Minor Arsenopyrite Research Articles

Genesis of Xinjiazui Gold Deposit: In Situ Geochemical Constraints from Arsenopyrite

The Xinjiazui gold deposit marks a notable significance in prospecting within the Back-Longmenshan tectonic belt, located on the northwest margin of the Yangtze Block, China. Despite the extensive studies conducted on this deposit, the source of the ore-forming materials remains unclear, leading to ongoing debates regarding the genesis of this deposit. This study analyzed in situ (EPMA and LA-ICP-MS) trace elements and S-Pb isotopes of arsenopyrite, solely from the principal metallogenic stage and paragenetic with native gold. The results show that the gold in arsenopyrite occurs as invisible gold (Au3+), with an average concentration of 9.38 ppm, whereas the concentrations of magma-related elements, such as W, Sn, Mo, and Bi, are very low. The sulfur isotopes (34S) of arsenopyrite range from 8.32‰ to 10.16‰, aligning closely with the deep metamorphic basement (Pt3l). Meanwhile, the lead isotopes in arsenopyrite display characteristics typical of those found in orogenic belts. A comprehensive analysis of the abundance of gold indicated that the metallogenic materials (sulfur and gold) primarily originated from Pt3l. Additionally, the arsenopyrite thermobarometer indicated that the Xinjiazui gold deposit formed in a medium–low-temperature, medium metallogenic environment (5.57–8.69 km), with a sulfur fugacity (log f (S2)) below −8.4. Combined with previous research results, this study proposes that the Xinjiazui gold deposit is a subduction-related mesozonal orogenic gold deposit. In gold prospecting and exploration in the Back-Longmenshan tectonic belt, it is essential to focus on the distribution of brittle-ductile shear zones and location of the quartz veins associated with pyrite and arsenopyrite mineralization.

Unraveling the impact of high arsenic, fluoride and microbial population in community tubewell water around coal mines in a semiarid region: Insight from health hazards, and geographic information systems

High arsenic (As), fluoride (F-), and microbial pathogens coexist in semiarid conditions afflicting > 240 million people worldwide including Pakistan. Groundwater quality has declined due to geogenic and manmade activities providing suitable ground for ubiquity, bioavailability, and toxicity of contaminants. We tested the health hazard, distribution, and apportionment of As, F-, and microbes in groundwater around coal mines in Quetta, Pakistan. The range of As, and F- concentrations in groundwater were 0.2–16.6 µg/L, 0.4–18.5 mg/L. Both, As and F- correlate with high HCO3-, pH, Na+, SO42-, Fe, and Mn, and negatively with Ca2+ water. The coalfield showed many folds higher As 15.8–28.5 µg/L, and F- 10.8–34.5 mg/L compared to groundwater-wells. Geochemical phases revealed saturation of groundwater with calcite, dolomite, fluorite, gypsum, and undersaturation with halite-mirabilite, and arsenopyrite minerals. The positive matrix factorization (PMF) model assessed five-factor solutions: geogenic, industrial, coal mining, sulfide & fluoride-bearing mineral-dissolution, and agriculture pollution delivered As, F-, and microbial contamination. About 24.6 % and 64.4 % of groundwater samples exceeded the WHO guidelines of As 10 µg/L, F- 1.5 mg/L. The carcinogenicity, and non-carcinogenicity of As, and F- were higher in children than adults. Therefore, health hazards in children are of great concern in achieving sustainable management goals.

RETRACTED: A semi-arid climate's use of exploratory data analysis (EDA) as a reliable non-parametric method for geochemical mapping

In this study, exploratory data analysis (EDA) methods, specifically boxplots, were employed to examine the composition of stream sediments in the Collo area of Northeast Algeria. The region's diverse lithological formations, interactions between permanent and temporary watercourses, intermittent flash floods, rugged topography, and fluctuating climatic conditions contribute significantly to data variability. Utilizing the boxplot's capabilities, our analytical approach successfully identified outliers, recorded the actual distribution of data, and determined skewness without the need for prior data processing, often required in conventional statistical studies. The boxplot proved to be an effective tool, offering insights into the geographical distribution of elemental concentrations, including iron (Fe), zinc (Zn), copper (Cu), arsenic (As), chromium (Cr), and lead (Pb). Geochemical mapping, driven by a robust class selection mechanism developed from the boxplot, revealed strong geographical correlations. A notable northeastern anomaly, characterized by elevated concentrations of Pb, Zn, Cu, and As, aligned with known base-metal sulfide and arsenopyrite mineralization sites. Additionally, outlier data for Cr indicated proximity to a plagioclase-lherzolite intrusion and known chromite deposits. The geographical distribution of iron, corresponding with known magnetite and hematite resources, was effectively highlighted using robust class selection based on boxplot analysis. This comprehensive investigation underscores the value of EDA methods in identifying mineralization trends amid the complex variability of the Collo area.

