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Study of native gold from the Luopensulo deposit (Kostomuksha area, Karelia, Russia) using a combination of electric pulse disaggregation (EPD) and hydroseparation (HS)
Abstract
The mineralogy of a gold–sulphide–arsenopyrite ore from the Kostomuksha iron deposit region was studied by scanning electron microscopy (SEM) in hydroseparation (HS) products from various non-magnetic fractions (40–300 μm) after EPD crushing. The computer controlled hydroseparator CNT HS-11 produced a 100× concentration of native gold grains together with other ore minerals. Selection of >150 native gold grains from HS concentrates shows a grain size distribution of 1–154 μm (average 33 μm). Measured, upgraded gold reports as liberated grains (46.0%), as intergrowths with arsenopyrite (14.2%), löllingite (19.7%), native bismuth (17.1%), and in association with pyrrhotite (0.9%) and chlorite/apatite (2.0%). High recoveries of native gold are explained in terms of the combined effects of selective grain-boundary fracture induced by EPD crushing, resulting in preservation of metallic mineral aggregates and grain boundaries, even within large native Au/Bi particles (such soft particles would otherwise show significant changes during normal comminution methods). High gold recoveries should thus be possible using traditional gravity and flotation followed by cyanidation. A combined EPD/HS protocol demonstrates the unique possibilities of this technology for laboratory-scale gravity recoverable gold (GRG) testing.
... From a statistical analysis of Auto-SEM-EDS liberation data, Vizcarra [22] suggested that most of the differences reported in literature may not be statistically significant at a high confidence level. Qualitative research has also been carried out into phase boundary fracture during electric pulse breakage (SELF-RAG) and microwave pre-treatment [23][24][25][26][27]. ...
... Penberthy [36] was also aware of this phenomenon. Qualitative assessments based on particle images have been used to make valuable contributions and these play an important role in the understanding of fracture mechanisms [23][24][25]. Disadvantages of qualitative work are that it may be subjective, and observations are difficult to translate into parameters to be used for the development of models. ...
In comminution, liberation has been recognised as a more important performance indicator than size reduction because the degree of liberation of valuable minerals dictates the theoretically achievable grade-recovery curve for downstream separation processes. The degree of liberation of a certain mineral within an ore, ground to a specific particle size distribution, will be dependent on the primary ore texture, the mineral grade and grain size distribution , and the degree and nature of phase boundary fracture, which can, allegedly, be linked to the breakage mechanisms employed within the comminution device. The occurrence of enhanced liberation through phase boundary fracture is desirable, and in recent years, studies have focused on whether or not certain comminution devices enhance this phenomenon. However, comparatively little attention has been paid to quantifying phase boundary fracture in typical mineral processing operations. In this study, a novel approach to quantify phase boundary fracture is proposed which is based on the conservation of grain shape. The approach is demonstrated through a mineralogical analysis of UG2 ore sampled from the discharge of a primary ball mill. Phase boundary fracture was found to be the mechanism responsible for producing 50% PGM liberation at a grind of 40% passing 75 μm, rather than a grind of 50% passing 3 μm which would be required under theoretical random breakage assumptions.
... As a result, individual mineral grains are released, retaining their natural size and shape, facilitating the assessment of grain dimensions, morphology, crystal structure, physical and textural features, and chemical compositions. Several authors (e.g., Andres 1995, Bluhm et al. 2000, Gnos et al. 2007, Cabri et al. 2008) have described the general principle of operation for high-voltage fragmentation. The application of high-voltage discharge pulse disaggregation is a novel sample processing technique for gold mineralogy. ...
... The application of high-voltage discharge pulse disaggregation is a novel sample processing technique for gold mineralogy. Cabri et al. (2008) published a promising report on electric pulse disaggregation (EPD) by CNT Spark-2 in the process mineralogy of precious metals and related ore types. ...
A short-pulsed high-voltage selective fragmentation test was performed on samples from the Oiva gold-quartz dyke to liberate gold and related minerals using selFrag laboratory scale equipment. SelFrag was able to release individual grains of gold, electrum and other minerals of interest, preserving their original texture, shape and size, and provided an opportunity for detailed study of their morphology, surficial features, grain size and composition. The mineralogy of gold/electrum and associated ore minerals was studied by light and electron microscopy using various non-magnetic, heavy mineral concentrates (<200 μm and 2 mm-200 μm) of the fragmented samples. As a result, a number of gold/electrum grains were recovered from fragmented and preconcentrated samples. The composition of gold/electrum varied from about 27.15 to 96.06 wt% Au and from 3.5 to 72.85 wt% Ag, with an Ag/Au ratio of 0.04-2.68. Morphologically, gold/electrum grains were irregular, globular, branched, grooved, subrounded, flaky, and commonly <50 μm in size. Although chalcopyrite was relatively common, other sulphides were generally fine grained, disseminated and rare. Gold/electrum was goethite-quartz hosted and infrequently associated with silver telluride, bismuth telluride, native bismuth, Ag sulphide and Ag halide. Based on mineralogical evidence, the primary electrum might have been deposited with chalcopyrite and other base metal sulphides, and partially remobilized by either late-stage hydrothermal fluid or supergene processes for the depletion of its silver to form fine-grained native gold. Such secondary enrichment might also be supported by the presence of secondary acanthite, iodargyrite and covellite, which might only be possible to recover using selective fragmentation and consecutive preconcentration processes.
