Pb-Zn Mineralization Research Articles

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.

Deep exploration of W-Sn and Cu polymetallic deposits in middle Qin-Hang metallogenic belt, South China

Field and microscopic structural investigations, trace element and C–O isotopic analyses of calcite, zircon U−Pb dating of dikes, and wide-field electromagnetic sounding are conjointly conducted in the middle part of the Qin−Hang metallogenic belt to decipher the spatial−temporal evolution and genetic relationship of structure−magma- mineralization. The data reveal four deformation events: D1 is a W-to-E-thrusting event; D2 is characterized by SE-to-NW thrusting; D3 is a NW−SE-oriented extensional event accompanied by large-scale magma intrusion and W–Sn and Cu–Pb–Zn mineralization; D4 is a dextral strike−slip event after mineralization. Two stages of calcite are identified during D3 and Stage II calcite is characterized by LREE-enriched REE patterns, with low δ18OSMOW (from 9.78‰ to 12.3‰), identical to those of calcite in the deposits, confirming that they are closely related to mineralization. Wide-field electromagnetic profiles further display the geometric characteristics of structures, granitic plutons, and orebodies from shallow to deep (~5 km) level. It is believed that some giant concealed W−Sn and Cu−Pb−Zn orebodies are developed in the contact zones between plutons and limestone at a depth of 1.5−4 km. It is reasonable to suggest that this method is feasible for the study on the deep exploration of W−Sn and Cu−Pb−Zn polymetallic deposits.

English

An integrated geoelectrical study combining electrical resistivity tomography (ERT) and induced polarization (IP) have been used to delineate potential zones of Lead-Zinc mineralization in Umuobuna, Uburu, Ohaozara local government area, southeastern Nigeria. The wenner array configuration was used to acquire resistivity and induced polarization data sets along three traverses of approximate length of 1 km each and spacing of 5 to 25 m, using ABEM Terrameter SAS 1000. The profiles were inverted using RES2DINV software for 2D imaging to delineate possible zones of Pb-Zn mineralization and the geological structures at selected locations in the study area. The ERT surveys were carried out along the IP lines for comparison of anomalies across the profiles. The potential zones of Pb-Zn mineralization display contrasting values of resistivity and chargeability along the traverses. Resistivity values ranging from 7.53 to 7525 ?m and corresponding chargeability values of between -15.6 and 354 ms, respectively were encountered at some intervals along the traverses. These zones occur at width range 19.5 to 74.5 m and depths of between 0.9 and 15.5 m. Having a low to moderate resistivity and a corresponding high chargeability values at similar width range may be suggestive of Pb-Zn mineralization and test drilling is needed at the anomalous sites for confirmation. Key words: Pb-Zn, ERT, IP, resistivity, chargeability, mineralization.

Ecological Risk Assessment and Source Analysis of Heavy Metals in the Soils of a Lead-Zinc Mining Watershed Area

In this study, concentrations of Cr, Mn, Pb, Cu, Zn, As, Cd, Sb, and Fe were determined in soils of a Pb-Zn mine watershed in northern Guangxi, China, for ecological risk assessment and source analysis. The atomic fluorescence spectrometry and ICP-OES were used to determine concentrations of heavy metals (HMs), and the total amount of Mn, Cu, Zn, As, Cd, and Pb exceeded the limit. Among them, the weak acid extractable fraction (F1) state masses of Pb, Mn, and Zn accounted for a higher ecological risk. The study area was divided into three distinct areas: highest concentrations of HMs were distributed in front of the Sidi River mountain (1# and 2#) and at the subterranean river entrance (5# and 6#), followed by the area along the river and the irrigated area of the river (3# and 4#), and the central highlands and southwestern parts had low concentrations (7# and 8#). The ecological risk assessment results indicate Cd is of extremely high ecological risk, Pb and Mn are of medium minor ecological risk, Zn is of minor ecological risk, and the rest have almost no impact on the eco-environment. The source apportionment results showed that Cu, Zn, Cd, Sb, and Pb were mainly controlled by anthropogenic activities, such as mining; Cr, Fe, and As were mainly influenced by natural processes, such as soil-forming parent rocks; and Mn is jointly controlled by mining and soil-forming parent rocks. This study can provide scientific guidance and technical support for soil risk control or remediation in mining areas.