In situ LA-ICP-MS trace elements in sphalerite from the Fankou Pb-Zn deposit, South China: Implications for ore genesis

Sphalerite is one of the most ubiquitous and abundant sulfides in the Fankou Pb-Zn deposit, Guangdong province, South China, which is hosted predominately in Middle-Upper Devonian and Lower Carboniferous carbonate strata. Two main generations of sphalerites were identified during the filed investigation and microscopic observation: Sphalerite I (including Sp Ia and Sp Ib), “brownish-red” in color, coexists with pyrite, galena, pyrrhotite, chalcopyrite and minor arsenopyrite. By contrast, Sphalerite II (including sphalerite IIa and Sp IIb),“yellow” in color, is associated with galena, pyrite, calcite, and dolomite. The EMPA and LA-ICP-MS analyses show that: (1) Sphalerite I contains higher Fe, Ga, Ge, and Ag, but relatively lower Zn, Sn, Sb, and Pb, compared to sphalerite II; (2) Iron, Mn, Cd, Ga, Ge, In and Sn occur in solid substitution with rhythmically banded compositional changes, with Cu, Sb, and Pb likely also present in solid substitution or microscopic inclusions in the Fankou sphalerite; (3) Possible trace element substitution mechanisms are summarized as follows: (1) Zn2+ ↔ (Fe2+, Mn2+, Cd2+), (2) potential coupled substitutions of 2Zn2+ ↔ Cu+ + Ga3+, 3Zn2+ ↔ 2Cu+ + Ge4+ and 3Zn2+ ↔ 2Ag+ + Ge4+. Principal component analysis (PCA) of selected sphalerite from deposits of the Jinding Pb-Zn deposit, MVT, SEDEX, skarn, VMS, and the Fankou Pb-Zn deposit reveal significant differences. Our study suggests that crystallization temperatures and trace and minor element behaviors of sphalerite from the Fankou deposit were similar to those of sphalerite from typical Mississippi-valley-type (MVT) deposits.

The Peña do Seo W-Sn deposit, NW Iberia: Petrology, fluid inclusions and O-H-S isotopes

The Peña do Seo W-Sn ore deposit in NW Iberia consists mainly of quartz veins hosted in schists. Vein mineralogy comprises wolframite, cassiterite and minor molybdenite. Peraluminous S-type granites and minor metaluminous granitoid breccias crop out in the same location. Whole rock geochemistry, mineral characterization, fluid inclusions and stable isotope geochemistry have been combined to infer hydrothermal mineralization conditions. A pre-ore stage (0) involving the alteration of host rocks, three stages of mineralization (I, II and III), and a supergene stage (IV) have been identified. Stage I (oxide-halide-sulfide stage) consisted of a cassiterite-pyrite-fluorite mineralization in granitoid breccias. Stage II (main oxide stage) involved wolframite-rich selvages and wolframite-cassiterite-(molybdenite) quartz veins. Stage III (main sulfide stage) consisted of a sulfide mineralization in quartz veins comprising pyrite and minor arsenopyrite and chalcopyrite. Three types of fluid inclusions were found in vein quartz: (1) aqueous two-phase inclusions, with homogenization temperatures (Th) between 445 °C and 280 °C and moderate salinities (9-14 wt.% NaCl eq.), (2) aqueous-carbonic three-phase fluid inclusions, with Th from 340 °C to 260 °C and low salinities (2-7 wt.% NaCl eq.), and (3) aqueous two-phase fluid inclusions, with Th from 270°C to 155 °C and low salinities (0-6 wt.% NaCl eq.). δ18O values in quartz from mineralized veins range from +11.2‰ to +13.4‰, and between +15.0‰ and +15.4% in quartz from mineralized granitoid breccias. δ34S values in sulfides (pyrite, arsenopyrite and chalcopyrite) range between +13.0 ‰ and +37.1 ‰, thus suggesting a marine source of sulfate and possible equilibration with host-rock sulfides. δD values in muscovite and chlorite from quartz veins range between -105.7 ‰ and -71.5 ‰ and between -69.4 ‰ and -67.1 ‰, respectively, indicating a transition from magmatic to magmatic-metamorphic conditions. An aqueous (H2O–NaCl) magmatic-hydrothermal fluid led to the W-Sn mineralization, as deduced from the studied fluid inclusions and isotopic signatures. High W and Sn contents in the peraluminous granites indicate that the W-Sn mineralization in Peña do Seo could partially be related to the granites and granitoid breccias. Whereas the Sn (± W) likely derived from hydrothermal fluids exsolving from the crystallizing magmas, host quartz schists would have supplied other elements required for wolframite deposition such as Fe and Mn. Sulfide mineralization in stage III was probably driven by fluid dilution.

