Supernormal enrichment of cadmium in sphalerite via coupled hydrothermal dissolution-reprecipitation process

doi:10.21203/rs.3.rs-2597990/v1

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Supernormal enrichment of cadmium in sphalerite via coupled hydrothermal dissolution-reprecipitation process

https://doi.org/10.21203/rs.3.rs-2597990/v1

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published 07 Oct, 2023

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The supernormal enrichment of cadmium, as well as other critical elements are frequently observed in the sphalerite of sedimentary-hosted zinc deposits. However, the physico-chemical processes that are responsible for their mineralization is still poorly understood. Here we display a coupled dissolution-reprecipitation model that could explain the occurrence of cadmium from solid solutions up to several wt.%, sulfide nanoparticles, and independent mineral inclusions in sphalerite. The selective dissolution by oxidative acidic fluids causes depletion of zinc and concentration of cadmium in the lattice of primarily formed sphalerite, especially at interface of structural defects, such as low-angle tilt boundaries. Further dissolution triggers reprecipitation of cadmium-poor sphalerite nanocrystals as relics, followed by deposition of amorphous cadmium-rich sulfide nanoparticles as fillings in dissolution pores by reaction between cadmium ions and released reduced sulfur from sphalerite lattice. The cadmium is derived from both dissolution of primary Cd-rich sphalerite and re-supply by highly-evolved oxidative acidic fluid rich in cadmium. Growth and/or passivation of these amorphous nanoparticles finally forms greenockite blebs and/or nanocrystals in sphalerite. This model provides insights for critical-element redistribution and mineralization via hydrothermal processes. Similar mechanisms may also have broad implications in synthesis of sulfide nanomaterials used in green energy technologies.

Earth and environmental sciences/Solid Earth sciences/Geology/Economic geology

Earth and environmental sciences/Solid Earth sciences/Mineralogy

Sphalerite

cadmium

sulfide nanoparticles

coupled dissolution-reprecipitation reaction

critical element

Sphalerite is one of the major industrial minerals not only for zinc, but also for critical elements, including cadmium, gallium, germanium, indium¹, and sometimes silver and gold². Solid-state processes, such as dynamic recrystallization for germanium³, and phase re-equilibration during diffusion for indium⁴ has been proposed to explain redistribution and concentration of critical elements in sphalerite. However, the aforementioned mechanisms are hard to explain the supernormal enrichment of cadmium (Cd) in undeformed sphalerite of hydrothermal origin. Local Cd concentration up to several wt.% as a major component ⁵, and/or as independent Cd minerals such as greenockite (CdS) inclusions in sphalerite⁶ have been frequently observed in some Mississippi valley-type Pb-Zn deposits. These evidences require mechanisms for supernormal enrichment of Cd, and perhaps other critical elements via aqueous processes under low-temperature hydrothermal conditions.

It has been thermodynamically predicted that high Cd concentration as solid solutions in sphalerite favors total reduced sulfur (ΣS_red) deficient (SO₄²⁻-dominated), oxidative, low-T (100 ~ 200℃) hydrothermal conditions, but is inhibited at contrary conditions⁷. Recent studies have revealed that the formation of Zn-rich greenockite and/or Cd-rich sphalerite generally involves partial dissolution of primary sphalerite and/or wurtzite, indicating that mineral-fluid interaction may play a key role for supernormal enrichment of cadmium^8,9. Here we present nanoscale mineralogical evidence for a coupled dissolution-reprecipitation reaction model that could well explain the supernormal enrichment of Cd in sphalerite. In this model, extremely Cd-rich domains in sphalerite are formed by hydrothermal dissolution of primary growth zones of sphalerite, simultaneously in company with precipitation of CdS nanoparticles and/or bulk greenockite crystals in dissolution pores during mineral-fluid interaction between sphalerite and oxidative acidic hydrothermal fluid, which transports cadmium, lead, as well as silver.