... Hydro separation can readily separate the gold particles (which are heavy minerals) from silica minerals (which are light minerals). In other words, discharging light minerals such as quartz and retaining heavy minerals such as gold particles in a glass tube are possible by adjusting the speed of water injected into the glass tube [9]. Therefore, through observation of the heavy minerals separated by hydro separation using X-ray diffraction (XRD) analysis and SEM-BSE images, the separation efficiency of invisible gold and the morphology of the invisible gold trapped in sulfide minerals can be identified. ...
The purpose of this study was to liberate gold from sulfide minerals in a gold concentrate through microwave-nitric acid leaching and to separate the light minerals in an insoluble residue using a hydro-separation process. The representative sulfide minerals in the gold concentrate were pyrite with minor galena. Mineralogical characterization was conducted on the gold concentrate using 1715.20 g/t based on lead-fire assays. During the leaching experiment, the effect of nitric acid concentration was studied. The results indicated that the metal leaching rate of the gold concentrate increased with increasing nitric acid concentration. After the microwave-nitric acid leaching, the resulting main feature was consistent with the increased exposure to reactive sulfide minerals and decrease in weight. Characterization techniques such as X-ray diffraction (XRD), scanning electron microscope energy dispersive spectroscopy (SEM-EDS) and scanning electron microscope backscattered electron imaging (SEM-BSE) were performed to characterize the minerals in the insoluble residue using microwave-nitric acid leaching and the hydro-separation process. The XRD patterns of the insoluble residues were compared. The intensities of the pyrite peak decreased and disappeared under different nitric acid concentrations, whereas intensities of the quartz peak increased. The hydro-separation process focused on the separation of heavy (e.g., native gold) and light (e.g., quartz) minerals from the insoluble residues. After the hydro-separation treatment process, the heavy minerals exhibited typical diffraction lines of gold, as obtained using the XRD analysis.
... As one of the potential technical means of reducing the energy consumption of comminution, pre-weakening of ore particles by high voltage pulses (HVP) has attracted the attention of researchers over the past few years (Usov and Tsukerman, 2006;Wang et al., 2011;van der Wielen et al., 2013;Razavian et al., 2014). Pre-weakening, liberation (Andres, 1977(Andres, , 1995Andres et al., 2001;Lastra and Carbri, 2003;Ito et al., 2006;Cabri et al., 2008) and the recently reported pre-concentration (Zuo et al., 2015;Shi et al., 2015b) are the three applications of HVP breakage technology. In breakage using HVP, a high voltage electrical pulse is transferred to the solid dielectric immersed in water, causing electrical breakdown and disintegration (Andres, 1995). ...
Currently the effect of the pre-weakening of ore particles by high voltage pulses is evaluated by the percentage change of A ∗ b values between pulse-treated and untreated ore particles. The values of A ∗ b, widely used as an ore breakage competence indicator in the mineral industry, are determined from the parameters of the JKMRC breakage models. In this study a t10-based method was developed to predict the degree of size reduction, t10, of pulse-treated particles from that of untreated particles broken at the same size/energy level. This method incorporates one parameter, CAb, which is equivalent to the percentage change of A ∗ b values.
... There are a number of reports demonstrating the effectiveness of mineral liberation by high voltage pulses (Andres, 1977(Andres, , 1994(Andres, , 2010Anon, 1986;Andres et al., 2001;Lastra et al., 2003;Cabri et al., 2008). In the pulses liberation process, drill cores or rocks of 30 mm in size were fragmented into a product in micron size, consuming over 90 kWh/t specific energy (Andres et al., 2001). ...
Factors affecting electrical comminution performance were investigated through experimental work and numerical simulations. The effects of feed size, under-sieve classification, incremental breakage and energy input level on particle pre-weakening and mineral liberation were tested with six ore samples. Using commercial software, COULOMB 3D, simulation was used to explore the trends between the electrical field distribution/intensity, and the ore particle electrical/mechanical properties. These results were used to interpret the differences in breakage and liberation for various ores. The results showed that the induced electrical field is strongly dependent on the electrical properties of minerals, the grain size, the location of the conductive minerals in rocks, and the particle shape/orientation. Understanding how the machine-related factors and ore-related factors affect the electrical comminution performance will assist in the machine scale up development.