Differential flotation of pyrite and Arsenopyrite: Effect of pulp aeration and the critical importance of collector concentration

• Differential oxidation of pyrite and arsenopyrite achieved with pulp aeration. • Recovery of pyrite and arsenopyrite was high when singularly treated. • Xanthate adsorption removed high FeOOH removal from arsenopyrite compared to pyrite. • Adsorption of xanthate on heavily oxidised arsenopyrite surface was slow. • Selectivity was lost at high xanthate concentration. Differences in the oxidation rate and extent of model pyrite and arsenopyrite minerals, augmented by pulp aeration, was investigated using dissolved oxygen demand tests and X-ray photoelectron spectroscopy (XPS) analysis. Flotation studies of single mineral admixture coupled with zeta potential measurements, UV–Vis spectroscopy analysis of collector concentration and ex-situ metal ions in solution after collector addition were ascertained to shed light on reasons for observed window for selective flotation. The highest selectivity was achieved with low collector concentration of 1 × 10 -5 M PAX and selectivity index of 5.2 after 6 min flotation with collector concentration playing a critical role in attaining a good selectivity. Fast adsorption of xanthate and simultaneous oxidation to dixanthogen on slightly oxidised pyrite surface starved heavily oxidised arsenopyrite surface of the collector species, at low collector concentration, leading to its depression. The study was extended to the flotation of an auriferous refractory ore where similar observations were made. 62.7% rejection of pyrite was achieved in the staged flotation process.

NEW GEOLOGICAL DATA ON ORLEA MINING FIELD, ROŞIA MONTANĂ AU-AG EPITHERMAL DEPOSIT, APUSENI MOUNTAINS, ROMANIA

New geological data on the Orlea mining field, Roșia Montană ore deposit, Romania were obtained by fieldwork carried out in the underground level +730 m, where three types of mineralized structures hosted by the Vent Breccia formation were studied, i.e., (i) flatly dipping vein with rhodochrosite gangue, (ii) steeply dipping tectonic breccia dyke, and (iii) steeply dipping base metal vein, respectively. The Vent Breccia is a polymictic matrix-supported breccia with sedimentary (clay, sandstone), volcanic (dacite), and metamorphic (quartzite, garnet micaschist) clasts. Four types of hydrothermal alterations were identified, i.e., (i) K-metasomatosis (adularia I); (ii) phyllic alteration (sericite); (iii) silicification; and (iv) potassic alteration (adularia II). The ore mineral assemblage consists of electrum, pyrite, chalcopyrite, sphalerite, galena, and minor arsenopyrite and pyrrhotite. The higher-grade ore body is the intermediate-sulfidation flatly dipping vein with rhodochrosite gangue grading up to 101g/t Au. The tectonic breccia dyke is a low-sulfidation ore body illustrating the evolution from early banded vein structure to late/final open-space clast supported tectonic breccia dyke.

Bismuth–Telluride-Gold Mineralisation from Parsoi Area in Eastern Mahakoshal Belt, Sonbhadra District, UP, India

Abstract The Palaeoproterozoic eastern Mahakoshal belt of Central India Tectonic Zone (CITZ) is known for gold occurrences. Gold occurs predominantly in quartz veins and quartz-carbonate veins. It is associated with pyrite, pyrrhotite and arsenopyrite mineral assemblages. The secondary alteration products such as ‘scorodite’ and ‘mansfieldite’ are also associated with gold mineralisation. Recent investigations carried out in Parsoi area, have indicated the association of gold with bismuth, bismuthinite and telluride. This is the first record of bismuth from the Mahakoshal belt. The studies of the bismuth tellurides contribute to the assessment and evaluation of concentrations of gold resources.

Petrology and Fluid Inclusion Study of W+Sb±Au Quartz Vein Mineralization in Sebuku Island, South Kalimantan, Indonesia

Sebuku Island in South Kalimantan province has hosted one of the largest Fe-Ni laterite deposits in Indonesia. Surface mapping has discovered new ore deposit types, notably quartz-bearing W+Sb±Au ore veins in the northern Sebuku. This study aims to characterize this newly-discovered deposit type and understand its origin. We present geological mapping, petrographic and ore microscopic observations, and data from XRD, bulk-ore major and trace element (XRF and ICPMS), as well as fluid inclusion microthermometric analyses. The results show that the host rocks are composed of metasandstone and metapelitic rocks. The quartz veins are associated with narrow alteration zones, comprising silicic, sericite and argillic types, which are strongly controlled by NE-trending dextral and SE-trending sinistral strike-slip faults. The veins trend approximately N120oE, and have massive, brecciated, drusy, comb and bladed textures. Ore minerals comprise mainly wolframite, stibnite, kermesite, tripuhyite, and minor arsenopyrite, pyrite and Fe-Ti oxides. The ores contain up to 958 ppm W and 1,220 ppm Sb, with wolframite and stibnite being the main ore minerals. Medium homogenization temperatures (Th) were found for the fluid inclusions, ranging from 238 to >350°C, which correspond to moderate fluid salinity of 1.4 to 5.4 wt.% NaCl eq. Based on those characteristics, the W+Sb±Au mineralization in Sebuku is similar to a mesothermal type