The Origin of Carbonate Components in Carbonate Hosted Pb-Zn Deposit in the Sichuan-Yunnan-Guizhou Pb-Zn Metallogenic Province and Southwest China: Take Lekai Pb-Zn Deposit as an Example

The Lekai lead–zinc (Pb-Zn) deposit is located in the northwest of the Sichuan–Yunnan–Guizhou (SYG) Pb-Zn metallogenic province, southwest China. Even now, the source of the metallogenic fluid of Pb-Zn deposits in the SYG Pb-Zn metallogenic province has not been recognized. Based on traditional lithography, rare earth elements (REEs), and carbon–oxygen (C–O) isotopes, this work uses the magnesium (Mg) isotopes of hydrothermal carbonate to discuss the fluid source of the Lekai Pb-Zn deposit and discusses the fractionation mechaism of Mg isotopes during Pb-Zn mineralization. The REE distribution patterns of hydrothermal calcite/dolomite are similar to that of Devonian sedimentary carbonate rocks, which are all present steep right-dip type, indicating that sedimentary carbonate rocks may be serve as the main source units of ore-forming fluids. The C–O isotopic results of hydrothermal dolomite/calcite and the δ13CPDB–δ18 OSMOW diagram show that dolomite formation is closely related to the dissolution of marine carbonate rocks, and calcite may be affected to some extent by basement fluid. The Mg isotopic composition of dolomite/calcite ranges from −3.853‰ to −1.358‰, which is obviously lighter than that of chondrites, mantle, or seawater and close to that of sedimentary carbonate rock. It shows that the source of the Mg element in metallogenic fluid of Lekai Pb-Zn deposit may be sedimentary carbonate rock rather than mantle, chondrites, or seawater. In addition, the mineral phase controls the Mg isotope fractionation of dolomite/calcite in the Lekai Pb-Zn deposit. Based on the geological, mineralogical, and hydrothermal calcite/dolomite REE, C–O isotope, and Mg isotope values, this work holds that the mineralization of the Lekai Pb-Zn deposit is mainly caused by basin fluids, influenced by the basement fluids; the participation of basement fluids affects the scale and grade of the deposit.

Application of biochar and compost improved soil properties and enhanced plant growth in a Pb-Zn mine tailings soil.

This study evaluated the effect of biochar and compost on physiochemical properties, heavy metal content, microbial biomass, enzyme activities, and plant growth in Pb-Zn mine tailings. In this study, a pot experiment was conducted to evaluate the effects of biochar, compost, and their combination on the availability of heavy metals, physicochemical features, and enzyme activities in mining soil. Compared to separate addition, the combined application of biochar and compost was more effective to improve soil pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), and potassium (AK). All amendments significantly decreased CaCl2-extractable Pb, Zn, Cu, and Cd. Soil enzyme activities were activated by biochar and compost. Meanwhile, the addition of biochar and compost decreased heavy metal content in plant tissues and increased plant biomass. Pearson's correlation analysis showed that plant biomass was positively correlated with nutrient levels, microbial biomass, and enzyme activities, whereas it was negatively correlated with CaCl2-extractable heavy metals. These results enhance our understanding of the ecological functions of biochar and compost on the restoration of mining soil and reveal the potential benefit of organic amendments on the improvement of mining soil quality.

Preparation of phosphorus-modified biochar for the immobilization of heavy metals in typical lead-zinc contaminated mining soil: Performance, mechanism and microbial community