... This methodology is considered as the most feasible way to achieve intergranular breakage (the ideal method for liberation) and had been the main focus of electrical breakage study in the past half century. A number of research outcomes have been reported (Andres, 1977(Andres, , 1995Andres et al., 2001;Cabri et al., 2008;Ito et al., 2006;Lastra and Carbri, 2003). In most cases the liberation of minerals was found to be improved by electrical breakage in comparison with mechanical comminution, but at the cost of increased energy consumption. ...
... The experimental results indicated that higher percentage of the liberated minerals and lower fine particles in electrical comminution exist in comparison with the case of mechanical comminution. Cabri et al. [12][13][14][15][16][17][18][19][20][21][22] at the Institute of CNT-MN in Canada have also investigated electrical and electrohydraulic disaggregation and especially the development of instruments in practical field of mineral processing. Lastra et al. [13] compared the liberation study of minerals in Merensky reef samples crushed by electrical and conventional crusher, and showed that the liberation of chromite, Pentlandite, pyrrhotite and PGM using electrical crusher was higher than that obtained by conventional jaw crusher. ...
Mechanical size reduction processes in the mineral processing industry are energy intensive. In this study, a novel High Voltage Electric Pulses Crusher (HVEPC) was designed and developed to pre-weaken and crush a phosphate ore. To compare the effectiveness of the new HVEPC in crushing with the conventional crushers, several rock samples of a phosphate ore were used and the effect of the capacitor, the voltage level and voltage rise time on the phosphate ore breakage was investigated. Comparing the particle size distribution of the crushed samples using both the HVEPC and the conventional crushers revealed the difference between their breakage mechanisms. The final results showed that applying the high voltage pulses at specific energy of 3-5 kWh/t could significantly increase and extend the cracks and microcrakcs inside the rocks and consequently lead to decline in the Bond crushability and Abrasion indices of the crushed samples by 10.6% and 28.1%, respectively.
... Using different GSTs, flow rates, and impulse regimes, the total amount of final heavy mineral concentrates for each size fraction is reduced to about 10 mg. This method has been successfully applied to rock samples previously (e.g., Cabri et al. 2008;Zaccarini et al. 2009). For this study, the method has been adapted for limonite samples and follows Aiglsperger et al. (2011) with the aim to concentrate very low PGM contents in soft rocks. ...
Two Ni-laterite profiles from the Loma Caribe peridotite (Dominican Republic) have been investigated for their platinum group element (PGE) geochemistry and mineralogy. One profile (Loma Peguera) is characterized by PGE-enriched (up to 3.5 ppm total PGE) chromitite bodies incorporated within the saprolite, whereas the second profile is chromitite-free (Loma Caribe). Total PGE contents of both profiles slightly
increase from parent rocks (36 and 30 ppb, respectively) to saprolite (∼50 ppb) and reach highest levels within the limonite zone (640 and 264 ppb, respectively). Chondrite-normalized PGE patterns of saprolite and limonite reveal rather flat shapes with positive peaks of Ru and Pd. Three types of platinum group minerals (PGM) were found by using an innovative hydroseparation technique: (i) primary PGM inclusions in fresh Cr-spinel (laurite and bowieite), (ii) secondary PGM (e.g., Ru- Fe-Os-Ir compounds) from weathering of preexisting PGM (e.g., serpentinization and/or laterization), and (iii) PGM precipitated after PGE mobilization within the laterite (neoformation).
Our results provide evidence that (i) PGM occurrence and PGE enrichment in the laterite profiles is independent of chromitite incorporation; (ii) PGE enrichment is residual on the profile scale; and (iii) PGE are mobile on a local scale leading to in situ growth of PGM within limonite, probably by bioreduction and/or electrochemical metal accretion.
... Although the PSD of coarse (Wang and Stephansson, 1996;Lin et al., 2000;Salinas et al., 2005) and fine (Cabri et al., 2005(Cabri et al., , 2008 mineral aggregates were studied using the machine vision method, the approach followed generally was simplified (e.g., grain size is evaluated from equivalent circle diameter) and particles were grouped into only manageable number of groups (≤15). While the proposed machine vision approach for PSD analysis in this paper uses several groups based on distinct particle lengths and the weighting parameter based on modeled geometrical volume. ...