Textural and compositional features: Sphalerite host and sulfide inclusions. Samples were collected from the Jinding deposit, Yunnan Province, Southwestern China (26°24′36′′ N, 99°25′28′′ E, Supplementary Fig. 1a-b). The Jinding deposit, within the Mesozoic-Cenozoic Lanping basin, Sanjiang Tethys Orogen^10,11, hosts zinc ores rich in cadmium grading 0.01 to 0.2 wt.%¹². It is regarded as a subtype of the Mississippi valley-type zinc-lead deposit that hosted in a thrust-triggered salt-diapiric mélange^13,14. Three major stages of mineralization are identified in the Jinding deposit^15,16, represented by (S1) fine-grained disseminated pyrite-marcasite-sphalerite-bitumen replacing pre-ore calcite cement of quartz sand, (S2) pyrite-galena halo that replaced pre-ore calcite and overprinted onto S1, and (S3) coarse-grained crystalline galena-sphalerite-greenockite-barite vein (Supplementary Fig. 1c). The studied cadmiferous sphalerite is derived from galena-dominated S3 veins, and corresponds to colloform sphalerite precipitated from low temperature (79 ~ 173℃) hydrothermal fluids, with high salinities ranging from 24.5 to 27.4 wt.% NaCl + CaCl₂ equiv¹⁷.

The cadmiferous sphalerite is dark greenish-grey crystalline, accompanied with coarse-grained galena and calcite (Supplementary Fig. 1c). It presents complex core-mantle-rim (CMR) textures with multi-nucleation centers. The cores of the sphalerite are highly porous, showing mosaic and/or fan-shaped zoning patterns with bright contrast under the BSE image, indicating high Cd concentration (Fig. 1a). The mantles of sphalerite are smoother than the core, with less and smaller pores under BSE image. They are much darker, and showing no zonation patterns, indicating less but more homogenous Cd substitution ratios than the cores (Fig. 1a). The rims of sphalerite are slightly brighter than the mantle, presenting cloudy zonation under BSE image, which transits outward to vague oscillatory zonation. From core to rim, the crystallinity of sphalerite increases, confirmed by euhedral sphalerite with perfect crystal facade at the outermost zone of the rim (Fig. 1a).

Various forms, sizes, and distribution patterns of greenockite and galena inclusions in the sphalerite have been observed. The most common forms are blebs, dots, and less frequently, euhedral crystals (Fig. 1b-d). Two distribution patterns of greenockite inclusions are recognized: 1) An irregular distribution of inclusions, characterized by Cd-depleted, “pure” sphalerite mantle alternates with Cd-rich cores and rims that containing many greenockite and minor galena blebs. 2) A regular distribution of inclusions where the greenockite traces along crystal growth boundaries of the sphalerite (Fig. 1a, yellow circles,). Such a pattern is also exemplified by galena inclusions growing concordantly along zone boundary of Cd-rich and Cd-poor sphalerite domains (Fig. 1c). The former pattern clearly suggests sulfide inclusions are from younger generation than their Cd-rich sphalerite host. The reason is that these inclusions are mostly arbitrarily oriented, highly related to the hypogenic dissolution pores and discordant with the growth direction of the sphalerite host (Fig. 1a-b). However, two potential modes of formation of the latter pattern are possible. The first is by coprecipitation of sphalerite and greenockite during simultaneous supersaturation of CdS and ZnS in the hydrothermal fluids. The second is by dissolution-reprecipitation reaction between the sphalerite and Cd-(Pb)-bearing solutions at the mineral-fluid surface during sphalerite growth.

EPMA point analyses of the sphalerite host revealed that the Cd concentrations of Cd-rich, inclusion-bearing sphalerite host (Core, 5.20 ~ 8.67 wt.%) are significantly higher than those of Cd-poor sphalerite domains (Mantle, 0.48 ~ 3.00 wt.%). The cores are more enriched in Ag (100 ~ 920 ppm) than the mantle (< detection limit), yet more depleted in Pb (< detection limit) than the mantle (50 ~ 2990 ppm). The greenockite inclusions are characterized by relatively high Zn concentrations (0.28 ~ 2.14 wt.%), and highly depleted in Pb (< detection limit). The galena inclusions are moderately enriched in Zn (0.04 ~ 0.98 wt.%), and Cd (up to 0.85 wt.%). Notably, extremely high concentration of Cd (1.83 wt.%, JD-40) and Ag (1.13 wt.%, JD-5) in galena inclusions are detected, implying existence of Cd and/or Ag sulfides or native metals (Supplementary Table 1).

