Search

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study presents the results of a two-stage autoclave processing of a copper–arsenic concentrate. Copper concentrate is an important raw material to produce copper and other metals. However, in some cases, the concentrate may contain increased amounts of arsenic, which makes further processing difficult. Therefore, the development of modern hydrometallurgical methods for processing copper concentrate with a high arsenic content is an urgent task, which could lead to the optimization of the raw material processing process and the improvement of the quality of the concentrate. It has been established that the optimal conditions for the sequential two-stage autoclave processing of copper–arsenic concentrate are: t = 220–225 °C, τoxidation = 20 min, τtot = 90 min, Po2 = 0.4 MPa, and L:S = 10:1, [H2SO4]initial = 40 g/dm3; in this case, 85% of zinc, 44% of iron, and 78% of arsenic, respectively, are extracted into the solution during both stages and the loss of copper was about 0.01%. This is explained by the fact that at the first stage (oxidation) of the autoclave processing of the copper–arsenic concentrate, copper, together with iron, leaches into the solution, and at the second stage (reduction), copper precipitates out of the solution in the form of chalcocite. Copper in the residue after autoclave leaching is in the form of Cu2S, iron is in the form of pyrite (FeS2), and lead is in the form of anglesite (PbSO4), respectively. The obtained micrographs and EDX mappings clearly show no iron arsenates. This confirms that at the oxidative stage of the developed process, arsenic, removed by 78%, remains in the solution. The remaining arsenic is associated with tennantite, indicating the effectiveness of the treatment process in removing arsenic from the copper–arsenic concentrate. A second important observation is the presence of pronounced areas of copper sulfides in the microphotos without iron and arsenic impurities. This confirms that copper is deposited as chalcocite during the reduction phase of the process, which is the desired result. [ABSTRACT FROM AUTHOR]

Despite its growing importance as a Cu resource, studies on tennantite bioleaching are highly limited. One of the key challenges in processing such Cu-As sulfides is their refractoriness and the solubilisation of toxic As. The ultimate goal is to achieve selective bioleaching of Cu with simultaneous immobilisation of As in the leach residues. This study investigated the effectiveness of activated carbon (AC)-assisted bioleaching of tennantite concentrate using a mixed culture containing various "strong" and "weak" Fe-oxidising bacteria/archaea plus a S-oxidising bacterium, with particular emphasis on controlling the solution redox potential (Eh). In the initial flask bioleaching tests, a steady increase in Eh (up to 840 mV) was observed, reflecting the activity of "strong" Fe-oxidisers. In this situation, AC dosing effectively suppressed the Eh value and the highest Cu dissolution (70%) was obtained in the AC-0.01% system, while simultaneously immobilising As. In order to maximise Cu dissolution and As immobilisation, it was found preferable to target the Eh range of 650-700 mV during bioleaching. The next bioreactor tests used the mixed culture of the same origin, but had been subcultured a few generations further on tennantite concentrate. The Eh level remained unexpectedly low (~630 mV) for most of the leaching period, regardless of the AC dosage. It was later found that the bioreactor systems were almost exclusively dominated by Sb. thermosulfidooxidans, a "weak" Fe oxidiser with high Cu/As tolerance. In this case, there was no need to artificially suppress the Eh level by AC dosing and Cu leached readily to a final Cu dissolution of ~60% while As dissolution was suppressed to ~15%. Thus, depending on the microbial community that develops at the processing site, Eh control can be achieved either naturally by the activity of "weak" Fe-oxidisers as the predominant survivors under high Cu/As stress, or artificially by the addition of an Eh regulator such as a carbon catalyst. [ABSTRACT FROM AUTHOR]

In the present work the effect of alkaline sulfide leaching (ASL) on the extraction of copper and zinc from low-grade copper concentrate containing chalcopyrite, tennantite, sphalerite, and pyrite during batch and continuous bioleaching experiments was studied. It was demonstrated that ASL and further bioleaching may be a promising approach for treatment of copper–zinc concentrates containing tennantite as this approach allows increasing copper extraction degree in comparison to one-stage bioleaching by 1.6–2.3 times. Thus, ASL was shown to be effective for pretreatment of tennantite containing concentrates to improve bioleaching for copper extraction. At the same time, ASL led to decrease in zinc extraction by 1.4–1.5 times. Therefore, the development of combined hydrometallurgical processes including ASL and bioleaching for effective metal leaching requires further studies to avoid negative effect on zinc extraction.

This study presents the results of a two-stage autoclave processing of a copper–arsenic concentrate. Copper concentrate is an important raw material to produce copper and other metals. However, in some cases, the concentrate may contain increased amounts of arsenic, which makes further processing difficult. Therefore, the development of modern hydrometallurgical methods for processing copper concentrate with a high arsenic content is an urgent task, which could lead to the optimization of the raw material processing process and the improvement of the quality of the concentrate. It has been established that the optimal conditions for the sequential two-stage autoclave processing of copper–arsenic concentrate are: t = 220–225 °C, τoxidation = 20 min, τtot = 90 min, Po2 = 0.4 MPa, and L:S = 10:1, [H2SO4]initial = 40 g/dm3; in this case, 85% of zinc, 44% of iron, and 78% of arsenic, respectively, are extracted into the solution during both stages and the loss of copper was about 0.01%. This is explained by the fact that at the first stage (oxidation) of the autoclave processing of the copper–arsenic concentrate, copper, together with iron, leaches into the solution, and at the second stage (reduction), copper precipitates out of the solution in the form of chalcocite. Copper in the residue after autoclave leaching is in the form of Cu2S, iron is in the form of pyrite (FeS2), and lead is in the form of anglesite (PbSO4), respectively. The obtained micrographs and EDX mappings clearly show no iron arsenates. This confirms that at the oxidative stage of the developed process, arsenic, removed by 78%, remains in the solution. The remaining arsenic is associated with tennantite, indicating the effectiveness of the treatment process in removing arsenic from the copper–arsenic concentrate. A second important observation is the presence of pronounced areas of copper sulfides in the microphotos without iron and arsenic impurities. This confirms that copper is deposited as chalcocite during the reduction phase of the process, which is the desired result.

