Base Metal Sulfides Research Articles

Sandstone-hosted uranium deposits of the Colorado Plateau, USA

More than 4,000 sandstone-hosted uranium occurrences host over 1.2 billion pounds of mined and in situ U3O8 throughout the Colorado Plateau. Most of the resources are in two distinct mineral systems with deposits hosted in the Triassic Chinle and Jurassic Morrison Formations. In the Chinle mineral system, base metal sulfides typically accompany mineralization. The Morrison mineral system is characterized by V/U ratios up to 20. The uranium source was likely volcanic ash preserved as bentonitic mudstones in the Brushy Basin Member of the Morrison Formation, and lithic volcanic clasts, ash shards, and bentonitic clay in the lower part of the Chinle Formation. Vanadium originated from two possible sources: iron–titanium oxides that are extensively altered in bleached rock near deposits or from similar minerals in variably bleached red beds interbedded with and beneath the Morrison. In Chinle-hosted deposits, in addition to volcanic ash, a contributing source of both vanadium and uranium is proposed here for the first time to be underlying red beds in the Moenkopi and Cutler Formations that have undergone a cycle of reddening-bleaching-reoxidation. Transport in both systems was likely in groundwater through the more permeable sandstones and conglomerate units. The association of uranium minerals with carbonate and more rarely apatite, suggests that transport of uranium was as a carbonate or phosphate complex. The first comprehensive examination of paleoclimate, paleotopography, and subsurface structure of aquifers coupled with analysis of the geochronology of deposits suggests that that there were distinct pulses of uranium mineralization/redistribution during the period from about 259 Ma to 12 Ma when oxidized mineralizing fluids were intermittently rejuvenated in the Plateau in response to changes in tectonic regime and climate. Multiple lines of evidence indicate that deposits formed at ambient temperatures of about 25 °C to no greater than about 140 °C. In both systems, deposits formed where groundwater flow slowed and was subject to evaporative concentration. Stagnant conditions allowed for prolonged interaction of U- and V-enriched groundwater with ferrous iron-bearing reductants, such as illite and iron–titanium oxides, and more rarely organic material such as plant debris. Paragenetically late in the sequence, reducing fluids introduced additional organic matter to some deposits. Reducing fluids and introduced organic matter (now amorphous and altered by radiolysis) may originate from regional petroleum systems where peak oil and gas generation was from ∼ 82 to ∼ 5 Ma. Our novel analysis indicates that these reducing fluids bleached rock and protected affected deposits from remobilization during exposure and weathering that followed uplift of the Plateau (∼80 to 40 Ma).

Sources, transport, and deposition of metal(loid)s recorded by sulfide and rock geochemistry: constraints from a vertical profile through the epithermal Profitis Ilias Au prospect, Milos Island, Greece

Drill core samples from the Profitis Ilias Pb-Zn-Cu-Ag-Au vein mineralization on Milos Island, Greece provide new insights into (i) the metal sources, (ii) the primary vertical metal(loid) distribution, and (iii) the supergene enrichment processes in a transitional shallow-marine to subaerial hydrothermal environment. Metal contents of unaltered and altered host rocks combined with Pb isotope analyses of hydrothermal sulfides suggest that most metal(loid)s were derived by leaching of basement rocks, whereas the distinct enrichment of Te is related to the addition of Te by a magmatic fluid. The trace element contents of base metal sulfides record decreasing Au, Te, Se, and Co, but increasing Ag, Sb, and Tl concentrations with increasing elevation that can be related to progressive cooling and fluid boiling during the hypogene stage. The formation of base metal veins with porous pyrite hosting hessite inclusions at ~ 400 m below the surface was triggered by vigorous fluid boiling. By contrast, the enrichment of native Au associated with oxidized Fe and Cu phases in the shallower part of the hydrothermal system resulted from supergene remobilization of trace Au by oxidizing meteoric water after tectonic exhumation to subaerial levels. Disseminated pyrite with higher Tl/Pb ratios and locally elevated Hg concentrations relative to vein pyrite reflects infiltration of the host rocks by boiled liquids and condensed vapor fluids. The vertical and temporal evolution of the Profitis Ilias mineralization, therefore, provides unique insights into the transport and precipitation of Au, Ag, Te, and related metal(loid)s by multiple fluid processes.