Kinetics and mechanism of arsenopyrite leaching in nitric acid solutions in the presence of pyrite and Fe(III) ions

The main sulphide minerals that serve as gold carriers in low-grade raw materials are pyrite and arsenopyrite. Traditional methods of processing such refractory raw materials rely on high-pressure or pyrometallurgical oxidisation, which destroys the crystal lattice of sulphides and releases gold particles. An alternative method of oxidation is leaching with nitric acid. The study examined the kinetics and oxidation mechanism of the natural mineral arsenopyrite in nitric acid media, along with the effect of pyrite on the kinetic characteristics of dissolution. Using the shrinking core model (SCM), it was shown that during the first 5 min of the process, the kinetic of the reaction is controlled by the chemical reaction. Further in the course of the process, the mode changes, which is confirmed by the new shrinking core model. During the period from 5 to 60 min the model was fitted according to diffusion through a product layer and interfacial transfer. The addition of Fe(III) ions and an increase in the concentration of nitric acid have a similar effect on the nitric acid leaching of arsenopyrite, which is associated with an increase in the oxidation potential of the system. The influence of pyrite on the leaching of arsenopyrite is probably associated with its catalytic action in the early stage of the process, which is due to the role of an alternative surface for the reduction of nitrate ions in electrochemical contact with arsenopyrite. The difference in the mechanisms of arsenopyrite oxidation in the presence of Fe(III) ions and pyrite was confirmed by the SEM-EDX analysis.

Tracing mineralization history from the compositional textures of sulfide association: A case study of the Zhenzigou stratiform Zn-Pb deposit, NE China

The Qingchengzi Orefield located in northeastern China hosts more than ten Pb-Zn deposits and several Au-Ag deposits. Among those, the Zhenzigou Zn-Pb deposit displays a typical stratiform morphology, comprising ore bodies in layers and lenses. The ore minerals are simply composed of sphalerite, galena, pyrite, and pyrrhotite, together with minor arsenopyrite, marcasite, and argentite. A sulfide association of sphalerite-galena-pyrite-arsenopyrite was selected for this study; the interior compositional texture of the sulfide association was investigated by means of LA-ICPMS spot and mapping analysis, with the aim of constraining the ore genesis, fluid evolution history and element partitioning behavior. The results show that three distinct fluids were involved in the mineralization, namely an episode of sedimentary fluids at ∼2052 Ma which is responsible for the precipitation of pyrite core (Py0), an episode of metamorphic fluids at ∼1800 Ma which formed an overgrowth of pyrite (Py 1) and new crystallization of sphalerite (Sph1) and arsenopyrite (Aspy1), and a final episode of hydrothermal fluids related to the Triassic magmatism, forming another overgrowth of pyrite (Py2), sphalerite (Sph2) and arsenopyrite (Aspy2), together with minor precipitation of galena (Ga). The sedimentary fluids are relatively low in temperature (<150 °C), enriched in Cu, Pb, Zn, Ag, and depleted in Co, Ni, and As. Pyrite is the main precipitated sulfide mineral, scavenging most of the available trace elements. The late metamorphic and magmatic fluids are high in temperature (>300 °C) and have remobilized As, Co and Ni but only at mineral grain scale. The late metamorphic and magmatic fluids are enriched in In, Cd, Au, As, Ag, Cu, Pb, Sb, Sn, Co and Ni, and depleted in Bi, W, Mo, Te, and Se. The partitioning of most of the metals from the fluids into the sulfide minerals was controlled by the metals’ availability in the fluids and by the compatibility with crystal structure through direct or coupled substitutions. Pyrite acts as the main host of Co, Ni, Pb, and As; arsenopyrite hosts a major amount of Sb and Pb, and a minor amount of Au; sphalerite is the primary host of Cd, In, Cu, and the secondary host of Ag and Sn; galena is the primary host of Ag, Sb, Sn, and subordinately hosts Cd, In and As. In particular, a remarkable amount of In and Cd was carried by the hydrothermal fluids associated with the Triassic magmatism, indicating that the contribution of magmatic hydrothermal fluids to the mineralization is significant. In conclusion, our in-situ geochemical evidence of sulfide minerals reinforces a sedimentation-metamorphism-magmatic-hydrothermal reworking model for the Zhenzigou stratiform Zn-Pb mineralization. This case study underlines the significance of compositional textures of coexisting sulfide minerals when assessing the ore genesis. Overall, our study demonstrates that, by integrating trace element mapping and spot analysis on coexisting sulfide minerals, it is possible to re-construct the fluid evolution history, resolve the metal behaviors associated with fluids evolution, and review the contribution of individual fluids to mineralization.