The use of modified biochar for the remediation of heavy metal (HM) has received much attention. However, the immobilization mechanism of biochar to multiple HMs and the interaction of different forms of HMs with microorganisms are still unclear. K2HPO4-modified biochar (PBC) was produced and used in a 90-days immobilization experiment with soil collected from a typic lead-zinc (Pb–Zn) mining soil. Incubation experiments showed that PBC enhanced the transformation of Cd, Pb, Zn and Cu from exchangeable (Ex-) and/or carbonate-bound forms (Car-) to organic matter-bound (Or-) and/or residual forms (Re-). After scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDS), X-ray diffractometry (XRD), fourier transform infrared (FTIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) analysis, the mechanisms of HM immobilization by PBC were proposed as precipitation (PO43-, HPO42-, OH- and CO32-), electrostatic attraction, complexation (–COOH, –OH and R–O–H) and the indirect roles of soil parameter variations (pH, moisture and microbial community). Microbial community analysis through high-throughput sequencing showed that PBC reduced bacterial and fungal abundance. However, addition of PBC increased the relative proportions of Proteobacteria by 15.04%–42.99%, Actinobacteria by 4.74%–22.04%, Firmicutes by 0.76%–23.35%, Bacteroidota by 0.16%–12.34%, Mortierellomycota by 4.00%–9.66% and Chytridiomycota by 0.10%–13.7%. Ex-Cd/Pb/Zn, Car-Cd/Zn and Re–Cd/Pb/As were significantly positively (0.001<P≤0.05) correlated with bacterial phyla of Crenarchaeota and Methylomirabilota, and Re–Cu and Ex-/Car-/Fe–Mn oxide-bound (Fe–Mn-)/Or-As were significantly positively correlated (0.001<P≤0.05) with the bacterial phyla of Proteobacteria and Bacteroidota. While Car-Cd/Zn and Re–Pb/As were positively correlated (0.01<P≤0.05) with fungal phyla of Ascomycota, Glomeromycota, Kickxellomycota, Basidiomycota and Mucoromycota. The bacterial network contained more complex interactions than the fungal network, suggesting that bacteria play a larger role in HMs transformation processes. The results indicate that PBC is an effective agent for the remediation of HMs polluted soil in Pb–Zn mining areas.

Microbiology of an abandoned Pb–Zn mine: Impact on environmental metal contamination

• Hydrozincite exhibits significant control on heavy metal mobility in other abandoned mining sites. • No morphological similarity between biomineralized hydrozincite and hydrozincite in Victoria Mine. • Microbiological effects on metal attenuation and aqueous geochemistry are negligible. • Microbial growth patterns and community structure represent oligotrophic conditions. Large-scale Zn, Pb, Cu, Fe and Ag mining ceased over 70 years ago in the Aran Valley (Catalonia, Spain). Some of the abandoned mining relics (e.g. tunnels, processing facilities and tailings dumps) exhibit elevated concentrations of metals in the associated water systems, thus posing a health risk in the neighboring ecosystem. In this study, the largest underground zinc mine in the area was chosen as a field site to showcase the processes affecting metal mobility in the environment. The precipitation of hydrozincite (Zn 5 (CO 3 ) 2 (OH) 6 ) that occurs along the walls and ground of galleries where water flows serves as a metal (e.g. Zn, Ni, Cd) polishing mechanism. We focus on the microbiology at the site and its potential impact on metal mobility. Microbial DNA was sampled from several locations inside and outside of the mine and subsequently sequenced. This is used to further determine the relative diversity of each community to make comparisons between indoor and outdoor locations. By way of DNA sequencing of local communities, microbial batch experiments, and morphological comparisons to samples known to be a product of biomineralization, it is confirmed that the mineral forms abiotically at the mine. Graphical Abstract. .

Heavy metal contamination, accumulation, and risk assessment in a paddy field near Pb-Zn mine, in Guangxi Province, China

Heavy metal contamination, accumulation, and risk assessment in a paddy field near Pb-Zn mine, in Guangxi Province, China

Mineralogical and Fluid Inclusion Evidence for Reworking of Au Mineralization by Ag-Sb-Base Metal-Rich Fluids from the Bytíz Deposit, Příbram Uranium and Base-Metal Ore District, Czech Republic