The massive sulfide deposits (VMS) from Mănăilă are associated with the metamorphic formations of the Tulgheș Lithogroup from the Bucovinian Nappes of the Crystalline-Mesozoic Zone in the Eastern Carpathians, Romania. The following types of ore were identified: pyrite-polymetallic, pyrite copper, compact and precompact copper, and quartz-precompact copper. The polymetallic mineralization consists of pyrite, chalcopyrite, sphalerite, galena, and subordinately arsenopyrite and tennantite. The copper, especially the quartz-copper mineralizations, have a distinct mineralogical composition compared to the other metamorphosed mineralizations of the Tulgheș Lithogroup. These types of deposits from Mănăilă contain large amounts of bornite and chalcocite along with chalcopyrite. Tennantite is abundant and has up to a 3.57 wt.% of bismuth. Wittichenite was identified for the first time in the metamorphic mineralizations and mawsonite was identified as the first occurrence in Romania. An unnamed mineral with the formula: C u , F e 11 P b , A g S 7 was also identified, belonging to the sulfides group. The compact and precompact pyrite-rich ores, located in sericite ± quartzite schists and covered by rhyolitic metatuffs, are of hydrothermal-sedimentary type metamorphosed in the greenschist facies. The source of the quartz-copper mineralization would be the retromorphic or metasomatic hydrothermal solutions that circulated through major fractures. [ABSTRACT FROM AUTHOR]

The nature of tennantite (Cu12As4S13), chalcopyrite (CuFeS2) and sphalerite (ZnS) particles' mixture dissolution in nitric acid (HNO3) media was investigated in this study. The effects of temperature (323–368 K), HNO3 (1–8 mol/L) and Fe3+ (0.009–0.036 mol/L) concentrations, reaction time (0–60 min) and pyrite (FeS2) additive (0.5/1–2/1; FeS2/sulf.conc.) on the conversion of the minerals were evaluated. It has been experimentally shown that the dissolution of the mixture under optimal conditions (>353 K; 6 mol/L HNO3; FeS2/synt. conc = 1/1) allows Cu12As4S13, CuFeS2 and ZnS conversion to exceed 90%. The shrinking core model (SCM) was applied for describing the kinetics of the conversion processes. The values of Ea were calculated as 28.8, 33.7 and 53.7 kJ/mol, respectively, for Cu12As4S13, CuFeS2 and ZnS. Orders of the reactions with respect to each reactant were calculated and the kinetic equations were derived to describe the dissolution rate of the minerals. It was found that the interaction between HNO3 solution and Cu12As4S13, CuFeS2 and ZnS under the conditions investigated in this are of a diffusion-controlled nature. Additionally, the roles of Fe(III) in the initial solution and FeS2 in the initial pulp as catalysts were studied. The results indicated that the increase in Fe3+ concentration significantly accelerates the dissolution of the mixture, while the addition of FeS2 forms a galvanic coupling between FeS2, and Cu12As4S13 and CuFeS2, which also accelerates the reaction rate. The results of the study are considered useful in developing a hydrometallurgical process for polymetallic sulfide raw materials treatment. [ABSTRACT FROM AUTHOR]

High-arsenic copper flotation concentrates, in which the major arsenic-bearing mineral was tennantite, were leached with an alkaline sulphide system. At a pulp density of 5 wt% solids with 100–150 g/L Na2S and 50 g/L NaOH, over 91 wt% As was dissolved within 2 h at 100°C. From concentrates containing 3.4–4.9 wt% As, leach residues containing <0.5 wt% As were obtained making them suitable as a smelter feed without a penalty for arsenic. Copper dissolution ranged from 16 to 22 wt% Cu, with significant amounts of calcium, iron and sulphur also dissolved. In a leach at 34.0 wt% solids, excellent arsenic extraction was obtained (97.9 wt% As), but the levels of copper, calcium, and iron dissolution were 0.5, 1.1, and 0.2 wt%, respectively, meaning excellent selectivity for arsenic was achieved. X-ray diffraction and electron probe microanalyses indicated the mechanism for arsenic dissolution from tennantite, and bornite abundance in the residue. [ABSTRACT FROM AUTHOR]

In the present work the effect of alkaline sulfide leaching (ASL) on the extraction of copper and zinc from low-grade copper concentrate containing chalcopyrite, tennantite, sphalerite, and pyrite during batch and continuous bioleaching experiments was studied. It was demonstrated that ASL and further bioleaching may be a promising approach for treatment of copper–zinc concentrates containing tennantite as this approach allows increasing copper extraction degree in comparison to one-stage bioleaching by 1.6–2.3 times. Thus, ASL was shown to be effective for pretreatment of tennantite containing concentrates to improve bioleaching for copper extraction. At the same time, ASL led to decrease in zinc extraction by 1.4–1.5 times. Therefore, the development of combined hydrometallurgical processes including ASL and bioleaching for effective metal leaching requires further studies to avoid negative effect on zinc extraction. [ABSTRACT FROM AUTHOR]

Bioleaching may be effectively used to extract nonferrous metals from sulfide ores and concentrates. At the same time, some minerals are refractory and their bioleaching rate is often comparatively low that does not allow the required metal extraction rate to be achieved. In the present work, we studied the two-stage process, which included stages of biological and chemical leaching, to improve copper extraction from low grade Cu–Zn sulfide concentrate containing chalcopyrite, tennantite, pyrite, and sphalerite. Bioleaching was conducted in the continuous mode in three laboratory scale reactors connected in series. The pulp density was 10% and the residence time was 7 days. The temperature was 40 °C in the 1st reactor and 50 °C in the 2nd and 3rd reactors. Bioleaching allowed the extraction of 29.5 and 78% of Cu and Zn, respectively. The solid bioleach residue obtained was then treated for additional Cu and Zn recovery using high temperature leaching at 90 °C for 25 h. The liquid phase of the bioleaching pulp contained Fe3+ ions, which is the strong oxidant, and the leach solution was supplemented with NaCl. In the presence of the maximal NaCl concentration (1 M), Cu and Zn extraction reached 48 and 84%. Thus, two-stage leaching may allow to increase bioleaching efficiency and may be used to improve the bioleaching rate of refractory minerals, such as chalcopyrite. [ABSTRACT FROM AUTHOR]

