Copper Iron Sulfide Research Articles

Alternative processes for treatment of chalcopyrite —A review

Amongst the alternative processes to treat chalcopyrite, the hydrometallurgical routes without pretreatment and with pretreatment, such as oxidative roasting are considered quite attractive. Investigation of direct leaching processes involving different lixiviants such as sulphuric acid, chloride, nitric acid, ammoniacal solution and biological systems have been summarised highlighting the major development in the recent past. The problem associated with the iron dissolution in these processes calls for adequate purification and control methodology before recovery of the metal by electrowinning. Sulphation roasting is one of the important pretreatment techniques that may be adopted to recover copper from the sulphides. The iron control problem can be obviated to a great extent by choosing conditions for the sulphation roasting to produce water soluble copper sulphate and converting iron to its insoluble oxides. Another aspect of the sulphation roasting process is its suitability for smaller, pocket and complex deposits with less air pollution due to fixation of sulphur with metal. This review summarises the work carried out on oxidative roasting of chalcopyrite and related constituents such as copper sulphide and iron sulphide. Factors which have a bearing on the process, such as kinetics and mechanism of reactions and roasting in presence of additives using different oxidants are summarised Research on thermal analysis and the use of the fluidised bed reactor are also described.

The use of helium gas to reduce beam scattering in high vapour pressure scanning electron microscopy applications

AbstractBoth image quality and the accuracy of x‐ray analysis invariable pressure scanning electron microscopes (VPSEMs) are often limited by the spread of the primary electronbeam due to scattering by the introduced gas. The degree of electron scattering depends partly on the atomic number Z of the gas, and the use of a low Z gas such as helium should reduce beam scattering and enhance image quality. Using anuncoated test sample of copper iron sulphide inclusions in calcium fluorite, we show that the reduction in beam scatter produced by helium is more than sufficient to compensate for its reduced efficiency of charge neutralisation. The relative insensitivity to pressure of x‐ray measurements in a helium atmosphere compared with air, and the consequent ability to work over a wider range of working distances, pressures, and voltages, make helium potentially the gas of choice for many routine VPSEM applications.

Polyoxyethylene intercalation in lamellar copper iron sulfide

The insertion of polyethyleneoxide in a lamellar copper iron sulfide of formula CuFeS 2 by an exchange reaction of potassium from KCuFeS 2 with an aqueous solution of the polymer was performed. The characterization of the new compound by X-ray diffraction and IR absorption spectroscopy shows that the layer structure of the precursor has been retained and that the polymer adopts a zigzag configuration between the layers.

Formation of copper—iron sulfide minerals during corrosion of artifacts and possible implications for pseudogilding

AbstractAdherent films of the gold‐colored metal sulfides pyrite (FeS2), pyrrhotite (Fe1−xS), and chalcopyrite (CuFeS2) are known to exist on metallic and nonmetallic artifacts of Classic times. Consideration of the action of bacterial consortia containing sulfate reducing bacteria (SRB) during microbiologically influenced corrosion (MIC) and analyses of appropriate trajectories on Eh‐pH stability diagrams indicate that these films can be understood either as a result of natural processes over archaeological times or of deliberate pseudogilding. Methods of discriminating natural sulfide deposition from pseudogilding are suggested. © 1993 John Wiley & Sons, Inc.

Origin of rare earth element-enriched hematite breccias at the Olympic Dam Cu-U-Au-Ag deposit, Roxby Downs, South Australia

