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Degraded water quality and environmental impacts caused by weathering of sulfide-bearing mine wastes are a legacy remaining at many historical mine sites. Release and mobilization of toxic metals (e.g., Zn and Cd) in mine drainage are often associated with weathering of primary sulfide minerals and precipitation and dissolution of secondary minerals. This study aims to couple field-scale measurements of physicochemical parameters with μm- and nm-scale mineralogical characterization to investigate sphalerite weathering and controls on Zn and Cd migration in an uncovered mine waste-rock pile. Elevated concentrations of Zn and Cd, potentially harmful to the receiving environment, were detected in waste-rock pore water and seepage. A suite of analytical techniques, including scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDS), scanning transmission electron microscopy (STEM) with EDS, electron microprobe analysis (EMPA), and synchrotron-based micro X-ray fluorescence (μ-XRF) mapping and micro X-ray absorption near edge structure (μ-XANES) spectroscopy were utilized in a high-resolution investigation of elemental- and secondary-mineral associations with sphalerite grains. EMPA and μ-XRF elemental maps and STEM investigations show depletion of Zn, Fe, S, and Cd, local enrichment of Cu, and distinct dissolution pits at the margins of sphalerite grains. Using μ-XANES, the speciation of solid phases containing Zn, Cu, Fe, and S indicates the dominance of primary sphalerite with microscopic inclusions of chalcopyrite, along with sparse occurrence of secondary Cu-bearing sulfides formed during weathering. These results suggest sphalerite oxidation leads to congruent dissolution without formation of distinct secondary-mineral coatings. Sphalerite weathering significantly contributes to elevated aqueous concentrations of Zn and Cd. Field-scale observations and mineralogical investigations indicate common occurrence of Fe-oxyhydroxides in the waste-rock pile. Seepage chemistry and surface complexation modeling results suggest that pH-dependent variations in reactions on the surfaces of the Fe-oxyhydroxides control aqueous concentrations of Zn and Cd, and the Zn/Cd ratio in the seepage. This work highlights the importance of understanding the mechanisms of sulfide-mineral oxidation and subsequent surface precipitation and adsorption, such that appropriate remediation action can be implemented to limit mobilization of metals to sensitive ecosystems.

The determination of fractionation factors associated with important biogeochemical processes controlling Ni availability in the environment is necessary to confidently use Ni isotope signatures as tracers in environmental studies. In this paper we present experimental results on Ni isotope fractionation during the precipitation of Ni secondary minerals (Ni hydroxide, Ni hydroxycarbonate and Ni sulfide minerals) that can control Ni fate and mobility in settings where high dissolved Ni(II) concentrations may pose a serious threat to the environment. Results show a preferential partition of lighter isotopes into the solid phase with associated fractionation factors e of −0.40‰ ± 0.04‰, −0.50‰ ± 0.02‰, and −0.73‰ ± 0.08‰ relative to the hydroxide, carbonate and sulfide systems, respectively. Early kinetically induced isotope fractionation, followed by possible re-equilibration with the reacting solutions was suggested for the three investigated systems. Distortions of Ni-O bonds in the octahedra constituting the structures of Ni hydroxide and hydroxycarbonate minerals could have also contributed to the isotopic fractionation measured in these systems. In contrast, for Ni sulfide system, the magnitude of Ni isotope fractionation seemed to be determined by water and sulfide ligands exchange in solution prior to mineral nucleation. Although there is insufficient evidence to determine whether complete equilibrium occurred in the three studied systems, the fractionation factors reported in this study can provide useful indicators of Ni isotope fractionation associated with fast precipitation of secondary minerals involved in the sequestration of Ni from contaminated environments. These findings also contribute to the characterization of Ni isotope systematics which is still in the early stages of development.

Volatile elements and compounds found in extra-terrestrial environments are often the target of In Situ Resource Utilization (ISRU) studies. Although water and hydroxide are most commonly the focus of these studies as they can be used for propellant and human consumption; we instead focus on the possible exploitation of sulfur and how it could be utilized to produce building materials on the Moon, Mars and Asteroids. We describe the physical and chemical pathways for extracting sulfur from native sulfide minerals, manufacturing sulfuric acid in situ, and using the produced acid to dissolve native silicate minerals. The final products of this process, which we call the Silicate-Sulfuric Acid Process (SSAP), include iron metal, silica, oxygen and metal oxides, all of which are crucial in the scope of a sustainable, space-based economy. Although our proposed methodology requires an initial investment of water, oxygen, and carbon dioxide, we show that all of these volatiles are recovered and reused in order to repeat the process. We calculate the product yield from this process if it were enacted on the lunar highlands, lunar mare, Mars, as well as an array of asteroid types.

The surface of Mars has experienced progressive oxidation, resulting in the formation of sulfate minerals as evidenced from surface exploration missions. However, no clear evidence for the presence of sulfate minerals has been reported within Martian meteorites. This study examined sulfur speciation in impact glasses of three basaltic shergottites, Elephant Moraine (EETA) 79001, Larkman Nunatak (LAR) 06319, and Dhofar 019, using X-ray absorption near-edge structure (XANES) spectroscopy. The measured XANES spectra were classified into four types: (1) sulfide, (2) highly reduced sulfide glass (∼IW+1), (3) mixture of sulfide and sulfate, and (4) sulfate. The sulfate spectra observed from EETA79001 and LAR 06319 were mixed with sulfide from the reduced igneous host rock as impact glasses were formed by shock on the surface of Mars, both sulfide and sulfate would have possibly originated on Mars. Besides, highly reduced sulfide present in the same impact glasses is inconsistent with secondary alteration on the oxic Earth’s environment. In contrast to EETA79001 and LAR 06319, all of the XANES spectra from Dhofar 019 showed the only sulfate, whose origin is most likely from terrestrial alteration. Combining with the geochemical signatures of volatile elements (e.g., D/H, C, and halogens) in impact glasses of EETA79001 and LAR 06319, we propose two possible scenarios for the formation of sulfate species to the shergottite host-rocks: (i) oxidation of sulfide minerals by subsurface oxic water in Mars, or (ii) precipitation of sulfate mineral derived from Martian subsurface water. The difference between the two models is the source of S(VI) species, whether it originated from (i) magmatic sulfide in shergottite or (ii) sulfate ion in the subsurface water/ice. Both models indicate that the ancient (∼4 Ga) water reservoir might have already been oxic, and it requires post-magmatic water–rock interaction that formed sulfate minerals whose oxidized signatures were incorporated into impact glass.

Sediment-hosted marine sulfur cycling has played a significant role in regulating Earth's surface chemistry over our planet's history. Microbially-mediated reactions involving sulfur are often accompanied by sulfur isotope fractionation that, in turn, is captured by sulfate and sulfide minerals, providing the opportunity to track changes in the microbial utilization of sulfur and thus the marine sulfur cycle. Studying sulfur diagenesis within the Bornholm Basin, Baltic Sea, we explore the interplay between carbon, sulfur and iron, focusing on the fate of sulfur and the dynamics of the sulfur and oxygen isotopic response as a function of the varying thickness of the organic carbon-rich Holocene Mud Layer (HML) across the basin. Using a one-dimensional reaction-transport model, porewater sulfate and sulfide profiles were used to calculate net sulfate reduction rates (SRR) and net sulfide production rates, respectively. These calculations suggest a positive relationship between the thickness of the HML and net rates of sulfate reduction and sulfide production. Given that ascending sulfide is enriched in 34S relative to that produced in-situ, a heightened sulfide flux promotes spatially variable precipitation of 34S-enriched pyrite (δ34S ≈ −10‰) close to the sediment–water interface. Modeling results indicate that this isotopically “heavy” sulfide is formed as a consequence of mixing between ascending sulfide (up to +6.3‰) and that produced in-situ (ca. −40‰). Further, we show that the sulfur and oxygen isotopic composition of porewater sulfate is controlled by the net SRR: when the net SRR is high (i.e., in sulfide-replete settings) the downcore increase in δ18OSO4 is dampened relative to increase in δ34SSO4, whereas when net SRR is low (i.e., in iron-rich parts of the basin) downcore δ18OSO4 values increase while δ34SSO4 values remain invariant. We conclude that sedimentation rates and open system diffusion strongly influence the distribution of sulfur species and their sulfur isotopic composition, as well as the oxygen isotopic composition of sulfate, through the interaction between iron, sulfur and methane. This work highlights the importance of considering diffusion to better understand open system diagenesis and the δ34S signatures of sulfate and sulfide in both modern settings and ancient rocks.

Highly Siderophile Elements (HSEs; Os, Ru, Ir, Rh, Pt, Pd, Au and Re) combined with their isotopic systematics (Re-Os and Pt-Os) are powerful tools for tracking evolution and genesis of mantle derived magmas. Given sulfides (accessory sulfide minerals and/or molten sulfides) are the primary hosts of HSEs in the mantle and low-degree carbonated melts are extracted from large portions of mantle volume, partitioning of HSEs between sulfide and carbonated melt might play a critical role in distributing HSEs between the mantle and crustal reservoirs. Although, partitioning of HSEs and chalcophile elements between sulfide melt and silicate melt has been previously studied, partitioning of these elements between sulfide melt and carbonated melts has not received much attention. Here we use high P-T experiments to determine the partitioning of HSEs and chalcophile elements (Ni, Co, Mo, Os, Ru, Pd, Pt and Re) between (i) sulfide melt and carbonated silicate melt (CO2 ~ 17 wt.%) and (ii) sulfide melt and carbonatitic melt (CO2 ~ >30 wt.%) at a pressure (P) of 3 GPa and temperatures (T) of 1300–1600 °C in graphite capsules. All experiments produced quenched Fe-sulfide melt blobs + carbonated silicate melt matrix. Concentrations of major elements were measured using electron microprobe, and HSEs and chalcophile elements were measured using LA-ICP-MS. We find that all the elements measured are compatible in the sulfide melt to varying degrees and their Dsulfide/carb. melt sequence is Mo D ¯ ) for carbonated peridotite using our experimentally measured D values, we model the HSE contents of mantle derived low-degree partial melts using an aggregate fractional melting equation and compare the primitive mantle normalized HSE patterns of our model with natural kimberlites, carbonatites, ocean island basalts, and alkaline basalts. We also calculate proportions of sub-lithospheric continental mantle (SCLM) xenolith detritus in the natural kimberlite and carbonatite samples from Karelian, Kaapvaal, Canadian shield and North China craton by using mass balance calculations based on Ru concentration in the primary carbonated melt and the SCLM xenoliths. Our calculations show that detritus proportion in natural kimberlites are 2–28% for Karelian, 7–28% for Kaapvaal, and 6–16% for Canadian shield, which are in agreement with previous studies using various other proxies. We also show that the extent of Re/Os fractionation is less for events of carbonate melt metasomatism as compared to similar events of basaltic melt metasomatism.