Ore-fluid source of multiphase gold mineralization at Tuanshanbei in the central Jiangnan Orogen (NE Hunan, South China): Insight from geology, quartz H-O and monazite in-situ Nd isotope compositions

The Jiangnan Orogen is China’s third largest gold province, and has undergone complex orogenic processes and tectonic overprinting, forming multistage magmatism, deformation, metamorphism, and gold mineralization. Our field studies indicate that the Tuanshanbei gold ores (central Jiangnan Orogen) have two generations of auriferous quartz-ankerite-pyrite-arsenopyrite veins (Q2 and Q3), with the latter containing abundant ankerite and base metal sulfides. Both Q2 and Q3 veins are younger than the emplacement of the Tuanshanbei granodiorite vein-ore host, and cut by post-ore diabase dikes. Q2 veins were likely associated with the Early Devonian near N-S-directed shortening, along sub-horizontal EW-/WNW-striking transpressive faults, whereas Q3 veins (hosting ∼ 70% of the total Au resource), were primarily hosted in the Early Triassic moderately-/steeply-dipping NW-striking tensional/transtensional faults and moderately-dipping NE-/NNE-striking transpressive faults, associated with NW-SE-directed shortening. Discrete structural styles and mineral assemblages from Q2 and Q3 suggest superimposing gold mineralization at Tuanshanbei. To determine the source(s) of the ore-forming aqueous-carbonic fluids, we conducted mineralogical and in-situ LA-(MC)-ICP-MS Nd-isotope analyses on two generations of hydrothermal monazite, and H-O isotope analyses on the quartz from Q2 and Q3 veins.The results suggest that the Tuanshanbei ore fluids have δD = −66.7 to −57.6‰ (Q2) and −66.8 to −66.2‰ (Q3), and calculated δ18OH2O = 4.5–9.7‰ (Q2) and 6.1–7.8‰ (Q3). The H-O isotopic data suggest a metamorphic and/or magmatic water source for the ore fluids. Hydrothermal monazite (coexists with native gold and auriferous sulfides) from Q2 and Q3 veins displays subtle heterogeneous BSE response along cracks and grain margin, suggesting alteration there. The 147Sm/144Nd and 143Nd/144Nd ratios of altered parts of Q2 and Q3 monazite grain are significantly perturbed via dissolution–recrystallization by the hydrothermal fluids, whereas their initial Nd isotope compositions seem to be less affected. The unaltered Q2 and Q3 monazite samples have similar initial εNd values (Q2: −8.07 to −7.36, Q3: −10.87 to −9.99) to the Neoproterozoic Cangxiyan Group greenschist–amphibolite-facies metamorphic rocks. Geological and structural evidence suggest both Q2 and Q3 ore-forming events were related to metamorphism, typical of orogenic gold deposits. We interpreted that various parts of the basement were metamorphosed (to near the greenschist-amphibolite-facies boundary) at different times, during which the gold-bearing metamorphic fluids produced migrated into the same structural conduits and deposited the ores there in two ore-forming episodes.

Hydrothermal Pentlandite (Ni,Fe)9S8 from Kambalda, Western Australia: Occurrences, Formation Conditions, and Association with Orogenic Gold

Abstract Pentlandite, (Ni,Fe)9S8, most commonly occurs in mafic or ultramafic rocks in association with other sulfide minerals, including pyrrhotite and chalcopyrite. However, at a few localities pentlandite has been found in hydrothermal settings. At Kambalda in Western Australia, hydrothermal pentlandite occurs in three different vein types: (1) sulfide veins, (2) quartz-calcite veins associated with biotite-epidote alteration, and (3) calcite veins containing arsenides and base metal sulfide minerals. In all three vein types, pentlandite (1) is restricted to veins crosscutting magmatic Ni sulfide lenses, (2) only occurs within <10 m of sulfide bodies, and (3) is associated only with pyrrhotite. In some cases, the pentlandite in the hydrothermal veins has higher Fe and lower Co contents compared to that in the magmatic Ni sulfide ores. The sulfarsenide minerals also show a bimodal distribution in terms of their chemistry: those associated with hydrothermal veins are dominated by Ni, whereas those associated with a primary magmatic origin are rich in Co. Intermediate compositions are observed, notably where hydrothermal sulfarsenide minerals directly overgrow earlier magmatic sulfide minerals. Thermodynamic calculations show that the hydrothermal pentlandite-pyrrhotite assemblages can form from highly reduced, hydrothermal fluids at near neutral pH. Pentlandite deposition can be triggered by an increase in pH and/or a decrease in temperature. Associated gangue minerals, such as biotite, feldspar, and quartz, are likely deposited as a result of concomitant fluid–rock interaction. High fluid temperatures (i.e., 400–500 °C) favor pentlandite formation due to an increase in Ni solubility. The pentlandite-pyrrhotite-biotite assemblage has a narrow stability field coinciding with a field of elevated Au solubility, which prevents coprecipitation of native gold with this mineral assemblage. In contrast, the pentlandite-arsenide mineral assemblage shows a larger stability field which overlaps with conditions allowing Au precipitation. The modeling results suggest that identification of the mineral assemblages in which pentlandite occurs is important in mineral exploration, one implication being that pentlandite-rich, hydrothermal veins will be expected to be Au-free. Conversely, pentlandite-poor or -absent veins, possibly containing Ni-arsenide minerals, may contain gold and could thus be indicative of enhanced prospectivity for gold.