Reliable and accurate measurement of particle size and subsequent analysis of particle size distribution (PSD) is central to characterization of particulate minerals. Traditionally PSD of particulate materials was determined using standard mechanical sieving, but it was shown to be deficient in accurate particle size measurements, hence PSD analysis. In this paper a highly inexpensive machine vision based approach was proposed as an alternative to mechanical sieving. The test mineral used was ball-milled celestite. This machine vision approach used a document scanner as imaging device and a user-coded java ImageJ plugin performed the image processing and automated the PSD analysis. The acquired color images were preprocessed to binary images and the particles analyzed after grouping them based on their distinct length. Volumes of all particles were evaluated assuming a prolate spheroid geometry from measured lengths and widths. A new approach of using sum of volumes as weighting factor (Svolume) was utilized for particle grouping in ASABE Standard PSD analysis. The plugin also evaluated several significant dimensional (16) and distributional (27) parameters that characterize the PSD of samples. Standard mechanical sieving of samples was performed for experimental verification and results compared with machine vision method. The cumulative undersize PSD followed a log-normal distribution, and the plot against particle size exhibited a linear trend. Shapes of log-normal plot of cumulative undersize PSD were similar between both methods; however, the mechanical sieving curves lagged by 0.2-0.5 mm. The deviation was attributed to the “falling-through” effect of longer particles through sieve openings.
... Oberthü r and Weiser (2008) note the common association between native gold, native bismuth and maldonite (together with Bi tellurides and sulfosalts) with reactions between pyrrhotite, lö llingite and arsenopyrite, and note that secondary hydrothermal reactions are likely to be important in controlling Au distribution in these deposits, possibly leading to upgrade of existing deposits. A detailed analysis of the association of Au minerals at the Luopensulo deposit, Kostomuksha area, Russia, provides further support for the importance of such a remobilization scenario (Cabri et al., 2008). This deposit was intensively hydrothermally altered, and 17% of the Au was found associated with native Bi; the remaining of the Au was associated with arsenopyrite (14.2%), lö llingite (19.7%), or occurred as isolated grains (46%). ...
The role of polymetallic melts in scavenging ore components has recently been highlighted in the context of fluid-poor metamorphosed ore deposits. In contrast, the role of polymetallic melts in systems dominated by hydrothermal fluids remains poorly understood. Using a simple Au–Bi model system, we explored experimentally whether such polymetallic melts can precipitate directly from a hydrothermal fluid, and investigated the ability of these melts to scavenge Au from the solution. The experiments were conducted in custom-built flow-through reactors, designed to reproduce a hydrothermal system where melt components are dissolved at one stage along the flow path (e.g., Bi was dissolved by placing Bi-minerals along the fluid path), whereas melt precipitation was caused further along the flow path by fluid–rock interaction. Bi-rich melts were readily obtained by reaction with pyrrhotite, graphite or amorphous FeS. When Au was added to the system, Bi–Au melts with compositions consistent with the Au–Bi phase diagram were obtained. In the case of fluid reaction with pyrrhotite, epitaxial replacement of pyrrhotite by magnetite was observed, with textures consistent with an interface-coupled dissolution–reprecipitation reaction (ICDRR). In this case, the metallic melt precipitated as blebs that were localized at the replacement front or within the porous magnetite.
... Oberthü r and Weiser (2008) note the common association between native gold, native bismuth and maldonite (together with Bi tellurides and sulfosalts ) with reactions between pyrrhotite, lö llingite and arsenopyrite, and note that secondary hydrothermal reactions are likely to be important in controlling Au distribution in these deposits, possibly leading to upgrade of existing deposits. A detailed analysis of the association of Au minerals at the Luopensulo deposit, Kostomuksha area, Russia, provides further support for the importance of such a remobilization scenario (Cabri et al., 2008). This deposit was intensively hydrothermally altered, and 17% of the Au was found associated with native Bi; the remaining of the Au was associated with arsenopyrite (14.2%), lö llingite (19.7%), or occurred as isolated grains (46%). ...
... Particles smaller than about 15 μm pose practical problems for mounting because of possible bias due to particle loss during sieving and polishing. Where there is concern that conventional mechanical crushing of samples will fracture a significant proportion of mineral grains resulting in a biased distribution of their size and shape, electric pulse disaggregation (EPD; Cabri et al. 2008) may be used instead. EPD applies a series of high voltage electric shocks to a sample placed in a water bath, which preferentially liberates mineral grains by fracturing along grain boundaries. ...
The Jiaodong gold province, one of the main gold-producing areas in China, includes disseminated stockwork Jiaojia-type and auriferous quartz vein Linglong-type gold deposits. In this chapter, two types of typical gold deposits, such as Linglong and Jiaojia gold deposits, were carried out to conduct comparative studies aim to reveal genesis of Jiaodong-type gold deposit. Pyrites, the main gold-bearing mineral, has been analyzed by using micro-geochemistry. Micro-geochemistry of gold grains was also analyzed. These works aim to the source of ore-forming fluids and materials.