Mineral separation by flotation is a water-intensive process; thus, recycling and reusing the process-water have essential environmental and financial impacts for ore beneficiation plants. The recycled water contains different ions, which affect flotation responses. Several investigations focused on the effects of monovalent and divalent ion contents of the recycled water and seawaters on the flotation recovery. However, there is a gap in exploring the influence of trivalent ions on the metallurgical responses of sulfide flotation. This work is going to fill this gap by exploring and comparing the effect of Na+, Mg2+, and Al3+ on the chalcopyrite and pyrite's flotation responses. Different flotation experiments and surface analyses were considered to assess and compare these multivalent cations' impacts on the flotation responses. Outcomes indicated that compared to Na+ and Mg2+, Al3+ could significantly change both minerals' surface properties, relatively improved pyrite's floatability, and decreased the chalcopyrite recovery. Adsorption of Al(OH)3(s) on the minerals surface and the collector - Al(OH)3(s) aggregate could explain these variations.

This study presents experimental, geochemical modeling, and field data focusing on the partitioning of osmium (Os) between pyrite and fluid upon precipitation at conditions representative of mid-ocean ridge hydrothermal environments. Dissolved Os partitions strongly into pyrite upon precipitation at experimental conditions, 350 °C and 50 MPa, with a representative relative Os/Fe partition coefficient, D Pyrite - F l u i d Os / F e , between 10 and 15. Integrating the experimentally determined D Pyrite - F l u i d Os / F e into a geochemical model indicates that a significant amount of Os is retained within the subseafloor due to sulfide precipitation induced by mixing of conductively heated seawater with pristine high temperature hydrothermal fluids that are enriched in dissolved metals, such as Os and Fe. Comparison with existing Os concentration and isotopic data of hydrothermal fluids and sulfide minerals from a wide range of hydrothermal systems with the experimental and modeling constraints suggest that modern high temperature hydrothermal systems are a minor source of unradiogenic Os to the modern global ocean dissolved Os budget due to the majority of Os being sequestered into sulfide minerals formed within and on the seafloor.

A hot-pressure technique was used to sinter block-shaped, malleable, and compact arsenopyrite, based on the purified natural material. The results show that 500 °C and 1.0 GPa are the optimum temperature and pressure conditions, while at temperatures below 500 °C the product would become powdery or present visible cracks. Electron probe analysis (EPMA), X-ray diffraction (XRD), and Raman tests confirmed the purity of the samples with a molecular formula of Fe1.00As1.02S1.03. The calculated density was 6.2185 ± 0.0132 g/cm3, close to the unit cell density of 6.2389 g/cm3. The sample can easily be machined in a circular truncated cone shape, and used as an autoclave stopper at 440 °C and above 40 MPa for 35 h. Sintering results provide a possibility for further research on the electrochemical corrosion of sulfide minerals at high temperature and pressure. The hot-pressure procedure developed here provides a reference and inspiration for sintering other similar samples in this field.

Coal mine spoil is a long-lasting legacy of historic coal mining operations that continues to impact water quality across Appalachia. Metal(loid) release from abandoned coal mine spoil, which can be a significant source of acid mine drainage (AMD), is dependent on speciation and distribution within the parent coal shale. This work aimed to determine how the micron- and sub-micron scale mineralogy, morphology, and texture of metal(loid)-bearing phases in a coal-shale control the rate and release of metal(loid)s during subsequent weathering through two primary objectives: (1) determine the microscale speciation and distribution of Fe and other metal(loid)s in a parent coal shale, and (2) determine the amount of metal(loid)s released during simulated weathering of shale physically crushed into silt- to sand-sized particles. This work was accomplished through a combination of electron microscopy and synchrotron-based X-ray microprobe analyses. This suite of techniques also provides insight into the geochemical history of the coal shale that could not be determined by bulk techniques. Trace elements were associated with either Fe-sulfides or with other phases that included metal(loid)-sulfides, aluminosilicates, and organic matter. Three distinct pools of Fe-sulfides were present: (i) larger mm-scale grains, with minimal internal fractures; (ii) μm- to mm-scale aggregates of μm-scale crystals forming secondary coatings on the larger mm-scale grains, and (iii) μm- to mm-scale aggregates forming framboidal grains. Fe-sulfide mineralogy was dominated by pyrite with minor contributions of marcasite and a S(-II)-bearing phase. Larger pyrite grains and their secondary coatings contained homogeneous distributions of Fe and Mn as well as other trace metal(loids) including V, Ti, Cr, As, Se, Cu, and Zn. The fine-grained pyrite aggregates were strongly enriched in As and Se and contained discrete Cu- and Zn-bearing particles. Clays and organic matter surrounding the sulfide minerals were identified by micro-XRD and FT-IR spectroscopy. Simulated batch weathering of the physically crushed shale resulted in metal(loid) release that varied as function of size fraction and time. Metal(loid) release increased with decreasing particle size from sand-sized to silt-sized fractions. Although small amounts of Fe were released into solution after two days, the bulk of Fe release occurred after 10 days and continued for six months, after which Fe was gradually removed from solution. The weathering trends for Mn, Cu, Zn, and Ni were similar to Fe. In contrast, As and Se were characterized by rapid release into solution followed by removal prior to 10 days. These results indicate that micrometer-scale metal(loid) distribution within Fe sulfides controlled metal(loid) release into solution during simulated weathering of a coal shale. Specifically, elements concentrated in mineral coatings (As, Se) were rapidly mobilized in a short-lived pulse whereas elements associated with the larger grains (Fe, Mn, Cu, Zn, and Ni) exhibited a delayed but prolonged release into solution. The non-concomitant contaminant release indicates that an understanding of the textural relationships in the source material is required to understand weathering trends. This work highlights the importance of non-point sources of AMD, and addressing these sources is a critical step in improving water quality in the region.

Sulfide minerals occur in many types of extraterrestrial samples and are sensitive indicators of the conditions under which they formed or were subsequently altered. Here we report that chemical and petrographic analyses of Fe,Ni sulfides can be used to determine the metamorphic type of the host LL chondrite, and constrain their alteration conditions. Our data show that the major- and minor-element compositions of the pyrrhotite-group sulfides (dominantly troilite) and pentlandite vary with degree of thermal metamorphism experienced by their host chondrite. We find that Fe,Ni sulfides in LL3 chondrites formed during chondrule cooling prior to accretion, whereas those in LL4 to LL6 chondrites formed during cooling after thermal metamorphism in the parent body, in agreement with previous work. High degrees of shock (i.e., ≥S5) caused distinct textural, structural, and compositional changes that can be used to identify highly shocked samples. Distinct pyrrhotite-pentlandite textures and minerals present in Appley Bridge (LL6) suggest that they cooled more slowly and therefore occurred at greater depth(s) in the host parent body than those of the other metamorphosed LL chondrites studied here. Sulfides in all LL chondrites studied formed under similar sulfur fugacities, and the metamorphosed LL chondrites formed under similar oxygen fugacities. The data reported here can be applied to the study of other LL chondrites and to sulfides in samples of asteroid Itokawa returned by the Hayabusa mission in order to learn more about the formation and alteration history of the LL chondrite parent body.

Coal gangue accounts for a large proportion of the solid waste in China, and greater attention has been focused on the concentrations of potentially hazardous trace elements (PHEs) than on the potentially useful trace elements (PUEs), such as selenium (Se). Chinese coal gangue is enriched in Se, and the arithmetic mean value is 2.87 mg/kg (0.06–17 mg/kg), which is 97 times higher than the average Se concentration in the upper continental crust. For coal gangue deposited during different periods, the arithmetic mean Se values are 4.25 mg/kg (C1) > 4.15 mg/kg (C2-P1) > 3.95 mg/kg (P2) > 2.65 mg/kg (T3) > 1.73 mg/kg (J1-J2) > 1.47 mg/kg (J3-K1) > 0.66 mg/kg (E–N). The Se content in lignite coal gangue is 0.88 mg/kg (0.06–4.90 mg/kg), which is 0.26 and 0.21 times lower than that in bituminite and anthracite gangue. Pearson correlation results indicate that carbonates and aluminosilicates are the dominant carriers of selenium in J3-K1 and J1-J2 coal gangue, respectively. Selenium in late Carboniferous and early Permian coal gangue probably are likely primarily associated with sulfide minerals. In addition, crushed Se-enriched coal gangue powder is considered to be a potential resource for Se-enriched fertilizer, although As (avg = 90 mg/kg) and Cr (1.07 mg/kg) are enriched in early Carboniferous and late Triassic coal gangue. The findings suggest that a comprehensive system for managing resources (e.g., coal gangue) should be developed to improve the recovery and utilization of these resources and promote a more eco-friendly society and resource conservation in China.

