Pb Mineral Research Articles

Stability of lead immobilization by Aspergillus niger and fluorapatite under different pH conditions.

The combination of Aspergillus niger (A. niger) and fluorapatite (FAp) has been applied in lead (Pb) immobilization. However, the different pH can affect the stability of the immobilized Pb minerals. This experiment explored the stability of Pb immobilization by A. niger and FAp under different pH conditions. A. niger can grow normally in a pH range from 2.5 to 6.5 conditions. Meanwhile, more than 99 % of Pb cations were removed by A. niger and FAp under a pH range from 3.5 to 6.5. More importantly, only less than 1.23 % Pb was released again under pH 3.5-5.5. The strong acidic conditions (pH 1.5) inhibited the growth of A. niger and caused a lower Pb removal ratio of 37.86 %. In addition, the formed minerals of lead oxalate and lead/calcium oxalate coprecipitate dominate the Pb remediation by A. niger and FAp. The pH > 5.5 condition could decrease the stability of Pb immobilization via the low calcium/lead ratios. The combination of A. niger and FAp shows great potential in Pb remediation at a pH range from 3.5 to 5.5, suitable for fungal growth and Pb minerals stability. This research provides new insight into Pb remediation by phosphate-solubilizing fungi and FAp in various acidic environments.

U–Pb geochronology of carbonate-hosted Pb–Zn ores reveals plate-tectonic evolution of eastern Asia during the early Paleozoic

The Mississippi Valley–type (MVT) deposits reached their maximum abundance during the final assembly of Pangea. The intense orogenic activity during this assembly in relatively low latitudes created abundant opportunities for the migration of sedimentary brines into the interior carbonate platforms landward of the orogenic belts, leading to the formation of MVT deposits. Thus, dating the MVT deposits can potentially aid in the reconstruction of the plate tectonic evolution during the assembly of Pangea. The Yangtze Craton hosts significant carbonate-hosted Zn–Pb deposits (> 60 Mt Pb + Zn metals), accounting for 30% of China’s Zn–Pb resources. However, determining the timing of zinc and lead mineralization in these reservoirs is challenging. This study employs LA-ICP-MS U–Pb geochronology on calcites to date Zn–Pb deposits hosted in Lower Cambrian limestone in the Huayuan orefield. Three generations of calcite formation were dated: the first recorded the pre-ore deposition of Lower Cambrian limestone at 517 ± 10 Ma, the second marked a hydrothermal event linked to stratiform sphalerite ore formation at 501.4 ± 8.4 Ma, and the third was associated with discordant breccia-hosted Zn–Pb mineralization at 397.5 ± 9.6 Ma. Our results indicate that Paleozoic carbonate-hosted Pb–Zn mineralization in the Yangtze Craton is linked to (1) the final assembly of Gondwana in the late Cambrian-early Ordovician (520–480 Ma); and (2) the intracontinental orogeny response to Jiangnan Uplift (420–400 Ma). This study highlights the temporal relationship between low temperature carbonate-hosted mineralization and orogenic events that are consistent with classic MVT models worldwide. It also contributes geochronological data for the reconstruction of plate-tectonic evolution during Pangea assembly. Furthermore, it demonstrates the potential of in situ U–Pb calcite geochronology to date ore deposits lacking syn-ore minerals suitable for traditional dating methods.

Origin of hydrothermal dolomitization in the Huize Zn–Pb ore district, SW China: Insights from in situ U–Pb dating, fluid inclusion, and C–O–Sr–Mg isotope analyses

The temporal and genetic association between Mississippi Valley-type (MVT) Zn–Pb mineralization and hydrothermal dolomitization remains controversial. To determine the origin of hydrothermal dolomite and its genetic links with the MVT ore deposit, detailed petrographic observations and geochemical analyses were conducted on various carbonates from the giant Huize MVT Zn–Pb ore district in SW China. The following paragenetic sequence of the carbonates (from the early to late stages) was established: host limestone (ML), early diagenetic micritic dolostone (D1), late diagenetic or pre-ore fine- to medium-grained ferroan dolostone (D2) and medium- to coarse-crystalline non-ferroan dolostone (D3), pre-ore reworked D3 dolomite (D3o), ore-related void-filling dolomite cement (DC), and calcite cement (CC) related to sulfide mineralization. D2, D3, DC, and CC exhibit higher homogenization temperatures for fluid inclusion than the burial temperature, indicating a hydrothermal origin. Geochemical data indicate that D2, D3, D3o, DC, and CC display oxygen isotope depletion and radiogenic Sr isotope enrichment signatures relative to D1. Their parent fluids have more positive δ18O values and similar or lower δ26Mg values relative to those of D1 and seawater. These geochemical proxies indicate that the pre-ore hydrothermal dolomites (D2 and D3) formed from modified seawater circulated in the underlying sandstone aquifers through fault-related thermal convection. DC and CC, related to Zn–Pb mineralization, were formed by the dissolution and reprecipitation of preexisting carbonates. Sphalerite shows higher temperatures and salinities compared with D2 and D3 dolostones, indicating that the ore-forming fluid, different from the hydrothermal dolomitizing fluid, originated from a deep-sourced brine. In situ U–Pb dating of D3o reveals that the pre-ore hydrothermal dolomitization occurred at 253.7 ± 8.7 Ma, and a late-stage hydrothermal imprint occurred at 203 ± 11 Ma, likely related to tectono-thermal events, including the Emeishan large igneous province and Indosinian Orogeny, respectively. These findings imply that the hydrothermal dolomitization and Zn–Pb mineralization in the Huize ore district are likely associated with the multistage basin and basement fluid flows driven by elevated geothermal gradient and tectonic compression, respectively. The void-filling DC and CC and their cathodoluminescence characteristics are useful indicators for MVT Zn–Pb ore exploration.