Hematite breccias, the host rocks to Cu-U-Au-Ag ore at the Olympic Dam deposit, occur as steeply dipping, northwest-striking, dikelike bodies within fractured granite. The breccia complex has a strike length of over 5 km and extends to depths greater than 1 km. Both the deposit as a whole and the individual breccia bodies are zoned from weakly brecciated, sericitized and hematized granite on the margins, through heterolithic breccias, to hematite-quartz microbreccia at the center. Hematite occurs as euhedral laths and fine-grained aggregates in the matrices of all breccia types, in veins and fragments, as pseudomorphs after feldspar, and rarely as pseudomorphs after siderite and magnetite. Relict magnetite is rare, and most iron oxide was deposited as hematite. Heterolithic breccias include fragments of earlier breccia and veins. Minor sedimentary rocks, including bedded hematite and laminated barite, also are present as clast components. In the upper portion of the deposit, volcaniclastic conglomerate and siltstone occur in a fault-bounded block approximately 500 X 500 m in plan view.Copper-iron sulfides occur as interstitial grains (most common), microveinlets, and rare clasts. They are most abundant in heterolithic breccias and are zoned laterally from chalcocitebornitc to chalcopyrite-pyrite. Zonal boundaries are subparallel to steep breccia contacts. Copper-iron sulfides commonly are intergrown with fluorite and locally rim corroded quartz grains. The breccias are highly enriched in light (LREE) and heavy rare earth elements (HREE) (avg = approximately 5,000 ppm REE in hematite-rich rocks). Total LREE content and La/Lu ratios are correlated with hematite abundance; maximum La values (10,000 X chondrite) occur in hematite-quartz microbreccias from the geographic center of the deposit. Five hydrothermal REE phases have been identified: bastnaesite, florencite, monazite, xenotime, and britholite(?). They occur in all breccia types and in a variety of habits: disseminated in quartz-sericite matrices of granite breccia, in quartz-sericite veins, interstitial to hematite laths, intergrown with barite in laminated sedimentary rocks, and as inclusions in hematite and in sulfide grains.The hematite breccias formed by progressive hydrothermal brecciation and iron metasomatism of the granite host. Minor sedimentary components preserved as blocks and fragments within the upper portion of the deposit point to a near-surface environment for the breccia complex. Textural relations indicate that most of the copper was introduced late relative to hematization and brecciation. Based on spatial relations between barren zones, oxidized sulfide grains, and high-grade chalcocite ore, some supergene redistribution of copper probably occurred. The abundance of REE in hydrothermal phases, REE enrichment of altered relative to unaltered wall rock, concentration of REE in the center of the system, and variable slopes of chondrite-normalized patterns, combined with the lack of evidence of intrusion of unusual magmas at the present level of exposure, attest to extensive transport and deposition of REE by hydrothermal fluids responsible for hematization and breccia formation. This study demonstrates hydrothermal REE mobility on a scale previously undocumented and suggests that REE may be particularly mobile in F-rich hydrothermal systems.

Mineralogy, parageneses, and phase relations of copper-iron sulfides in the Atlantis II deep, red sea

New investigations are carried out on the mineralogy and mineral chemistry of sulfide assemblages obtained in samples from one core in the hydrothermally active, southwest basin of the Atlantis II deep, Red Sea. The most abundant sulfide phases are the exsolved intermediate solid solution (ISS) and chalcopyrite. Sphalerite, pyrrhotite, marcasite, mackinawite, and presumably wurtzite are also observed. Two distinct groups of paragenesis were encountered: (a) Intermediate solid solution with sphalerite incrustations and intergrowths, and (b) intermediate solid solution barren of sphalerite intergrowths. The first group is confined to the upper part of the Co zone and the SOAN zone (Backer and Richter 1973), and the second is present in the entire core 100-3-7. An optically isotropic chalcopyrite is found for the first time as a natural mineral in Atlantis II, Red Sea. Yet its existence as a novel phase needs x-ray confirmation. It exhibits a lower reflectivity than normal chalcopyrite and is isotropic. Chalcopyrite occurs either as a single phase or in association with tetragonal chalcopyrite. Our investigations indicate that the formation of Atlantis II deposits is a result of complex processes. These processes are characterized by compositional changes in the ore-bearing fluids and the change in sulfur fugacity (especially with depth). The presence of exsolved chalcopyrite lamellae in ISS indicates slow cooling below 450°C. However, it is difficult to understand why the cubic chalcopyrite is not converted to the tetragonal form even though the temperature of transformation lies above 450°C (470° – 500°C, Cabri 1973). The Cu/Fe ratio changes in the exsolved chalcopyrite lamellae from core to rim of the composite grains. The ratio is higher in the rims. This suggests that primary inhomogenous ISS grains formed from solutions with a continuous increase in the Cu/Fe ratio. Slow cooling is also required to account for the exsolution of chalcopyrite lamellae in ISS. The low sulfur content in isotropic chalcopyrite is also suggestive of low fs2. The low S content in the chalcopyrite may be the controlling factor for the sluggish conversion from cubic to tetragonal chalcopyrite. Mackinawite lamellae show the same orientation in ISS and exsolved isotropic chalcopyrite indicating that mackinawite exsolved before the breakdown of ISS. This strongly suggests that mackinawite is stable above 300°C (contrary to experimental results by Zoka et al. 1973). Pyrrhotite was probably formed by the sulfurization of ilvaite. The pyrrhotite grains with several complex successive zones show the sequence of the sulfurization episodes.