Due to land uplift after the last ice age, previously stable Baltic Sea sulfidic sediments are becoming dry land. When these sediments are drained, the sulfide minerals are exposed to air and can release large amounts of metals and acid into the environment. This can cause severe ecological damage such as fish kills in rivers feeding the northern Baltic Sea. In this study, five sites were investigated for the occurrence of acid sulfate soils and their geochemistry and microbiology was identified. The pH and soil chemistry identified three of the areas as having classical acid sulfate soil characteristics and culture independent identification of 16S rRNA genes identified populations related to acidophilic bacteria capable of catalyzing sulfidic mineral dissolution, including species likely adapted to low temperature. These results were compared to an acid sulfate soil area that had been flooded for ten years and showed that the previously oxidized sulfidic materials had an increased pH compared to the unremediated oxidized layers. In addition, the microbiology of the flooded soil had changed such that alkalinity producing ferric and sulfate reducing reactions had likely occurred. This suggested that flooding of acid sulfate soils mitigates their environmental impact.

Sulfide-rich tailings produced by mineral processing are prone to oxidation and cause many pollution problems in the surrounding environment; therefore, this issue has become a focus of attention. The Tongling Shuimuchong tailings reservoir contains a large amount of sulfide minerals, especially pyrrhotite and pyrite. This reservoir features obvious oxidation in the surface layer, and the slab is very hard. Mineralogical and environmental geochemical analyses were performed on tailings with different degrees of oxidation in the Shuimuchong tailings reservoir to investigate the influence of the formation of the hard oxidized layer on environmental pollution in the tailings pond. The samples were first subjected to particle-size analysis. The shallow tailings were mainly composed of medium particle; the proportions of coarse particle and fine tailings particles were equal; and the proportions of clay and silt were less than those of the other size fractions. Mineralogical analysis showed that pyrrhotite and pyrite were replaced by residual structures in the oxide layer. The secondary minerals goethite, hematite and jarosite were attached to the edges and fractures of sulfide minerals. The samples were geochemically analyzed to determine the total concentrations of 5 elements, the pH and the major anions. The maximum SO42− concentrations of 33,970 and 32,749 mg/kg were observed at a depth of 40 cm in profiles 1 and 2, respectively. Metal sulfide mineral oxidation in the tailings lowered the pH of the materials to values less than 4. The concentration of HCO3− (122–635 mg/kg) in the tailings samples was very low, and the concentration of CO32− was zero. As (53.2–133.7 mg/kg), Pb (24.2–307.5 mg/kg) and Hg (0.03–0.06 mg/kg) were concentrated in the highly oxidized layer at the surface; the Cd content (0.23–10.5 mg/kg) increased with decreasing oxidation degree of the tailings; and the Cr content (38.0–54.9 mg/kg) fluctuated around a certain value.

The pretreatment of middlings and coarse refuse material collected from a Pocahontas No.3 coal source using calcination was investigated for the potential of improving the leaching recovery of rare earth elements. Calcination at 600 °C significantly and preferentially improved light REE (LREE) recovery to values in the range of 80–90% using 1.2 M HCl. The positive effect was due to the increased pore diameter and volume as well as thermal decomposition of the minerals associated with the LREEs. Heavy REE recovery was not increased after calcination at 600 °C due to the need for higher temperatures to achieve thermal decomposition of HREE minerals. Furthermore, some HREEs were also associated with sulfide minerals (e.g., pyrite) which were transformed into low-solubility oxides (e.g., hematite) after roasting at 600 °C. Based on the leaching characteristics of the major elements (Fe, Al, Ca and Mg) and REEs along with SEM-EDX data, it was concluded that REEs in the two samples mainly occurred as phosphate minerals. In the middlings, some of the minerals were completely encapsulated by kaolinite, which was less apparent in the coarse refuse. In addition, it was found that a portion of the REEs (10–25%) in the samples were associated with the organic matter and micro-dispersed minerals in the organic matrix, was released after calcination and easily recovered using 0.1 M (NH4)2SO4 solution at pH 5. Scandium primarily occurred in mineral forms with minimum amounts associated with ion-adsorbed clays and organic association.

Bioleaching of sulfidic copper-zinc concentrates with different copper and zinc contents using two consortia of acidophilic microorganisms that grew at 30 and 35 °C was investigated. The average leaching rate of copper is directly proportional to its content in the concentrates and is significantly lower than zinc. Hereby with the ratio of copper and zinc, equal to 7.3, the leaching rates of copper and zinc were 53.8 and 80.3 mg L−1 day−1 in experiment at 30 °C, and 57.1 and 84.2 mg L−1 day−1 respectively in experiment at 35 °C. With the ratio of 1.4, the leaching rates of copper and zinc were 23.1 and 159 mg L−1 day−1 for consortium grew at 30 °C and 25.8 and 168 mg L−1 day−1 for consortium grew at 35 °C, respectively. The specific rates of copper leaching was in the range 22.9–28.1 mg g−1 day−1 at 30 °C and 25.5–31.5 at 35 °C. The specific extraction rate of zinc increased from 216 to 304 mg g−1 day−1 and from 229 to 319 mg g−1 day−1 in the experiments at 30 and 35 °C, respectively, with an increase in the copper-to-zinc ratio for the concentrate from 1.4 to 7.3. Thus, the more copper in the concentrate, the higher the specific rates of zinc leaching, which indicates the galvanic interactions between sulfide minerals. The content of copper in the residues was increased by 3–5% while zinc content decreased from 7.36 and 2.64 to 0.993 and 0.0034%, respectively. The obtained data indicate a high selectivity of zinc bioleaching from copper-zinc concentrates in comparison with copper. The development of research in this direction will improve the efficiency of copper-zinc concentrates processing using bioleaching.

Desulfurization is a novel approach for the reclamation of abandoned mine sites that can have environmental and economic benefits, particularly when combined with the recovery of valuable elements. Desulfurization by flotation produces sulfide-lean tailings, which can be used as cover materials, and sulfide-rich concentrates, which may contain valuable sulfide-associated metals such as gold. Because unreclaimed, aged tailings are often at advanced stages of the weathering process the surfaces of sulfide minerals are usually encapsulated by oxidation products. This surface oxidation reduces sulfide hydrophobicity and, thus, flotation efficiency. Therefore, the main goal of this study was to evaluate how effectively various mechanical pretreatment processes enhance the flotation process for aged tailings. After initial characterization of an aged tailings sample, various parameters were adjusted to optimize the desulfurization process. Subsequently, several mechanical pretreatments (i.e., agitation, attrition, regrinding) were tested. Results show the possibility to produce a concentrate rich in sulfides and gold.

Our study of the primary and supergene gold from the Suzdal and Raigorodok deposits in Kazakhstan confirms that during the formation of the regolith in both deposits, invisible and fine gold is released from the host sulfide minerals during their oxidation and destruction; and transported in the form of soluble thiosulfate complexes by near-surface solutions. Upon contact with a geochemical barrier, gold can be deposited as crystalline aggregates. In the deposition of this gold the role of geochemical barriers, such as variations of redox, pH and sorption are very important. Evidence of the past processes of dissolution, redistribution and aggregation of gold in the regolith in these deposits is provided by the following features: 1) The presence of dissolution and growth structures on the surface of newly formed gold; 2) The size of the gold grains increases and newly formed gold microcrystals appear on the surface of the grains; 3) Changes in the composition of native gold (e.g. decrease of silver content); 4) The accumulation of gold in subhorizontal localized layers within the regolith; 5) Gold association with supergene minerals (limonite, jarosite, goethite, Mn-hydroxides, opal, gypsum, calcite, clay minerals, etc.). This detailed study of the specific compositional and structural features of supergene gold and the physicochemical conditions of regolith environment allowed the recognition of the releasing, dissolution, transfer and aggregation processes of gold in the regolith.

The leaching from mine tailings results in contamination of nearby groundwaters and rivers by hazardous metals like copper (Cu), zinc (Zn), and iron (Fe). In this study, unweathered tailings samples at depths of 1 to 3 m were collected from a tailings dam of an abandoned mine located in the north of Hokkaido, Japan. The mechanisms of long-term tailings weathering were assessed through leaching of hazardous metals by three column experiments. Measurements of mineralogical and chemical constituents, observation by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), sequential extraction of the tailings, and chemical analyses of the leachates were carried out to determine the processes responsible for the leaching of Cu, Zn, Fe, and sulfate ion (SO42−). The contents of Cu, Zn, and Fe in the tailings were mainly associated with ion exchangeable and sulfide fractions. The pH values of the effluents from the columns were 3.0–3.7 throughout the experiments over 84 weeks, and approximately 15–23% of Cu, 35–45% of Zn, 2.5–4% of Fe and 15–20% of S were leached. Higher concentrations of Cu, Zn, Fe, and SO42− at the beginning of the experiments were observed, which could be attributed to the dissolution of soluble sulfate minerals present in the tailings. This indicates that the formation and dissolution of secondary soluble sulfate minerals contributed to Cu and Zn leaching. The continuous leaching of Cu, Zn, Fe, and SO42− suggests the oxidation of pyrite and other sulfide minerals. During these processes, ferrihydrite, goethite, lepidocrocite, and maghemite were formed and these minerals also acted as a sink for Cu and Zn by adsorption, and/or co-precipitation. These results mean the significance of the long-term behavior of hazardous metals released from mine tailings dams, which could provide helpful information on the management of tailings dams after mine closure.