Effectiveness of LOF, iForest and OCSVM in detecting anomalies in stream sediment geochemical data

This paper compares three unsupervised machine-learning algorithms – local outlier factor (LOF), Isolation Forest (iForest) and one-class support vector machine (OCSVM) – for anomaly detection in a multivariate geochemical dataset in northeastern Iran. This area contains several Au, Cu and Pb–Zn mineral occurrences. The methodology incorporates single-element geochemistry, multivariate data analysis and application of the three unsupervised machine-learning algorithms. Principal component analysis unveiled diverse elemental associations for the first seven principal components (PCs): PC1 shows a Co–Cr–Ni–V–Sn association indicating a lithological influence; PC2 shows a Au–Bi–Cu–W association suggesting epithermal Au mineralization; PC3 shows variability in Zn–V–Co–Sb–Cu–Cr; PC4 shows a Au–Cu–Ba–Sr–Ag association indicating Au and polymetallic mineralization; PC5 reflects Zn–Ag–Ni–Pb related to hydrothermal mineralization; and PC6 and PC7 show element associations suggesting epithermal and intrusive-related polymetallic mineralization. It was found that OCSVM performed slightly better than LOF and iForest in detecting anomalies associated with known Cu occurrences, and it successfully delineated dispersion from all known Au occurrences. LOF outperformed iForest and OCSVM in identifying all four Pb–Zn occurrences, and the three methods substantially limited the areas of the anomaly class. The analysis showed that LOF produced a less cluttered anomaly map compared to the isolated patterns in the iForest map. LOF was accurate in identifying anomalies associated with Au–Pb mineralization, while iForest detected anomalies associated with Pb–Zn–Cu occurrences and neighbouring Pb–Zn occurrence. OCSVM performed similarly in the northern and western areas but displayed unique discrepancies in the SE and west by detecting anomalies associated with two Cu occurences and a Pb–Cu occurrence. This study examined the influence of contamination fraction on detection of geochemical anomalies, revealing a noteworthy rise in the count of mineral occurrences delineated by anomalies when the contamination fraction increases from 5 to 10%. However, even with a 35% contamination fraction, some Cu occurrences remained outside the anomaly category, indicating potentially overlooked geochemical signals from mineral occurrences due to sampling schemes.

Reactive transport numerical modeling of intermediate sulfidation epithermal deposit: A case study of Haopinggou Ag-Au-Pb-Zn deposit, Henan province, China

The Haopinggou Ag-Au-Pb-Zn deposit is the only deposit that simultaneously contains Au and Ag-Pb-Zn vein-type ores at the Xianyu ore field in Xiong'ershan District, Henan Province, China. The early-stage gold-bearing pyrite-quartz veins are cut or surrounded by late-stage silver-bearing Pb-Zn-sulfide veins. However, there is controversy whether these two-stage veins were formed from distinct fluid systems associated with discrete mineralization events or via hydrothermal evolution processes of individual mineralization events. To study the metallogenic dynamics of how the Au and Ag-Zn-Pb veins were formed at the same depth in the Haopinggou deposit under these two distinct metallogenic models, we established a series of reactive transport numerical models. We studied the influence of the temperature of the hydrothermal fluid, fault permeability, and HS−, Au+, and Ag+ concentrations on the mineralization of Au, Ag, Pb, and Zn. Based on the model results, two distinct mechanisms causing Au and Ag to precipitate at the same depth has been established: (1) Under the assumption of the single hydrothermal fluid metallogenic model, the deep part of the early Au precipitation will be overlapped by the shallow part of the late Ag precipitation due to temperature and permeability decreases, causing Au and Ag to precipitate at the same deep depth; (2) Under the assumption of the distinct hydrothermal fluids metallogenic model, the shallow part of the early Au precipitation will be overlapped by the late Ag precipitation due to high concentration of HS−, causing Au and Ag to precipitate at the same shallow depth. The metallogenic mechanisms behind these two controversial understandings indicate that the deeper parts of the Haopinggou deposit have a high metallogenic potential for gold or silver.

