flow. This study provides a deep insight into the evolution of Jiangsu RSRs, and is of great value to the Jiangsu coastal protection.

Исследование химического и изотопного Pb состава в дирхемах из Подболотьевского могильника

A series of silver dirhams and their imitations, originating from the burials of the Podbolotyevo burial ground left by the Muroma tribe, was studied by XRF, neutron diffraction and analysis of the isotopic composition using the Pb-Pb method. The burial ground is located near the city of Murom, Vladimir Region of Russia. The collection obtained from the excavations of this site includes finds of 40 original Arabic silver coins and silver coin replicas. The analyzed sample consists of 34 coins and includes dirhams dating back to the 9th century BC which are replicas of the Abassid dirhams; and the main array of coins dates back to the first third of the 10th century and the second half of the 10th century. The chemical composition studies of the metal by X-ray diffraction method showed that high-grade, “yellow” and multicomponent silver were used for minting dirhams. It was found out that there is a sharp drop in the silver content in the dirhams dating back from the middle to the second half of the 10th century, which reflects the general trend in Arabic coinage. It is also noted that in the sample from the Podbolotyevo burial ground, dirhems coin replica coins were made of high-grade silver. Silver purity for some of the coins from the analyzed sample was checked by neutron diffraction using a specialized DN-6 diffractometer at the IBR-2 high-flux reactor. The isotopic composition of lead in silver in coins from the analyzed sample was studied by the method of multicollector mass spectrometry with ionization of matter in inductively coupled plasma (MC-ICP-MS). The obtained data on the isotopic composition of Pb in the silver of the coins showed that the precious metal for minting both Arab dirhams at the mints of ash-Shash, Samarkand, Bukhara, and their replicas comes from the deposits in Central Asia. It has been established that the Lashkerek and Ilak deposits turned out to be the source of silver for some dirhams from the Podbolotyevo burial ground, however, mixed silver from several deposits was mainly used.

Sulfide Pb-Zn mineralization in the Tianshuihai terrane, northwest Tibetan plateau: A case study of the Huoshaoyun Pb-Zn deposit

The Tianshuihai terrane, located in the northwest of the Tibetan plateau, is a newly known metallogenic district of Pb-Zn deposits in China, with a prospective resource of Pb and Zn over 30 Mt. Lead and Zn mineralization in the terrane comprises two types of non-sulfide and sulfide. However, the genesis of sulfide Pb-Zn mineralization and its relationship to regional geological evolution remain enigmatic. In this paper, a detailed mineralogical and geochemical study of the Huoshaoyun Pb-Zn deposit combine with a synthesized review of the evolution of the Tianshuihai terrane provide comprehensive constraints on the genesis of sulfide Pb-Zn mineralization and what geological events of which it may have been part. Economic orebodies in the Huoshaoyun deposit are hosted by a sequence of unmetamorphosed, flat-lying carbonate complex of Middle Jurassic age. Ore minerals consist predominantly of smithsonite and cerussite with variable sphalerite and galena. The sulfide minerals are texturally early and were replaced by non-sulfide minerals. Sulfur isotope compositions of galena are remarkably inhomogeneous, range from −18.52 to 25.40 ‰. Conversely, lead isotope compositions of galena display fairly uniform 206Pb/204Pb (18.485–18.785), 207Pb/204Pb (15.640–15.764), and 208Pb/204Pb (38.781–39.303) ratios. We thus propose that sulfide Pb-Zn mineralization in the Huoshaoyun deposit belongs to Mississippi Valley (MVT) - type. The metals were most probably sourced from the regional strata, e.g., the Permian Shenxianwan, Triassic Keleqinghe, and Jurassic Longshan formations. Sulfide Pb-Zn mineralization in the Tianshuihai terrane likely occurred sometime between the Oligocene to Early Miocene in a paleo-forland basin, coincided with the widespread potassic and ultra-potassic magmatic activities, a marked change in tectonic regime from compressional to extensional, an elevated heat flow in the Tibetan Plateau, and a great MVT-type Pb-Zn mineralization event in the Tethys tectonic domain. This study raises awareness about the presence of MVT-type Pb-Zn deposits in the Tianshuihai terrane and the great potential for Pb-Zn exploration in this region.