Biodegradation mechanism of arsenopyrite mine tailing with Acidithiobacillus ferrooxidans and influence of ferric supplements

Microbial mobilization of arsenopyrite minerals under oxic conditions are well known; however, little is known about how the metals can be mobilized through biodegradation of mine tailings. Therefore, the role of inoculated Acidithiobacillus ferrooxidans on the mobility of arsenic and iron was examined for a sample of South Korean mine tailing. Two modes of interactions (i) direct contact, and (ii) non-contact were examined along with the monitoring of Eh-pH values and cell density. Direct contact of Acidithiobacillus ferrooxidans could mobilize metal ions more efficiently than the non-contact mode of interaction albeit revealed that the overall interaction was governed by a co-operative mechanism. A direct-contact biotic study resulted in the higher mobilization of arsenic (~69%) than the non-contact biotic system (~44%), but the maximum mobilization (~80%) could be achieved with 6 g/L ferric supplement to the direct-contact system. The ferric-improved mobilization was higher up to seven days from the starting time, thereafter, the surface passivation [KFe3(SO4)2(OH)6 and S0] sieged the mobilization progress. Finally, the interaction mechanism proposed in this study suggests that the storage with intact coating on tailings can limit the microbial degradation to prevent arsenic mobilization to the environment.

Genesis of the giant Caixiashan Zn-Pb deposit in Eastern Tianshan, NW China: Constraints from geology, geochronology and S-Pb isotopic geochemistry

The Caixiashan Zn-Pb deposit is the largest carbonate-hosted Zn-Pb deposit in Eastern Tianshan, NW China. The deposit comprises the No. Ⅰ, Ⅱ, III and IV ore zones with a proven reserve of 131 Mt ore at 3.95% Pb + Zn. The orebodies generally occur as irregular lenses and pods in altered carbonate rocks of the Mesoproterozoic Kawabulake Group near faults. The mineralization is characterized by massive, disseminated and vein/veinlet sulfides including pyrite, pyrrhotite, sphalerite and galena with minor arsenopyrite and chalcopyrite, as well as sulfosalt minerals of Ag, As, Sb and Pb. The mineralization is associated with tremolite, chlorite, silica and carbonate alterations. Rb-Sr isotopic dating of sphalerite and pyrrhotite yields an isochron age of 337.2 ± 5.7 Ma, which is interpreted as the mineralization age. Zircon U-Pb dating reveals that stocks of diorite, quartz diorite, K-feldspar granite and monzonitic granite that occur in the deposit area were emplaced at 348.2 ± 3.7 Ma, 351.9 ± 3.5 Ma, 333.6 ± 3.6 Ma and 330.0 ± 3.6 Ma, respectively. These age data suggest that the mineralization is coeval with Carboniferous granitic magmatism. The δ34SV-CDT values of sulfides (excluding the syn-sedimentary pyrite) range from −2.42‰ to 19.1‰, suggesting that the reduced sulfur was mainly derived from thermal sulfate reduction (TSR) of seawater-derived sulfates in the marine sedimentary basement rocks and minor contribution by replacement of syn-sedimentary pyrite, as well as a possible input of magmatic sulfur. The Pb isotopic compositions of sulfides, with 206Pb/204Pb ranging from 17.074 to 17.361, 207Pb/204Pb from 15.422 to 15.614, and 208Pb/204Pb from 36.685 to 37.303, partly overlap with those of basement rocks of the Mesoproterozoic Kawabulake Group and the Carboniferous intrusions, suggesting that the ore metals were derived from both the basement and Carboniferous magmatism. On the basis of the spatio-temporal relations between hydrothermal alterations/mineralization and Carboniferous magmatism, we conclude that the Caixiashan Zn-Pb deposit is a high-temperature carbonate replacement deposit related to concealed granitic intrusions, which were formed in an arc environment related to the subduction of the South Tianshan Ocean plate beneath the Central Tianshan massif during the Carboniferous time. The results of this study indicate that there is a great potential of finding more large-scale Zn-Pb deposits similar to Caixiashan in Eastern Tianshan.