In the Zajkan Pb–Zn–Cu (Au–Ag) deposit of the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran, mineralization occurs as quartz-base metal sulfide veins hosted by Eocene volcanic and volcaniclastic rocks of the Karaj Formation. Four stages of ore formation are identified at Zajkan: (1) quartz-chalcopyrite-pyrite veins, (2) quartz-galena-sphalerite ± chalcopyrite ± pyrite veins and breccias, (3) quartz-hematite veins and breccias, and (4) barren quartz-carbonate veinlets. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, galena, and trace amounts of hematite; gangue minerals are mainly quartz, sericite, chlorite, and calcite. The main wall-rock alteration is silicification, and intermediate argillic, and propylitic alteration. The coexistence of different types of fluid inclusions (LV, VL, and V) in individual fluid inclusion assemblages in quartz and sphalerite suggests boiling and heterogeneous trapping. Excluding the heterogeneously entrapped fluid inclusions, the microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were formed at temperatures between 217 and 273 °C from fluids with salinities between 1.7 and 6.4 wt% NaCl equiv. The oxygen isotopic compositions (δ18Owater-VSMOW of +3.7 to +1.1‰) indicate that the ore-forming fluids were mainly derived from magmatic water with the input of meteoric water in the later ore-stages. Sulfur isotopic values of sulfide minerals vary over a narrow range from −5.0 to −0.9‰VCDT (averaging −2.2‰VCDT), suggesting that sulfur was derived from a homogeneous magmatic source. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Zajkan. Our data suggest that the Zajkan deposit is an intermediate-sulfidation style epithermal mineralization. The estimated ore formation depth of Zajkan indicates minor denudation in the region and may imply a great prospecting potential for other epithermal mineralization in the THMB.

Thallium (Tl) is a well-recognized hazardous heavy metal with very high toxicity. It is usually concentrated in sulfide minerals, such as pyrite (FeS2), sphalerite (ZnS), chalcopyrite (CuS) and galena (PbS). Here, this study was carried out to investigate the indigenous microbial communities via 16S rRNA gene sequence analysis in typical surface sediments with various levels of Tl pollution (1.8–16.1 mg/kg) due to acid mine drainage from an active Tl-containing pyrite mining site in South China. It was found with more than 50 phyla from the domain Bacteria and 1 phyla from the domain Archaea. Sequences assigned to the genera Ferroplasma, Leptospirillum, Ferrovum, Metallibacterium, Acidithiobacillus, and Sulfuriferula manifested high relative abundances in all sequencing libraries from the relatively high Tl contamination. Canonical correspondence analysis further uncovered that the overall microbial community in this area was dominantly structured by the geochemical fractionation of Tl and geochemical parameters such as pH and Eh. Spearman's rank correlation analysis indicated a strong positive correlation between acidophilic Fe-metabolizing species and Tltotal, Tloxi, and Tlres. The findings clarify potential roles of such phylotypes in the biogeochemical cycling of Tl, which may facilitate the development of in-situ bioremediation technology for Tl-contaminated sediments.

Hexavalent chromium (Cr(VI)) is an environmental concern due to the carcinogenic and mutagenic effect on living organisms. Sulfide minerals based Cr(VI) reduction is an economical and efficient strategy for Cr(VI) remediation. In this study, Cr(VI) reduction through the synergistic effect between chemoautotrophic bacteria and sulfide mineral is systematically investigated. Sulfide minerals dissolution and Cr(VI) reduction performance highly depends on mineral acid soluble property. Cr(VI) reduction capacity of pyrrhotite, pyrite, marcasite and sphalerite was 50, 104, 104 and 44 mg/g (Cr(VI)/mineral) respectively in the biotic system. Acidithiobacillus ferrooxidans (A. ferrooxidans) significantly enhanced pyrite and marcasite based Cr(VI) reduction kinetic and capacity. Proton consumption, iron coprecipitation and the biological activity deficiency in the abiotic system significantly inhibited Cr(VI) reduction. Elemental sulfur and secondary iron mineral as the main composition of the passivation layer inhibited sustainable Cr(VI) reduction. A. ferrooxidans facilitated acid nonsoluble mineral dissolution and surface passivation layer removal, and promoted Cr(VI) reduction. Acid nonsoluble sulfide mineral disulfide bond rapture, S°/Sn2− oxidization, and Fe(III)/Cr(III) dissolution were accelerated by A. ferrooxidans, which facilitated Cr(VI) reduction reactive sites regeneration. Our study demonstrated that chemoautotrophic bacterial accelerated Cr(VI) reduction reaction through promoting acid nonsoluble sulfide mineral dissolution. This research is of environmental and practical significance to remediate redox sensitive contaminant based on the synergistic effect between sulfide minerals and chemoautotrophic A. ferrooxidans.

The Dry Creek Zn-Pb-Cu-Ag-Au volcanogenic massive sulfide (VMS) deposit, in east-central Alaska, occurs in a Late Devonian sequence of peralkaline rhyolite tuff, minor graphitic argillite, and local peralkaline quartz-porphyry rhyolite intrusions. Principal mineralized facies are semi-massive and massive sulfide in variably silicified and graphitic rhyolite tuff, massive sulfide in graphitic argillite, disseminated sulfides in graphitic and non-graphitic rhyolite tuff, and vein-hosted sulfides in a subvolcanic, peralkaline quartz-porphyry intrusion. In situ analysis of the sulfur isotope composition of sulfide minerals from all facies of the deposit shows a total range in δ34S values from −48.0 to 23.1‰. This remarkable 71.1‰ variation is more than twice the largest range known for sulfides in nearly all individual VMS deposits, both modern and ancient, which typically is High-precision CA-ID-TIMS U-Pb geochronology of zircons from a synvolcanic peralkaline quartz porphyry intrusion yields a weighted mean 206Pb/238U date of 363.02 ± 0.43 Ma (2σ total uncertainty). This date indicates that the formation of graphitic and sulfidic sediments at Dry Creek, and contemporaneous VMS mineralization, occurred at least 3.6 m.y. before, and hence are unrelated to, widespread black shale deposition during the Hangenberg Event at ca. 359 Ma.

The Qin–Hang ore belt in South China, which serves as the boundary between the Yangtze and Cathaysia blocks, is marked by extensive Jurassic porphyry-skarn-metasomatic Cu–Pb–Zn polymetallic mineralization. In this contribution, S and Pb isotopic compositions of the Baoshan Cu–Pb–Zn deposit in the western portion of the Qin–Hang ore belt were analyzed to determine the ore-forming material sources in the area. This is coupled by the first systematic collection, compilation and interpretation of previously published S and Pb isotopic data of multiple sulfide minerals to reveal the metal origin and accumulation mechanism of the Cu–Pb–Zn mineralization from the significant deposits in the region (i.e., Dexing, Qibaoshan, Shuikoushan, Baoshan, Huangshaping, Tongshanling and Dabaoshan). The results show that Cu mineralization is characterized by low and narrow δ34S (‰) range of values (–5 to 6) and Pb isotopic ratios (208Pb/204Pb = 38.0–39.0, 207Pb/204Pb = 15.4–15.8, and 206Pb/204Pb = 17.7–18.7), which are consistent with those of local porphyries. In contrast, the Pb–Zn mineralization reveals higher and more variable δ34S (‰) values (–4 to 18) and Pb isotopic ratios (208Pb/204Pb = 38.0–39.5, 207Pb/204Pb = 15.3–16.0, and 206Pb/204Pb = 18.0–19.0) that correspond to wall-rock and basement rock compositions in the region. This indicates that the sulfur and lead that formed the Cu mineralization in the Qin–Hang ore belt was mainly sourced from regional magmatism with mantle contributions, whereas the sulfur and lead for the Pb–Zn mineralization was likely derived from the host sedimentary rocks and Proterozoic metamorphic basement rocks, respectively. The S and Pb isotopic data, combined with the geochemical signatures of mineralization-related porphyries, suggest that the Cu was sourced from the deeper levels along with mantle-derived magmas. In contrast, the Pb–Zn probably originated from the crust, with partial melting of the crystalline basement in the Cathaysia Block. Consequently, a three-stage genetic model is proposed to explain the ore-forming processes of the Qin–Hang Cu-polymetallic belt in South China.

The leaching of copper-zinc concentrates with different sulfide mineral content by biogenic ferric iron has been studied. It was determined that chalcopyrite, sphalerite, pyrrhotite, and pyrite were in the range of 29–55, 11–3.9, 34–14, and 12–13%, respectively. The rate of copper leaching was shown to decrease from 5.1 to 2.6 g/L/h, while its content in the concentrate decreased from 19.2 to 10.1%. The rate of zinc leaching increased from 2.9 to 5.3 g/L/h, while its content in these concentrates increased from 2.64 to 7.36%. The results indicate that the specific rates of copper leaching remained unchanged in all the concentrates studied and were within 0.20 and 0.27 g/g/h. We suggest that this was primarily associated with the dependence of this parameter on the rest potential of chalcopyrite. The specific rate of zinc leaching varied from 0.73 to 1.14 g/g/h and depended significantly on the ratio of contents of sulfide minerals in the concentrates. This rate was also found to increase with an increase in the chalcopyrite content in the concentrate, which indicated the presence of galvanic interactions between the minerals. At the same time, sphalerite and pyrrhotite, which are the minerals with a low rest potential, acted as dissolving anodes, while chalcopyrite and pyrite, having high rest potentials, were cathodes. The possibility of predicting the efficiency of zinc and iron removal during ferric leaching of the copper-zinc concentrates was shown in the context of sulfide mineral content.

Trace elements in coal mine water have pollution potential to environmental water bodies. By process of water-rock interaction in coal seam and coal host rock, trace elements may immigrate from solid matrix to water, including oxidation, dissolution, ion-exchange, adsorption-desorption, etc. Water parameters and occurrence of trace elements in the solid matrix are keys to leaching behavior. In site observation and leaching experiments were designed and implemented so as to model these processes, analyze leaching behavior and mechanisms. The data composes a matrix by two dimensions, samples and trace elements, which were used to analyze trace element occurrence in coal, host rock and leaching behavior in the coal/rock leaching water, by method of multivariate analysis. Analytical results showed major occurrence of trace elements in the coal and host rock and key controlling mechanism of trace elements during water-rock interaction: in coal host rock seam, Se/Cd/Hg/As occurred in sulfide minerals, Be and V occurred in carbonate minerals, Cr and Pb occurred in clay minerals, respectively. Se, As and Hg immigrated through dissolution of sulfide minerals, Cr immigrated through transformation of clay minerals. In coal seam, Se/Cr/Pb occurred in clay minerals, As and Hg occurred in sulfide minerals. Se, Pb and Cr immigrated through transformation of clay minerals, As and Hg immigrated through dissolution of sulfide minerals, respectively.