Stratiform copper deposits hosted by low-energy sediments; IV, Aspects of sulfide precipitation

Theoretical modeling of the sequences and amounts of Ag, Co, Cu, Fe, Mn, Pb, and Zn precipitated from 25 degrees C, 3-molal chloride waters saturated with dolomite or calcite, quartz, talc, gypsum, and initially, hematite or goethite was performed assuming parameters of constant chloride molality, pH, and concentrations of major dissolved species. Precipitation sequences were modeled by progressively increasing H 2 S fugacities from a minimum defined by the cuprite-native copper join to a maximum defined by the rhodochrosite-alabandite join in the respective waters. The initial contents of Ag, Co, Cu, Fe, Mn, Pb, and Zn in the waters were defined by source and transport constraints outlined in Haynes and Bloom (1987). Successive modeling runs were made at pH values of 7.6, 6.6, and 6.1, with pH controlled by the CO 2 -calcite (or dolomite) buffer in all waters. The choice of parameters, as well as their variation during the runs, was constrained by a hypothesis that most sulfide deposition in stratiform copper deposits hosted by low-energy sediments occurs within 50 cm of the sediment-water interface during bacterial sulfate reduction (Haynes, 1986a). Initial water compositions approximated continental, closed-basin waters derived from basaltic and granitic provenances, respectively, so that the likely total compositional range of probable source rocks for stratiform copper deposits was represented in the modeling.A generalized precipitation sequence is native silver-chalcocite-bornite-galena-linnaeite-sphalerite-cattierite-pyrite. Native copper appears prior to chalcocite at a pH above 6.6 if the initial copper concentrations in the waters are 800 ppm or at a pH above 7.2 if copper concentrations are 100 ppm. Linnaeite does not precipitate at pH values less than 6.3. Precipitation of CoCO 3 and rhodochrosite occurs in basalt-derived waters upon acidification from an initial pH of 7.6. Chalcocite, galena, linnaeite, sphalerite, and alabandite are the most abundant phases precipitated, and all, with the exception of alabandite, precipitate at H 2 S fugacities above the hematite-pyrite join. The amounts of bornite, covellite, and pyrite precipitated are small and chalcopyrite precipitation does not occur.Precipitation of all lead, cobalt, and zinc, as sulfides, requires H 2 S fugacities above 10 (super -12) bars at a pH of 7.6 or above 10 (super -9) bars at a pH of 6.6. Chalcocite is the only sulfide precipitated if H 2 S fugacities do not exceed 10 (super -14) bars at a pH of 7.6 or 10 (super -12) bars at a pH of 6.6.Modeling predicts a sulfide zonation sequence and metal ratios similar to those observed in stratiform copper deposits hosted by low-energy sediments. Modeling demonstrates that H 2 S fugacity in host rocks exerts an important control on metal ratios. If H 2 S fugacities do not exceed 10 (super -14) bars, deposits will consist of copper and silver, with no associated lead, zinc, and cobalt; if H 2 S fugacities exceed 10 (super -12) bars, deposits will have associated trace or minor lead, minor or significant cobalt, and minor or major zinc, depending on the source rock and transport constraints detailed in Haynes and Bloom (1987).Modeling suggests that chalcocite precipitation resulting from pyrite replacement is unlikely because the amount of copper removed from the water by such a process will be less than 2 ppm. However, precipitation of hematite or copper-iron sulfides will accompany pyrite replacement if iron saturation limits are locally exceeded. Local precipitation of hematite or copper-iron sulfides as a result of pyrite replacement is consistent with the occurrence of hematite-chalcocite intergrowths at White Pine and the occurrence of associated leucoxenebornite in the Kamoto Principal deposit.Modeling fails to predict the small cobalt contents in stratiform copper deposits with associated lead and zinc, and it fails to predict the occurrence of abundant chalcopyrite and bornite in most large stratiform copper deposits hosted by low-energy sediments. Small cobalt contents of deposits such as those within the German Kupferschiefer are probably caused by limited cobalt availability in source rocks during the metal-leaching episode. Relatively large amounts of bornite and chalcopyrite possibly originated by a postburial alteration of chalcocite-pyrite composite grains deposited during the bacterial sulfate reduction episode. Evidence for such postburial alteration is currently not diagnostic and clearly requires further research.Modeling was performed using parameters constrained by the hypothesis previously described by Haynes (1986a). Because predicted zonal sequences and predicted metal ratios, with the explicable exceptions of chalcopyrite, most bornite, and cobalt, are similar to those observed in stratiform copper deposits, the hypothesis could be a realistic description of the cause and timing of native copper, native silver, chalcocite, some bornite, galena, sphalerite, linnaeite, and cattierite precipitation in such deposits.