This mineralogical and fluid inclusion study was conducted on an Au-bearing quartz–sulfide vein encountered in the deep parts of the Bytíz deposit in the Příbram uranium and base-metal district, Bohemian Massif, Czech Republic. The samples were taken where the Au-bearing vein is crosscut by the common base-metal Zn-Pb ore vein Bt23C. The early mineralization of the Au-bearing vein is composed mainly of quartz (Q-1 to Q-3), illite–muscovite, Fe-Mg chlorite, arsenopyrite, and Au-Ag alloys, showing a wide range of compositions (4–69 at. % Ag) and a decrease in Au/(Au + Ag) ratios during vein evolution. Younger hydrothermal processes led to the crystallization of nests and veinlets composed of late quartz (Q-4), carbonates (siderite, dolomite–ankerite and calcite), base-metal sulfides (galena, sphalerite, chalcopyrite, and tetrahedrite), a suite of Ag and Bi-tellurides, and acanthite. The input of Sb is manifested by the partial to complete replacement of some gold grains by aurostibite and an unnamed (Ag,Au)-Sb oxide with a composition close to AuSbO3. The fluid inclusion study, combined with chlorite thermometry and arsenopyrite thermometry, showed that the early mineralization crystallized from progressively cooled (from 300 to 400 °C down to ca. 180 °C), diluted (1.2–7.0 wt. % NaCl eq.) aqueous solutions. The late portion of the mineralization formed from aqueous fluids with highly variable salinity (0.2–23.4 wt. % NaCl eq.) and homogenization temperatures decreasing from ca. 250 °C to &lt; 50 °C, which compare well with the base-metal mineralization of the vein Bt23C and other base-metal veins of the Příbram ore area. Our study illustrates the nature and intensity of the processes of the reworking of the early gold mineralization mediated by the younger Ag,Sb-rich base-metal fluids, giving rise to Příbram’s typical late-Variscan vein Zn-Pb mineralization.

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.

Genetic Relationship between Mississippi Valley-Type Pb–Zn Mineralization and Hydrocarbon Accumulation in the Wusihe Deposits, Southwestern Margin of the Sichuan Basin, China

The coexistence of numerous Mississippi Valley-type (MVT) Pb–Zn deposits and oil/gas reservoirs in the world suggests a close genetic relationship between mineralization and hydrocarbon accumulation. The Wusihe MVT Pb–Zn deposits are located along the southwestern margin of the Sichuan Basin. Based on the spatiotemporal relation between Pb–Zn deposits and paleo-oil/gas reservoirs, ore material sources, and processes of mineralization and hydrocarbon accumulation, a new genetic relationship between mineralization and hydrocarbon accumulation is suggested for these deposits. The Wusihe Pb–Zn deposits are hosted in the Ediacaran Dengying Formation dolostone, accompanied by a large amount of thermally cracked bitumen in the ore bodies. The Pb–Zn deposits and paleo-oil/gas reservoirs are distributed along the paleokarst interface; they overlap spatially, and the ore body occupies the upper part of the paleo-oil/gas reservoirs. Both the Pb–Zn ore and sphalerite are rich in thermally cracked bitumen, in which µm sized galena and sphalerite may be observed, and the contents of lead and zinc in the bitumen are higher than those required for Pb–Zn mineralization. The paleo-oil/gas reservoirs experienced paleo-oil reservoir formation, paleo-gas reservoir generation, and paleo-gas reservoir destruction. The generation time of the paleo-gas reservoirs is similar to the metallogenic time. The source rocks from the Cambrian Qiongzhusi Formation not only provided oil sources for paleo-oil reservoirs but also provided ore-forming metal elements for mineralization. Liquid oil with abundant ore-forming metals accumulated to form paleo-oil reservoirs with mature organic matter in source rocks. As paleo-oil reservoirs were buried, the oil underwent in situ thermal cracking to form overpressure paleo-gas reservoirs and a large amount of bitumen. Along with the thermal cracking of the oil, the metal elements decoupled from organic matter and H2S formed by thermochemical sulfate reduction (TSR) and minor decomposition of the organic matter dissolved in oilfield brine to form the ore fluid. The large-scale Pb–Zn mineralization is mainly related to the destruction of the overpressured paleo-gas reservoir; the sudden pressure relief caused the ore fluid around the gas–water interface to migrate upward into the paleo-gas reservoirs and induced extensive metal sulfide precipitation in the ore fluid, resulting in special spatiotemporal associated or paragenetic relations of galena, sphalerite, and bitumen.

Quantitative Mineralogy in Characterization of Historical Tailings: A Case from the Abandoned Balya Pb–Zn Mine, Western Turkey

Quantitative Mineralogy in Characterization of Historical Tailings: A Case from the Abandoned Balya Pb–Zn Mine, Western Turkey

Constraints of C[sbnd]H[sbnd]O[sbnd]S[sbnd]Pb isotopes and fluid inclusions on the origin of the giant Zhugongtang carbonate-hosted Pb–Zn deposit in South China