The goal of this work was to study the bioleaching of arsenic-containing polymetallic concentrate that contained 6.2% Cu, 7.3% Zn and 1.7% As, depending on different temperatures and in the presence of CO2 and molasses in the medium, as well as the difference in the composition of microbial population formed under various conditions. A mixed population of moderately thermophilic and thermotolerant acidophilic microorganisms formed during the continuous bioleaching of copper concentrate was used as an inoculum. The experiments were carried out in a continuous mode in laboratory scale reactors, with a temperature range of 40 °C to 60 °C. To assess the effect of CO2 and molasses on metal leaching and microbial population composition, the experiments were carried out in three reactors: CO2 (~0.01 L/min) was supplied into the first reactor; 0.02% molasses were added to the pulp of the second reactor; and no additional carbon sources were supplied into the control reactor. The highest copper recovery (27%) was achieved at 50°C in the experiment with molasses, while the highest zinc recovery (82.1%) was reached at 45°C in the control experiment. Additional carbon sources affected the extraction of non-ferrous metals only at 60 °C and increased the extraction of copper and zinc by 12.6% and 24.2%, respectively. Both the temperature and carbon source used affected the microbial population composition. The main microbial genera revealed in the populations by next generation sequencing (NGS) were bacteria of the genera Sulfobacillus and Acidithiobacillus, as well as archaea of the genera Ferroplasma, Acidiplasma, and Cuniculiplasma. At low temperatures (40 and 45 °C), Acidithiobacillus, Sulfobacillus, and Ferroplasma predominated, while at temperatures 50–55 °C, the decrease in relative abundance of these genera occurred, and the predominance of Acidiplasma archaea was observed. The usage of both CO2 and molasses led to the increase in Sulfobacillus and Acidiplasma in relative abundance. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Mineral Processing Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bioleaching may be effectively used to extract nonferrous metals from sulfide ores and concentrates. At the same time, some minerals are refractory and their bioleaching rate is often comparatively low that does not allow the required metal extraction rate to be achieved. In the present work, we studied the two-stage process, which included stages of biological and chemical leaching, to improve copper extraction from low grade Cu–Zn sulfide concentrate containing chalcopyrite, tennantite, pyrite, and sphalerite. Bioleaching was conducted in the continuous mode in three laboratory scale reactors connected in series. The pulp density was 10% and the residence time was 7 days. The temperature was 40 °C in the 1st reactor and 50 °C in the 2nd and 3rd reactors. Bioleaching allowed the extraction of 29.5 and 78% of Cu and Zn, respectively. The solid bioleach residue obtained was then treated for additional Cu and Zn recovery using high temperature leaching at 90 °C for 25 h. The liquid phase of the bioleaching pulp contained Fe3+ ions, which is the strong oxidant, and the leach solution was supplemented with NaCl. In the presence of the maximal NaCl concentration (1 M), Cu and Zn extraction reached 48 and 84%. Thus, two-stage leaching may allow to increase bioleaching efficiency and may be used to improve the bioleaching rate of refractory minerals, such as chalcopyrite.

The goal of the present work was to study the bioleaching of chalcopyrite (CuFeS2), enargite (Cu3AsS4), and tennantite (Cu12As4S13) by pure and mixed cultures of moderately thermophilic microorganisms belonging to the groups predominant in technological processes (Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans SH-1, and Acidiplasma sp. MBA-1) under different conditions (temperature of 40 to 60°C, presence of Fe2+ ions, pyrite (FeS2), and pyrrhotite (FeS)). Bioleaching of copper from chalcopyrite and enargite was shown to depend on temperature and to be almost independent of the composition of microbial culture. Under optimal conditions (50–55°C), after 30 days 25–27 and 14% of copper was leached from chalcopyrite and enargite, respectively. Increase in the temperature up to 60°C led to the inhibition of copper bioleaching from both minerals. The optimal temperature for tennantite bioleaching was 45°C, while the rate of bioleaching was significantly dependent on the composition of the microbial culture. In an experiment with a mixed culture of all three strains, 26% of copper was leached, while in experiments with pure cultures of A. caldus MBC-1, S. thermosulfidooxidans SH-1, and Acidiplasma sp. MBA-1, after 30 days 12, 21, and 18% of copper was leached, respectively. Addition to the medium of Fe2+ as ferrous sulfate resulted in an increased rate of copper leaching from enargite and tennantite, which may be explained by the fact that Fe3+ ions are generated during microbial Fe2+ biooxidation to Fe3+, which is a strong oxidizing agent and plays an important role in the leaching of sulfide minerals. In the presence of pyrite and pyrrhotite, the rates of enargite and tennantite leaching increased, probably due to the presence of Fe3+ ions in the medium, which were generated during the biooxidation of iron sulfide minerals. The results of the work demonstrated that different environmental factors affected the bioleaching of copper minerals in different ways, which is of practical importance, in particular, for planning the trials for bioleaching of mineral raw materials. [ABSTRACT FROM AUTHOR]

Oscillatory zoning in tennantite-(Fe) crystals found in carbonate–sulfide aggregates at the Darasun gold deposit has been studied. Similar elements have been distinguished in zoned crystals: core, "identical oscillatory rhythm," rhythms with crystallographic and wavy oscillatory zoning, and rim with poorly defined fine oscillatory zoning. Oscillatory zoning is due to considerable variations in the contents of semimetals (As and Sb) and formally divalent metals (Fe and Zn). Variations in As and Sb are coupled with changes in Fe and Zn, respectively. Both As and Fe contents increase in zoned crystals from the center to the edge: Sb/(Sb + As) ratio varies from 0.44 to 0.03, while Fe/(Fe + Zn) ratio varies from 0.38 to 0.75. The evolution of the composition of zoned tennantite-(Fe) crystals is similar to that of the fahlore at the deposit and to that in pseudomorphic rhythmically zoned tennantite aggregates. A negative relationship between Sb/(Sb + As) and Fe/(Fe + Zn) ratios has been revealed: it is stronger in the internal rhythms than in the external. The oscillatory zoning formed under conditions close to local equilibrium under the influence of external factors at the early crystal growth stages. The composition of zones reflects (random) fluctuations of the external parameters caused by variations in physicochemical conditions (T, fS2, fO2, and pH) and fluid composition, by fluid boiling or mixing of fluids from different sources. Subsequently, changes in the crystal morphology, irregular fluctuations in crystal compositions, and various trends in the behavior of components were caused by the appearance of a concentration gradient at the mineral–fluid boundary and kinetic phenomena on the mineral growth surface. The zoning developed under the influence of "internal" mechanisms under conditions far from equilibrium due to the interrelation between the growth of zones enriched in one component, resulting from the concentration gradient at the crystal–fluid boundary, and the incorporation of another component, in particular, as a result of the self-organization process uninfluenced by external factors. It has been concluded that the oscillatory zoning in fahlore is caused by the difference in solubility of the end-members of the tennantite–tetrahedrite solid solution due to changes in the metal and semimetal migration conditions with a decrease in temperature and fluid salinity. Hence, the oscillatory zoning in tennantite-(Fe) crystals at the Darasun deposit was related to self-organization processes complicated by random fluctuations (noise) of the external parameters. [ABSTRACT FROM AUTHOR]

The structure of synthetic tennantite Cu12As4S13 was investigated at various temperatures in the 90–293 K range. It crystallizes in space group. No structural transformation was observed in this temperature range. The structures were refined in anharmonic approximation for atomic displacements and electron density maps were refined using the maximum entropy method. Both approaches indicate a noticeable static disorder of the copper atoms in the triangular sulfur coordination and neighbouring site at high temperatures, whereas these split copper sites are well defined at lower temperatures. One particle potential is used to describe the behaviour of atoms at these copper sites. Such behaviour may be the structural reason for changes in magnetic properties. [ABSTRACT FROM AUTHOR]

The structure of synthetic tennantite Cu12As4S13 was investigated at various temperatures in the 90–293 K range. It crystallizes in space group. No structural transformation was observed in this temperature range. The structures were refined in anharmonic approximation for atomic displacements and electron density maps were refined using the maximum entropy method. Both approaches indicate a noticeable static disorder of the copper atoms in the triangular sulfur coordination and neighbouring site at high temperatures, whereas these split copper sites are well defined at lower temperatures. One particle potential is used to describe the behaviour of atoms at these copper sites. Such behaviour may be the structural reason for changes in magnetic properties. [ABSTRACT FROM AUTHOR]