Redox conditions and biochar pyrolysis temperature affecting As and Pb biogeochemical cycles and bacterial community of sediment from mining tailings

Despite the widespread use of biochar for soil and sediment remediation, little is known about the impact of pyrolysis temperature on the biogeochemistry of arsenic (As) and lead (Pb) and microorganisms in sediment under reducing conditions. In this study, we investigated the effects of pyrolysis temperature and the addition of glucose on the release and transformation of As and Pb, as well as their potential effects on the bacterial community in contaminated sediments. The addition of biochar altered the geochemical cycle of As, as it favors specific bacterial groups capable of changing species from As(V) to As(III) through fermentation, sulfate respiration and nitrate reduction. The carbon quality and content of N and S in solution shaped the pH and redox potential in a way that changed the microbial community, favoring Firmicutes and reducing Proteobacteria. This change played a fundamental role in the reductive dissolution of As and Pb minerals. The addition of biochar was the only efficient way to remove Pb, possibly as a function of its sorption and precipitation mechanisms. Such insights could contribute to the production or choice of high-efficiency biochar for the remediation of sediments subjected to redox conditions.

Organic Amendments to Short Rotation Coppice (SRC) Plantation Affect Species Richness and Metal Accumulation of Spontaneously Growing Herbaceous Plants

Excess potentially toxic metals (PTMs) in soils require ad hoc approaches to salvage. Hence, this study explored the shoot accumulation of cadmium (Cd), lead (Pb), and zinc (Zn) by herbaceous plants growing under previously established Salix and Populus clones Short Rotation Coppice (SRC) with compost and sewage sludge applications in an abandoned metallurgical site, Podlesí, Czech Republic; PTM decontamination of soils. Soils within the SRC experimental site and outside considered as control were analyzed for their chemical properties by multi-analytical techniques. Shoots of spontaneously growing herbaceous plants under trees in the site and without trees in control were determined for pseudo-total Cd, Pb, and Zn contents. Moderately to slightly acid soils, high cation exchange capacity, and C/N ratio supported mineralization and relative mobility of total Cd (7.7–9.76), Pb (1541–1929), and Zn (245–320 mg kg−1) in soils. Although soil amendments improved chemical properties, compost application supported higher species richness than sewage sludge. Over 95% of plants accumulated Cd and Zn above the WHO threshold and green fodder in the Czech Republic, with 36% Pb above the regional limit (40 mg kg−1). Approximately 100, 50, and 6% of herbaceous species had Cd, Pb, and Zn accumulation, respectively, higher than published average upper limits in plants (0.2 Cd, 10 Pb, and 150 Zn mg kg−1). Dicots recorded higher Cd content, Tenacetum vulgare (L.), Hypericum maculatum (Crantz), and Cirsium arvense (L.); Stachys palustris (L.), Lamium perpereum (L.), and Campanula patula (L.) for Pb; Glechoma hederaceae (L.), C. patula, and C. arvense for Zn in all treatments. Appropriate soil amelioration of SRC-supported PTM mobility and excess herbaceous species shoot accumulation, growth, and richness.

Metal sources and fluid pathways of karst-hosted Mississippi Valley-type Zn–Pb deposits in the fold-thrust belt: A case study of the Changdong deposit in the southeastern Himalayan-Tibetan orogen

The metal sources and fluid pathways for Mississippi Valley-type (MVT) Zn–Pb deposits in fold-thrust belts remain open topics of debate. To develop a more comprehensive understanding of these issues, this study presents the sulfide morphology, S and Pb isotopes, and trace element data of the paleokarst-hosted Changdong MVT Zn–Pb deposit in the “Sanjiang” fold-thrust belt. Bulk Pb isotopic ratios for galena were homogenous and indicated potential metal sources. These sources include Triassic to Early Jurassic volcanic rocks at the western margin of the Simao Basin, Cenozoic intrusive rocks at the eastern margin, and Jurassic clastic rocks. The spatial distribution of the in situ Pb isotopic ratios, combined with the spatial relationship between the faults and ore bodies, suggest that the tensile faults acted as vertical pathways for the fluid. The galena grains displayed oscillatory zones of As and Sb elements, indicating that alternating ore-forming fluids with varying chemical compositions entered the local reservoir. The δ34SV-CDT values of sulfides in substage I range from −19.3 to 29.6 ‰, and in substage II, they range from −21.2 to 52.6 ‰. The high fractionation degree (approximately 38.9 ‰) and the presence of microspherulitic morphology suggest that the reduced sulfur originated from a bacterial sulfate reduction. A GGIMFis geothermometer revealed that the precipitation temperatures of substage I sphalerite ranged from 56.68 to 211.58 °C and were higher than substage II. This indicated that the mixing of Zn–Pb-bearing fluid with reduced sulfur was the main controlling factor for sphalerite precipitation, and the temperature decrease represented another important factor. In the fold-thrust system, the complete process of Zn–Pb mineralization was established as follows: the fluid extracted metals from regional rocks and then migrated laterally over long distances. During the regional transition from compression to extension, metal-bearing fluid was injected into the deposit along the normal faults through seismic pumping. The fluid was then mixed with reduced sulfur to precipitate Zn–Pb sulfides. This study provides new insights into the metal sources and fluid pathways of MVT Zn–Pb deposits developed in a fold-thrust belt.