Accessory Minerals in the Chromitite Ores of Dzharlybutak Ore Group of Kempirsai Massif (Southern Urals, Kazakhstan): Clues for Ore Genesis

The paper provides results of a detailed mineralogical study of some chromitite ores from two deposits in the Southern Urals of Kazakhstan: Almaz-Zhemchuzhina and Geofizicheskoe-VII. It is revealed that the main ore minerals are Cr-spinel with high Cr# (Cr/(Cr + Al) = 0.8–0.83), as well as serpentine and chlorite, replacing primary olivine. Chromium spinel grains contain mineral inclusions, which are distributed rather unevenly. The most common mineral inclusions are olivine (serpentine) and amphibole; phlogopite, pyroxenes, and base metal sulfides are rare. Olivine from inclusions in chromite is the highest in magnesium (Fo97–98), and is anomalously high in nickel (up to 1.8 wt.% NiO). The closure of exchange reactions between olivine and chromite occurred in the temperature range of 700–850 °C and in the oxygen fugacity range of −1.04 … +2.8 ΔFMQ, which most likely corresponds to the upper mantle settings of the fore-arc basin. A few tens of monomineral grains and polymineral intergrowths of platinum group minerals (PGMs) were found in chromite aggregates. Notably, monomineral grains are mainly represented by Ru, Os, and Ir disulfides, while in polymineral inclusions, iridium prevails (with widespread native phases, sulfides, and sulfoarsenides). PGM grains included in chromite are often associated with hydrous silicates: amphibole, and less often with phlogopite or chlorite. Discussed in the paper is the possible genesis of ores and inclusions. As a preliminary conclusion, we suggest that the solid-phase processes played the most significant role in the crystallization of Cr-spinel in the investigated chromitite ores.

Adsorption of Rare Earth Metal Cations by Base Metal Sulfides in the Broken Spur and TAG Hydrothermal Fields, Atlantic Ocean

Adsorption of Rare Earth Metal Cations by Base Metal Sulfides in the Broken Spur and TAG Hydrothermal Fields, Atlantic Ocean

Adsorption of Rare Earth Metal Cations by Base Metal Sulfides in the Broken Spur and TAG Hydrothermal Fields, Atlantic Ocean

The article presents the results of sorption of rare earth metal cations on samples of deepsea polymetallic sulfides of the hydrothermal fields of the Broken Spur and TAG of the Mid-Atlantic Ridge. The main minerals of these samples were respectively marcasite, pyrrhotine, pyrite, sphalerite and chalcopyrite, pyrite, and marcasite. It has been established that these sulfide minerals of iron, copper and zinc are natural adsorbents. The exchange capacity of sulfide minerals for rare earth metal cations is in the range of 0.006‒0.061 mg-eq/g. The exchange complex of sulfide minerals consists of cations of alkaline, alkaline-earth metals and basic cations of metals of the crystal lattice – Fe, Zn, Cu (in very limited quantities). The mechanism of absorption of rare earth metal cations is ion-exchange, equivalent to the exchange cations of sulfide minerals. It was found that in the composition of sulfide minerals, rare earth metal cations are almost completely in sorbed form (more than 90% of the total amount); The chemically bound form can be, apparently, only for Lu and Dy cations. The mineral composition of sulfide deposits is preserved in the products of exchange reactions, new phases do not appear.