Phase relations among silicates, copper iron sulfides, and aqueous solutions at magmatic temperatures; reply

Phase relations among silicates, copper iron sulfides, and aqueous solutions at magmatic temperatures; reply

Phase relations among silicates, copper iron sulfides, and aqueous solutions at magmatic temperatures; discussion

Phase relations among silicates, copper iron sulfides, and aqueous solutions at magmatic temperatures; discussion

Strata-bound copper-iron sulfide mineralization in a Proterozoic front arc setting at Boksputs, Northwest Cape, South Africa ? a possible Besshi-type deposit

A low-grade, copper-iron sulfide deposit is present at Boksputs in the Northwest Cape, South Africa. It occurs in the Proterozoic amphibolite belt, the Areachap Group, along the eastern margin of the Namaqua mobile belt.

A Study of the Hydrothermal Stability of Copper for Use as a Container Material for Nuclear Waste

AbstractThe hydrothermal stability of copper has been studied to assess its suitability as a container material for disposal of nuclear waste in the proposed repository site at Hanford, Wa. The experiments (Cohassett basalt, synthetic Grande Ronde #4 groundwater, and copper powder with a water:rock:Cu-powder mass ratio of 20:1:1) were conducted at 300°C, 30 MPa, using Dickson rocking autoclaves for periods up to 3000 hours. Redox was calculated from dissolved H2 measured by gas chromatograph and He-ionization detector.After ca. 100 hours the solution Cu concentration stabilized at 2–3 ppm, near Cu saturation, and did not vary significantly during the remainder of the experiment. The in situ solution pH was slightly alkaline. The copper powder showed little evidence of etching. The Cu concentration did not reflect oxide-coating spallation effects such as those described by Johnston et al.[15]. Within 48 hours, the log fO2 values decreased rapidly toward the magnetite-hematite phase boundary (−31 at 300°C); this is well within the stability field of native copper. SEM and EDX analysis of the reaction products revealed a copper-iron sulfide. One experiment used copper powder containing ca. 5% cuprite. Oxygen released by the cuprite overwhelmed the buffering capacity of the basalt. The resulting log fO2 values stabilized near the copper-cuprite phase boundary (−23.1 at 300°C) with the solution remaining within the copper stability field. Copper purity is important as oxygen contamination or oxidation of the copper containers may strongly affect the repository redox and mobility of radionuclides.