Variations in the amenability of different ores to high voltage pulse (HVP) enabled pre-concentration has been observed, yet it is unclear which intrinsic properties of the ores caused the variation in HVP efficacy. The objective of this study is to investigate the influence of grade heterogeneity and gangue mineralogy on the efficacy of HVP enabled ore pre-concentration. Two ore samples with different mineralisation were treated with HVP and mechanical impact breakage, respectively. The results showed that Sample A with an intrusive vein-like mineralisation structure exhibited better pre-concentration efficacies for gold and copper after HVP pretreatment compared to Sample B, which had a finely disseminated copper mineralisation structure. Pretreatment by mechanical impact breakage presented negligible metal pre-concentration potential for both ore samples. The Constitution Heterogeneity determined from assaying randomly selected feed particles, showed that Sample A had a significantly greater grade heterogeneity than Sample B. It was found that the gold and copper grade heterogeneities of the two ore samples exhibited a positive linear correlation with the efficacy of HVP enabled pre-concentration. This is a consequence of heterogeneity resulting in distinct populations of mineralised and barren particles, a requirement necessary to achieve selective breakage. It is also proposed that the presence of conductive gangue minerals can play a role on the efficacy of HVP enabled pre-concentration, with the effect being positive or negative depending on whether or not the gangue has an association with the valuable minerals of interest.
The phenomena of high voltage pulse (HVP) selective breakage and HVP weakening have been reported separately in the literature, but the relation between the two HVP applications has previously not been investigated. Synthetic particles made of Epirez high strength grout were cast with and without embedded metalliferous minerals of chalcopyrite and pyrite and used in a study of HVP selective breakage and weakening. When metalliferous grains were embedded in the grout, there were added either as a single grain occurrence or as a fine disseminated texture. The HVP products were assessed using the JKRBT breakage characterisation method for the mineralised particles and the barren particles (with no metalliferous minerals contained), respectively. It has been found that the HVP weakening effect mainly occurs in the mineralised particles, with a reduction in particle competence (indicated by the relative change in A × b value) between 172% and 200% for the pyrite fines dispersed synthetic particles, and 70% relative reduction for the single chalcopyrite grain embedded synthetic particles. The barren synthetic particles do not exhibit a statistically significant weakening effect and appear much more competent than the mineralised particles after HVP treatment. This finding suggests that in mineral processing circuit design utilising the HVP technology, benefits associated with HVP weakening on the downstream comminution process would be maximised by combining the HVP pre-concentration and weakening applications, in doing so removing the barren unweakened rocks from the process.
High voltage pulse (HVP) selective weakening and selective breakage of mineralised particles have been previously reported. It was hypothesised that these effects were a consequence of metalliferous grains-induced electrical breakdown, but no microscale evidence was presented to test the hypothesis. In the present study, synthetic particles made of grout were cast with a single grain of metalliferous mineral embedded, or with many grains of fine metalliferous mineral dispersed, or with no metalliferous mineral present at all (the barren particle). HVP tests were performed in which a pair of synthetic particles consisting of a mineralised particle and a barren particle were subjected to one pulse loading. The HVP products were examined by X-ray Computed Tomography (X-ray CT) to extract the cracks/micro-cracks and domain breakdown channel propagation behavior. X-ray CT images showed that the majority of the cracks/micro-cracks were generated in the metalliferous grain(s) embedded synthetic particles, whereas no cracks/micro-cracks were observed in the barren particles. The X-ray CT images also confirmed that the electrical breakdown channels traveled through the metalliferous grains rather than through the grain boundary between the grout and the metalliferous grain, which had a detrimental effect upon the integrity of the metalliferous grains. The effect of metalliferous grain-induced HVP selective damage of mineralised particles is used to elucidate the mechanisms of HVP selective weakening and selective breakage of mineralised particles.