X-ray absorption spectroscopic study of Pd2+ on Ni site in pentlandite

Abstract Norilsk sulfide ores are one of the largest known sources of Pd on Earth. Palladium in these ores is presented in platinum-group minerals (PGM) and base metal sulfides (BMS), especially in pentlandite [(Fe,Ni)9S8]. Although several studies demonstrated high concentrations along with heterogeneous distribution of Pd in pentlandites from Norilsk, the form of Pd in pentlandite has not been established. Here, we provide the first evidence for Pd incorporation in the structure of pentlandite from Norilsk ores using X-ray absorption near edge structure (XANES) spectroscopy, synchrotron-based micro-X-ray fluorescence (μXRF), and electron backscatter diffraction (EBSD). We present the first ever measured XANES spectra of Pd in pentlandite and atokite [(Pd,Pt)3Sn] as well as in other common Pd minerals. Divalent Pd in pentlandite was detected by XANES. The Pd spectra in pentlandite show no similarities with Pd spectra in PGM, metallic Pd, PdS, PdCl2, and PdSO4 which signifies that Pd incorporates into the lattice of pentlandite. Substitution of Ni by Pd in the lattice of pentlandite is supported by negative correlations shown by μXRF and electron probe microanalysis (EPMA) and complies with the previous studies. The additional EBSD study demonstrates a resemblance in cell parameters of the Pd-rich and Pd-poor parts of the pentlandite grains and reflects that Pd incorporation into the pentlandite structure does not imply any notable structure distortion. The combination of analytical techniques used in the present study demonstrates the great potential of these methods for understanding the mechanisms of noble metal incorporation into ore minerals.

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

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

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

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

Mineralogical and Geochemical Characteristics of the H-Pit of the Chatree Gold Deposit, Central Thailand: A Case Study for Assessment of Acid Rock Drainage and Heavy Metal Sources

H-pit is one of the significant ore lenses of the Chatree mine in Thailand. Au-Ag mineralization mainly occurs as veins, stockworks, and minor breccias hosted by volcanic and volcaniclastic rocks. Disseminated pyrites are commonly present near mineralized veins in the hanging wall zone. This study aims to assess the acid rock drainage (ARD) potential and heavy metal content from the H-pit area. The results indicate that hanging wall rock is a potential acid-forming (PAF) material related to disseminated pyrite formed by hydrothermal alteration. In contrast, the footwall and ore zone materials are classified as non-acid forming (NAF). Because the ore zone has calcite in the veins, it may help buffer the material’s acidity. The results of heavy metal analysis reveal that the ore zone has significantly higher contents of As, Cd, Cu, Pb, and Zn than those in the hanging wall and footwall zones. Moreover, the hanging wall and footwall materials have exceeding values for As, Cd, and Zn compared to those in typical igneous rocks. These heavy metals are interpreted to be sourced from (1) the primary composition in base metal sulfides (e.g., Cu, Pb, and Zn), (2) the substitution of trace elements in sulfides (e.g., As and Cd), and (3) the substitution of trace elements in calcite (e.g., Mn), as evidenced in the EPMA results. In conclusion, the hanging wall rocks in this study containing high sulfur in proximity to the ore zone are a PAF material with heavy metal contaminant sources, whereas the footwall and ore zone materials have a lower potential to be such sources at the Chatree mine.

Processes of Enrichment of Trace Metals for High-Tech Applications in Hydrothermal Veins of the Ruhr Basin and the Rhenish Massif, Germany

ABSTRACTThe increasing demand for high-tech trace elements supports the need for systematic investigations of their primary occurrences. Mineralogy and trace element characteristics of hydrothermal base-metal veins from the Ruhr Basin (Ruhrgebiet) and the Rhenish Massif (Bergisches Land) in Germany were studied by energy-dispersive X-ray fluorescence mapping, laser ablation-ICP-mass spectrometry, and electron microprobe analyses. Quantitative trace element analysis proves elevated concentrations of Ge and Ga in sphalerite from the Ruhrgebiet. In addition to about 6 Mt of sphalerite-dominated ore, a potential of about 10 t of Ge is indicated to be concentrated in the Auguste Victoria and Graf-Moltke base-metal deposits in the Ruhrgebiet. Assessments on physicochemical fluid properties and metal sources using vitrinite reflectance analysis and host rock investigation indicate a genetic link between the Carboniferous carbonaceous rocks (hosting a number of coal seams) and significant trace metal enrichment in the veins. Gallium enrichment, outlining primary growth zones in ore stage 1 sphalerite, is facilitated by the alteration of Al-bearing minerals in adjacent host rocks due to intense fluid/rock interaction. Reduced Ga and very low In concentrations in ore stage 2 may reflect sealed fluid pathways or changes in the fluid properties. The high level of organic matter in the system probably supported enrichment of Ge in the hydrothermal fluids. The constantly high levels of fixation of Ge in sector zoning patterns of the sphalerite during both ore stages indicate a continuous supply. Elevated contents of Sb together with Cu, As, and Pb in sectors of the sphalerite grains point to a local enrichment of nanometer-scale inclusions of sulfosalt-like phases. Sphalerite of both districts and even of the two ore stages in the Ruhrgebiet shows variations in δ34S isotope compositions due to varying sulfur sources. Both the host rock composition and the presence of organic matter contributed to the trace metal enrichment in the Ruhrgebiet base-metal sulfides as compared to the low contents typical of base-metal ore from the Bergisches Land.