Environmental and health implications of Pb-bearing particles in settled urban dust from an arid city affected by Pb–Zn factory emissions

Metal-rich particles originating from non-ferrous metallurgical activities are the primary source of atmospheric metals in urban environments. These particles vary in size, morphology, and elemental compositions and they undergo weathering processes that alter their composition and affect their toxicity. This study focuses on lead (Pb)-rich particles in settled urban dust within an arid and dusty city, Torreón in North Mexico, affected by Met–Mex Peñoles complex, one of the world's largest Ag–Cd–Pb–Zn smelting and refining facilities in operating since 1901. Torreón is characterized by arid conditions, temperature fluctuations, and low humidity. Dry atmospheric particles were collected in 2015 and 2017 from Torreón's urban area within a 3 km radius of the Met–Mex Peñoles complex. We used various analytical techniques, including scanning electron microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray powder diffraction (XRD) to determine the size, morphology, elemental composition and mineralogy of Pb-bearing particles. Our analysis revealed a range of Pb-bearing particle sizes and morphologies with varying Pb (0.3 to 51–87.2%) and other element contents, such as As (0.04 to 1–3.4%), Cd (0.4 to 3.3–5.1%), Cu (0.51–14.1%), Hg (ND-0.6%), and Zn (1.7 to 79–90.3%). XRD analysis confirmed the presence of Pb and Zn sulfides, Pb carbonates, Pb sulfate, and Pb oxides in urban dust, both as individual particles and agglomerates. Primary Pb minerals were linked to fugitive feed concentrates and smelter flue gas at Met–Mex Peñoles, while secondary Pb minerals, like Pb carbonates, Pb sulfate, and Pb oxides, resulted from direct emissions and weathering processes. Compared to galena, secondary Pb minerals exhibit higher chemical availability in the environment, posing greater risks to the environment and human health. As the particles analyzed are presumed to be resuspended rather than freshly emitted by Met–Mex, the presence of secondary Pb minerals in settled urban dust is predominantly linked to weathering processes. The physical and chemical transformations in Pb-rich particles contribute to increased Pb bioavailability and toxicity in urban dust, with substantial implications for environmental and human health. These findings highlight the potential consequences of weathered Pb-rich particle in urban areas, particularly in the arid and dusty city of Torreón.

Metabolomics reveals the phytotoxicity mechanisms of foliar spinach exposed to bulk and nano sizes of PbCO3

PbCO3 is an ancient raw material for Pb minerals and continues to pose potential risks to the environment and human health through mining and industrial processes. However, the specific effects of unintentional PbCO3 discharge on edible plants remain poorly understood. This study unravels how foliar application of PbCO3 induces phytotoxicity by potentially influencing leaf morphology, photosynthetic pigments, oxidative stress, and metabolic pathways related to energy regulation, cell damage, and antioxidant defense in Spinacia oleracea L. Additionally, it quantifies the resultant human health risks. Plants were foliarly exposed to PbCO3 nanoparticles (NPs) and bulk products (BPs), as well as Pb2+ at 0, 5, 10, 25, 50, and 100 mg·L-1 concentrations once a day for three weeks. The presence and localization of PbCO3 NPs inside the plant cells were confirmed by TEM-EDS analysis. The maximum accumulation of total Pb was recorded in the root (2947.77 mg·kg-1 DW for ion exposure), followed by the shoot (942.50 mg·kg-1 DW for NPs exposure). The results revealed that PbCO3 and Pb2+ exposure had size- and dose-dependent inhibitory effects on spinach length, biomass, and photosynthesis attributes, inducing impacts on the antioxidase activity of CAT, membrane permeability, and nutrient elements absorption and translocation. Pb2+ exhibited pronounced toxicity in morphology and chlorophyll; PbCO3 BP exposure accumulated the most lipid peroxidation products of MDA and H2O2; and PbCO3 NPs triggered the largest cell membrane damage. Furthermore, PbCO3 NPs at 10 and 100 mg·L-1 induced dose-dependent metabolic reprogramming in spinach leaves, disturbing the metabolic mechanisms related to amino acids, antioxidant defense, oxidative phosphorylation, fatty acid cycle, and the respiratory chain. The spinach showed a non-carcinogenic health risk hierarchy: Pb2+ > PbCO3 NPs > PbCO3 BPs, with children more vulnerable than adults. These findings enhance our understanding of PbCO3 particle effects on food security, emphasizing the need for further research to minimize their impact on human dietary health.