Geology of the Ruby Creek copper deposit, southwestern Brooks Range, Alaska

At Ruby Creek, Alaska, a 1-km-diameter body of hydrothermal dolostone cuts through over 500 m of Middle to Late Devonian carbonate sediments and contains in excess of 100 million tons of 1.2 percent copper. It is one of several similarly mineralized dolostone bodies in the Cosmos Hills which occur near the boundary between a carbonate platform and a shale basin. A complex alteration sequence is recognized in the Ruby Creek body which shows distinct variations with depth. The alteration sequence is separated into two major stages: an early period of dolomitization with minor base metal mineralization (A and B dolostones) and a later period of fracture-controlled copper mineralization (C assemblage). Clasts of A dolostone in sedimentary breccias indicate alteration began during early diagenesis.Early alteration resulted in progressive dolomitization of the host limestone and produced a zonal arrangement of low iron dolostone (A dolostone) around a ferroan dolostone (B dolostone) to siderite core. Siderite-bearing assemblages are either adjacent to, or replace, argillaceous lithologies. Alteration in footwall shale (now phyllite) is not recognized but may have been structurally displaced. Sulfide mineralogy also exhibits spatial and temporal variations. Sulfides are sparse in the A and upper, low iron B dolostones. Pyrite is a common accessory with later ferroan B dolostone and is commonly associated with minor sphalerite, barite, and barium silicates. In the core of the system, pyrrhotite, chlorite, and barium silicates are present with the siderite-bearing assemblage. A zone of discontinuous massive to semimassive iron sulfide separates the siderite-bearing zone from overlying ferroan B dolostones. Late assemblages of massive pyrite, often cobaltiferous, with minor sphalerite, occur in the middle and upper portions of the system adjacent to unaltered argillaceous beds. Conversion of dolomite to calcite accompanied pyrite deposition in these zones. Sulfur isotope studies suggest that temperatures in the core of the system during the early alteration stage exceeded 300 degrees C. Reflectance studies of organic material contained within the various dolostones indicate that the alteration was produced by several fluid pulses, at least one of which carried hydrocarbon.Dolomite veins (C veins) associated with the second major stage of mineralization show a distinct zonation. Veins are most abundant just above the massive iron sulfide layers separating ferroan dolostones from siderite-bearing assemblages. Vein density decreases toward the periphery of the system. Mineralogy also displays distinct spatial variations. Deep in the system the veins contain dolomite with sparse quartz, in the middle of the system dolomite, chalcopyrite with minor calcite, and pyrite are present. On the edge of the system the veins contain dolomite and calcite with minor sphalerite, pyrite, and fluorite. Massive copper sulfides are, in large part, restricted to former zones of massive pyrite. Chalcopyrite, replacing earlier pyrite, is the dominant copper-iron sulfide but is in turn replaced by bornite and finally chalcocite-digenite. Bornite- and chalcocite-rich assemblages display dolomite-destructive alteration and concurrent calcite precipitation. These copper-rich zones contain carrollitc apparently formed from the breakdown of cobaltiferous pyrite. Fluid inclusion studies indicate decreasing temperatures in the veins outward from the core of the system. Deep veins yield temperatures of up to 215 degrees C whereas veins on the periphery of the system give temperatures of approximately 125 degrees C. Zones of massive copper sulfides formed at temperatures between 100 degrees and 120 degrees C. The copper mineralization predates a Jurassic-Cretaceous period of deformation and metamorphism and appears to be a continuation of A and B dolostone alteration.

Stratiform copper deposits hosted by low-energy sediments; I, Timing of sulfide precipitation, an hypothesis