Trace element composition of base metal sulfides from the sediment-hosted Dolostone Ore Formation (DOF) Cu[sbnd]Co deposit in northwestern Namibia: Implications for ore genesis

The Dolostone Ore Formation (DOF) copper‑cobalt mineralization is a recently discovered sediment-hosted deposit in Neoproterozoic low-grade metamorphosed carbonates and fine-grained siliciclastics in the Pan-African Kaoko Belt in Namibia. Six mineralization styles have been identified in the DOF. They comprise both brittle and ductile (micro)textures and include sulfides occurring in disseminations, clusters, nodules, pressure shadows, veins and the locally termed “DOF event”.Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in situ trace element analyses of base metal sulfides (sphalerite, chalcopyrite, pyrite and pyrrhotite) show distinct groupings of the mineralization styles. Sphalerite and chalcopyrite from the dissemination, cluster and nodule mineralization styles show similar trace element composition trends (e.g., Fe, Co, Ni, Se, Cd for sphalerite and Co, Ni, Se and Bi for chalcopyrite) that differ from vein and pressure shadow sphalerite and chalcopyrite which group together. Pyrite compositions in cluster and nodule types show a similar trace element grouping in elements such as Co, Ni, As, Se, Sb, Tl and Pb. In contrast, pyrites from pressure shadows and veins show a decoupling in elements such as Se, Sb, Tl and Pb, that grouped together in the aforementioned pyrite mineralization styles. GeGaInMnFe in sphalerite (GGIMFis) geothermometry indicates that the sphalerite (and associated sulfides) from all mineralization styles crystallized at temperatures at or above 310 ± 50 °C. This temperature range corresponds with the regional metamorphism induced by the Damaran orogeny. Thus, the DOF copper‑cobalt mineralization is related to, or at least strongly overprinted by, Damaran metamorphism and deformation.Trace element differences in the sphalerite-chalcopyrite groupings reveal that the vein and pressure shadows mineralization styles were formed at lower temperatures than the other ones but still above the GGIMFis closing temperature of 310 ± 50 °C. Evidence is vacant for a typical low-temperature, early sediment-hosted copper mineralization. This work demonstrates the strength of using trace elements for deducing the ore-forming system of polyphase sulfide deposits.

Preliminary chemical and mineralogical characterization of tailings from base metal sulfide deposits in Serbia and North Macedonia

Tailings of old mines often contain metals, which were not of economic interest or could not be recovered with the existing technology at the time of active mining. This is especially true for metals that often occur as by-products in Cu-Pb-Zn-(Ag-Au) ores as Sb, Mo, Ge, and In. A fundamental characterization of some tailings is presented in terms of their mineralogy and content of valuable metals which could be extracted to finance a possible remediation and improve the supply of the EU with critical metals. Tailings from active and abandoned mines in Serbia (Bor, porphyry Cu/Au; Krivelj, porphyry Cu/Au; Blagodat, hydrothermal Pb-Zn; Lece, epithermal Au; Rudnik, hydrothermal/skarn Pb-Zn) and North Macedonia (Sasa, Pb-Zn; Probištip, Pb-Zn; Bučim, porphyry Cu; Lojane, fault-bound vein-type low-temperature As, Sb, Cr at the contact of rhyolite and serpentinite) were studied. Analysis for major and trace elements used a multi-method approach (lithium borate fusion and ICP-MS/OES analysis, gravimetric analysis, instrumental neutron activation analysis, total digestion ICP-OES, infrared spectroscopy) with mineral identification by scanning electron microscopy. Concentrations of the major commodity elements (Cu, Pb, Zn, Au, Ag) varies within several orders of magnitude depending on mineralogy and ore type. Critical metals (Co, Ga, Ge, Sb) contents are low with some exceptions. Some tailings contain moderate to elevated potentially toxic element levels (As, Cd, Pb, Tl). For the sample from Probištip which yielded the highest valuable metal concentrations (>5000 ppm Pb, 4020 ppm Zn), a heavy mineral concentrate of the sand size fraction (0.06 mm to 0.5 mm) was produced and analyzed by SEM and LA-ICP-MS for additional rare phases and trace elements. In all tailings studied, additional milling would be needed to separate ore from gangue minerals. Increasing metal prices might facilitate feasibility studies for some of the localities in the future, despite the limited quantitative information about the characterized tailings.