The volcanogenic massive sulfide (VMS) deposits in the Troodos ophiolite (Cyprus) are ancient analogues for modern day seafloor massive sulfide mineralisation formed in a supra-subduction zone environment. In this study we present the first detailed in situ study of trace elements in sulfides from twenty VMS deposits hosted in the Troodos ophiolite to better understand factors that influence the distribution, enrichment and incorporation of trace elements in different sulfide minerals.\ud \ud On a mineral scale, trace elements exhibit systematic variations between pyrite, chalcopyrite and sphalerite. Pyrite preferentially incorporates As, Sb, Au and Te, whilst chalcopyrite is enriched in Co and Se. Sphalerite is trace element poor with the exception of Ag and Cd. Selenium averages 278 ppm (n = 150) in chalcopyrite but only 42 ppm (n = 1322) in pyrite. Bismuth and Te in pyrite show a weak positive correlation (R2 = 0.35) in some VMS deposits possibly linked with the occurrence of Bi-telluride inclusions. Trace element concentrations also vary between colloform and euhedral pyrite, with an enrichment of Au, As, Sb, Cu and Zn in colloform compared to euhedral pyrite.\ud \ud Time resolved laser ablation profiles reveal that the trace element distribution on a mineral scale is not uniform and varies with crystallographic effects, fluctuating physicochemical fluid conditions such as temperature, pH, fS2, fO2 and ligand availability during sulfide precipitation. Incorporation mechanisms in sulfides differ between elements in pyrite, Ag, As, Se and Pb are hosted in solid solution or as nanoscale inclusions, whilst Au, Sb and Te may form micro-scale inclusions.\ud \ud On a regional scale (20 km) the distribution of trace elements exhibits systematic variations between three major structural domains; namely the Solea, Mitsero and Larnaca grabens. The VMS deposits of the magmatic-tectonic Solea graben are enriched in Se, Co, Te, Au and Cu relative to Mitsero, which is a purely extensional feature. Therefore, we hypothesise that a variable magmatic volatile influx related to a) ‘magma’ volume, b) migration of the magmatic-hydrothermal crack front and associated brine liberation or c) a variation in protolith metal concentration are responsible for regional scale variations in VMS geochemistry. This is suggested to be intrinsically linked to the spreading architecture of Troodos.

Long-term influence of geogenic CO2 affects soil conditions and pedogenesis. Mobilization of metals and metalloids from soil to solution has been reported to occur in natural CO2 degassing sites, so-called mofettes. We determined metal(loid)-specific spatial distribution patterns in soil around a mofette as well as metal(loid) pore water concentrations along a CO2 gradient (0–98% CO2 in soil air). Depletion of Mn, Co, and Ni in soil in the mofette center was caused by leaching due to the long-term soil acidification leading to correspondingly low pore water concentrations and thus indicating no recent influence of CO2 on metal(loid) mobility. Iron and As were also depleted in soil within the mofette center where pedogenic Fe (oxyhydr)oxides could not form due to absence of oxygen. Small-scale variations in redox conditions lead to ongoing Fe cycling and the repeated reduction of Fe (oxyhydr)oxides resulted in increased Fe and As pore water concentrations at high CO2. Precipitation in form of sulfide minerals caused immobilization and accumulation of Cd, Cu, and Zn directly in the degassing center. The highest mobilization risk occurred within 2–4 m distance from the degassing center, where complexation with dissolved organic matter (DOM) increased the mobility of Al, As, Cr, Cu, Fe, and Zn. Our results show that CO2 as soil-forming factor influences the spatial distribution of metal(loid)s. The highest metal(loid) mobilization risk after long-term CO2 influence arises from accumulation of scarcely degraded organic matter, which can easily dissolve and form mobile metal(loid)-DOM complexes.

With the production of a large amount of metal tailings, backfill is one of the best models for waste management and has been widely used in many mines. Metal deposit, especially lead-zinc mines, usually contain sulfide minerals, mainly pyrite. Sulfide attack would cause the strength degradation of cemented materials and decrease the structural stability. This study aimed to understand the effect of sulfide on the long-term strength of lead-zinc tailings cemented paste backfill (CPB). CPB specimens with four sulfur contents (2 wt%, 5 wt%, 10 wt%, 15 wt%) were prepared to investigate their physicochemical characteristics in 28–360 days. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) analyses of the CPB specimens were also conducted to obtain valuable information. The results showed that the highest strength of CPB was achieved at curing 90 days. Sulfide showed early strength agent property and the early strength of CPB with sulfur content of 5 wt% was improved. The internal system of CPB was alkaline, and sulfate mainly involved in cement hydration reaction. SEM observed that CPB specimens had compact structures, and calcium silicate hydrate (C-S-H) was produced. After 90 days, under the influence of sulfide, the strength of all the CPB specimens decreased, and the strength of CPB specimen with the highest sulfur content decreased the most. The pH value of the solution continuously decreased and eventually became acidic. A large amount of sulfate accumulated. The hydrated calcium silicate decomposed in the acidic environment. The number of expansive ettringite and gypsum products increased, and the number of large pores increased. Sulfide reactivity includes sulfate and acid attack. Large internal defects lead the strength and stability deterioration. This study compared the differences between sulfide erosion and sulfate attack, then provided some advice for the disposal of high sulfide tailings.

The Moeda Formation is the basal unit of the Minas Supergroup in the Quadrilatero Ferrifero, Brazil, and has quartz-pebble metaconglomerate that hosts Au–U mineralization, commonly assumed to be detrital in origin. The Au–U mineralization occurs immediately above an unconformity with the underlying Archean Rio das Velhas greenstone sequence. In this work, we focus on the Moeda metaconglomerate in its U-bearing portions in the Gandarela syncline: the southern sector, near the syncline axis; and the western limb, near the Palmital gold deposit. The metaconglomerate has mica seams that host zircon, xenotime, rutile, nodules of organic matter and sulfide minerals. The sulfide assemblage includes four generations of pyrite along with Fe–Ni–Cu–Co–Zn–Pb–Mo sulfides. A Sb–As sulfosalt assemblage of gersdorffite, stibnite and ullmannite is late in relation to pyrite and other sulfides. Gold is argentiferous with minor Hg. Uranium minerals include uraninite, coffinite, brannerite and uranyl arsenates. An early generation of uraninite and brannerite occurs as inclusions in organic-matter nodules, mainly in the southern sector. A late generation of uraninite formed due to a low-temperature hydrothermal overprint. Coffinite and late-stage brannerite are products of hydrothermal alteration of zircon and rutile, respectively. Uranyl arsenates have Ni as the prevalent cation; they formed as replacement of arsenic minerals, such as gersdorffite, by oxidized fluids containing U. Microstructural data and mineral chemistry favor a hydrothermal hypothesis analogous to an unconformity-related setting, rather than a detrital, placer-deposit model for the occurrence of U in the Moeda metaconglomerate.

In our study we explore the applicability of rutile as a pathfinder for orogenic gold deposits, which are an important source of this metal worldwide. We analysed rutile associated with orogenic Au deposits from three different Precambrian terranes, the Capricorn Orogen, the Barberton Greenstone Belt and the Ashanti Belt, all of which formed under greenschist conditions and share similarities in the style of mineralisation. Microtextural evidence from scanning electron microscopy and electron back-scatter diffraction indicates that rutile formed during the main deformation and alteration stage in these rocks, and is therefore related to mineralisation. We used electron microprobe and laser ablation ICP-MS to investigate the trace element compositions of rutile and we compared our results to other gold deposits. We find that hydrothermal rutile from gold deposits contains certain trace element characteristics, in particular high Sb concentrations (up to ∼1500 ppm in Au deposits of the Capricorn Orogen), that are distinct from rutile from non-mineralised rocks of various petrogenetic origin. Other elements, such as W and Sn, are found to be more enriched in rutile from other rock types, namely felsic magmatic rocks and hydrothermal veins, and are therefore not diagnostic of Au mineralisation in this type of deposits. We also find that the presence of sub-µm-scale inclusions – in particular Zr-(Si, Th)-bearing phases, sulfide minerals and native Au – can severely affect analyses of this type of rutile and compromise the applicability of Zr-in-rutile geothermometry.

The ability of some typical gangue minerals and activated carbon to adsorb gold(I) (preg-robbing) in non-ammoniacal thiosulfate solutions was examined at different calcium thiosulfate concentrations. In the absence of calcium thiosulfate, sulfide minerals such as pyrite and chalcopyrite, and carbon were highly preg-robbing with 100% gold being adsorbed within half an hour. The oxide minerals examined including kaolinite, goethite and hematite were significantly less preg-robbing under the same conditions. The presence of free thiosulfate can significantly reduce or eliminate the preg-robbing of gold on mineral surfaces. With an initial thiosulfate concentration of 0.1 M, gold adsorption by oxide minerals was completely eliminated, while that of sulfide minerals and carbon was insignificant at 0.2 M free thiosulfate. Copper(I) was found to enhance the preg-robbing of gold by oxide minerals but to reduce the preg-robbing of gold by sulfide minerals and by carbon. Similar effect of silver(I) was observed except for chalcopyrite. Trithionate, a by-product of thiosulfate degradation, has no significant effect on the preg-robbing of gold(I). Tetrathionate, another by-product of thiosulfate degradation, significantly increases the preg-robbing of gold(I) onto pyrite. Activated carbon enhances the degradation of tetrathionate to trithionate and thiosulfate, the latter helps stabilise the gold(I) in solution.