Jiaodong gold concentrated area is one of the most important gold in China. There are two typical deposit types, such as 'altered fracture-type' and 'quartz vein-type', which host the mostly ore deposits in Jiaodong Peninsula. The Sanshandao and Xinli gold deposits, typical 'altered fracture-type' ore deposits, are located in northwestern Jiaodong Peninsula and both of them are controlled by Sanshandao-Cangsang fault. Gold is embodied as intergranular, fissure-filling and inclusion in gold-bearing minerals which are consisted of pyrite, galena, sphalerite and chalcopyrite. Various morphological types of gold grains were found in photomicrograph, which include schistic, elliptoid, stumpy and slabby. Through back-scattered electron images (BSE) and secondary electron image of gold grains, we found a lot of cavities and pits in the surface and dark gray areas resulted from impurities containing in the that. The data of electronic microprobe analysis (EMPA) shows that the Au content is 63.34% ∼ 72.54% with high Ag content (27.39% ∼ 36.34%), which belong to electrum. The Scanning Electron Microscope and Energy Dispersive Spectrum (SEM-EDS) micro-analysis of gold grains contain that the major elements is Au and Ag, and the trace elements include N (6.12% ∼ 9.79%), O (1.89% ∼ 6.18%), W (0.42% ∼ 0.84%), P (6.32% ∼ 10.38%), Fe (1.62% ∼ 3.37%). Compared to the micro-analysis of gold grains from Linglong gold deposit, one of typical 'quartz vein-type' gold deposits in Jiaodong, both of them have the same elements such as Au, Ag, N, O and Fe, but the contents of N, O and Fe of gold grains in this article are less than Linglong gold deposit. We detected W in the micro-analysis of gold grains from Xinli and Sanshandao gold deposits without Linglong gold deposit. The low content of O indicates precipitation of Au occurs in reducing conditions and 'altered fracture-type' gold is stronger than 'quartz vein-type' gold deposits. N implied that small amount of meteoric water mixed in the ore fluids, and the fluids of 'altered fracture-type' are less admixed meteoric water than 'quartz vein-type'. P implied that there is mantle-derived ffuid mixing. W is origin of primary magma fluid formed by early cretaceous magmatism and the precipitation of W and Au indicates the weak alkalic conditions. The analysis of combining micro-chemistry with H-O isotope implies the source of ore fluid of Jiaodong gold deposit is mixed kinds of origins. The Early-Cretaceous intermediate-basic dykes show similarity origin of metal to the gold ore. The Au(HS)2- complex is as the most likely gold bisulfide complex for gold transport.
In this study, the effect of minerals composition, particle size and shape as well as electrodes distance from iron-phosphate ore samples, was investigated by using a commercial software. Comparison between high voltage pulses and conventional crushing showed that minerals of interest in the electrical comminution product are better liberated than in the conventional comminution. In order to elucidate and confirm the experimental results, numerical simulation of electrical field distributions/intensity were performed. The software uses the finite element method, a numerical technique for calculating approximate solutions of partial differential equations with known boundary conditions. Magnetite, apatite and quartz were the basic minerals of iron-phosphate ore components, and the main material property used in the simulations was electrical permittivity. The results showed that the induced electrical field was strongly dependent on the electrical properties of minerals, the feed particle size and the location of the magnetite mineral (due to higher permittivity) in the ore. The angle of particle contact surface with high voltage electrode was an important factor in the intensity of electrical field. Smaller contact angle resulted in higher intensity of the electrical field. Electrical discharge within the material was converted to electrohydraulic discharge within the surrounding water environment by increasing the distance between the high voltage electrode and the material contact surface.
EPD (Electric Pulse disaggregation) and HS (hydroseparation) are exceptional technologies for research, concentration, evaluation, and mineral extraction of specific minerals such as precious metals (Au, Ag, PGM), kimberlites (extraction and concentration of indicator minerals), zircons and baddeleyite (recovery of objects for geochronology), and even gemstones (method of evaluation and production of the 100% gemstone concentrate of ideal crystals) etc. EPD is used for recovery of pristine undamaged crystals of diamond, emerald, ruby, sapphire etc, including large crystals. It was tested on various hard ores and was
especially successful for recovery of “soft“ minerals from “hard“ matrix. EPD products are very convenient for HS processing, resulting in representative concentrates of all heavy minerals including the finest particles (5-10 pm). The combined EPD and HS method enables high sensitivity (20 ppb) for evaluation of precious metal ores providing objective information about original grain size, associations, and recovery using a very small amount of sample (1-3 kg). Latest developments of EPD and HS techniques at CNT Mineral Consulting
Inc. include the HS-21 hydroseparator (50 kg/hr) and the Spark-21 EPD (5 t/hr), which enables use of both techniques for prospecting and mineral processing of industrial size samples of certain ores.
A method based on single-particle tests has been developed to characterise the pre-weakening effect of high voltage pulses on ores. A pre-weakening index, PWI, defined as the percentage change in ore breakage resistance indicator (A*b) per unit of specific energy, is used to evaluate the energy efficiency of an electrical comminution machine, and to assess an ore's amenability to pre-weakening by high voltage pulses. A reduced JKRBT (JK Rotary Breakage Tester) testing procedure using five tests (instead of the standard 12 tests per sample) to determine the ore breakage parameters, makes characterisation by high voltage pulse pre-weakening more practical. A gold-copper ore sample treated by high voltage pulses, based on single-particle tests with a specific energy of 1.6 kWh/t, achieved an A*b change from 31 to 84 at a nominal particle size of 30 mm, representing a 171% pre-weakening result. X-ray tomography images show the induced cracks/microcracks in the pulses-treated rocks. The pre-weakening effect was found more pronounced for larger fragments, suggesting that the use of high voltage pulses to pre-weaken AG/SAG mill feed may result in more significant benefits in terms of energy savings or increased throughput than pre-weakening ball mill feed.