The Use of Acid Mine Drainage (AMD) in the Flotation of a Platinum-Group-Minerals-Bearing Merensky Ore

Water scarcity is compelling mining houses to not only recycle process water but to also identify alternative sources of make-up water in concentrators. South Africa has significant volumes of acid mine drainage (AMD) generated from vast mining operations. This study investigated the viability of using AMD as a replacement for potable water in the flotation of a platinum-group-minerals (PGM)-bearing Merensky ore. Rougher and cleaner flotation testwork was conducted at laboratory scale to compare the performances of potable water (baseline water), AMD treated with Ca(OH)2, and AMD treated with the Veolia process. Water analysis showed that the three water types differed in pH, water hardness, conductivity, and total dissolved solids. The results showed the AMD treated with Ca(OH)2 was detrimental to PGM recovery compared to potable water at depressant dosages of 50 g/t. Specifically, AMD treated with Ca(OH)2 achieved a PGM rougher recovery of 67.8%, while potable water achieved a PGM rougher recovery of 88.4%. Depressant dosage optimisation and treatment of the AMD using the Veolia process were investigated as potential strategies to mitigate the detrimental effects of the AMD treated with Ca(OH)2 on the flotation performance of a Merensky ore. The AMD treated with the Veolia process achieved a PGM rougher recovery of 70.8%. Thus, treatment of the AMD was beneficial, though the PGM and base metal sulphides (BMS) recoveries were still lower than those achieved in potable water. Reducing the depressant dosage to 25 g/t in AMD treated with Ca(OH)2 resulted in the highest PGM, Cu, and Ni rougher recoveries of 91%, 60.2%, and 58%, respectively. The AMD treated with Ca(OH)2 at lower depressant dosage outperformed the potable water in terms of PGM and BMS recoveries and concentrate grades, indicating that AMD has the potential to replace potable water as make-up water in Merensky ore processing plants. The results showed that depressant optimisation is important to achieve superior metallurgical results when using AMD treated with Ca(OH)2. The use of AMD in Merensky ore processing plants not only conserves freshwater in minerals processing plants but also reduces high volumes of contaminated effluents.

High-pressure phase relations in the system Fe–Ni–Cu–S up to 14 GPa: implications for the stability of sulfides in the earth’s upper mantle

Base metal sulfides (Fe–Ni–Cu–S) are ubiquitous phases in mantle and subduction-related lithologies. Sulfides in the mantle often melt incongruently, which leads to the production of a Cu–Ni-rich sulfide melt and leaves a solid residue called monosulfide solid solution (mss). However, the persistence of crystalline sulfide phases like mss in the Earth’s mantle at higher temperatures and pressures deep within the Earth has long been up for debate, as the presence of both mss and sulfide melt in mantle rocks implies the fractionation of chalcophile elements during mantle melting. Recent studies have shown that the average mantle sulfide (45 wt.% Fe, 16 wt.% Ni, 1 wt.% Cu, and 38 wt.% S), is fully molten at average mantle potential temperatures (1300–1400 ^{circ }C) up to 8 GPa (ca. 240 km). However, sulfide inclusions found in diamonds show a broad compositional spectrum, ranging from Ni-poor and Fe-rich (eclogitic), to Ni-rich and Fe-poor sulfides (peridotitic), with their Cu contents being generally low. The wide compositional variety of diamond-hosted sulfide inclusions raises the possibility that results on the melting properties obtained from this average mantle sulfide compositional may not reflect that found in those inclusions. As such, further investigation of the melting properties of sulfides from a wide compositional range is necessary. Here, we present the results of an experimental study where the melting properties of typical sulfide compositions found in diamond inclusions associated with eclogites and peridotites have been determined. Experiments have been carried out between 0.1 MPa and 14 GPa, and between 920 and 1590 ^{circ }C, on box muffle furnaces, end-loaded piston cylinder, and multi-anvil apparatuses. Results show that solid mss in Fe-rich, Ni-poor sulfide inclusions associated with eclogites persist to higher pressures and temperatures compared to their less-refractory, more Ni-rich peridotitic counterparts to the depth of the mantle transition zone (410 km depth). Our results have implications for the recycling of chalcophile elements during subduction-related processes and the entrapment of sulfides in diamonds.