Pioneer discovery of Cd-rich sulfide nanoparticles in the sphalerite host. Focused ion beam (FIB) nano-sampling was conducted on a sulfide inclusion bleb in the Cd-rich core of the sphalerite host. It displays bright contrast similar to those of greenockite and galena inclusions (Fig. 1e). The HAADF-STEM image on the FIB section show that three non-crystalline aggregates are hosted in a dissolution pore of the sphalerite host (Fig. 1f). The bright-field TEM (BF-TEM) image and selective area electron diffraction (SAED) pattern reveal that the greenockite-like aggregate on the left is polycrystalline, and consists of randomly oriented cylindric greenockite nanoparticles (NPs) in an amorphous matrix (Fig. 2a). High-resolution TEM (HRTEM) observations confirm that the greenockite NPs (~ 25 nm) are poorly crystalline, with distorted areas in lattice along [001] zone axis. (Fig. 2b). The qualitative TEM-EDS spectrum of the aggregate show that it is composed of Ag-Cd-S with extremely high Ag concentrations (Supplementary Fig. 2a). However, no Ag minerals, such as argentite (AgS) or native silver (Ag), are detected in SAED patterns, suggesting that Ag is dominantly incorporated into the amorphous matrix.

The BF-TEM image and SAED pattern of galena-like aggregate on the middle confirm that it is composed of numerous rectangular galena NPs (Fig. 2c). The galena NPs (~ 15 nm) are angular and well crystallized with perfect lattice planes, and without any defect under the HRTEM image (Fig. 2d). Detectable Ag and Cd (Ag > Cd) concentrations in the aggregate by qualitative TEM-EDS spectrum suggest Ag and Cd substitution for Pb in the lattice of the galena NPs (Supplementary Fig. 2b). Notably, nanoscale veins of galena-like aggregate penetrating into porous domain of the sphalerite host are observed under the HAADF-STEM image (Fig. 1f), suggesting the accumulation of galena-like aggregate took place shortly after sphalerite dissolution.

Polycrystalline sphalerite-like aggregate is recognized within porous domain of the sphalerite host (Fig. 1F), as confirmed by the BF-TEM image and SAED pattern (Fig. 2e). It is mainly composed of rounded sphalerite NPs distributed around nanoscale dissolution pores (Fig. 2e). Under the HRTEM observation, two sphalerite nanocrystals attach to each other by crystallization via particle attachment (CPA), and show typical sphalerite-type {111} single stacking faults and {111} twin boundaries (Fig. 2f), as confirmed by additional rays and spots in the SAED pattern (Fig. 2f). The qualitative TEM-EDS spectrum reveal major composition of ZnS, with trace concentrations of Cd and Ag (Cd > Ag) (Supplementary Fig. 2c).

The sphalerite host is crystallized, and is in transitional contact with the sphalerite-like aggregate, as confirmed by BF-TEM image and SAED pattern (Fig. 2g). It is highly distorted with enormous stack faults (Fig. 2g). A few very thin wurtzite-like lamellas (< 5nm) are also recognized in the sphalerite lattice (Fig. 2h). The qualitative TEM-EDS spectrum indicate that the sphalerite host is slightly more enriched in Cd, but far more depleted in Ag than the sphalerite-like aggregate (Supplementary Fig. 2d), suggesting Ag enrichment tend to be more enhanced in amorphous phase or nanocrystalline sphalerite.

Supernormal Cd enrichment in the sphalerite lattice by oxidative dissolution. The Cd concentration in the Cd-rich core of sphalerite (5.20 ~ 8.67 wt.%) accompanied with greenockite inclusions is significantly higher than the Cd-poor inclusion-free mantle of sphalerite (0.48 ~ 3.00 wt.%) (Supplementary Table 1), as well as cadmiferous sphalerite from the Niujiaotang Zn-Cd deposit (0.82 ~ 2.34 wt.%)⁶. Such a significant change of composition in a single crystal-scale requires further discussion. The ore texture observation and EPMA analyses suggest that the Cd-rich domains in sphalerite are more porous than the Cd-poor domains (Fig. 1a-c). Such a phenomenon indicates hydrothermal dissolution took place simultaneously during or shortly after Cd-rich sphalerite crystallization. The inhomogeneous nature of fan-shaped and cloudy zonation patterns in Cd-rich sphalerite also asks for replacement origin rather than direct precipitation origin. The compositional inhomogeneity in Cd-rich sphalerite favors fluid-mineral reaction, rather than precipitation from hot solutions, because the rate of aqueous diffusion of trace elements is higher than that of the fluid-mineral reaction¹⁸.