The recent progress in electrical comminution using high-voltage pulses and the technical challenges in order to bring this technology to the mining industry are outlined. Pre-weakening ore particles and preferential liberation of minerals at coarse sizes are the two major research outcomes that may have potential benefits for the industry. A particle pre-weakening characterization method by single-particle/single-pulse test has been developed. The emerging challenges for the mining industry to realize the benefits of this novel comminution technology include scale-up for industrial application, hybrid circuit design, maximization of pulse-induced cracks, and study of the downstream processing effects.
Over the past two decades, the application of indicator mineral methods to mineral exploration has expanded significantly such that they are now used to explore globally for a broad spectrum of commodities. Indicator mineral suites have been identified for a variety of ore deposit types including diamond, Au, Ni-Cu, PGE, metamorphosed volcanogenic massive sulphide, porphyry Cu, U, Sn and W. Indicator minerals, which include ore, accessory and alteration minerals, are sparse in unconsolidated sediments, thus sediment samples must be concentrated in order to recover and examine them. Because most indicator minerals have a moderate to high specific gravity, processing techniques involving density separation, in combination with sizing and magnetic separation, are used to recover them from sediment samples. This paper reviews the commonly used processing methods including panning, hydroseparation, tabling, Knelson concentrators, spiral concentrators, dense media separators, jigs and various types of magnetic separators, as well as mineral selection and mineral chemistry determinations. Monitoring of quality control is essential at each stage in these processing, picking and analytical procedures. When reporting indicator mineral results, processing methods, fraction weights and size ranges, and laboratory name should be recorded, in addition to indicator mineral abundance data.
As the penetration of variable renewable generation increases in power systems worldwide, planning for the effects of variability will become more important. Traditional capacity adequacy planning techniques have been supplemented with integration studies, which have been carried out in power systems with high targets for renewable generation. These have highlighted the increased variability that a system may experience in the future. As system planning techniques evolve with the demands from variable generation, the flexibility of a system to manage periods of high variability will need to be assessed. A metric may be required to measure the flexibility of a power system for use in planning studies with multi-year horizons. Compared to generation adequacy metrics, system flexibility assessment is more data intensive and requires more detailed system modeling. An algorithm for scenario development in generation planning with high penetrations of variable generation is presented.
A reliable and accurate measurement of particle size and particle size distribution (PSD) is central to characterization of particulate minerals. Using mineral celestite (SrSO4) as the test material, an inexpensive machine vision approach as an alternative to standard mechanical sieving was proposed and results were compared. The machine vision approach used a user-coded ImageJ plugin that processed the digital image in a sieveless manner and automated the PSD analysis. A new approach of employing sum of volumes (ΣVolume) as weighting factor was developed and utilized in the ASABE standard PSD analysis. The plugin also evaluated 22 significant dimensions characterizing samples and 21 PSD parameters. According to Folk and Ward's classification, the PSD of ball-milled celestite was “very finely skewed” and “leptokurtic”. The PSD of celestite followed a lognormal distribution, and the plot against particle size exhibited almost a linear trend for both machine vision and mechanical sieving methods. The cumulative undersize PSD characteristics of both methods matched closely when the width-based mechanical sieving results were transformed to lengths by applying the shape factor (width/length). Based on the study, this machine vision approach can be utilized for PSD analysis of particulate minerals and similar products.
Garutiite (Ni,Fe,Ir) is a new hexagonal polymorph of native Ni discovered in chromitite from Loma Peguera, Dominican Republic. The mineral was identified in heavy mineral concentrates obtained through the use of electric pulse disaggregation (EPD) and hydroseparation (HS) techniques. It forms as anhedral, botryoidal grains typically 10–60 mm in size (maximum of 110 mm). Grains are single or composite, frequently porous and zoned, and occasionally display an unusual lamellar internal texture. Associated minerals include hexaferrum, ferrian chromite, chlorite-group minerals, serpentine-group minerals, awaruite, irarsite, laurite, native Ru and unidentified species including Ru–Os–Ir-Fe and Pt–Ni–Fe–Ir compounds, Pt(Ni,Fe)3, (Fe,Ru,Ni,Os,Ir,Co)2S and RhNiAs.