Multithematic Geoscience Data Integration for Identification of Mineral Potential Areas in Parts of Central Indian Precambrian Craton

Abstract The paper highlights the results of multi-thematic geoscience data integration involving geological, geophysical, geochemical and remote sensing data sets, for an area of 4000 Sq. Km in parts of Precambrian Bastar craton, Chhattisgarh. The present team has been able to identify two discrete mineral potential areas for base metal sulphides, Sn, W and REE in sheared and altered felsic volcanics in Kotra-Bhansula area and for gold in propylitically altered meta basalts in Bhursatola-Khampura area. The dataset utilized during collation and integration includes (i) high resolution aeromagnetic data (ii) 1:50000 geological data covering litho-structural and mineralisation attributes (iii) 1:50 k geochemical data for 61 elements (iv) multispectral ASTER satellite data and its derivative alteration maps. Thematic data and derivative maps were studied and interpreted for evaluation of concerned parameters for estimating their role in mineralisation. The data integration has been implemented in three steps beginning with GIS based spatial modelling using Fuzzy logic method resulting into production of mineral favourability map, followed by detailed field evaluation and characterization of the identified mineral favourability areas. Eventual identification of potential areas was based on synthesis of modelling output, field outcome and laboratory results of analyses carried out on critical samples collected from mineral favourability areas. The identified two mineral potential areas are recommended for further detailed exploration for gold, base metal, Sn, W and REE through surface and sub-surface probing.

Highly siderophile element behavior in the subduction zone mantle: Constraints from data on the Yap Trench peridotites

The highly siderophile elements (HSEs) in peridotites from the Yap Trench are investigated to understand their behavior in the subduction zone mantle, which is characterized by high melt depletion and metasomatism. Results reveal that the abundance of HSEs in Yap Trench peridotites is extremely low compared with that in oceanic peridotites from the mid-ocean ridge and other subduction-zone environments, indicating the extensive extraction of the sulfide melt. Chondrite-normalized HSE patterns are heterogeneous and exhibit strong fractionation of platinum-group elements (PGEs) and slight enrichment of Re and Au. The Ru/Ir (1.64–16.12), Os/Ir (0.15–7.19), and Pt/Pd (0.53–13.17) ratios in most of the studied samples are higher than those in CI chondrite (Ru/Ir: 1.49; Os/Ir: 1.06; and Pt/Pd: 1.67). These suprachondritic PGE ratios result from the exhaustion of the base metal sulfide (BMS) and the formation of platinum-group minerals and alloys, such as Os–Ru-rich sulfides and PtFe alloys, that are selectively enriched with certain HSEs. Mantle metasomatism appears to have no systematic influence on PGEs, although it may increase the abundance of Re and Au in the Yap Trench peridotites. Moreover, compared to abyssal peridotites, subduction-related peridotites have fractionated PGE patterns, particularly for the iridium group, suggesting that subduction conditions may promote the fractionation of the PGEs. However, suprachondritic PGE ratios are generally observed in subduction-related peridotites with a low Al2O3 content (<1 wt%) instead of subduction-related fertile samples. This suggests that highly depleted and subduction-related conditions are required for the fractionation of PGEs. We recommend that the high oxygen fugacity, hydrous melting, and high degree melting of the subduction-zone mantle may result in the exhaustion of the BMS in highly depleted peridotites, promoting the formation of platinum-group minerals and HSE-rich alloys, in which the HSEs are significantly fractionated.