Early Fimiston and late Oroya Au–Te ore, Paringa South mine, Golden Mile, Kalgoorlie: 4. Mineralogical and thermodynamic constraints on gold deposition by magmatic fluids at 420–300 °C and 300 MPa

The Golden Mile deposit (1767 t Au) in the Archean Yilgarn Craton, Western Australia, is controlled by D2 strike-slip and D3 reverse faults displacing folded tholeiitic greenstones. Granodiorite and monzodiorite dykes emplaced into the faults predate and are synchronous with propylitic and sericite–ankerite alteration overprinted by the ore. Arsenopyrite and chlorite thermometry and fluid-inclusion data indicate ore formation at 420 ± 30 °C and 300 MPa and cooling to the ambient temperature at 10 km depth (250–300 °C). Fimiston refractory ore (7 g/t Au) in propylitic Golden Mile Dolerite is zoned from inner albite–ankerite to outer ankerite–phengite–quartz replacement. Pyrite–magnetite is overprinted by pyrite–hematite ± anhydrite. Arsenical pyrite encloses chalcopyrite, tennantite, gold and tellurides. Gold thio-sulfide complexes, buffered by magmatic SO2 and H2S in the fluid, were destabilised during the ankerite–pyrite replacement of propylitic chlorite, a reaction releasing hydrogen ions for the hydrolitic alteration of adjacent albite. Gold deposition was assisted by declining gold, silver, tellurium and sulfur solubility as the fluid cooled. Dissolved sulfate is recorded in pyrite by negative δ34S (− 10 to − 5‰) at magmatic Δ33S (0–0.2‰). Oroya ore bodies are subdivided into oxidised pyrite lodes (5 g/t Au) in propylitic GMD and reduced lodes (30–120 g/t Au) characterised by Stage 1 silica–pyrite and siderite–chlorite replacement in ankerite-rich wall rocks. Rapid cooling, an acidic fluid and the retrograde solubility of ankerite facilitated replacement and the deposition of minor arsenopyrite, pyrrhotite, chalcopyrite, sphalerite and gold. Locally, the H2S-rich fluid (log fS2 = − 5.8 ± 0.5 bar at 420 °C) was reduced by organic methane. Oroya Stage 2 ore fills crosscutting veins and cements breccia. Quartz, chalcedony, dolomite–ankerite, calcite, V-muscovite, V-chlorite and V-tourmaline form the gangue of pyrite–telluride ± magnetite ore. Altaite–tellurium myrmekites were deposited at ≥ 400 °C as melt droplets together with tellurantimony, altaite, calaverite, montbrayite and petzite. As fluid temperature and tellurium fugacity declined, free gold, krennerite, coloradoite and melonite also crystallised joined by sylvanite and hessite below 350 °C. Finally, trace covellite and digenite precipitated at high fluid sulfidation states.

Metallogenesis of the Hengjiangchong gold deposit in Jiangnan Orogen, South China

The Hengjiangchong gold deposit is located in northeastern Hunan of the central Jiangnan Orogen, South China. Distribution of auriferous sulfide–calcite–quartz vein-type orebodies are controlled by NW-/WNW-trending ductile shear zones, and hosted in the Lengjiaxi Group (Gp.) low-grade metamorphic sequences and the Hengjiangchong granite. Ore minerals include mainly pyrite, arsenopyrite, pyrrhotite, chalcopyrite, sphalerite, galena, and native gold, whilst the major alteration styles include silicic, sericite, carbonate and chlorite. Alteration/mineralization can be divided into three stages: quartz–calcite–pyrite–arsenopyrite mineralization (Stage 1), quartz–calcite–polymetallic sulfide mineralization (Stage 2), and quartz–calcite ore-barren alteration (Stage 3). Two types of fluid inclusion (FI) are present in the auriferous sulfide–calcite–quartz ore veins: CO2-bearing (C) and H2O-rich (W) type. Petrographic and microthermometric analyses of the FIs yielded homogenization temperatures for Stage 1, 2, and 3 to be 254–377, 191–339, and 134–223 °C, respectively, with corresponding salinities of 2.22–10.37, 2.23–9.98, and 1.56–4.94 wt% NaClequiv. Pressures of Stage 1 and 2 mineralization are estimated to be 280–370 and 170–300 MPa, respectively. δ18O and δD values are determined to be 9.8–10.1‰ and −70.2 to −68.7‰ (Stage 1), 7.4–8.1‰ and −72.4 to −71.2‰ (Stage 2), and 2.7 to 2.9‰ and −79.1 to −73.0‰ (Stage 3), respectively. These results indicate that the primary ore-forming fluids were derived from a metamorphic source. For the auriferous sulfides, their δ34S values are of −15.4 to −7.5‰, whilst their 208Pb/204Pb, 207Pb/204Pb, and 206Pb/204Pb values are of 38.663–44.861, 15.637–15.769, and 18.301–20.936, respectively. Both the stable and radiogenic isotopic data indicate that ore-forming fluids and metals were derived from a deeper and higher metamorphic grade source (e.g. underlying metamorphosed rocks). Fluid immiscibility and fluid–rock interactions were likely critical for the gold ore precipitation. The Hengjiangchong deposit exhibits many features of orogenic gold deposits, such as the structural control on orebody distribution, alteration and mineralization styles, and FI microthermometric and H–O–S–Pb isotopic features. Therefore, the Hengjiangchong is best classified as an orogenic gold deposit.