The study of fahlores is one of the most effective areas of mineralogical research that allows deciphering the conditions for formation of ore deposits, which in its turn is the scientific basis for their search, exploration and rational mining. The main aim of the study was to reveal mineralogical-geochemical features and evolution of the composition of fahlores, as well as features of the ore-forming hydrothermal fluids that formed the Ak-Sug gold-molybdenum-copper-porphyry deposit. Research methods: field studies, detailed mineralogical studies with ore mineralization in polished sections (polished sections) with Olympus polishing microscope and electron microscope MIRA 3 LMU (Tescan Orsay Holding) combined with X-ray microanalysis systems INCA Energy 450+Xmax-80 and INCA Wave 500 (Oxford Instruments Nanoanalysis Ltd). Results. We revealed variations in composition of the fahlores group minerals of the Ak-Sug gold-molybdenum-copper-porphyry deposit, which are represented by the minerals of the tennantite-tetrahedrite series. The latter are developed as part of three mineral associations corresponding to three generations. For the fahlores, a latent smooth zoning is characteristic, due to an increase in the Sb content to the outer zones. Evolution of compositions of the I generation fahlores: Cu-tennantite - Fe-tennantite - Zn-tennantite, II generation: Cu-tennantite - Zn-tennantite - Zn-tennantite-tetrahedrite. Fahlores of the III generation is represented by Zn-tennantite-tetrahedrite. The presence of high-copper tennantite, Zn-tennantite, Zn-tennantite-tetrahedrite, and mineralogical features of the Ak-Sug ore deposits indicate a relatively increased oxidation potential of ore-forming hydrothermal fluids. The main factors of ore deposition were a change in the oxidation-reduction character, variations of fS2, fSe2, fTe2 and temperature decrease of ore-bearing fluid.

Natural samples containing tetrahedrite-tennantite, bournonite-seligmannite and geocronite-jordanite from the Coranda-Hondol ore deposit, Romania, were investigated by Raman spectroscopy to determine its capability to provide estimates of solid solutions in three common and widespread sulfosalt mineral series. Raman measurements were performed on extended solid solution series (Td1 to Td97, Bnn25 to Bnn93 and Gcn24 to Gcn67, apfu). The tetrahedrite-tennantite and bournonite-seligmannite solid solution series show strong correlations between spectroscopic parameters (position, relative intensity and shape of the Raman bands) and the Sb/(Sb+As) content ratio, while Raman spectra of geocronite-jordanite shows no evolution of Raman bands. In order to simplify the method used to estimate the Sb/(Sb+As) content ratio in tetrahedrite-tennantite and bournonite-seligmannite series, several linear equations of the first-order polynomial fit were obtained. The results are in good agreement with electron microprobe data. Moreover, a computer program was developed as an analytical tool for a fast and accurate determination of Sb/(Sb+As) content ratio by at least one spectroscopic parameter. These results indicate that Raman spectroscopy can provide direct information on the composition and structure of the tetrahedrite-tennantite and bournonite-seligmannite series. [ABSTRACT FROM AUTHOR]

By thermodynamic calculation and analysis, a hypothesis is suggested and provided that tennatite gets easily converted to Cu 3 As which exists in slag in the traditional pyrometallurgy process. Due to the formation of Cu 3 As, the economic value of high-arsenic silver bearing copper ore is greatly reduced, and the copper recovery ratio declines. Arsenic in the silver bearing copper ore is a punitive element in a trade. It is verified that arsenic could be removed from tennantite and most of sulfur is retained satisfactorily at low oxygen pressure. Investigation has been carried out for arsenic removal from a silver bearing copper ore. The copper ore was roasted in nitrogen atmosphere (> 99%) at temperatures ranging from 923.15 K to1123.15 K. By suitably adjusting the main reaction conditions, nearly 98% arsenic was removed at 1053.15 K for 3 h in nitrogen atmosphere, while most of the sulfur was particularly retained in the copper ore. After the arsenic removal, the arsenic content was reduced from 7.81% to 0.13% and the copper ore could be used for feeding the smelter. Compared with the traditional method of arsenic removal from copper ore by roasting in oxygen, our proposed method of arsenic removal in nitrogen atmosphere at temperature of 1053.15 K is more effective. [ABSTRACT FROM AUTHOR]

The subject of this research was the chemical composition of ten mineral samples from the tetrahedrite series from Czech historical silver deposits Příbram, Obecnice, Zvěstov, Ratibořské Hory, Stará Vožice, Jáchymov, Kutná Hora, Stříbrná Skalice and one tetrahedrite sample from the iron deposit Mníšek pod Brdy. An empirical formula was calculated for each sample based on average analytical data. Samples from Příbram and Obecnice near Příbram are slightly Ag-enriched tetrahedrites (0.22-1.85 apfu Ag). The sample from Zvěstov is Ag-poor tennantite (Ag 0.12 apfu; As 2.52 apfu). Tetrahedrite from Mníšek pod Brdy is rich in Zn (1.57 apfu) and slightly Hg-enriched (0.31 apfu). Samples from Ratibořské Hory - Stará Vožice ore district are freibergites (Ag 4.97; 5.34 apfu) as well as the sample from Kutná Hora (Ag 4.33 apfu). Tetrahedrite from Stříbrná Skalice is slightly Ag-enriched (0.18 apfu). The sample from Jáchymov is Bi-rich tennantite as twelve analyses showed the average content of As 2.52 apfu and the content of Bi in range of 0.72 - 1.48 apfu. [ABSTRACT FROM AUTHOR]

Copper sulfide concentrates with high contents of deleterious impurities such as arsenic and antimony must be pretreated before conventional smelting to prevent atmospheric pollution with toxic compounds. In this work, the selective removal of arsenic and antimony from enargite–tennantite concentrates by a hydrometallurgical process was studied. The process consists of an alkaline digestion using a small volume of concentrated NaHS–NaOH solutions to obtain soluble arsenic and antimony compounds and insoluble copper sulfides. The soluble arsenic and antimony is separated from the copper sulfide by water leaching of the digested material. The experiments were carried out using a copper–arsenic concentrate with 15.1% As and 1.42% Sb. The results showed that the digestion temperature and the concentrations of NaHS and NaOH were the most important variables affecting the rate of arsenic and antimony removal. The rate of the digestion reaction was analyzed by using the unreacted shrinking core model controlled by the diffusion of S 2 − ions through the layer of the product copper sulfide. An experimental activation energy value of 57 kJ/mol was determined for the arsenic removal in the range of temperature of 60–90 °C. [ABSTRACT FROM AUTHOR]