Separation and preparation of level I standard lead concentrate from lead ore via S-HGMS technology: description of separation mechanism

ABSTRACT To eliminate the adverse effects of traditional lead ore flotation methods, such as high reagent cost, complex operation process, and a large amount of wastewater, a superconducting high gradient magnetic separation (S-HGMS) technology was proposed to prepare level I standard lead concentrate (IGC) from lead ore. Under optimal conditions including a magnetic flow ratio of 0.076 T·s/m, a pulp concentration of 1.5%, a slurry flow velocity of 500 mL/min, and a 90% mass fraction of minus 45 μm, the Pb grade of the IGC product increased from 45.36% to 68.79% with 55.43% of Pb recovery, while all Cu, Zn, As, Fe, MgO, and Al2O3 concentrations of IGC decreased. The obtained IGC product meets the standard of level I in YS/T319–2013. The characterization results showed that lead ore comprised galena, sphalerite, and chalcopyrite. After S-HGMS, galena was effectively concentrated in the IGC product, while sphalerite and chalcopyrite were separated into the tailings. The magnetic field intensity and mineral magnetization characteristics were vital factors affecting the Pb grade and recovery of the IGC product. The S-HGMS technology efficiently achieved the preparation of the IGC product from lead ore, without using flotation agents and generating wastewater, and provides a valuable guideline for separating Cu – Pb, Zn – Pb, and Cu – Zn – Pb minerals.

Phosphogypsum/titanium gypsum coupling for enhanced biochar immobilization of lead: Mineralization reaction behavior and electron transfer effect

The hazards caused by Pb pollution have received worldwide attention. Phosphogypsum (PG) and titanium gypsum (TG) have the disadvantage of limited adsorption capacity and poor dispersion when used as heavy metal adsorbents on their own. The excellent pore and electron transfer capacity of biochar makes it possible to combine with PG and TG to solidify/stabilize Pb2+. In this study, the mechanism of Pb2+ adsorption/immobilization by rice husk biochar (BC) combined with PG/TG was investigated in terms of both mineral formation and electron transfer rate. The removal rate of Pb2+ by BC composite PG (BC/PG-Pb) or TG (BC/TG-Pb) was as high as 97%–98%, an increase of 120.9% and 122.5% over BC. Adsorption kinetics and mineral precipitation results indicate that the main removal of Pb2+ from BC/PG-Pb and BC/TG-Pb is achieved by PG/TG induced Pb-sulfate and Pb-phosphate formation. The addition of PG/TG significantly enhances the formation of stable Pb-minerals on the biochar surface, with the proportion of non-bioaccessible forms exceeding 50%. The four-step extraction results confirm that P and F in PG/TG are key in facilitating the conversion of Pb minerals to pyromorphite. The rich pore structure of biochar not only disperses the easily agglomerated PG/TG onto the biochar surface, but also attracts Pb2+ for uniformly dispersed precipitation. Furthermore, the excellent electrical conductivity and smooth electron transfer channels of biochar facilitate the reaction rate of Pb2+ mineralization. Overall, the use of biochar in combination with PG/TG is a promising technology for the combination of solid waste resourceisation and Pb remediation.

Xenotime reveals Caledonian hydrothermal overprint on Neoproterozoic Cu mineralization, East Greenland

Constraining the age of many types of ore deposits remains challenging because of the lack of radiogenic isotopes incorporated into common ore-forming minerals. The timing of pre-Caledonian-hosted Cu mineralization along the entire c. 1200 km long East Greenland Caledonides remains virtually unknown, hampering our knowledge of ore deposit timing and genesis in a frontier exploration region. Here, automated mineral analysis of a series of nodular, disseminated and vein-hosted Cu- ± Pb-mineralized metasedimentary rocks in central East Greenland reveals detrital zircon and hydrothermal xenotime, both amenable to U–Pb geochronology. Detrital zircon geochronology of a co-deposited quartzite reveals an age distribution highly similar to the Cryogenian ( c. 700 Ma) upper Eleanore Bay Supergroup. Hydrothermal xenotime U–Pb analyses adjacent to nodular and disseminated chalcocite across three proximal samples have variable amounts of common Pb that together yield a well-defined single discordia with a lower concordia intercept of 438 ± 13 Ma (2 σ ). This age is within uncertainty of the onset of Caledonian regional metamorphism and granitoid production and clearly post-dates deposition of the upper Eleanore Bay Supergroup by several hundred million years. Considering a published chalcocite Pb–Pb isochron age of 680 ± 65 Ma, the hydrothermal xenotime U–Pb ages imply that Caledonian-driven fluid activity, sourced from metamorphic reactions or from granitoids, remobilized diagenetic Cu and Pb mineralization. Chalcocite Pb–Pb isotopes show that dissolved and reprecipitated portions are volumetrically minor, radiogenic and Pb-poor, implying that fluids stripped most of the Pb from the system. Thus, it is likely that remobilization was localized on the grain scale, although some Cu and Pb was transported away from diagenetic sites, perhaps into veins. Although Caledonian metamorphism and granitoid emplacement is widespread in central East Greenland, the full extent of their roles in upgrading Cu mineralization remains to be ascertained. Supplementary material: Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6675384 Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle

Time-of-flight neutron diffraction applied to the identification of crystalline phases in historical mosaic glasses

We present a completely non-destructive study of the crystalline phases present in the vitreous matrix of ancient mosaic glass tesserae, based on the application of the time-of-flight neutron diffraction (ToF-ND) technique. In contrast, standard phase analysis techniques may involve a sample preparation step, which is not compatible with the requirement of damage prevention of archaeological artefacts. Moreover, superficial or spot investigation by standard methods may not provide a complete description of the samples, especially in the case of inhomogeneous materials such as mosaic glasses, whereas ToF-ND can investigate the whole glass composition at the centimetre scale. The present study aims to obtain a bulk characterization of the glasses in terms of their mineralogical phase composition. Six glass specimens of ancient mosaic glass tesserae, that had been previously analysed with other non-destructive techniques to obtain their chemical and phase composition, were investigated by ToF-ND. These tesserae come from archaeological excavations or mosaics under restoration from different archaeological sites and geographical areas (Italy, Greece, and Syria) and date from the 1st to the 11th century AD. Several crystalline phases based on Ca, Sb, Sn, Cu and Pb minerals were identified, confirming the mineralogical phases identified with Raman spectroscopy in previous analyses. In addition, several other phases were identified for five of the samples. It is concluded that ToF-ND is an extremely important complementary tool for non-destructive bulk investigations of mosaic glass tesserae, which can overcome the heterogeneity of this kind of archaeological material.

Green and cost-efficient functionalized clay adsorbent enables one-step ultraefficient removal of Pb(II) at very low and high concentrations

It is always a huge challenge to purify wastewater containing very low or high concentrations of heavy metal ions to drinking water level (World Health Organization (WHO) guidelines) by one-step static or dynamic adsorption with a highly efficient, cost-effective, and environmentally friendly adsorbent. In response to this challenge, a green, low cost and powerful porous silicate/Fe3O4 adsorbent (named MCSiMg49) with ultra-strong purification ability towards the Pb(II) in both low- and high-concentration wastewater was developed using natural abundant, safe, and nontoxic palygorskite-rich clay as the starting material and water as the only solvent. The adsorbent possesses a high specific surface area of 332.41 m2/g (2.81 times that of raw clay), and was proven to be the best one to date that can purify deeply Pb(II) in water. The adsorption capacity of the adsorbent towards Pb(II) reached 499.3 mg/g, and 99.8% of Pb(II) can be removed from 800 mg/L Pb(II) solution after adsorption with 3 g/L of the adsorbent, which is significantly superior to other adsorbents and commercial activated carbon (AC). The adsorption column packed with MCSiMg49 (1 g, upper layer) and clay (1 g, lower layer) can remove completely Pb(II) from natural water (e.g., Yangtze River water or Yellow River water) (concentration: 50 mg/L), and 3000 mL clean drinking water (WHO guidelines) was obtained by a one-step filtration process. The MCSiMg49 adsorbent is easy to use in both dynamic and static adsorption, because it can be quickly recycled from the solution by external magnetic field after use. The adsorption of Pb(II) on the adsorbent was mainly driven by the cooperation of electrostatic attraction, ion exchange, chemical complexation and in situ mineralization of Pb(II).

Super-stable mineralization of Cu, Cd, Zn and Pb by CaAl-layered double hydroxide: Performance, mechanism, and large-scale application in agriculture soil remediation

The synthesized CaAl-layered double hydroxide (CaAl-LDH) shows excellent performance in potentially toxic metals (PTMs) removal, and the removal capacity of CaAl-LDH toward Cu2+, Zn2+ and Pb2+ in aqueous solution is 502.4, 315.2 and 600.0 mg/g respectively. Cu2+ and Zn2+ are removed through isomorphic substitution of laminate Ca and dissolution-reprecipitation, leading to the formation of CuAl-LDH and ZnAl-LDH mineralization products. Pb2+ is removed by the complexation and precipitation to form Pb3(CO3)2(OH)2. The application of CaAl-LDH in laboratory-scale soil remediation shows that target PTMs are gradually mineralized into relatively stable oxidizable and residual state, and the immobilization efficiency of available Cu, Zn, Cd and Pb reaches 84.62 %, 98.66 %, 96.81 % and 70.27 % respectively. In addition, practical application in farmland results in the significant reduction of available Cu, Zn, Cd and Pb with the immobilization efficiency of 30.15 %, 67.30 % and 57.80 % and 38.71 % respectively. Owing to the super-stable mineralization effect of CaAl-LDH, the content of PTMs in the roots, stems and grains of cultivated buckwheat also decreases obviously, and the growth and yield of buckwheat are not adversely affected but improved. The above prove that the super-stable mineralization based on CaAl-LDH is a promising scheme for the remediation of PTMs contaminated agriculture soil.