The Sichuan–Yunnan–Guizhou (SYG) metallogenic province on the western margin of the Yangtze Block has long been a research focus and is an important region of Pb–Zn mineralization in China, but its genesis is poorly constrained. This study examines the Zhugongtang carbonate-hosted Pb–Zn deposit (>3.0 Mt, 0.09–35.04 wt% Pb + Zn), the largest discovery made in the past decade in the southeastern part of the SYG metallogenic province. Fluid inclusions from sphalerite and calcite, CHO–isotopes from calcite, and S–Pb isotopes from sulfide minerals in the Zhugongtang Pb–Zn deposit were analyzed to understand the sources and genesis of the metals and hydrothermal fluids. Fluid inclusions in sphalerite and calcite from the largest ore body indicate that the fluids of the main mineralization stage had low temperatures (105 °C–210 °C) and moderate salinities (0.35–12.89 wt% NaCl equiv.). The sulfides are characterized by narrow ranges of sulfur isotope compositions (δ34Spyrite = +14.27 ‰ to +15.89 ‰, δ34Ssphalerite = +14.31 ‰ to +15.53 ‰, and δ34Sgalena = +10.64 ‰ to +12.97 ‰), indicating that reduced sulfur was derived from sedimentary sulfate in the Devonian to Permian carbonate host rocks by thermochemical sulfate reduction with the addition of organic matter. The δ13CPDB and δ18OSMOW values of calcite range from − 8.6 ‰ to +0.82 ‰ and +15.45 ‰ to +19.41 ‰, respectively, which are similar to values for mantle, marine carbonate rocks, and sedimentary organic matter. The negative correlation between δ13CPDB and δ18OSMOW values indicates that CO2 in the hydrothermal fluids was sourced from marine carbonate rocks and sedimentary organic matter. Calculated δ18OH2O and δDH2O values range from +3.5 ‰ to +7.5 ‰, and −93 ‰ to −52 ‰, respectively, indicating that the ore-forming fluids were dominantly metamorphic, but diluted by meteoric water that had reacted with organic matter. The galena samples yield 206Pb/204Pb values of 18.52 to 18.82, 207Pb/204Pb of 15.68 to 15.93, and 208Pb/204Pb values of 38.97 to 39.96. The μ and ω values of the sulfides range from 9.61 to 10.07 and 38.84 to 43.67, respectively. These data plot on the upper crust Pb evolution curve, generally in the field of Devonian to lower Permian sedimentary rocks, although the value for one sample falls in the field of Proterozoic metamorphic rocks, pointing to a complex origin for the ore-forming materials. Overall, the fluid inclusion and isotope data, together with geological evidence, suggest that the ore-forming fluids of the Pb–Zn deposit were sourced from deep metamorphic water with the features of low temperatures and moderate salinities, and the ore-forming metals were sourced from Devonian to lower Permian sedimentary rocks and partly from basement rocks. The genesis of the Zhugongtang ore is typical of SYG-type deposits.

Leaching of heavy metal(loid)s from historical Pb–Zn mining tailing in abandoned tailing deposit: Up-flow column and batch tests

This study aims to investigate the water-leaching characteristics of heavy metal(loid)s (HMs) from historical Pb–Zn mine tailing of an abandoned tailing deposit in eastern China. Up-flow column and batch leaching tests were conducted at different liquid-to-solid (L/S) ratios to estimate the releases of HMs and investigate the controlling mechanisms. Calcite and silicate were the dominant minerals in the tailing and the HMs contents followed the order of Zn (2371 mg/kg) > Pb (2061 mg/kg) > Cu (109 mg/kg) > Cr (47.8 mg/kg) > As (15.9 mg/kg) > Cd (5.1 mg/kg). Moreover, considerable fractions of Pb, Zn, and Cd existed in the acid-soluble forms (41–47%). Column and batch leaching tests consistently showed that limited quantities (<0.002%) of HMs could be leached from this historical tailing. In particular, variations in column conditions (e.g., length, flow rate, and initial saturation) significantly affected the release fluxes from the columns but had a relatively limited effect on the leaching mechanisms. The estimated results of HM release suggested that the leaching process was predominantly solubility-controlled and the dissolution of Ca-bearing minerals (e.g., calcite) primarily controlled the release of HMs. The studied tailing had a limited impact on the quality of the surrounding aquatic environments because the water-leaching concentrations of HMs were generally lower than the Chinese standards for drinking water. Only for Pb, the leaching results in column tests were significantly lower than those in batch tests; whereas the results in column tests for other HMs were comparable to those in batch tests to a certain extent. Based on the column test results, the amounts of HMs potentially released from the abandoned tailing deposit (height, 10 m; footprint area, 30,000 m2; tailing dry density, 1.9 × 103 kg/m3) followed a decreasing order of Zn (4.2 × 105 kg) > Cu (2.3 × 104 kg) > Pb (1.4 × 104 kg) > Cr (2.3 × 104 kg) > Cd (1.6 × 103 kg) > As (1.2 × 103 kg) over the 75-year assessment period (corresponding to an L/S ratio of 10 L/kg with an annual precipitation of 1500 mm).