The studied Cd-rich sphalerite host is characterized by anomalous reverse nonstoichiometry (sulfur < metal, supplementary Table 1), high density of {111} stack faults, and wurtzite-like lamellas (Fig. 2g-h). These features suggest low fugacity of sulfur during sphalerite precipitation^2,19, or partial oxidation took place on existing sphalerite²⁰. The partial oxidation model is more favored because both Cd and Zn (R = 0.69), as well as Cd and S (R = 0.88) are negatively correlated in Cd-rich sphalerite. Whereas no correlation is found in Cd-poor sphalerite and cadmiferous sphalerite in the Niujiaotang deposit, despite nonstoichiometry also occurs in these sphalerites. A plausible explanation is Cd substitution for Zn is accompanied with O substitution for S during oxidative dissolution on sphalerite, which causes relative increase of Cd concentration in sphalerite²⁰.

Low-angle tilt boundary, a planar defect, has been recognized within the Cd-rich sphalerite host by HR-TEM observation (Fig. 2i and 2k). The TEM-EDS mapping reveals that further Cd-enrichment took place along and near the low-angle tilt boundary (Fig. 2j and 2l). The observation fills the gap of mineralogy evidence for trace element preferential incorporation into planar defects in sphalerite, which has long been proposed by Johan (1988)²¹. Previous study has predicted or observed crystallographic-controlled Cd incorporation preference: Along [111] or [110] growth zones^22,23. However, such phenomenon was not observed in this study, suggesting that Cd incorporation in planar defects is not lattice-controlled. Thus, we tentatively propose that further supernormal Cd enrichment in the low-angle tilt boundary did not take place during sphalerite growth, rather, it happened via hydrothermal dissolution by Cd-bearing oxidative acid fluid along primarily existing structural defect since it represent a weak interface for alternation.

Cd-rich sulfide nanocrystal formation via coupled dissolution-reprecipitation reaction. Sulfide nanoparticles are generally formed via exsolution from host sulfides by posterior modification²⁴, microbial metabolisms by sulfate-reducing bacteria (SRB)²⁵, and supersaturation nucleation during hydrothermal fluid mixing²⁶. Recently, the hydrothermal coupled dissolution-reprecipitation reaction is considered as effective approach for nanocrystal formation²⁷. This mechanism generally involves dissolution of an existing mineral and precipitation of a new phase composed of nanoparticles at the dissolving mineral-fluid interfaces²⁸.

For the first time, non-crystalline Cd-rich sulfide aggregates was discovered in a dissolution pore of Cd-rich sphalerite host (Fig. 1f). The transition relationship between porous sphalerite-like aggregate and defect-rich crystalline sphalerite indicates pre-existence of a bulk sphalerite crystal that partially dissolved to form nanocrystals and dissolution pores (Fig. 3a). The TEM-EDS mapping further confirm the accumulation of amorphous Cd-Ag-S and Pb-S NPs at the wall of, and as fillings in nanoscale dissolution pores, respectively (Fig. 3a). Such a phenomenon indicates that dissolution of the sphalerite host is in accompany with simultaneous formation of the sphalerite NPs, and latter precipitation of Pb-S and Cd-Ag-S NPs. It is further confirmed by the appearance of nanoscale vein of galena NPs crosscutting the sphalerite NPs (Fig. 1f and 2e), and amorphous Cd-Ag-S NPs penetrating galena and sphalerite NPs (Fig. 3b, EDS mappings).

Under HAADF-STEM observation, abundant nanometric protrusions and etch pits appear around a dissolution pore, simultaneously with reprecipitation of galena and sphalerite NPs in the center of the dissolution pore (Fig. 3c, EDS mappings). These textures are indicators for hydrothermal oxidative dissolution of ZnS that mediated by H⁺ in the presence of other metal species^29,30. Generally, such process results in the release of Zn²⁺ and oversaturation of reduced sulfur species at the surface of porous ZnS^31,32. We speculate further reaction between redundant sulfur and Cd²⁺ and Pb²⁺ in aqueous phase at fluid-mineral interface may result in PbS and CdS oversaturation, causing their nucleation in the dissolution pores of the sphalerite-like aggregate. This process is also confirmed by metal deficiency relative to sulfur in greenockite inclusions, which is in contrast with their sulfur deficient sphalerite host. The Cd source for formation of greenockite may be dual-sourced. Both redistribution of Cd formerly contained within dissolved Cd-rich sphalerite, and addition of Cd together with Cu, Ag, and Pb during greenockite NPs formation may occurred^9,30. Apart from Cd enrichment, only traces of Ag (100 ~ 920 ppm) and Pb (< detection limit) incorporate into the Cd-rich sphalerite (Supplementary Table 1). Thus, it is of necessity for metal supply by hydrothermal fluids that rich in Cd, Ag, and Pb.