The Eagle Ni-Cu magmatic sulfide deposit in the Upper Peninsula of Michigan is hosted in mafic-ultramafic rocks associated with the 1.1 Ga Midcontinent Rift event. The deposit consists of massive, semi-massive and disseminated sulfide textural zones located in two closely spaced funnel-shaped intrusive bodies, called the Eagle and Eagle East intrusions. The intrusions are surrounded by metamorphosed supracrustal Paleoproterozoic rocks of the Michigamme Formation and at depth by a Neoarchean migmatitic banded gneiss. δ34S values were obtained from sulfide minerals separated by micro-drilling from different parts of the intrusions and the surrounding rocks. The δ34S values from the intrusions cluster within a small range between 1 and 3‰ relative to V-CDT regardless of the mode of occurrence, textural type, mineral type and location of the sample. However, disseminated sulfide minerals in the metasedimentary country rocks of the Michigamme Formation show a substantially greater range in δ34S values between 4 and 35‰ with a median of 7.7‰ while disseminated sulfides in the basement granite-gneiss show values ranging from −9 to 13‰ with a median of 2.5‰. The narrow range of δ34S values within the intrusions despite wide variabilities in the surrounding country rocks can be explained by the incorporation of crustal sulfur by a mantle-derived magma, followed by a homogeneous mixing of the immiscible sulfide liquid, with a silicate liquid to sulfide liquid ratio (R-factor) of 200 or more. The assimilation of crustal rocks and the mixing of the resultant immiscible sulfide liquid must have been facilitated by the rapid movement of magma along a narrow conduit system.

This work proposes a method for the evaluation of the effect of galvanic interactions between intergrown sulfide-mineral grains present in a thiosulfate leaching system, based on a combination of electrochemical measurements. Several common associated minerals in complex sulfide ore (CSO), as well as high purity sulfide minerals (pyrite, arsenopyrite, chalcopyrite, sphalerite, and galena), were used to develop and test the method. The reactivity of the CSO and each individual sulfide mineral in an ammoniacal thiosulfate solution was determined by voltammetry and chronoamperometry, using carbon paste electrodes and rotating disk electrodes (RDE). Secondary phase formation and the surface alteration of both the individual and associated minerals were evaluated by in-situ Raman spectroscopy and ex-situ cyclic voltammetry in 0.1 M NaNO3 aqueous solution. Chalcocite (Cu2S) and covellite (CuS) were identified as intermediate products of chalcopyrite leaching, while pyrite was oxidized to ferrous hydroxide and later to magnetite. Results showed that pyrite in CSO acts as a cathodic side, promoting the reduction of oxygen. Thus, the oxidation of pyrite was delayed due to the galvanic protection offered by arsenopyrite and chalcopyrite. Mineralogy and evaluation of the mineral textures both of the ore and its modification as a result of leaching were used to validate the method.

Publisher's version (útgefin grein), The CarbFix method was upscaled at the Hellisheiði geothermal power plant to inject and mineralize the plant’s CO2 and H2S emissions in June 2014. This approach first captures the gases by their dissolution in water, and the resulting gas-charged water is injected into subsurface basalts. The dissolved CO2 and H2S then react with the basaltic rocks liberating divalent cations, Ca2+, Mg2+, and Fe2+, increasing the fluid pH, and precipitating stable carbonate and sulfide minerals. By the end of 2017, 23,200 metric tons of CO2 and 11,800 metric tons of H2S had been injected to a depth of 750 m into fractured, hydrothermally altered basalts at >250 °C. The in situ fluid composition, as well as saturation indices and predominance diagrams of relevant secondary minerals at the injection and monitoring wells, indicate that sulfide precipitation is not limited by the availability of Fe or by the consumption of Fe by other secondary minerals; Ca release from the reservoir rocks to the fluid phase, however, is potentially the limiting factor for calcite precipitation, although dolomite and thus aqueous Mg may also play a role in the mineralization of the injected carbon. During the first phase of the CarbFix2 injection (June 2014 to July 2016) over 50% of injected carbon and 76% of sulfur mineralized within four to nine months, but these percentages increased four months after the amount of injected gas was doubled during the second phase of CarbFix2 (July 2016 – December 2017) at over 60% of carbon and over 85% of sulfur. The doubling of the gas injection rate decreased the pH of the injection water liberating more cations for gas mineralization. Notably, the injectivity of the injection well has remained stable throughout the study period confirming that the host rock permeability has been essentially unaffected by 3.5 years of mineralization reactions. Lastly, although the mineralization reactions are accelerated by the high temperatures (>250 °C), this is the upper temperature limit for carbon storage via the mineral carbonation of basalts as higher temperatures leads to potential decarbonation reactions., This publication has been produced with support from the European Commission through the projects CarbFix (EC Project 283148), CO2-React (EC Project 317235), CarbFix2 (EC Project 764760), S4CE (EC Project 764810) in addition to Reykjavik Energy.

The giant Yulong porphyry Cu (Mo Au) deposit, located in the eastern Tibetan Plateau, is a typical post-subduction porphyry Cu ± Mo ± Au deposit formed in an intracontinental strike-slip fault system, and it is also one of the largest porphyry Cu deposits in China with reserves of 6.5Mt Cu @ 0.62% and 0.41Mt Mo @ 0.042%, respectively. In this study, sulfur and lead isotopic compositions of sulfides and ore-related porphyry samples were determined to constrain the sources of ore-forming materials and ore-forming process. Sulfides (e.g., pyrite, chalcopyrite and molybdenite) from phyllic alteration zone, where the Cu and Mo mineralization mainly occurred, have uniform δ34S values ranging from −0.6 to +2.1‰ (average + 1.1‰), which indicates a magmatic origin of the sulfur. In situ Nano-SIMS sulfur isotope analysis further reveals that pyrites formed in potassic alteration stage have systematically negative δ34S values ranging from −0.2 to −9.7‰ (average − 4.5‰), whereas pyrites formed in phyllic alteration stage have systematically positive δ34S values ranging from +1.1 to +3.2‰ (average + 2.1‰). This regular variation is considered to be resulted from disproportionation of aqueous SO2 and subsequent sulfate reduction, further suggesting a magmatic origin of the sulfur. The sulfides have initial Pb isotopic compositions ((206Pb/204Pb)i = 18.616–18.812, (207Pb/204Pb)i = 15.670–15.740, (208Pb/204Pb)i = 38.956–39.080) deviating from those of the ore-related porphyries ((206Pb/204Pb)i = 18.549–18.718, (207Pb/204Pb)i = 15.647–15.662, (208Pb/204Pb)i = 38.794–39.888), but more close to those of the ore-hosting strata ((206Pb/204Pb)i = 18.423–18.761, (207Pb/204Pb)i = 15.654–15.713, (208Pb/204Pb)i = 38.867–39.062). The shift of Pb isotopic compositions of sulfide minerals toward those of ore-hosting strata indicates that the ore-hosting strata had provided a significant amount of Pb for ore formation, and most probably suggests fluid-rock interaction processes in the hydrothermal system. Our study represents a case study in which ore-hosting strata had provided a significant amount of ore-forming materials for porphyry Cu ± Mo ± Au formation in the post-subduction setting.

The Zhengchong gold deposit is located in the central Jiangnan Orogen Belt, where gold ore occurs mainly as quartz veins, altered slates, and minor breccias hosted by shear zones in the Lengjiaxi Group. Based on its vein crosscutting relationships, mineral assemblages, and paragenetic sequences, mineralization in this deposit is divided into four stages: Stage 1: quartz(Q1)–pyrite stage, Stage 2: quartz(Q2)–pyrite–arsenopyrite stage, Stage 3: quartz(Q3)–pyrite–polymetallic sulfide mineral stage, and Stage 4: quartz(Q4)–carbonate stage. Two types of fluid inclusions have been recognized in the quartz grains: CO2-bearing fluid inclusions (C-type) and aqueous fluid inclusions (W-type). Fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312–406 °C and 4.65–9.21 wt% NaClequiv (Stage 1), 252–324 °C and 2.20–8.10 wt% NaClequiv (Stage 2), 193–296 °C and 2.24–14.04 wt% NaClequiv (Stage 3), and 127–209 °C and 2.57–6.59 wt% NaClequiv (Stage 4). The co-occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during Stages 2 and 3 of mineralization, possibly as a result of episodic pressure decreases linked to fault-valve activity. Laser Raman spectroscopic analysis results reveal that small quantities of CH4 and N2 are present in the Stage 2–3 fluid inclusions. Fluid inclusion data and microthermometric results show that the ore fluids were low-salinity and CO2-rich, yielding both CO2 inclusions (C-type) and aqueous inclusions (W-type). The trapping pressures estimated from the C-type inclusions are 80–180 MPa for Stages 2 and 3, yielding gold mineralization depths of ∼7–8 km. The mineralizing fluids had calculated δ18OH2O values ranging from +3.7‰ to +8.2‰ and δD values from −75.2‰ to −61.8‰, indicating derivation mainly from metamorphic fluids. The sulfide minerals yield δ34S values of −8.9 to −0.1‰ and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 17.83–18.12, 15.67–15.76, and 38.03–38.62, respectively, which differ significantly from the isotopic composition of the granodiorite (δ34S = −2.4‰ to +1.0‰; 206Pb/204Pb = 18.57–19.28; 207Pb/204Pb = 15.69–15.76; 208Pb/204Pb = 38.97–40.34). However, the S–Pb isotopic compositions of the sulfide minerals are similar to those of slates of the Lengjiaxi Group in the study area. The Zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity, low density, and CO2 enrichment with limited admixture of magmatic fluids. Based on similarities to other orogenic gold deposits, we infer that the Zhengchong orebody represents an orogenic gold deposit formed during the Late Ordovician Jiangnan Orogeny caused by collision of the Yangtze and Cathaysia blocks.