Evidence of a distal axis inactive high-temperature hydrothermal field on the ultraslow spreading Southwest Indian Ridge: Insights from mineralogy and geochemistry studies

The development of hydrothermal activities on mid-ocean ridges is primarily influenced by magmatic and tectonic activities close to the ridge axis. On slow and ultraslow spreading ridges featured by limited magma supply, prolonged hydrothermal activity can also occur in non-transform offsets (NTO), where sustained ultramafic-related hydrothermal circulation happens due to prolonged hydrothermal processes associated with the expose of ultramafic rocks. In contrast, basalt-hosted hydrothermal fields are barely developed in NTOs, especially in off-axis area, due to insufficient magma supply. In this study, we reported the occurrence of a distal axis (∼9.5 km) basalt-hosted hydrothermal field (50.63°E) on the NTO of segment 27 of the ultraslow spreading Southwest Indian ridge. The hydrothermal products are characterized by layered crusts mainly composed of oxides, such as limonite and goethite, rich in Fe and depleted in Si. These crusts contain high contents of trace elements derived from seawater, such as P, As, Mo, U, and Sb and show REE pattens with negative Eu and mostly positive Ce anomalies. However, the high Cu content (1.82 ± 0.89 wt%, N = 27), low absorption ratio of Cu (18.39 ± 12.71%, N = 9), and residual chalcopyrite altered by goethite suggest prior high-temperature hydrothermal activity. Lead isotopic composition with basaltic rocks signatures that distinct from those of low-temperature crusts of seawater origin also support this conclusion. The Fe-rich crusts appears to be the result of high-temperature sulfides altered by late-stage low-temperature diffuse flow. This field is currently the furthest known distal axis basalt-hosted hydrothermal field located in NTOs of ultraslow spreading ridges. The hydrothermal circulation is likely due to a combination of off-axis normal fault and gabbro diking. Our results emphasize the occurrence of distal axis basalt-hosted high-temperature hydrothermal activities on NTOs of ultraslow spreading ridges, and may lead to an increased estimation of hydrothermal heat and chemical influx to the ocean.

Lead isotopes and rare earth elements geochemistry of global phosphate rocks: Insights into depositional conditions and environmental tracing

Phosphate rock bears both geologically and environmentally significant information. Rare earth elements and yttrium (i.e., REY) characteristics have been commonly used for reconstructing the redox conditions of depositional environments and the effects of post-depositional diagenetic alteration on phosphate rock. In addition, phosphate rock is typically enriched in a range of trace elements such as uranium (U) and cadium (Cd) that can be dispersed as contaminants into the environment with phosphate mining and phosphate fertilizer application. Here we report the lead (Pb) isotope compositions combined with Pb and REY concentrations of both global sedimentary and igneous phosphate rocks, aiming to evalute the geological origin of phosphate rocks over time and the potential of using them for environmental tracing. Phopshate rock samples analyzed in this study were sourced from major economic phosphate deposits in the world, including China, Southern Tethys (e.g., Morocco, Tunisia, Israel), the U.S., India, South Africa and Russia. Our results show a wide range of 208Pb/204Pb (35.70 to 60.58), 207Pb/204Pb (15.20 to 18.25), and 206Pb/204Pb (16.369 to 71.806) ratios in the phosphate rocks, with sedimentary phosphate rocks being significantly more radiogenic than igneous rocks. The majority of sedimentray phosphate rocks show a notable isotopic overprinting by non-radiogenic terrestrial Pb, except for those from Israel and Morocco that have the most radiogenic Pb isotope compositions. Correspondingly, phosphate rocks with more radiogenic Pb isotope ratios show relatively pristine seawater REY features, likely suggesting their preservation of the original oxic seawater conditions and/or minimal diagenetic alteration. In contrast, phosphate rocks with less radiogenic Pb isotope compositions show REY indications for more anoxic seawater redox conditions and/or greater diagenetic alteration. We further evaluate the potential utility of Pb isotopes for tracing the associated contamination with phosphate rock mining and fertilizer application in the environment. In most cases, the radiogenic Pb isotope composition of phosphate rocks and corresponding P-fertilizers is distinctive from both natural crustal Pb and major anthropogenic Pb sources (e.g., Pb ore deposits and pesticides), which provides a great advantage for applying Pb isotopes as an environmental tracer for metal(loid) contamination from phosphate sources. The combination of Pb isotope ratios and REY proxies could further constrain the Pb source discrimination. Overall, this study provides new Pb isotopic and REY geochemical data on global phosphate rocks and fertilizers, which lays the groundwork for future regional and local studies on both their geological and environmental implications.

Age and mineralization origin of the Zhongshangou Au deposit, Zhangjiakou goldfield, North China: Constraints from molybdenite Re-Os age and sulfides S-Pb isotopes

The Zhangjiakou goldfield, located in the northern North China Craton (NCC) margin, is a typical gold mineral province in China, containing over 67 gold deposits with 260 t gold reserve. However, gold mineralization age in this district has not been well constrained. Here, we integrate mineral paragenesis, molybdenite Re-Os age and in situ sulfides S and Pb isotopes from the Zhongshangou Te-rich Au deposit to constrain the timing and origin of gold and tellurium mineralization. Molybdenite Re-Os dating yielded a weighted average age of 381.7 ± 2.0 Ma (2σ, MSWD = 0.37, n = 7). Molybdenite has similar δ34S value (-12.9 to −8.5‰, n = 10) to other sulfide minerals (23 pyrite, 2 chalcopyrite and 2 bornite, δ34S = -13.6 to −5.6‰). Lead isotope compositions also show no difference among these sulfide minerals. Considering the mineral paragenesis and S-Pb isotopes, we suggest that molybdenite coprecipitated with gold, tellurides and other types of sulfides from the ore-forming fluids, and that the molybdenite Re-Os data could represent the timing of Zhongshangou gold and tellurium mineralization. New and published age data define a ca. 380 Ma Au-Te mineralization event for the Zhangjiakou goldfield. These Au deposits were genetically associated with the Devonian alkaline magmatism.