As discussed above, a Cd-, Ag-, and Pb-bearing metalliferous, oxidative and acid fluid is required for coupled dissolution-reprecipitation models for Cd-rich sulfide NPs’ nucleation. In the Jinding deposit, previous study has confirmed that from stage 1 disseminated galena (109 ~ 432 ppm Cd, 56 ~ 66 Zn/Cd), stage 2 vein-type pyrite (23 ~ 1659 ppm Cd, 30 ~ 175 Zn/Cd), to stage 3 coarse grained galena (1983 ppm, 20 Zn/Cd), the Cd concentrations and Cd/Zn ratios in fluid inclusions increase significantly³³. The increase of Cd/Zn ratios may be attributed to temperature decrease from early to late stage, and/or H₂S-dominated hydrothermal nature of fluids in early stage during massive precipitation of pyrite and marcasite (Spplementary Fig. 1b-c), which forbids Cd corporation into sphalerite of stage 1 and stage 2, and relative condensation in stage 3⁷. Notably, the massive precipitation of pyrite and marcasite can also produce superfluous H⁺ that needed for acid leaching of sphalerite³⁴. Form early to last stage, the hydrothermal fluid gradually becomes oxidative, as confirmed by barite-only veins that crosscut Cd-rich sphalerite domains (Fig. 1a). Thus, a late-stage, highly evolved hydrothermal fluid can serve as candidate, as proposed by Tarkian and Breskovska (1989)³⁵, for Cd supernormal enrichment via hydrothermal coupled dissolution-reprecipitation reaction.

The mechanism is also thermodynamically favored. It is found that sphalerite with moderately high Zn/Cd ratios (> 20, Cd content < 8 wt.%) are relatively stable, and dissolved at much slower rates than sulfides with low Zn/Cd ratios under acid and oxidative conditions³⁶. The Cd-rich nanoparticles appear exclusively within the Cd-rich sphalerite domains, which is more likely to be dissolved by oxidative acid hydrothermal fluids to provide metals and open space for nanoparticle nucleation. Previous studies also support the relative solubilities of sulfide follow the trend of ZnS > PbS ≥ CdS under acid and oxidized aqueous conditions³⁷, which is in agreement with the formation trend of ZnS→PbS→Cd-Ag-S NPs. Besides, The Cd- and Pb-dopped sphalerite exposed to oxygen and acid can form a series of sulfide voltaic cells including ZnS-PbS and ZnS-CdS pairs. The ZnS with a lower electrochemical potential act as anodes and are prone to oxidative dissolution, whereas the CdS and PbS act as cathodes with higher electrochemical potentials and are protected from oxidation, and can remain in sphalerite and/or oversaturate to form sulfide NPs³⁸.

Theoretically, minerals pass through a transitory nanocrystal stage during formation³⁹. However, this stage tends to be transitory and metastable, and rarely be preserved in geological settings⁴⁰. In this study, naturally formed sphalerite, galena, and greenockite nanocrystals, as well as their crystalline counterparts was identified in Cd-rich sphalerite from a MVT Zn-Pb deposit, asking for further interpretation. One possible mechanism is proposed for preservation of Cd-rich sulfide nanoparticles: Appearance of natural organic matters (NOMs), especially carboxylic acids (C₆H₅O₇³⁻) in hydrothermal fluids, as passivators against nanoparticle recrystallization^41–43. Notably, hydrocarbon-bearing aqueous inclusions as well as solid bitumen are ubiquitously distributed in sphalerite-rich ores of the Jinding deposit⁴⁴. Besides, extremely Cd-isotope fraction in sphalerite in the Jinding deposit has been attributed to the presence of bacterial metabolic Zn-carboxylate in hydrothermal fluids⁴⁵. The NPs observed are hosted in dissolution pores. As sphalerite forms from hydrothermal solutions that rich in organic matters, organic molecules in relics of those solutions can be capsulated in dissolution pores, coating the NPs’ surface, and inhibiting the aggregation of these NPs⁴⁶. However, if organic molecules are absent and Cd is sufficient at sub-micron hydrothermal environments, greenockite and/or galena NPs will soon grow and coarsen to form bulk minerals.