Age and source of the Küre/Ödemiş arsenopyrite-gold mineralization (Menderes Massif, Turkey) determined by Re-Os-He isotopes

The Menderes Massif (MM) is considered to be one of the principal regions hosting vein-type quartz-arsenopyrite orogenic gold deposits and occurrences in Turkey. Gold mineralizations in the MM can be grouped into: (i) schistosity-conformable E-trending veins and (ii) shear-controlled NW-trending veins. Arsenopyrite is one of the major gold-bearing minerals in these deposits or occurrences. Rhenium–Osmium isotopic dating of two types of arsenopyrite from the schistosity-conformable and vein-type Küre (Ödemiş) gold deposit has yielded two groups of model ages (maximum ages) at 557–574 Ma and 246–250 Ma, respectively. The data suggested that the quartz-arsenopyrite gold deposit formed in the Neoproterozoic and Early Triassic, with the former and the latter corresponding to Pan-African compressional orogenesis and Palotethys rifting, respectively. Fluid inclusions in Küre arsenopyrite have 3He/4He ratios of ~0.08–0.09 Ra (Ra = 1.39x10-6, the 3He/4He ratio of air) being within the range of middle to upper crustal values. A minor helium contribution of mantle fluids to the Küre gold deposit is possible because the 4He concentrations in arsenopyrite are enriched 170 to 9520 times relative to argon and typical atmospheric values, indicating that contribution of atmospheric He to the mineralizing fluids is negligible, and 0.08–0.09 Ra is slightly above typical crustal 3He/4He ratios. Arsenopyrite yields relatively non-radiogenic initial Os isotopic compositions, also indicating possiblecontribution from mantle fluids. Carbonic fluid inclusion type-2 (H2O-CO2-NaCl ± CH4) in quartz of NW-trending veins at Küre are gas–liquid-hydrate-crystal-rich and their homogenization temperatures (Th) range from 244 to 387 °C. Salinity values range from 0.2 to 5.7 wt% NaCl equiv. The homogenization temperatures (Th) of aqueous fluid inclusions type 1 (H2O-NaCl) in quartz from NW-trending veins at Küre vary between 237 and 358 °C whereas salinity values range from 1.7 to 7.7 wt% NaCl equiv. Quantitative EPMA spot analyses on arsenopyrite minerals have shown that As concentrations in EW-trending and NW-trending veins range from 32.5 to 33.8% and 32.3–33.8%, respectively. Based on a phase diagram for the Fe–As–S system along with the arsenopyrite geothermometer, the ranges of temperature and corresponding logf S2, at which arsenopyrite is in equilibrium with pyrite are between 380 and 480 °C, and −7.4 and −4.3 for Apy-1, respectively. These values are between 390 and 475 °C, and −7.0 and −4.5 for Apy-2, respectively.

Flotation enrichment of resistant gold ores

Ores of the Vasilkovsky deposit include arsenopyrite, pyrite, pyrrhotite, marcasite, gold, chalcopyrite, sphalerite, galena, faded ore (tennantite)S, bismuthine, native bismuth, lellingite, molybdenite, cubanite, bornite, antimonite, relict minerals, magnetite, apatite and apatite chromite, sericite, chlorite, potassium feldspar, tourmaline), quartz, carbonates (siderite, ankerite, calcite), fluorite, barite. Arsenopyrite is the main ore mineral. It contains the bulk of gold, as well as impurities - copper, cobalt, nickel, bismuth, zirconium, titanium, lead, zinc, antimony, silver, molybdenum. Bismuth and its minerals are widespread, they are constantly associated with arsenopyrite, forming intergrowths with native gold, less often with chalcopyrite and faded ore. Native gold is distributed very unevenly, forms the finest precipitates ranging in size from tenths of a micron to 0.063 mm, grows together with quartz, arsenopyrite, pyrite and bismuth minerals. Rich ores were formed by combining bismuthcontaining associations with arsenopyrite. The role of gold in arsenopyrite increases with depth. Ores are of the gold-quartz-sulfide type. Quartz in ore up to 90 %, sulfides from 3 to 5 %. The content of harmful impurities (arsenic) reaches 2 % or more. Ores are refractory, require special technology for the beneficiation and extraction of gold.