The authors discuss flotation of fahl ore. It is proved that tennantite should be separated into an individual copper product in order to enhance overall copper recovery and mitigate ecological impact by means of preventing arsenic volatilization under smelting. Single mineral fractions of pyrite, chalcopyrite, tennantite, secondary sulfides, sphalerite and quartz sampled in the Ural region, as well as the samples of copper-zinc ore containing fahl ore are examined. The research involves oxidation of copper sulfides and pyrite under grinding in different conditions. Concentration of oxygen and sulfur-bearing ions is under control. The differences in oxygen consumption, oxidation of pyrite, tennantite and other sulfides are used to develop the mode of tennantite separation from other copper sulfides, sphalerite and pyrite. Based on the research findings, the authors recommend a flotation technology for copper-zinc pyritic ore with high content of tennantite to separate tennantite and secondary copper sulfides in different flotation circuits at varied pH. [ABSTRACT FROM AUTHOR]

Abstract: An investigation has been carried out for arsenic removal from a silver–copper ore. The copper ore was roasted in air, in nitrogen atmosphere and in vacuum at high temperature. It was found that arsenic was more easily removed in vacuum at lower temperature with shorter time. By suitably adjusting the main reaction conditions, almost 98.97% arsenic could be removed, while most of the sulfur was particularly retained in the copper ore. It was illustrated that arsenic could be completely removed on anaerobic conditions. After arsenic was removed, the copper ore with higher economic value could be used for feeding to the smelter. [Copyright &y& Elsevier]

Abstract: The preliminary results of the application of sulfuric acid baking followed by water leaching for the treatment of arsenopyrite (FeAsS), tennantite (Cu12As4S13), and tetrahedrite (Cu12Sb4S13) have been reported. Baking of pulverized minerals (P100 =106μm) at 200°C with a sulfuric acid/mineral powder ratio of 5/3 (g/g) in a muffle furnace for 7h resulted in the transformation of the mentioned minerals to water soluble compounds. Arsenopyrite transformed into FeSO4 and As2O3, both of which are highly soluble in water. Tennantite transformed into CuSO4 and As2O3 whereas tetrahedrite transformed into CuSO4 and Sb2O3. While CuSO4 and As2O3 completely dissolved in water, Sb2O3 did not dissolve, reporting to the leach residue. More than 63% of iron and arsenic from arsenopyrite, and more than 86% of copper from tennantite and tetrahedrite were extracted into water. [Copyright &y& Elsevier]

Abstract: In this study, the effects of sodium thiosulphate on chalcopyrite and tennantite at various pH values were investigated. Contact angle, flotation (Hallimond tube), zeta potential and X-ray photoelectron spectroscopy were used to observe these effects and to investigate the mechanisms involved. The addition of sodium thiosulphate depressed both chalcopyrite and tennantite at all pH values. Further addition of diethyl dithiophosphate significantly increased the flotability of chalcopyrite at all pH values as well as tennanite in acidic conditions, but not tennantite in alkaline conditions. In light of the zeta potential measurements and due to the stability of thiosulphate over the pH range, the coverage of sulphate resulting from the oxidation of thiosulphate was responsible for the depression of both chalcopyrite and tennantite in acidic conditions. Adsorption of diethyl dithiophosphate species on the mineral surface resulted in flotability of tennantite which was almost as high as that of chalcopyrite. In alkaline conditions, coverage of the copper thiosulphate complex was responsible for the depression. The copper thiosulphate complex inhibited adsorption of diethyl dithiophosphate species on the mineral surface. Higher coverage of the copper thiosulphate complex on tennantite caused an insignificant increase in its flotability in comparison to that of chalcopyrite which allowed the separation of tennantite from chalcopyrite. The XPS spectra supported the proposed mechanism of thiosulphate depression on these minerals. [Copyright &y& Elsevier]

Abstract: Atomic force microscopy (AFM) has been used to observe the morphology and surface characteristics of chalcopyrite and tennantite treated at pH 4 and 9. Mineral treated with DTP at pH 9 was also observed. It was found that new surface “islands” were formed on the minerals after these treatments. The occurrence of these islands as a product of reaction was amplified with increasing treatment time. Adhesion force measurements revealed that the formation of islands under acidic conditions (pH 4) lowered the adhesion force value compared to that under alkaline conditions (pH 9), thus rendering the surfaces of the minerals more hydrophobic. A similar tendency was observed in the adhesion force value of minerals surface-treated with DTP at pH 9. This phenomenon arose as a result of a propensity for the formation of elemental sulfur or metal-deficient sulfur-rich species at pH 4 and DTP species at pH 9. The more hydrophilic surfaces of both minerals indicated by higher values of the adhesion force after treatment at pH 9 may be attributed to the occurrence of metal hydroxide moieties. From the morphology images and adhesion force, it is apparent that the coverage of islands on the surface of a mineral determines its hydrophobicity or hydrophilicity. Moreover, it also shows the relative reactivities of the minerals, with tennantite being more reactive than chalcopyrite. Furthermore, the microscopic observation by AFM was consistent with the macroscopic observations of contact angle and flotability studies. [Copyright &y& Elsevier]