Formation of the Chalukou High Fluorine-Type Mo (–Zn–Pb) Deposit, NE China: Constraints from Fluorite and Sphalerite Rare Earth Elements and Sr–Nd Isotope Compositions

Fluorite is a widespread mineral in porphyry and hydrothermal vein Mo-polymetallic deposits. Here, fluorite is utilised as a probe to trace the fluid source and reveal the fluid evolution process in the Chalukou giant Mo (Pb–Zn) deposit, Northeast China, which is characterised as early porphyry Mo and later vein-style Zn–Pb mineralisation. A detailed rare earth element (REE) and Sr–Nd isotope study of fluorite combined with Sr isotopes of sphalerite is conducted for the Chalukou deposit. The chondrite-normalised REE patterns of fluorites from molybdenite veins show light REE (LREE)-enriched patterns, with negative Eu anomalies (δEu = 0.60) and weakly negative Y anomalies (Y/Y* = 0.72). The fluorites associated with sphalerite veins exhibit rare earth element (REE)-flat patterns with negative Eu anomalies (δEu = 0.65 to 0.99) and positive Y anomalies (Y/Y* = 1.37 to 3.08). In addition, during the progression from Mo to Zn–Pb mineralisation, the total concentration of REEs decreases from 839 ppm to 53.7 ppm, and Y/Ho ratios increase from 22.1 to 92.5. These features may be explained by the different mobilities of REE complexes during fluid migration. The Eu anomalies are considered to be inherited from source fluids. All the initial 87Sr/86Sr ratios of fluorite and sphalerite are between those of ore-forming porphyries and wall rocks (rhyolite), with fluorite ratios ranging from 0.706942 to 0.707386 and sphalerite ratios varying from 0.705221 to 0.710417. The majority of εNd(t) values of fluorite varying from −6.4 to −3.6 are also located between the ratios exhibited by ore-forming porphyries and rhyolite, whereas three εNd(t) values of fluorites ranging from −0.26 to 0.36 are close to those of ore-forming porphyries. All the isotopic features indicate that the Sr-Nd isotope ratios of hydrothermal fluid are derived from porphyries and disturbed by fluid–rock reactions. Together with a two-stage Sr–Nd isotope mixing model, we suggest that different sources and fluid–rock interactions (syn-ore intrusions and strata) finally influence the Sr–Nd isotopes of the ore-forming fluids, which are recorded by the majority of fluorite and sphalerite.

A novel chemical model for burial diagenesis and Zn–Pb sulphide precipitation within the Carboniferous Waulsortian Limestone, Ireland

Basin-scale processes such as regional fluid flow and organic maturation are commonly associated with the precipitation of Pb–Zn sulphide minerals. Despite extensive study, the origin of carbonate-hosted Pb–Zn mineralisation (Mississippi Valley-type and Irish-type) remains controversial, with deposits viewed as exceptional features derived from unusual basin conditions (e.g. regional hydrothermal fluid flux). In order to explore the links between mineralisation and broader-scale basinal processes, we have examined the relationship of base metal sulphides to regional diagenetic phases in the Waulsortian Limestone (Feltrim Formation) of the world-class Irish Midlands Zn–Pb province. Using combined sedimentology, petrography, and trace/rare earth element chemistry of regional calcite cements, we have reconstructed the basinal fluid history before, during and after sulphide mineralisation. The non-bright‐dull cathodoluminescence and trace metal composition of calcite cements indicates that the Waulsortian Limestone was subjected to three major chemical environments during progressive burial diagenesis: 1. Near-surface/shallow-burial oxic conditions; 2. subsurface euxinic conditions; and 3. subsurface ferruginous (ferrosulphidic) conditions. Zn–Pb mineralisation occurred under stage 2 euxinic conditions. We suggest that euxinic conditions were initiated when hydrocarbons entered the Waulsortian succession regionally, associated with the introduction of sour gas (H2S) accumulations. Mixing between more oxic base metal-bearing and H2S-bearing fluids produced ideal conditions for voluminous Zn–Pb sulphide precipitation. Increasing fluid anoxia then led to iron oxide dissolution with consequently increased iron sulphide precipitation, causing eventual depletion of H2S, and marked the onset of ferruginous conditions that terminated metal sulphide precipitation. Base metals were potentially derived from a range of sources that include Carboniferous seawater (and the dissolution of associated Mn/Fe oxyhydroxides), hydrocarbons, and basement-interacted basinal brines. The chemical model proposed by this study is compatible with existing data on the Irish Zn–Pb Orefield and indicates that sulphide mineralisation is linked to normal basin-scale processes such as subsidence, aquifer redox evolution and hydrocarbon generation. These results may explain many other global occurrences of carbonate-hosted Zn–Pb mineralisation and provide new insights into the chemical and redox processes that occur during burial diagenesis.