Zircon U–Pb geochronology, geochemistry, S–Pb–Hf isotopic compositions, and mineral chemistry of the Xin'gaguo skarn Pb–Zn deposit, Tibet, China

The Xin'gaguo deposit is representative of the skarn Pb–Zn polymetallic zone in the northern Gangdese porphyry metallogenic belt, Tibet. Pb–Zn mineralization is hosted in the Take'na formation skarn. The Xin'gaguo ore‐forming process can be divided into prograde skarn, retrograde skarn and quartz‐sulfides. Skarn minerals include garnet, diopside, and epidote, with minor wollastonite, actinolite, and chlorite. Metallic minerals are mainly sphalerite, galena, chalcopyrite, magnetite, and pyrrhotite, with minor arsenopyrite, marcasite, native bismuth, cosalite, and gersdorffite. The LA–ICP–MS zircon U–Pb age of the diorite is 59.66±0.52 Ma. Diorite samples are characterized by fractioned REE patterns with marked positive Eu anomalies, enriched LILEs (Rb, Ba, Th, U, and K) and depleted HFSEs (Ta, Nb, Zr, Hf, and Ti), belong to the calc‐alkaline series and have metaluminous compositions. Zircon εHf(t) values of the diorite are positive (5.7–11) and lie between the chondrite and mantle values. These geochemical characteristics suggest that the diorite was formed by the partial melting of a young metasomatized asthenospheric mantle wedge deriving basaltic rocks. The δ34S values of sulfides range from −4.7 to 4.5‰ and show a bimodal distribution, indicating interactions of magma‐derived ore fluid with biogenic sulfide minerals from the Take'na formation. The 206Pb/204Pb (18.5–18.629), 207Pb/204Pb (15.599–15.704), and 208Pb/204Pb (38.616–38.975) of sulfides show that ore‐forming metals were derived from mixed sources, in part from the Lhasa Terrane basement. Skarn mineral compositions imply that the ore‐forming environment was variable, and underwent at least three changes in oxidation‐reduction state. The geochemical characteristics of diorite indicate that the Xin'gaguo deposit formed within the Indo‐Asian continental collision tectonic setting.

Chemical oxidation of arsenopyrite using a novel oxidant—Chlorine dioxide

Arsenopyrite is a typical arsenic-containing mineral, and gold is generally hosted by arsenopyrite mineral which adversely affects gold leaching. In this study, a novel environmentally friendly oxidant, chlorine dioxide (ClO2), was used for the first time to efficiently oxidize arsenopyrite under acidic conditions, preventing the adverse effect of arsenopyrite on gold leaching. The addition of solid NaClO2 to acidic arsenopyrite slurry made the oxidation of arsenopyrite feasible for practical purposes, as NaClO2 generates ClO2 under acidic conditions, which then oxidizes arsenopyrite. For a 400 mL sample of arsenopyrite pulp with the initial concentration of 4.07 g/L (0.025 M), the oxidation efficiencies of Fe and As in arsenopyrite reached 94.25% and 85.39%, respectively for NaClO2 and H2SO4 concentrations of 0.125 M each, under magnetic stirring for 1 h at 30 °C in a constant-temperature water bath. At the end of the reaction, both the acidity and oxidation-reduction potential of the system increased, and the ClO2 concentration correspondingly decreased. Chemical composition analysis, X-ray diffraction analysis, particle size distribution measurements, scanning electron microscopy combined with energy dispersive spectrometer analysis, and X-ray photoelectron spectroscopy of arsenopyrite mineral ore and its oxidized residues were performed under different reaction conditions. Analysis results indicated that tiny amorphous precipitates of the oxidation by-products, such as FeAsO4·7H2O, H3AsO3, Fe2(SO4)3·7H2O, and hydrated ferric oxides would cover the surface of unreacted arsenopyrite at low H2SO4 concentration, which prevented the oxidation-reduction reaction from proceeding. As the concentrations of H2SO4 and NaClO2 increased, fine arsenopyrite particles were oxidized first, and ClO2 gradually eroded the surface of the unreacted arsenopyrite minerals to form cracks, defects, and pores, until arsenopyrite was fully oxidized. ClO2 presents several advantages: it can be easily prepared, it is a strong oxidant, and is non-polluting. Therefore, the procedure in this study is expected to be used as a novel method for preventing the effect of arsenopyrite enwrapping gold in refractory gold ores and for directly leaching gold.

Refractory gold ores and concentrates part 2: gold mineralisation and deportment in flotation concentrates and bio-oxidised products

ABSTRACT Gold mineralisation and deportment in two refractory flotation concentrates and their corresponding bio-oxidised products were investigated using several analytical techniques. One concentrate and its product show higher gold grades (28 and 38 g/t, respectively) than the other (17 and 23 g/t, respectively). The results showed that both visible, polydispersed and invisible gold particles were present in all four samples. The invisible gold was disseminated in arsenian pyrite and arsenopyrite mineral phases. Unliberated, visible gold particles were in complex gold associations with sulphides, silicates, and oxides. In addition, visible gold-sulphate mineral associations were also noticeable in the bio-oxidised products. Marked differences in gold mineralisation and association such as occurrence of gold in muscovite and jarosite-cemented gangue mineral agglomerates were notable between the two bio-oxidised products. Furthermore, combined jarosite and gypsum mineral encapsulation accounted for ≈ 43 wt.% Gold refractoriness in the lower gold-bearing bio-oxidised product.