Bedrock in arctic and subarctic regions is covered by glacial deposits making the discovery of new mineral deposits difficult. Indicator mineral methods using glacial sediment have thus been developed for mineral exploration in such drift-covered areas. However, sulfide indicator minerals have been under utilized because it was thought that they would not survive glacial transport and post-depositional oxidation during soil formation. In this contribution we show that the 0.25–1 mm non-ferromagnetic heavy mineral concentrates of Quaternary till and esker samples from the Churchill province in northern Quebec, Canada, contain thousands of pyrite and chalcopyrite grains and a few sulfarsenide grains. Accordingly, sulfide minerals do survive glacial and glaciofluvial transport, even in the relatively oxidizing environment of the eskers, and their presence indicates the potential presence of mineralized bedrock up ice. The study area is therefore ideal to test the use of sulfide mineral chemistry for mineral assessment and vectoring. The composition of the pyrite and chalcopyrite grains recovered from the glacial deposits have been determined by LA-ICP-MS and compared with known values for sulfides in magmatic and hydrothermal deposits. Although some elements (e.g. Ag, Cu, Zn, Pb, W, Ba, La, and Yb) are enriched in narrow rims on some sulfide grains, indicating their limited mobility during oxidation, most elements have not been mobilized and reflect initial sulfide compositions in bedrock sources. The binary diagram Co/Sb versus Se/As shows that most of the pyrite grains in surficial sediments are of magmatic origin although some are from hydrothermal sources. The hydrothermal pyrites are enriched in hydrothermal pathfinders (Au, Hg, Ag, Tl, Pb, Zn, Cu, and Mo). The ternary diagram Se-Cd-Ni shows that chalcopyrites from both magmatic and hydrothermal deposits are present in glacial sediments. The high Cd/Zn ratios of the hydrothermal chalcopyrites are indicative of a high crystallization temperature, typical of metamorphosed VMS or SEDEX deposits. Integrated maps combining bedrock geology, glacial transport directions, sample locations, and sulfide grain compositions and populations can be used to delineate target sectors for mineral exploration. Here sulfides have been transported over ~100 km roughly towards north, from sources in the Rachel-Laporte Zone and the Labrador Trough, where metasedimentary/metavolcanic rocks and mafic/ultramafic intrusive rocks are favorable hosts for hydrothermal and magmatic mineralization, respectively.

Shallow-sea hydrothermal systems are ideal for studying the relative contributions to sedimentary sulfur archives from ambient sulfur-utilizing microbes and from fluxes of hydrothermally derived sulfur. Here we present data from a vent field in Palaeochori Bay, Milos, Greece using a suite of biogeochemical analytical tools that captured both spatial and temporal variability in biotic and abiotic sulfur cycling. Samples were collected along a transect from a seagrass meadow to an area of active venting. The abundance and isotopic composition of sulfide captured in situ, together with geochemistry from sedimentary porewaters and the overlying water column and solid phase sulfide minerals , record evidence of ephemeral activity of microbial sulfate reduction as well as sulfide oxidation. The sulfur and oxygen isotope composition of porewater sulfates indicate active sulfate reduction within the transition zone between the vents and seagrass, rapid recycling of biologically produced sulfide within non-vent sediments, and reoxidation of abiotic sulfide within the vent field. A phylogenetic survey of sediments also indicates the pervasive presence of a suite of putative sulfur-metabolizing bacteria, including sulfate reducers and sulfide oxidizers , many of which can utilize intermediate valence sulfur compounds . The isotopic composition of pyrite in these sediments consistently records a microbially influenced signature (δ 34Spy of −4.4 to −10.8‰) relative to the hydrothermal endmember (δ34S ~ + 2.5‰), independent of distance from the vent source. The narrow range of pyrite δ34S across sediments with a highly variable hydrothermal influence suggests that physical mixing (e.g., by storm events) homogenizes the distribution of biogenic and hydrothermal Fe-sulfides throughout the region, overprinting the spatially and temporally variable interplay between biological and hydrothermal sulfur cycling in these environments.

Initial in situ sulfur (S) isotope measurements of the Martian bedrock in Gale Crater have revealed an unexpectedly wide range of δ 34 S values (−47 to +28‰). Generally, it is unclear what processes could have contributed to these large isotope fractionations. Therefore, we studied S sources and aqueous SO 4 2 − cycling in the Valles Caldera volcanic complex, New Mexico to better understand S isotope fractionations related to S degassing, hydrothermal activity, and low-temperature processes in aqueous environment. Overall, our study demonstrates that volcanic systems show large spatial heterogeneity in δ 34 S. Magmatic S sources are obvious in steam-dominated H2S degassing and precipitation of secondary minerals from hydrothermal fluids with low δ 34 S values of +0.9 ± 3‰. Locally, however, hydrothermal processes have resulted in more negative δ 34 S values in sulfide minerals (−18 to −4‰) and more positive δ 34 S values in sulfate minerals (−1 to +3‰). Major aqueous SO 4 2 − sources are oxidation of H2S from modern hydrothermal gas emission, and oxidation and dissolution of sulfide and sulfate minerals present in the hydrothermally altered bedrock and crater-lake sediments. The δ 34 S of aqueous SO 4 2 − in surface water and groundwater varies widely (−8 to +5‰) and is similar to major S endmembers that undergo oxidation and/or dissolution by active hydrological system. Minor SO 4 2 − contributions with more positive δ 34 S values (+9 to +14‰) come from deeply circulating geothermal fluids and negligible amounts from atmospheric deposition (+5 to +7‰ in snow). Elevated SO 4 2 − contents are mainly associated with modern and past H2S emissions and oxidations near the surface. On regional scale, however, most of the intracaldera bedrock is S-depleted, thus the SO 4 2 − contents are usually low in the surface aquatic system and younger sedimentary lake deposits formed at times of negligible near surface hydrothermal activity. In general, magmatic-hydrothermal processes apparently cause the largest δ 34 S variation in S-bearing minerals on volcanic terrains. Therefore, we infer that the measured wide range of δ 34 S values in the Gale sediments by the Curiosity rover on Mars can be explained by S isotope composition of magmatic-hydrothermal sulfide and sulfate minerals that were present in the initial igneous/volcanic rocks prior to crater formation. Later aqueous processes involved oxidation and dissolution of S minerals initially present in these rocks and led to subsequent formation of diagenetic fluids and alteration products enriched in SO 4 2 − with relatively large δ 34 S variation. Additionally, physical erosion, transport and deposition of detrital hydrothermal S minerals from igneous/volcanic rocks might be in part responsible for the measured wide range of δ 34 S in Gale Crater. These unique S isotope results, measured in situ on another planet for the first time, imply the importance of magmatic-hydrothermal fluids in S transport on early Mars and their subsequent alteration in low-temperature aqueous environments.

The Zn isotope composition of sedimentary archives reveals key biosphere–lithosphere interactions throughout geologic history. A recent Zn isotope study of Ediacaran cap carbonates from South Australia revealed that the local isotopic profile reflects global changes in oceanic chemistry. To examine this critical assumption, this study investigates a high-resolution zinc isotope profile of Marinoan post-glacial cap carbonates from the Yangtze Platform, South China. Stratigraphic variations in Zn isotope data from this study are similar to previously reported sections in South Australia and South China. The remarkable isotopic similarity between the two sections that were deposited on distant, geographically separated continental blocks demonstrates that the Zn isotopic variations reflect changing global signatures of the early Ediacaran ocean. This study highlights the value of Zn isotopes in sediments as a global proxy for paleoceanographic studies. We interpret the systematic stratigraphic changes in the Zn isotope composition of the studied post-glacial Marinoan carbonates as a global oceanic trend controlled mainly by varying inputs and outputs of Zn to the ocean. Decreasing δ66Zn values in the lowermost part of the section are attributed to the global precipitation of carbonate enriched in the heavier Zn isotope. A positive shift in the middle part of the section is explained by the non-quantitative removal of isotopically lighter Zn by sulfide minerals. Lower δ66Zn values in the uppermost part likely reflect the changing contributions of continental weathering and sulfide precipitation. Our data suggest that non-quantitative removal of Zn by sulfides is a previously unrecognized sink for zinc in the oceans.

This paper presents experimental data that revealed the potential for chemical element transport by low-temperature vapor-gas streams. The study was conducted on sulfide waste heap sites located in the Kemerovo region, Russia. Condensates of vapor-gas streams were collected and analyzed in the air above the waste heaps and during laboratory experiments using samplers specially designed for this purpose. The gas streams from a waste heaps are complex mixtures consisting of water vapor, sulfur- and selenium-containing compounds (sulfur dioxide SO2, dimethyl sulfide C2H6S, carbon disulfide CS2, dimethyl disulfide C2H6S2, dimethyl selenide C2H6Se, and dimethyl diselenide C2H6Se2), elemental sulfur (S6, S7, and S8) and various chemical elements, including rock-forming elements (Ca, Mg, Na, K, Si, Fe, Al, and Mn), metals (Cu, Zn, Pb, Ni, and Sn), and metalloids (As, Te, and Sb). The main sources of chemical elements in the gas streams are unstable secondary minerals associated with crystalline hydrates: gypsum CaSO4 × 0.5H2O, sideronatrite Na2Fe(SO4)2(OH) × 3H2O, serpierite CaCu3Zn(SO4)2(OH)6 × 3H2O, and copiapite (Mg,Zn,Fe2+Fe3+)4(SO4)6(OH)2 × 20H2O that formed during the oxidation of sulfide minerals. Some of the elements come from pore waters that are acidic, highly mineralized solutions. The mechanism of element migration from the pore waters is as follow: the water vapor phase transports elements in the form of aqueous ions, but complexed species (such as MeSO4(aq), MeCl(aq), Me(OH)+, etc.) remain in the salt residue. A significant contribution to the processes of transformation and transport of elements is made by biochemical methylation reactions, which occur in the presence of bacteria producers of methyl groups and are accompanied by the formation of volatile compounds of arsenic, selenium, sulfur, and tellurium.