Published interpretations on the timing of copper and copper-iron sulfide deposition in stratiform copper deposits hosted by low-energy sediments range from those postulating deposition during sedimentation to those postulating deposition later in the diagenetic history of the host sediments, with most favoring deposition during diagenesis. Interpretations of sulfide precipitation during diagenesis of the host sediments commonly favor a sulfide replacement of biogenic pyrite, and in some instances, replacement of anhydrite as well.A qualitative reexamination was made of published data on (1) sulfur isotopes, sulfide textures, and sulfide-nonsulfide mineral relationships in stratiform copper deposits hosted by low-energy sediments and on (2) timing of bacterial sulfate reduction, timing of pyrite formation, and timing of authigenic mineral formation in modern analogues of host sediments to ore. The reexamination is permissive of the hypothesis that chalcocite, but not necessarily copper-iron sulfides, in stratiform copper deposits was precipitated within 50 cm of the sediment surface and that most precipitated within a few centimeters of the surface, as a result of bacterial sulfate reduction. The reexamination reveals that evidence for a pyrite replacement origin of chalcocite is based upon equivocal interpretations of sulfide textures. Textures displayed by most bornite, chalcopyrite, and digenite can be interpreted to indicate an origin by replacement of preexisting pyrite-chalcocite composite grains.Limited porosity and permeability data on modern analogues of the host sediments and on clays are compatible with the hypothesis. The porosity and permeability data and published models of compacting shale and sandstone sequences indicate that flow of copper-transporting water was probably along, rather than across, the host-rock bedding.

Phase relations among silicates, copper iron sulfides, and aqueous solutions at magmatic temperatures

Recent estimates of the thermodynamic behavior of aqueous electrolytes at 2 kb and temperatures to 900 degrees C (McKenzie and Helgeson, 1984) have been combined with thermodynamic data for minerals, gases, and H 2 O (sub (l) ) (Helgeson and Kirkham, 1974; Helgeson et al., 1978; Helgeson, 1982b, 1984) to generate logarithmic activity diagrams for the system CuS-FeS-H 2 S-H 2 SO 4 -HCl-H 2 O at magmatic temperatures and pressures. Equilibrium constraints on the distribution of species in the aqueous phase coexisting with mineral assemblages in this system can be used to characterize the depositional environment of low-grade potassium silicate protores in the central zones of porphyry copper deposits. These protores apparently form at relatively high fugacities of H 2 S. For example, thermodynamic calculations indicate that the sulfide-oxide mineral assemblage in the deep zone of the Butte ore deposit described by Brimhall (1977) is uniquely consistent with a fugacity of H 2 S (sub (g)) (f (sub H 2 ) S) equal to approximately 15 bars, a fugacity of O 2 (f (sub O 2 ) ) equal to approximately 10 (super -16.3) bars, and a ratio of the activity of Fe (super +2) to the square of the activity of Cu (super +) (a (sub Fe (super +2) ) /a 2 (sub Cu (super +) ) ) in the aqueous phase of approximately 10 (super 5.6) at 600 degrees C and 2 kb, which applies to pre-Main Stage mineralization at Butte. With decreasing temperature and f (sub H 2 ) S), a (sub Fe (super +2) ) /a 2 (sub Cu (super +) ) ) increases dramatically. Calculations of this kind make it possible to assess source requirements for ore-forming solutions responsible for mineralization in magma-hydrothermal systems.

The effect of electrolyte composition on the cathodic reduction of CuFeS 2

The electrochemical reduction of CuFeS 2 mineral electrodes has been investigated by performing cathodic polarization curves, constant potential experiments, and cyclic polarization curves in various electrolytes. The effects of H 2SO 4, Fe 2+ and Cu 2+ concentrations have been examined as well as the effects of various dissolved gases, air, O 2, H 2S and N 2. Decreasing H 2SO 4 only shifts the curve to more negative potentials but initial concentrations of 0.36 M Fe 2+ cause up to a ten-fold enhancement in the observed current. The presence of oxygen or Cu 2+ also leads to an increase in the reduction current but in either case further increases in current are observed when Fe 2+ is added to the electrolyte. Chalcocite (Cu 2S) or djurleite (Cu 1.96S) have been identified as products of reaction, although it is possible that a thin layer of a different copper-iron sulfide may form as an intermediate based on the color changes which appear after cathodic excursions. In addition, scanning Auger microprobe analyses of these surfaces show an increasing Cu:Fe ratio as the time at potential is increased. The results also indicate that the solid product layer is porous. A mechanism which accounts for the observed current increase in the presence of Fe 2+ is proposed which involves a redox reaction between dissolved Fe 2+ and cupric ion in the copper sulfide product layer.