The role of fluid mixing in the formation of vein-type Zn-Pb deposits in eastern Guizhou Province, SW China: Insights from elemental compositions and chlorine isotopes of fluid inclusions

• Multiple fluid sources are identified by variation range of Cl isotopes and Cl/Br ratios from. • Vein-type Zn-Pb mineralization is triggered by mixing of evaporated seawater and magmatic hydrothermal fluids . • Quantitative model shows that the mixing volume ratios of both sources are between 1:9 and 4:6. Numerous hydrothermal vein-type Zn–Pb deposits worldwide are characterized by low-temperature metallogeny, no spatial relationship with plutons, and strong water-rock interaction, which result in the difficulty of constraining the fluid origin and the process of ore formation by traditional geochemistry. In this study, we employ chemical and chlorine isotopic composition of bulk fluid inclusions from ore-bearing and ore-barren quartz veins to constrain the possible sources of ore-forming fluids and the process of metal precipitation in the hydrothermal systems of the economic vein-type mineralization in eastern Guizhou Province, SW China. Our new geochemical data are indicative of two end-members in the systems, one identified in the ore-bearing veins with high K/Na, Li/Na, Cl/Br ratios, and δ 37 Cl values representing magmatic hydrothermal fluids, another distinguished in the ore-barren veins with low Cl/Br ratios and δ 37 Cl values representing evaporated seawater. We conclude there is a systematic variation of these geochemical data as the results of the mixing between the former and the latter end-member. In the meantime, the mixing is quantitively assessed to study the mixing volume ratios of both end-members. Based on our data and our own previous study, a genetic fluid mixing model involving the magmatic hydrothermal fluids related to deep magma activity and the evaporated seawater is established for the formation of the vein-type Zn–Pb deposits. This study provides a novel geochemical approach for recognizing hydrothermal mineralizing systems.

Carbonate mineral controls the transport of Cd from tailings to surrounding soils: An example from Cd-rich Niujiaotang Zn mine in Guizhou Province, Southwest China

Heavy metal pollution derived from the oxidation of sulfides in Pb-Zn mine tailings has been a common public concern. Although the oxidative dissolution of sphalerite will release cadmium into the soil environment, it is still unclear whether other minerals contain a large amount of cadmium and how much these minerals contribute to the surrounding environmental media. In this paper, XRD, particle size analyzer, SEM-EDS and improved BCR sequential extraction method were used to analyze cadmium rich zinc mine tailing and adjacent farmland soil in Duyun, Guizhou Province. The results show that the average contents of Pb, Zn, and Cd in tailing are 214 ± 71 mg/kg, 2668 ± 773 mg/kg, and 37.5 ± 9.97 mg/kg respectively. While in the surrounding soil, they were 519 ± 280 mg/kg, 3,779 ± 2614 mg/kg, and 30.8 ± 14.4 mg/kg respectively. The mineralogical composition of tailing is mainly dolomite and less pyrite. Cadmium in tailing is mainly in weak acid extractable state, indicating that cadmium mainly exists in dolomite of tailing. Pyrite in tailing generates acid through oxidation, which accelerates the dissolution of dolomite, thus releasing Cd from minerals and migrating to surrounding farmland, resulting in soil cadmium pollution. This study reveals an important process that has been neglected. Carbonate minerals play an important role in the migration of cadmium in the tailing of the Mississippi Valley-type (MVT) lead-zinc mine and the soils affected by the tailing.