The mining industry needs effective techniques to meet the future challenges of resources extraction. As the deposits become more and more complex, a very good knowledge of an orebody is necessary. Mineralogical characterization is an essential contribution to improve the knowledge on the ore and wastes for a given mining project. It could bring major advances in ore extraction, mineral processing, and integrated waste management. However, mineralogical analyses can be very tedious, when done manually. Consequently, automated mineralogy was developed during the last three decades to improve the rapidity of mineralogical characterization, so that mineralogical information can be routinely obtained. Nowadays, the systems commonly used are based on expensive equipment including scanning electron microscopes (SEM) with energy dispersive X-ray analyzers (EDX). Optical Microscopy (OM) is neglected, although this route can provide reliable and quick results, yet cheaper. In this study, the possibility of using optical microscopy in reflected light mode to automatically characterize opaque minerals is explored. The identification and quantification of six common sulfides from polymetallic ores (arsenopyrite, chalcopyrite, galena, pyrite, pyrrhotite, and sphalerite) were automatically accomplished on a polished section by optical microscopy. Six spectral images were acquired for multispectral image analysis. Five of them were acquired under a white light source, equipped with four different excitation filters (436 nm, 480 nm, 605 nm, and 650 nm). The sixth image was acquired under an UV-light source at 365 nm, after modifying the optical pathway to detect the reflectance of the minerals in the UV-spectrum without changing the acquiring camera. Two image analysis software solutions were then tested to automatically classify and quantify the six sulfide minerals. The classification was systematically done on the acquired multispectral images by grey thresholding with the Clemex Vision PE® software. The GOCAD® software used principal component analysis (PCA) analysis and a supervised K-means clustering method to classify the minerals. Then, the obtained results were compared to the SEM-EDS quantification, considered here as the reference. The differences between the computed surface areas were mainly due to the artifacts of the polished sections preparation. The two software solutions present promising results and could be fully exploited to proceed to other mineralogical analyses, such as mineral liberation, mineral associations, textures identification, and particle size distribution. This study is an initial step towards differentiate and identify sulfides via an optical route arguably reliable and cheaper to characterize mine products.

Molybdenum ore flotation techniques are constantly challenged by the emergence of complex sulfide minerals, such as bismuthinite, in the mineral processing industry. Conventional flotation depressants, such as sodium sulfide, used in Mo–Bi-containing ore flotation require high dosages, which leads to high cost and low selectivity. Therefore, in this study, pyrogallic acid (PA), a widely distributed organic source, is tested as an alternative depressant to selectively depress bismuthinite in Mo–Bi sulfide ores from Shizhuyuan. Results show that PA has a minimal effect on molybdenite recovery; by contrast, PA has a high depressing effect on bismuthinite amelioration. At 500 g/t PA, molybdenum recovery slightly decreases by 2 percentage points, and bismuth content in molybdenum concentrate sharply declines by 34 percentage points, with respect to samples floated without PA. Batch flotation tests demonstrate that PA addition affects froth stability, as indicated by the variations of solid and water recoveries. The superior selectivity of molybdenite over bismuthinite is promoted by increasing the PA dosage. On the basis of these findings, PA is a feasible option and thus can be used as a depressant for bismuthinite in the flotation of sulfide minerals.

Gold-bearing ores, especially the sulphidic ones, are often treated by flotation prior to cyanidation. Following flotation process, the flotation concentrate or tailings are redirected to the cyanidation circuit for gold extraction that may contain appreciable amounts of collector used in flotation, and also remained sulfide minerals, i.e., predominantly pyrite. This current research examines the effect of collector on gold leaching by conditioning gold prior to cyanidation and direct addition in cyanidation in a packed bed leach reactor. Effects of pyrite, and solid-liquid separation on gold leaching and its electrochemical behaviour in presence of collector were also investigated. It was found that conditioning of gold with Aerophine 3418A in absence of pyrite has a detrimental effect especially on leach kinetics of gold since it adsorbs onto gold and decreases its further dissolution. In presence of pyrite, a significant improvement was obtained in gold leaching due to the positive galvanic interactions. These findings suggest that although collector adsorption adversely affects gold leaching, i.e., partial passivation, yet galvanic interactions could continue to enhance its extraction. Following conditioning, solid-liquid separation prior to cyanidation is shown to moderately increasing gold leaching by up to 10%. When Aerophine 3418A was added directly during cyanidation, gold leaching showed a slight increase in absence of pyrite. Conversely, in presence of pyrite, a significant increase in gold leaching was observed. Moreover, if collector was added after the first one hour of cyanidation, gold leaching kinetics was enhanced. Cyclic voltammetry tests within open circuit potential findings support the cyanide leaching results. SEM-EDS analysis of leach residues has demonstrated that there is less amount of gold in the residue both when pyrite is present and collector is added directly. XPS analyses have confirmed the presence of metallic gold in leach residues. These results have revealed the effect of Aerophine 3418A on gold leaching is different when it is directly added than that of conditioning and the positive galvanic effect of pyrite occurs even in the presence of collector.

The weathering of sulfide minerals in waste rock controls drainage water quality and water treatment requirements at mine sites. The availability of oxygen strongly affects the weathering rate of sulfidic waste rock but poregas distributions in heterogeneous, unsaturated waste-rock piles and the governing physical transport processes remain scarcely studied on practice-relevant scales. Here, we investigate the spatiotemporal variations in poregas in five large-scale, instrumented waste-rock piles (10,000 ± 2000 m3) with different types of waste rock. Three piles with coarse, low-S waste rock exhibited atmosphere-like poregas compositions throughout, but two experimental piles with fine-grained, sulfide- and carbonate-rich waste rock contained localized hotspots with elevated temperatures, O2 levels 2%. Oxygen depletion and CO2 production from carbonate dissolution under acidic conditions was most pronounced during the wet season, when infiltrating precipitation strongly increased moisture content and repressed atmospheric gas exchange. Thus, spatial and temporal fluctuations in poregas were related to chemical reactivity and permeability of the waste rock as well as to seasonal climatic variations in hydrological transport. This study demonstrates that a quantitative understanding of these factors can lead to improved assessments of waste-rock weathering and drainage rates and therefore optimized design and management of waste-rock piles.

Pyrite is considered as a disturbing sulfide mineral in the beneficiation of sulfide minerals and coal and in order to prevent floating of pyrite in the flotation, different inorganic, organic and biological depressants could be used. The most important organic pyrite depressants are starch, dextrin, guargum, carboxymethyl cellulose (CMC), ethylene diamine tetra acetic acid (EDTA), Diethylenetriamine (DETA). In this paper, flotation experiments were carried out by modified Halimond tube. At first, flotation experiments were performed to obtain optimal pyrite flotation condition (suitable collector and frother for maximum recovery). In optimal condition (collector: KAX + KIPX , 16 ppm; collector condition time: 4 min; frother: Poly Propylene Glycol (A65), 20 ppm; frother condition time: 30 s), pyrite recovery increased to 95.63%. Flotation kinetics experiments were performed and various kinetic models were evaluated on pyrite flotation. The results showed that flotation kinetics of pyrite is second-order. After obtaining optimal condition for flotation and kinetic studies, the effects of type and dosage of different organic depressants including starch, dextrin, guargum, carboxymethyl cellulose, EDTA and DETA at three concentrations (50, 100, 150 ppm) at neutral pH were comprehensively investigated. The results of the experiments showed that DETA can significantly reduce the recovery of pyrite at 150 ppm by 44%.

Sulfide minerals are important in immobilizing toxic contaminants in reducing environments. Iron sulfide (FeS) is ubiquitous in anoxic conditions and is a good scavenger of various organic and redox sensitive contaminants and heavy metals. Despite its contaminant removal capabilities, FeS has not been used as a practical adsorbent in contaminant removal due to its rapid oxidation under atmospheric conditions. To increase its applicability, we developed a method of modifying FeS by the addition of NaBH4 to form the less oxygen-sensitive NaBH4–FeS. We conducted oxidation tests using laboratory batch testing and real-time synchrotron X-ray absorption spectroscopy (XAS). The Fe K-edge XAS results showed that the oxidation rate of NaBH4–FeS was eight times slower than that of unmodified FeS while maintaining comparable contaminant removal capacities for Cr(VI) and As(III). The results of mechanistic density functional theory (DFT) calculations demonstrated that the oxidation of FeS occurred through electron transfer from sulfur of FeS to an oxidizing agent of oxygen, and that the hydride ion provided by NaBH4 retarded electron transfer from the FeS surface.

Observations of the Earth from space either by satellites or aircrafts are significant approaches for mineral exploration, because of their capability of revealing hydrothermal alteration minerals and sensing the surface/subsurface fracture/fault zones. A study area that is situated in the Pan-African belt of Egypt is tested for targeting potential area of mineral resources involved the hydrothermal system using satellite imagery combined with aeromagnetic, geochemical and field data. Extracted alteration layers using ASTER data and major structures (fault/fracture zones) from DEM, ALOS/PALSAR and aeromagnetic data were prepared and integrated using Knowledge-driven technique in multicriteria-decision making tools for producing mineral prospect map. The results revealed five predictive areas of expected mineral occurrences ranging from excellent to very low. Spectral analysis using ASTER data allowed defining the key-hydrothermal minerals which revealed three successive zones of alterations e.g., argillic, phyllic and propylitic. Plausible areas of minerals fitting to the ore body representing the center of the extensive alterations. Field, geochemical, and ore microscopic investigations validated the results of integrated data. Field data revealed that the mineralization zones extend along NNE-SSW thrust trend that later modified by NW-SE, N-S and NE-SW strike slip faults. Hydrothermal processes related to later magmatic stages probably were responsible for destruction and remobilization of the primary minerals of the host metavolcanics. Microscopic examination revealed that Fe-Cu-Zn-Pb sulfide minerals are associated with auriferous quartz veins. Plausible areas of prospective interest for possible mineralization also were characterized using geochemical analysis. This study successfully displays the key role of integration approach for exploring mineral resources in arid regions.