The kinetics of diethyl dithiophosphate adsorption on chalcopyrite and tennantite has been studied by UV-visible spectroscopy at pH values of 4, 6, and 9. The concentration of diethyl dithiophosphate in the solution has been monitored as a function of time and pH for both minerals. It was found that the adsorption tendency of diethyl dithiophosphate on both minerals decreased with the increasing pH treatments. This is due to the existence of metal hydroxide species onto the mineral surface in more alkaline condition inhibiting the adsorption of diethyl dithiophosphate species. In comparison to that of chalcopyrite, tennantite possessed slightly higher adsorption of diethyl dithiophosphate in acid condition, while vice versa correlation observed at other pH treatments at where the coverage of metal hydroxide species obtained higher than that of chalcopyrite showing that the rate oxidation of tennantite is higher. An adsorption mechanism has been proposed and tested against the experimental kinetic data. Both the kinetic data and flotation studies are consistent with the proposed mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Large bulk-tonnage high-sulfidation gold deposits, such as Yanacocha, Peru, are the surface expression of structurally-controlled lode gold deposits, such as El Indio, Chile. Both formed in active andesite–dacite volcanic terranes. Fluid inclusion, stable isotope and geologic data show that lode deposits formed within 1500m of the paleo-surface as a consequence of the expansion of low-salinity, low-density magmatic vapor with very limited, if any, groundwater mixing. They are characterized by an initial ‘Sulfate’ Stage of advanced argillic wallrock alteration±alunite commonly with intense silicification followed by a ‘Sulfide’ Stage — a succession of discrete sulfide–sulfosalt veins that may be ore grade in gold and silver. Fluid inclusions in quartz formed during wallrock alteration have homogenization temperatures between 100 and over 500°C and preserve a record of a vapor-rich environment. Recent data for El Indio and similar deposits show that at the commencement of the Sulfide Stage, ‘condensation’ of Cu–As–S sulfosalt melts with trace concentrations of Sb, Te, Bi, Ag and Au occurred at >600°C following pyrite deposition. Euhedral quartz crystals were simultaneously deposited from the vapor phase during crystallization of the vapor-saturated melt occurs to Fe-tennantite with progressive non-equilibrium fractionation of heavy metals between melt-vapor and solid. Vugs containing a range of sulfides, sulfosalts and gold record the changing composition of the vapor. Published fluid inclusion and mineralogical data are reviewed in the context of geological relationships to establish boundary conditions through which to trace the expansion of magmatic vapor from source to surface and consequent alteration and mineralization. Initially heat loss from the vapor is high resulting in the formation of acid condensate permeating through the wallrock. This Sulfate Stage alteration effectively isolates the expansion of magmatic vapor in subsurface fracture arrays from any external contemporary hydrothermal activity. Subsequent fracturing is localized by the embrittled wallrock to provide high-permeability fracture arrays that constrain vapor expansion with minimization of heat loss. The Sulfide Stage vein sequence is then a consequence of destabilization of metal-vapor species in response to depressurization and decrease in vapor density. The geology, mineralogy, fluid inclusion and stable isotope data and geothermometry for high-sulfidation, bulk-tonnage and lode deposits are quite different from those for epithermal gold–silver deposits such as McLaughlin, California that formed near-surface in groundwater-dominated hydrothermal systems where magmatic fluid has been diluted to less than about 30%. High sulfidation gold deposits are better termed ‘Solfataric Gold Deposits’ to emphasize this distinction. The magmatic-vapor expansion hypothesis also applies to the phenomenology of acidic geothermal systems in active volcanic systems and equivalent magmatic-vapor discharges on the flanks of submarine volcanoes. [Copyright &y& Elsevier]

Abstract: Chalcopyrite (CuFeS2) occurs sometimes in association with As-bearing copper ores, such as enargite (Cu3AsS4) and tennantite (Cu12As4S13), especially in deep ore bodies. To employ oxidative pretreatment for recovering copper resources from these minerals, it is important to characterize the surface properties of enargite and tennantite as well as chalcopyrite. The minerals were oxidized in 0.013% H2O2 with O2 bubbling at pH 2, 5, and 11 followed by analysis with X-ray photoelectron spectroscopy. Elemental sulfur was formed most significantly at pH 2 in all sulfide mineral samples. Enargite was the most stable under the oxidative conditions. Arsenic in enargite was partly oxidized at pH 5. Substantial proportion of copper in tennantite was oxidized from Cu(I) to Cu(II) at pH 11. The dissolution rate of Cu from tennantite at pH 2 was by far the fastest, and incongruent dissolution of Cu occurred with suppression of As and S in tennantite. These selective differences in the oxidation may be of use in designing a flotation process for separation of these sulfide minerals. [Copyright &y& Elsevier]

Megascopic aggregates of covellite were found at thin vein in the old Martin gallery, the Krupka ore district, the Krušné hory Mountains, Czech Republic. Covellite forms abundant grains 0.1 - 2 mm in size in association with amorphous Fe-As-Si-O phase, tennantite and rare brochantite. It is opaque, dark indigo blue to dark purple with intense metallic luster and perfect cleavage. Covellite from Krupka is hexagonal, space group P63/mmc, the unit-cell parameters refined from X-ray powder data are: a = 3.794(2), c = 16.39(1) Å and V = 203.9(2) Å3. Chemical analyses yielded average composition Ag 0.83, Zn 0.03, Cu 65.16, Sb 0.02, S 33.05, total 99.08 wt. %, corresponding to (Cu0.99Ag0.01)Σ1.00S1.00 on the basis of 2 apfu. Associated tennantite is Zn-dominant member with average composition Ag 0.13, Fe 0.40, Cd 0.21, Zn 8.27, Cu 42.44, Sb 0.02, Bi 0.07, As 19.66, S 28.08, total 99.28 wt. % and empirical formula (Cu9.97Ag0.02)Σ9.99(Zn1.89 Fe0.11Cd0.03)Σ2.03(As3.92Bi0.01)Σ3.93S13.07 on the basis 29 apfu. The origin of macroscopic covellite at Krupka is interpreted as product of weathering of primary tennantite in conditions of supergene enrichment. [ABSTRACT FROM AUTHOR]

This paper describes the nitric acid dissolution process of natural minerals such as tennantite, chalcopyrite and sphalerite, with the addition of Fe (III) ions and FeS2. These minerals are typical for the ores of the Ural deposits. The effect of temperature, nitric acid concentration, time, additions of Fe (III) ions and FeS2 was studied. The highest dissolution degree of sulfide minerals (more than 90%) was observed at a nitric acid concentration of 6 mol/dm3, an experiment time of 60 min, a temperature of 80 °C, a concentration of Fe (III) ions of 16.5 g/dm3, and an addition of FeS2 to the total mass minerals at 1.2:1 ratio. The most significant factors in the break-down of minerals were the nitric acid concentration, the concentration of Fe (III) ions and the amount of FeS2. Simultaneous addition of Fe (III) ions and FeS2 had the greatest effect on the leaching process. It was also established that FeS2 can be an alternative catalytic surface for copper sulfide minerals during nitric acid leaching. This helps to reduce the influence of the passivation layer of elemental sulfur due to the galvanic linkage formed between the minerals, which was confirmed by SEM-EDX. [ABSTRACT FROM AUTHOR]

Fahlores from seven Austrian localities and from two additional localities in England and Slovakia have been investigated by reflected-light and scanning electron microscopy with energy dispersive analysis (SEM-EDA). The studied fahlores can be divided on the basis of their tetrahedrite (td)-content (td = Sb/(Sb+As) x 100) into chemically homogeneous tetrahedrite (td > 95%), tennantite (td < 5%) and intermediate fahlores with variable compositions. An additional, unique, fahlore type, represented by the "Schendleck-type" fahlore, is extremely inhomogeneous and varies in its td-content from nearly pure endmember tetrahedrite to nearly pure endmember tennantite. The studied samples exhibit a relatively wide range in the Me-element contents (Me = Fe + Zn + Hg + Cd) and show an Me excess (up to 2.5 apfu) in practically all fahlore types except tennantite. The measured Vickers microhardness number (VHN) in the studied samples correlates inversely with the Cu-content, which argues for the increase of the VHN with increasing Cu/Me substitution. [ABSTRACT FROM AUTHOR]