Hydrothermal evolution from porphyry- to epithermal-style mineralization in the Naozhi deposit, NE China

The Naozhi deposit in the Yanbian district of northeastern China contains polymetallic epithermal veins and subeconomic porphyry-style Cu mineralization within 2 km of each other. These two mineralization styles are genetically associated with 130–126 Ma andesites and dioritic–granitic intrusions. Isotopic ages determined on sericite (128.2 ± 2.9 Ma; 40Ar–39Ar plateau age) and sulfide (124.6 ± 2.7 Ma; Rb–Sr isochron) associated with the epithermal mineralization constrain the hydrothermal activity to at approximately 128 Ma. Three types of fluid inclusions, including halite-bearing, vapor-rich, and liquid-rich inclusions were trapped in quartz from porphyry-style veinlets associated with an assemblage of K-feldspar–biotite–magnetite. Based on microthermometry and the homogenization behavior of halite-bearing inclusions, they were trapped at lithostatic pressures of > 500 bars and at temperatures of ≥ 350 °C, whereas the vapor- and liquid-rich inclusions were trapped at pressures and temperatures of 110 ± 35 bars and ≤ 350 °C.Epithermal mineralization comprises four vein stages, which, from oldest to youngest, are quartz–pyrite, quartz–base metal sulfide, quartz–precious metal, and quartz–carbonate. The ore assemblage precipitated from low-salinity fluids (<10 wt% NaCl equiv.) at temperatures and pressures of ≤ 350 °C and ≤ 100 bars. The δ18OH2O (2.5 to −2.4 ‰) and δDH2O (−85 to −114 ‰) compositions of fluids related to porphyry- and epithermal-style mineralization indicate a mixture of magmatic and meteoric waters. The δ34SH2S (−3.1 to 4.5 ‰) values of fluids become isotopically heavier from the quartz–pyrite stage to the quartz–base metal sulfide stage, reflecting continuous reduction during epithermal mineralization. The mineral assemblage and chemical composition of sulfide minerals indicate a transition from oxidizing, high sulfidation porphyry-style fluids to reducing, intermediate–low sulfidation epithermal fluids, with log ƒO2 values ranging from −31 to > −33, and log ƒS2 values ranging from −7.0 to ≤ −13.4 during the epithermal veining stage. Metal deposition in the Naozhi magmatic–hydrothermal system resulted from cooling, sulfidation, neutralization, and boiling of predominantly magmatically sourced hydrothermal fluids that mixed with meteoric water.

Co-precipitation of gold and base metal sulfides during fluid boiling triggered by fault-valve processes in orogenic gold deposits

The extreme fluctuations in pressure during earthquakes are widely regarded as responsible for gold mineralization in quartz-vein-hosted gold deposits. However, it is barely noticed that base metal sulfides can precipitate together with gold during these processes. Here we present the phenomenon and unravel the mechanism of the co-precipitation of Au and base metal sulfides during the fluid boiling via geological study and thermodynamic modeling, respectively. The Bangbu deposit, a lode-type orogenic gold deposit in Tibet shows two mineralization substages of pyrite. The pyrite formed in the later substage is hosted in the wall rock selvages of laminated crack-seal quartz veins formed by the fault-valve processes. The pyrite grains are characterized by anhedral small crystals with porous textures and abundant native gold, chalcopyrite, galena, and sphalerite inclusions. They also contain higher concentrations of Cu, Pb, Ag, Sb, and Au, and lower concentrations of Co and Ni, compared to the euhedral large-grained pyrite formed in the initial substage. The textural and trace element characteristics of the pyrite indicate that vigorous boiling occurred during fault-valve behavior, which decreased the solubilities of Au, Cu, Pb, and Zn in the ore fluid in Bangbu. The co-precipitation of Au and base metal sulfides triggered by fluid boiling has also been reported in other orogenic gold deposits worldwide.Thermodynamic models are designed to acquire the predominant species and solubility of Au, Cu, Pb, and Zn in orogenic ore fluids under varied chemical conditions. The results show that Au, Cu, Pb, and Zn are dominantly transported as hydrosulfide complexes under lower mesozonal to epizonal deposit conditions. At temperatures of about above 350 °C, Au hydrosulfide species still predominates, but the predominant Cu, Pb, and Zn species change from hydrosulfide to chloride complexes. A sudden decrease in the reduced sulfur concentration during fluid boiling may be the most important mechanism controlling the precipitation of Au, Cu, Pb, and Zn in lower mesozonal to epizonal deposits. The decrease of logfS2 during fluid boiling can increase the fluid pH, resulting in the decrease of solubilities of base metal chloride complexes and thus explain the co-precipitation of Au and base metal sulfides in hypozonal deposits.