Genesis of the Hatu gold deposit: Constrained by in situ S[sbnd]Pb isotope geochemistry of pyrite

As the largest gold deposit in west Junggar, the Hatu gold deposit is located between the Anqi and Hatu faults in the Hatu-Sartohay district. The orebodies, composed of gold-bearing quartz veins and auriferous altered wall-rocks, are controlled by NE-, NW-, and EW-trending faults in Early Carboniferous volcano-sedimentary rocks. In this study, integrated textural, in situ sulfur and lead isotope analyses of pyrite grains in the host rocks and ores reveal new information on the sources of the ore-forming fluids and metal, as well as the mechanism of gold deposition. Framboidal pyrite in tuffaceous siltstone has a large δ34S range of −26.7 to +54.0 ‰, which is attributed to sulfur-reducing bacterial (SRB) activity during sedimentary-diagenetic process. Fine-grained subhedral pyrite in meta-basalt shows negative δ34S values from −26.7 to −12.1 ‰, which may be generated by reduction of seawater sulfate by ferrous iron bearing minerals during metamorphism. The δ34S values of four generations of hydrothermal pyrite (Py1–Py4) in the orebodies vary in a narrow range from +1.4 to −1.9 ‰. The sulfur isotopic characteristics of the hydrothermal pyrite are similar to most magmatic hydrothermal deposits, but differ from the metamorphic pyrite in meta-basalt and the framboidal pyrite in tuffaceous siltstone. In addition, the uniform in situ lead isotope ratios of hydrothermal pyrite resemble the lead isotopic compositions of the granitic plutons in the west Junggar, but differ from those of pyrite in meta-basalt. The progressive decrease of δ34S values from early-stage pyrite (+0.7 ‰ to +1.4 ‰) to late-stage pyrite (−1.9 ‰ to +0.4 ‰) corresponds to the major gold precipitation processes, which can be explained by gradual decrease of oxygen fugacity and increase of pH with decrease of temperature of a gold-bearing magmatic-hydrothermal system. A relatively stable environment for Au precipitation probably is a key factor controlling the scale of gold deposit, as the ore-forming fluid has enough time to form large gold deposit such the Hatu gold deposit.

The rise of bronze in Central Asia: new evidence for the origin of Bronze Age tin and copper from multi-analytical research

The Bronze Age in Central Asia was dominated by the Andronovo Culture and the Bactria-Margiana Archaeological Complex (BMAC). Both cultural entities produced bronze, however, the extent of bronze production and use varied considerably in space and time across their territories. The introduction and spread of bronze metallurgy in the region is commonly associated with the Andronovo Culture, but comparatively little is known about the copper and tin sources that were exploited to make the bronze. To shed light on this aspect, this paper examines 91 bronze artefacts from the Middle Bronze Age (MBA) and the Late Bronze Age (LBA) recovered from twenty sites of Andronovo and the BMAC through a combined evaluation of chemical and isotopic analyses. Trace element patterns and isotopic compositions of lead, tin, and copper are determined for the objects complemented by tin isotope analysis of Central Asian tin ores. The data shows a clear separation of two source areas in the MBA and LBA I: the BMAC obtained copper from polymetallic (tin-bearing) deposits in Iran (Deh Hosein, Nakhlak/Bagh Gorogh) and possibly Afghanistan, while the Andronovo Culture mainly used copper from the Tian Shan Mountains. With the transition to the LBA II, a change in the material basis can be recognised, in which the BMAC increasingly relied on metal deposits from the Andronovo territory. The most important result in this context is the analytical proof of the coextraction of copper and tin from the copper-tin mine at Mushiston, Tajikistan, and the first direct link of tin in bronze objects with a tin deposit. Mushiston apparently supplied both cultural macro regions with a “natural” bronze, which accounted for about one third of all objects analysed, but there is no indication yet that metal or ores from Mushiston were traded or used at a distance of more than 500 km. Moreover, the artefact data indicates a decline in the exploitation of the mine in the course of the developed LBA, while other copper and tin sources in the Tian Shan and probably the Hindukush were exploited. This testifies to the intensive use of the rich mineral resources of Central Asia and beyond, as well as the intensification of cultural and trade contacts between Andronovo and the BMAC.