Abstract: In order for the high-arsenic regions of the Northparkes copper–gold orebody to be beneficiated economically, tennantite ((Cu,Fe)12As4S13) present in the ore needs to be rejected to enable copper concentrates to meet the typical smelter penalty level of 2000 ppm As. Using a composite sample of high-arsenic drill cores from Northparkes it was possible to selectively separate tennantite from chalcopyrite (CuFeS2) and bornite (Cu5FeS4) using controlled-potential flotation. The separation was made on a bulk copper–arsenic concentrate after reducing the pulp potential to about −150 mV SHE at pH 12 and floating the tennantite from the other copper minerals. The basis of the separation relies on findings that the lower limiting pulp potential threshold for tennantite is lower than that for chalcopyrite such that there is a potential window in the reducing region where tennantite is strongly floatable but chalcopyrite is not. Little or no selectivity between tennantite and chalcopyrite was found in the oxidising pulp potential region for the range examined. From the composite sample tested, which had a head grade of 0.11% As and 1.2% Cu, it was possible to produce a low-arsenic high-copper concentrate containing 52% of the non-tennantite copper and assaying 2600 ppm As. Computer simulations have shown that for a feed containing a more typical arsenic and copper level (200 ppm As and 1% Cu) the efficiency of separation should be sufficient to concentrate about 61% of the copper in a product assaying less than 2000 ppm As. A conceptual flowsheet for arsenic rejection from Northparkes copper–gold ore, based on the findings from this study, is presented and discussed in this paper. [Copyright &y& Elsevier]

Copper is often associated with arsenic in mixed sulphide minerals such as enargite (Cu3AsS4) and tennantite (Cu12As4S13). Enargite, in particular, is the principal mineral in many deep epithermal copper-gold deposits. Most mining companies avoid exploiting such resources, because the arsenic can become a serious environmental liability or may considerably reduce the resource value due to hefty treatment charges. The few enargite deposits that have been exploited so far are usually rich in gold and silver. The first challenge in the exploitation of copper-arsenic sulphides is the effective separation of arsenic phases from other valuable minerals. In the last decade, though, it was shown that this is possible by pulp-potential adjustment (oxidative conditions) combined with pH adjustments (basic conditions) prior to flotation. In this way, two types of concentrate can be produced: one rich in arsenic and another low in arsenic but rich in other valuable metals. Arsenic-rich concentrates have traditionally been processed pyrometallurgically by reduction roasting to gaseous arsenic sulphide, which is then converted to arsenic trioxide. New pyrometallurgical technologies for the treatment of copper-arsenic sulphides include sulphidization roasting, sulphidization roasting and halogenation, and carbothermic reduction to copper arsenide. The hydrometallurgical treatment of copper-arsenic-antimony resources has been done by atmospheric leaching in alkaline sodium-sulphide solutions. Ultrafine grinding and ferric oxidation at atmospheric pressure, total pressure oxidation at temperatures above 220°C, and bacterial leaching have recently been tried on copper-arsenic sulphides, some with considerable success. [ABSTRACT FROM AUTHOR]

Abstract: Samples of polycrystalline pyrite previously deformed in tri-axial compression tests at a confining pressure of 300MPa and a strain rate of 2×10−4 s−1 but varying temperature were analysed in this study. Five samples including the original starting material have undergone analysis using forescatter orientation contrast (OC) imaging coupled with electron back scatter diffraction (EBSD) to determine how the micro-structures in pyrite and to an extent the surrounding minor phases have changed with increasing temperature. Between 550°C and 650°C the dominant deformation mechanism in pyrite is that of dislocation creep. Above 650°C this mechanism becomes less apparent and few if any dislocation walls are present within pyrite grains by 700°C. This is a result of either increased dynamic recrystallisation with temperature or a change in the dominant deformation mechanism. Dislocation creep occurs via lattice rotation, principally about a single 〈100〉 axis, but also about two separate 〈100〉 axes and more rarely about a single 〈110〉 axis. Deformation has not resulted in a crystallographic preferred orientation (CPO) within any of the samples. Shape change of pyrite grains has occurred and this can account for most if not all of the shortening applied, but dynamic recrystallisation of pyrite and grain boundary sliding accommodated along the minor phases are also likely to be important mechanisms in all of the samples. [Copyright &y& Elsevier]

Abstract: The Khusib Springs deposit in the Otavi Mountain Land, Namibia, is a small though high-grade carbonate-hosted Cu–Zn–Pb–Ag–(As–Sb–Ge) deposit of the “Tsumeb-type” containing approximately 300,000 t of ore grading 10% Cu, 1.8% Pb and 584 ppm Ag. A lens-shaped sulfide orebody, up to 10 m thick and elongated parallel to bedding, replaces limestone, locally brecciated, of the lower Tsumeb Subgroup (Damara Supergroup) in the northern limb of a large NE-trending synclinal structure. A prominent zone of dolomite alteration surrounds the orebody. In a drill core through the orebody, the uppermost 2 m are enriched in Zn (up to 5%) and Ag (up to 3350 ppm), but lower in Ge (<30 ppm) than the central and lower parts of the orebody, which are in turn enriched in Ge (up to 200 ppm) and Pb (up to 7%). Massive ore consists of a texturally complex mineral assemblage dominated by Zn-rich tennantite, enargite, galena and pyrite. Fe-poor sphalerite is abundant only in the uppermost part of the orebody and in the footwall where it forms a prominent zone of disseminated sphalerite±chalcopyrite±galena±pyrite. The upper zone of the massive ore is further characterized by a general lack of enargite, and the occurrence of a variety of late-stage phases including tetrahedrite, Ag-bearing tennantite, pearceite–polybasite and native silver. The central and lower parts of the orebody are composed of tennantite–enargite–galena ore with variable proportions of pyrite, but lacking sphalerite. Most Ge is hosted in Ge-bearing colusite [Cu26V2(As,Ge)6S32] forming small (usually <50 μm in size) grains along the margins of ore layers and veinlets. With the notable exception of enargite, the major sulfides contain only trace amounts of Ge (<100 ppm). Trace element analyses reveal a wide range of Ge concentrations in enargite, averaging to 500 ppm. Frequently, colusite is associated with deformed trails of phengitic, F-rich muscovite, rutile, apatite, tourmaline, dolomite and pyrite. Such trails are interpreted as former stylolites in the carbonate host rock, which has been replaced by sulfide ore. Colusite carries on average 4.0 wt.% Ge, up to 4.7 wt.% W and up to 4.4 wt.% Sn, and is occasionally accompanied by small amounts of Mo–W sulfides. Additional minerals identified in the ore include W-bearing germanite, Ge-bearing stannoidite, chalcopyrite, bornite, stromeyerite, minerals of the chalcocite-group, and covellite. Geochemical and mineralogical features of sulfide ores from Khusib Springs resemble some sulfide ores of the pipe-shaped polymetallic Ge-rich Tsumeb deposit. Similar to the latter, ore formation probably occurred during D2 deformation and metamorphism and involved highly saline, hot brines (up to 370 °C [Chetty, D., Frimmel, H.E., 2000. The role of evaporites in the genesis of base metal sulfide mineralization in the Northern Platform of the Pan-African Damara Belt, Namibia: geochemical and fluid inclusion evidence from carbonate wall rock alteration. Mineralium Deposita 35, 364–376]) carrying sulfur derived from evaporite sequences. A polyphase mineralization involving three successive stages is proposed: early sphalerite–pyrite–(chalcopyrite–bornite) mineralization is replaced by tennantite, enargite, galena and Ge-bearing colusite. A late stage mineralization overprints parts of the orebody at lower temperatures leading to precipitation of ‘schalenblende’ (Cu- and Ag-rich), digenite, tetrahedrite and pearceite–polybasite. The occurrence of small, but high-grade Ge-rich Cu–Zn–Pb–Ag deposits in the lower Tsumeb Subgroup has important consequences on the mineral potential of the area, because prospecting for Cu-rich ores has been traditionally performed in the uppermost Tsumeb Subgroup only, in relation to paleokarst structures. [Copyright &y& Elsevier]