Investigation of the surface oxidation of bornite by linear potential sweep voltammetry and X-ray photoelectron spectroscopy

The products of surface oxidation of a natural sample of the copper iron sulphide mineral, bornite, have been determined from analysis of linear potential sweep voltammograms and from X-ray photoelectron spectroscopic examination of the oxidized layer. Anodic oxidation of bornite in alkaline media results initially in the formation of an iron(III) oxide/hydroxide and an iron-free copper sulphide of stoichiometry Cu5S4. The latter species is oxidized further at higher potentials to form a copper sulphide of lower copper content and cupric hydroxide. Air oxidation involves the first of these two steps. In acid solution, anodic oxidation yields iron(II) ions rather than an iron oxide in the first stage and copper(II) ions in the second. Sulphate and elemental sulphur are not formed under the experimental conditions investigated.

Oxidation Kinetics of Mixed Copper-Iron Sulfide at 1173 K

Cinetique d'oxydation dans un melange N 2 −O 2 a 1173 K. Dans le stade initial de l'oxydation, Fe est oxyde preferentiellement pour former de la magnetite, la vitesse etant controlee par le transfert de masse de l'oxygene

Geology and mineralogy of the Cu?Ni?Co?U ore deposits at Talmessi and Meeskani, central Iran

Polymetallic hydrothermal veins and impregnations carry copper-iron sulphides (bornite, chalcopyrite, digenite, chalcocite) and nickel-cobalt arsenides (niccolite, rammelsbergite, safflorite, skutterudite) with bismuth and uranium as well as some copper arsenides (domeykite, koutekite etc.) in two dormant mines in the Anarak District. The geological and tectonic framework and the mineral associations of both occurrences have been investigated in detail. Both mineralizations can be attributed to Tertiary magmatism, but were deposited in two temporally distinct periods. The older copper sulphide mineralization is structurally controlled by pre-middle Ecocene tectonics and is linked to Eocene shoshonitic volcanism. The second, younger nickel-cobalt-silver-bismuth-uranium mineralization might be attributed to a granitic magmatism linked to a Miocene phase of movement.

Oxidation of mixed copper-iron sulfide

A rectangular plate of mixed copper-iron sulfide composed of bornite (Cu5FeS4) and troilite (FeS) was oxidized in an O2-Ar mixed gas stream at 1023 to 1123 K. At the start of the oxidation, iron was preferentially oxidized with the rapid formation of a dense Fe3O4 layer of about 10 μm thickness on the sample surface, without the evolution of SO2 gas. Following this reaction, layers of both Fe3O4 and Fe2O3 grew on the sulfide surface in accordance with the parabolic rate law. The diffusion of iron through the oxide layers was assumed to control the oxidation rate during this stage. The effect of oxygen partial pressure on the parabolic rate constants was minor and an apparent activation energy of 126 kJ/mol was obtained. During the later stages of the reaction, when the sulfur activity in the inner sulfide core increased, the oxidation proceeded irregularly to the interior of the remaining sulfide with the formation of a porous oxide and the evolution of gaseous SO2. The remaining sulfide core was found to be a mixture of bornite (Cu5FeS4) and djurleite (Cu1.96S).

Thermodynamics and mobility of copper in bornite (Cu 5FeS 4)

The thermodynamics and kinetics of copper transport in bornite (Cu 5FeS 4) have been investigated. Coulometric titration experiments on single-crystal and hot-pressed polycrystalline materials indicated a restricted range of composition for substoichiometric single-phase bornite, with materials of copper contents less than Cu 4.95FeS 4 existing as a two-phase mixture of bornite and a chalcopyrite-type phase (Cu 3FeS 4). For the polycrystalline material the van der Pauw technique was used to obtain the electronic conductivity (σ e) as a function of temperature and a six-point cell was used to measure the ionic conductivity (σ i) as a function of composition. Typical results obtained at 170°C were σ e=230 Ω −1 m −1 , σ i= 11 Ω −1 m −1 , activation energy for electronic conduction = 15 kJ mol −1. The transient behaviour of the electronic and ionic probe voltages during the six-point cell experiments have been tentatively interpreted in terms of the chemistry of the copper-iron sulphides.