Interpretation of hydrothermal alteration and structural framework of the Huize Pb–Zn deposit, SW China, using Sentinel-2, ASTER, and Gaofen-5 satellite data: Implications for Pb–Zn exploration

The Huize Pb–Zn deposit is one of the largest and high–grade Pb–Zn deposits in the world, containing more than 7 Mt Pb and Zn reserves at an ore grade of ∼30–35 % Pb + Zn. Therefore, brownfield exploration of additional Pb and Zn orebodies at Huize Pb–Zn deposit is of high priority. Hydrothermal alteration minerals and structural features are typically associated with Pb–Zn mineralization, which can be identified quickly and economically using a multi-source remote sensing satellite dataset. In this study, Sentinel-2, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and Gaofen-5 (GF-5) satellite remote sensing imagery were employed for brownfield exploration of additional Pb–Zn orebodies in the Huize Pb–Zn deposit. The Sentinel-2 satellite remote sensing imagery was used to interpret the structure and map oxides/hydroxides by implementing the band ratio (BR) and principal components analysis (PCA) method; the ASTER satellite data were applied to map argillic, quartz, and carbonate hydrothermal alteration minerals using the PCA method; the GF-5 satellite data were utilized to map hematite, kaolinite, calcite, and dolomite minerals by the mixture tuned matched filtering (MTMF) method; and the mapped hydrothermal alteration information was verified by field reconnaissance and laboratory analysis. Finally, remote sensing geological exploration characteristics of the Huize Pb–Zn deposit were summarized by comprehensively analyzing the hydrothermal alteration minerals and structural characteristics, and three new brownfield exploration target zones of Pb–Zn mineralization were delineated. The study can provide a reference for the brownfields exploration in the vicinity of an existing Pb–Zn deposit around the world.

Alleviation of heavy metal stress and enhanced plant complex functional restoration in abandoned Pb–Zn mining areas by the nurse plant Coriaria nepalensis

Heavy metal pollution caused by mining has been a topic of concern globally because it threatens ecological functions and human health. Nearly all current remediation strategies take into account only such short-term issues as how to reduce or stabilize the content of heavy metals in soil, how to reduce the toxicity of heavy metals, and how to preserve water, soil and nutrients. However, little attention is paid to such long-term issues as whether plants can survive, whether communities can be stabilized, and whether ecosystem functions can be restored. Therefore, improving plant diversity and community stability are key aspects of improved mine restoration. To explore the possibility of reconstructing plant complexes in mining areas, the local nurse plant Coriaria nepalensis was selected as the research object for a study in the Huize Pb–Zn mining area of southwest China. C. nepalensis could increase the contents of nutrient elements (C, N, and P), reduce the contents of heavy metals (Mn, Cu, Zn, Cd, and Pb), and strengthen the plant complex functions (diversity, functional traits, and complex biomass) in its root zone. In general, C. nepalensis can form fertility islands (survival islands) in mining areas, which facilitate the colonization and success of additional less stress-resistant species. We propose C. nepalensis as a key species for use in restoration based on its ability to restore ecosystem functions under extremely stressful conditions. We encourage combination of C. nepalensis with other nurse plants to reinforce the rehabilitation of ecosystem functions.

Effects of CaCl2 on concentration and speciation of soil Cd around a Pb-Zn mine

Remediation of Cd contaminated soil around mines is still the current academic focus. In order to discuss the activation and extraction effects of CaCl2 on concentration and speciation of soil Cd around a Pb-Zn mine, field investigation and soil sample collection were conducted. Batch experiment was used to study the influence of concentration and time on Cd activation and extraction. Cd contents were analysed. And Cd species were extracted by sequential extraction procedures. Results show that there are obvious concentration effect and time effect for Cd extraction by CaCl2. The best choice of CaCl2 concentration is 0.1 mol/L. And the best extraction time is 4h. Results also show that the percentage and content of exchangeable Cd is the lowest with the value of 9.1% and 0.16 mg/kg when the CaCl2 content is 0.1 mol/L. And the percentage and content of exchangeable Cd is the lowest with the value of 10.5% and 0.18 mg/kg when the extraction time is 4h. It is found that transformation of Cd species such as exchangeable, carbonates bound and Fe-Mn oxides bound should be the main reasons of concentration effect and time effect. And the extraction of soil Cd around a Pb-Zn mine by CaCl2 is a complex coupling process of dissolution, ion exchange, desorption, acidolysis, oxidation-reduction and complexation, etc. All of these above will aid to provide a basis for the research, development and application of remediation technology for Cd contaminated soil around this and other Pb-Zn mines.