The electrochemical oxidation and reduction of the surface of a natural tennantite has been investigated in 0.1 M HCl solution using cyclic voltammetry, chronoamperometry and a rotating ring-disc electrode. Subsequent surface analyses by in situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy (XPS), together with aqueous phase analysis by inductively coupled plasma-atomic emission spectrometry (ICP-AES) were used to aid in the interpretation of the electrochemical behaviour of this complex system, coupled with Nernst equation predictions of the surface reactions. The XPS results indicated that elemental sulfur, arsenic(III) and arsenic(V) oxides were formed on the surface at electrode potentials of 0 and 0.6 V (SCE), respectively. The Raman spectra of tennantite showed that elemental sulfur was detected on the electrode surface only at potentials ⩾1 V (SCE), at least for the charge densities passed after 500 s. At potentials <-0.4 V (SCE), the intensities of the characteristic Raman spectra for sulfur decreased with decreasing potentials, due to the dissolution of sulfur as H2S (and possibly arsenic as AsH3), leaving Cu3As or elemental copper and iron accumulating on the surface. [Copyright &y& Elsevier]

The common twinning of tetrahedrite and tennantite can be described as an order–disorder (OD) phenomenon. The unit OD layer is a one-tetrahedron-thick (111) layer composed of six-member rings of tetrahedra, with gaps between them filled with Sb(As) coordination pyramids and triangular-coordinated (Cu, Ag). The stacking sequence of six-member rings is ABCABC, which can also be expressed as a sequence of three consecutive tetrahedron configurations, named α, β, and γ. When the orientation of component tetrahedra is uniform, the α, β, γ, α sequence builds the familiar cage structure of tetrahedrite. However, when the tetrahedra of the β layer are rotated by 180° against those in the underlying α configurations and/or when a rotated α configuration follows after the β configuration (instead of γ), twinning is generated. If repeated, this could generate the ABAB sequence which would modify the structure considerably. If the rest of the structure grows as a regular cubic tetrahedrite structure, the single occurrence of the described defect sequences creates a twin. [ABSTRACT FROM AUTHOR]

A number of sediment-hosted, Carlin-type/-like gold deposits are distributed in the Youjiang basin of SW China. The gold ores are characterized by high As, Hg, and Sb contents but with low base metal contents (Cu+Pb+Zn < 500–1000 ppm). The Nibao deposit is unique among these gold deposits by having tennantite–tetrahedrite-series minerals in its ores. The deposit is also unique in being primarily hosted in the relatively unreactive siliceous pyroclastic rocks, unlike classic Carlin-type gold deposits that are hosted in carbonates or calcareous clastic rocks. In this study, we have identified tennantite-(Zn), tennantite-(Hg), and tetrahedrite-(Zn) from the tennantite–tetrahedrite-series mineral assemblage. The tennantite-(Zn) can be further divided into two sub-types of Tn-(Zn)-I; and Tn-(Zn)-II;. Tn-(Zn)-I; usually occurs in the core of a Tennantite–tetrahedrite composite and appears the darkest under the SEM image, whereas Tn-(Zn)-II overgrows on Tn-(Zn)-I and is overgrown by tetrahedrite-(Zn). Tennantite-(Hg) occasionally occurs as inclusions near the uneven boundary between Tn-(Zn)-I and Tn-(Zn)-II. An appreciable amount of Au (up to 3540 ppm) resides in the tennantite–tetrahedrite-series minerals, indicating that the latter is a major Au host at Nibao. The coexistence of tennantite–tetrahedrite-series minerals and Au-bearing pyrite indicates the Nibao ore fluids were more oxidized than the Carlin-type ore fluids. The tennantite–tetrahedrite series at Nibao evolved from Tn-(Zn)-I through Tn-(Zn)-II to tetrahedrite-(Zn), which is likely caused by Sb accumulation in the ore fluids. This indicates that the Nibao ore fluids may have become more reduced and less acidic during Au precipitation. [ABSTRACT FROM AUTHOR]

• H 2 O 2 and PAX are used in flotation of copper sulfide and arsenic-bearing copper minerals. • Selective flotation of these minerals is possible by using H 2 O 2 and PAX. • CuSO 4 and Cu(OH) 2 on enargite and tennantite surfaces promote selective PAX adsorption. • FeOOH and Fe 2 (SO 4) 3 cover chalcopyrite and bornite surfaces, reducing their floatability. Effect of oxidation treatment using hydrogen peroxide (H 2 O 2) on the floatability of copper sulfide minerals (i.e., chalcopyrite and bornite) and arsenic-bearing copper minerals (i.e., tennantite and enargite) is reported in this study. Pure mineral flotation shows that the floatability of each mineral significantly decreases after the oxidation treatment. Interestingly, flotation of mixed mineral of copper sulfide and arsenic-bearing copper minerals shows that enargite and tennantite exhibit a higher floatability compared to chalcopyrite and bornite after the oxidation treatment followed by the addition of potassium amyl xanthate (PAX). These flotation results indicate a possibility for selective flotation of copper sulfide and arsenic-bearing copper minerals. Indeed, bench-scale flotation tests show that the oxidation treatment using H 2 O 2 and the addition of PAX can deliver a satisfying separation of copper sulfide and arsenic-bearing copper minerals. Difference oxidation products (i.e., CuO, Cu(OH) 2, CuSO 4 , FeOOH, and Fe 2 (SO 4) 3) on each mineral surface are likely the cause of this different flotation behavior. Furthermore, these oxidation products may affect the adsorption amount of PAX on each mineral. Indeed, the adsorption tests show that PAX is adsorbed more on tennantite, bornite, and enargite compared to chalcopyrite owing to the formation of CuSO 4 and Cu(OH) 2 on the mineral surfaces under oxidizing conditions. A possible mechanism is proposed in this study to explain the selective flotation behavior of mixed minerals. [ABSTRACT FROM AUTHOR]