A comprehensive model for supernormal enrichment of Cd in sphalerite. We establish a coupled dissolution-reprecipitation reaction model of supernormal enrichment of Cd in sphalerite both as solid solutions and as nanocrystalline to bulk greenockite inclusions (Fig. 4). A preexisting sphalerite is required that is precipitated at a relatively high-temperature, reduced hydrothermal environment. Near neutral condition is supposed for carbonate buffering effect. Cd²⁺ incorporation into sphalerite as solid solutions in moderate concentration (~ 2 wt.%). Primary defect, such as low-angle tilt boundary, is formed during sphalerite growth (Fig. 4a). Since hydrothermal activity in most of MVT deposit is multi-pulsed, a highly evolved low-temperature, SO₄^2--dominated, and acidic hydrothermal fluid, where iron sulfide has been massively removed, and Cd, Pb and Ag has been further concentrated, injects into the space where sphalerite is precipitating. Acid leaching as well as oxidative dissolution take place at fluid-mineral interface (Fig. 4b). Subsequent reprecipitation of Cd-rich nanoparticles and bulk sulfide inclusions, as well as formation of porous domain of sphalerite is triggered by mixing of metals and reduced sulfur species as a result of oxidative dissolution. Further enrichment of Cd also happens in the sphalerite lattice as well as structural defects (Fig. 4c). As soon as fluid supply is cut off, normal precipitation of Cd-poor sphalerite take place. Cd concentration in newly formed sphalerite decreased because of excessive removal of the metal at the early stage (Fig. 4d).

Our investigation suggests hydrothermal process, such as coupled dissolution-reprecipitation reaction, can directly attribute to supernormal Cd enrichment, which provides new insights for critical-element mineralization. Such model may also be applicable to Ge redistribution during weathering of sphalerite in some non-sulfide Pb-Zn deposits⁴⁷, since chemical weathering by supergene fluids takes place primarily by dissolution-reprecipitation processes^48,49. The dissolution-reprecipitation reaction model for sulfide nanocrystal formation may also shed light on effective synthesis approach for II-VI semiconductor materials, such as ZnS, PbS, CdS nanomaterials. Actually, the complex sulfide, such as (Ni,Fe)₃S₄, has already been successfully prepared via a coupled dissolution-reprecipitation pathway by using a hydrothermal flow-through cell⁵⁰, which suggest its broad application prospect.

Electron probe microanalysis. EPMA was carried out on studied sphalerite, greenockite and galena using EPMA-1720 of SHIMADZU housed in the State Key laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing, to determine major element concentrations and elemental distributions. Elements including S, Zn, Pb, Cd, Ag, Fe, Mn, Sb, Co, Cu, and As were measured at 15 kV of accelerating voltage, 20 nA of current, 1 µm spot size, 30 s peak time and 15 s background time. The following standards were used: chalcopyrite (S-Kα, Fe-Kα, Cu-Kα), sphalerite (Zn-Kα), galena (Pb-Mα), Cd metal (Cd-Lα), Ag metal (Ag-Lα), rhodonite (Mn-Kα), antimony telluride (Sb-Lα), and cobaltite (Co-Kα, As-Lα). The EPMA analyzing results are shown in Supplementary Table 1.

TEM/STEM-EDS observation and analyses. The thin section for TEM study was prepared using focused iron beam (FIB)-SEM by cutting across sphalerite host, and greenockite and galena inclusions. The sampling location are shown in Fig. 1e. Then it was placed on a Cu grid and thinned. High resolution transmission electron microscopy (HRTEM) imaging and element X-ray energy-dispersive spectrometry (EDS) mapping was performed by using an FEI F200 Talos TEM. Ultrahigh resolution high angle annular dark field (HAADF) imaging and atom-scale EDS mapping was conducted on an FEI Titan G2 AC-TEM in Sinoma Institute of Materials Research, Guangzhou, China. Diffraction measurements were carried out by using DigitalMicrograph 3.11.1 and Winwulff 1.4.0 software. Data from the American Mineralogist Crystal Structure Database were used for indexing of the electron diffractions.

Acknowledgements

The National Natural Science Foundation of China (Number 92162101, 41872080), and the National Key Research and Development Project of China (Number 2020YFA0714802) supported this work. We thank Pro. Jun Deng’s research team at China University of Geosciences, Beijing for their field support, data analyses, constructive discussions, and comments.

Author contributions

Conceptualization: H.D., C.W. & J.D. SEM and EPMA works: H.D. & J.Z. FIB and TEM works: H.D. & R.H. Data Analysis: H.D. & C.W. Writing—original draft: H.D. & C.W. Writing—review & editing: all authors.

Competing interests

The authors declare no competing interests.

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Supernormal enrichment of cadmium in sphalerite via coupled hydrothermal dissolution-reprecipitation process

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