The occurrence of cobalt and implications for genesis of the Pusangguo cobalt-rich skarn deposit in Gangdese, Tibet

The Pusangguo cobalt-rich skarn deposit occurs in Gangdese, Tibet. In recent years, research on this deposit has detailed the geochronology, petrogenesis, fluid inclusions and skarn mineralogy, but there has been a lack of focus on the occurrence of cobalt. We present X-ray fluorescence, scanning electron microscopy and electron probe microanalyses that address this omission and help elucidate the genesis of cobalt-rich skarn deposits. Correlations between Co and other ore-forming elements (Cu, Pb, Zn and Ag) reveal that Co mineralization was synchronous with other metals. Photomicrographs and backscattered electron and X-ray maps of thin sections, confirm that cobalt mineralization is usually associated with chalcopyrite, sphalerite and other sulfides, which developed at the retrograde skarn stage with quartz, carbonate minerals, tremolite and other skarn-related minor phases. Three independent cobalt minerals are identified (cobaltite, carrollite, and linnaeite). The EPMA results further reveal two different occurrences of cobalt (independent cobalt minerals and isomorphous substitution Co in sulfides) in the Pusangguo deposit. Compared with chalcopyrite (mean Co content = 0.06 ± 0.06 wt.%, 1σ, n = 142) and galena (mean Co content = 0.02 ± 0.04 wt.%, 1σ, n = 82), both pyrite and sphalerite typically contain obviously higher Co contents (mean = 0.16 ± 0.17 wt.%, 1σ, n = 97 and 0.20 ± 0.10 wt.%, 1σ, n = 108, respectively). The correlations between Co and other elements indicate that Co + Ni replace Fe in pyrite via isomorphous substitution while Co + Fe replace Zn in sphalerite. These results further indicate that Co and Zn mineralization occurred at the same time. Combined with previously published Sr-Nd isotopic data on skarn minerals, the mineralization of Cu, Pb, Zn, Ag and Co were likely derived from, or share a common source with the intrusions at Pusangguo.

3D reflection seismic imaging of the Zinkgruvan mineral‐bearing structures in the south‐eastern Bergslagen mineral district (Sweden)

AbstractMineral exploration is facing greater challenges nowadays because of the increasing demand for raw materials and the lesser chance of finding large deposits at shallow depths. To be efficient and address new exploration challenges, high‐resolution and sensitive methods that are cost‐effective and environmentally friendly are required. In this work, we present the results of a sparse 3D seismic survey that was conducted in the Zinkgruvan mining area, in the Bergslagen mineral district of central Sweden. The survey covers an area of 10.5 km2 for deep targeting of massive sulphides in a polyphasic tectonic setting. A total of 1311 receivers and 950 shot points in a fixed 3D geometry setup were employed for the survey. Nine 2D profiles and a smaller 3D mesh were used. Shots were generated at every 10 m, and receivers were placed at every 10–20 m, along the 2D profiles, and 40–80 m in the mesh area. An analysis of the seismic fold coverage at depth was used to determine the potential resolving power of this sparse 3D setup. The data processing had to account for cultural noise from the operating mine and strong source‐generated surface waves, which were attenuated during both pre‐ and post‐stack processing steps. The processing workflow employed a combination of 2D and 3D refraction static corrections, and post‐stack FK filters along inlines and crosslines. The resulting 3D seismic volume is correlated with downhole data (density and P‐wave, acoustic impedance, reflection coefficient), synthetic seismograms, surface geology and a 3D model of mineral‐bearing horizons in order to suggest new exploration targets at depth. The overall geological architecture at Zinkgruvan is interpreted as two EW overturn folds, an antiform and a synform, affected by later NS‐trending folding. Two strong sets of shallow reflections, associated with the Zn–Pb mineralization, are located at the hinge of an EW‐trending antiform, while a strong set of reflections, associated with the main mineralization, is located at the overturned apex of the EW synform. The NS Knalla fault that crosses the study area terminates the continuation of the mineral‐bearing deposits at depth towards the west, a conclusion solely based on the reflectivity character of the seismic volume. This study illustrates that sparse 3D data acquisition, while it has its own challenges, can be a suitable replacement for 2D profiles while line cutting, and environmental footprints can totally be avoided.