The mineral is megascopically grey to grey-black with a metallic luster. In plane-polarized light, garutiite is white in color, exhibits a very weak anisotropy, and no pleochroism, bireflectance or internal reflections were observed. No cleavage was noted and the
hardness could not be determined owing to the porous nature of the mineral. The calculated density is 11.33 (1) g/cm3. Reflectance values (%) in air are: 63.8 at 470, 65.9 at 546, 67.0 at 589 and 68.0 at 650 nm. The average result of electron microprobe analyses (n ¼
42 from 27 grains) is: Ni 27.91, Fe 19.94, Ir 43.78, Pt 6.98, Co 0.55, Cu 0.43, Ru, 0.50, Rh 0.74, Os 0.67, total 101.51 wt%, corresponding to Ni0.421Fe0.316Ir0.202Pt0.032Co0.008Cu0.006Rh0.006Ru0.004Os0.003)P1 or the simplified formula, (Ni,Fe,Ir). Garutiite is the Ni analogue of hexaferrum, osmium and ruthenium and is classified as belonging to the osmium group. As such, the mineral is
considered to be hexagonal, crystallizing in space group P63/mmc with a 2.6941(4) and c 4.2731(6) A ° , V ¼ 26.86(1) A ° 3, Z ¼ 2. The strongest lines of the X-ray powder diffraction pattern [d(in A ° )(I)(hkl)] are: 2.330(50)(100), 2.136(30)(002), 2.046(100)(101),
1.576(30)(102), 1.3470(40)(110), 1.2155(40)(103). Based on its morphology, internal texture, and the associated minerals, garutiite is interpreted to be secondary in origin, i.e., having formed at low temperatures during post magmatic processes, such as
serpentinization and/or lateritization. The name honors Prof. Giorgio Garuti, in recognition of his contributions to the understanding of the mineralogy of platinum-group elements.
Platinum group element (PGE) rich ophiolitic chromitites associated with the Loma Peguera harzburgitic mantle have been investigated for Platinum group minerals (PGM) using electric pulse disaggregation (EPD) and hydroseparation (HS) techniques. Combination of these two techniques allows for efficient concentration of the heavy minerals, including PGM. The PGM have been analyzed by electron microprobe, by Raman spectroscopy and investigated for their reflectivity. The majority of the discovered PGM, on the basis of their chemical composition and optical properties, potentially represent new mineral species, including Ru,Os,Ir,Fe compounds, Ir(Fe,Ni)3, Ir(Ni,Fe)3, (Ir,Pt)(Fe,Ni), Pt(Ni,Fe)3, (Ru,Pt)(Fe,Ni), (Fe,Ru,Ni,Os,Ir,Co)2S and Rh,Ni,As.One disadvantage of an investigation of concentrates is that some in situ textural information is lost. However, on the basis of their morphology and some attached associated minerals, the presence of oxygen, altered chromite, and serpentine, we can argue that most of the discovered PGM are secondary in origin, i.e. formed at low temperature during post magmatic processes.
Naldrettite, Pd2Sb, is a new intermetallic mineral discovered in the Mesamax Northwest deposit, Cape Smith fold belt, Ungava region, northern Québec. It is associated with monoclinic pyrrhotite, pentlandite, chalcopyrite, galena, sphalerite, cobaltite, clinochlore, magnetite, sudburyite (PdSb), electrum and altaite. Other rarer associated minerals include a second new mineral (ungavaite, Pd4Sb3), sperrylite (PtAs2), michenerite (PdBiTe), petzite (Ag3AuTe4) and hessite (Ag2Te). Naldrettite occurs as anhedral grains, which are commonly attached or moulded to sulphide minerals, and also associated with clinochlore. Grains of naldrettite vary in size (equivalent circle diameter) from ∼10 to 239 mm, with an average of 74.4 mm (n = 632). Cleavage was not observed and fracture is irregular. The mineral has a mean micro-indentation hardness of 393 kg/mm2. It is distinctly anisotropic, non- pleochroic, has weak bireflectance, and does not exhibit discernible internal reflections. Some grains display evidence of strain-induced polysynthetic twinning. Naldrettite appears bright creamy white in association with pentlandite, pyrrhotite, clinochlore and chalcopyrite. Reflectance values in air (and in oil) for R1 and R2 are: 49.0, 50.9 (35.9, 37.6) at 470 nm, 53.2, 55.1 (40.3, 42.1) at 546 nm, 55.4, 57.5 (42.5, 44.3) at 589 nm and 58.5, 60.1 (45.4, 47.2) at 650 nm. The average of 69 electron-microprobe analyses on 19 particles gives: Pd 63.49, Fe 0.11, Sb 35.75, As 0.31, and S 0.02, total 99.68 wt.%, corresponding to (Pd1.995Fe0.007)2.002(Sb0.982As0.014S0.002)0.998. The mineral is orthorhombic, space group Cmc21, a 3.3906(1), b 17.5551(5), c 6.957(2) Å, V 414.097(3) Å3, Z = 8. Dcalc is 10.694(1) g/cm3. The six strongest lines in the X-ray powder-diffraction pattern [d in Å (I)(hkl)] are: 2.2454(100)(132), 2.0567(52)(043), 2.0009(40)(152), 1.2842(42)(115), 1.2122(50)(204) and 0.8584(56)(1.17.4).
Ungavaite, Pd4Sb3, is a new intermetallic mineral species discovered in the Mesamax Northwest deposit, Cape Smith fold belt, Ungava region, northern Quebec. It is associated with monoclinic pyrrhotite, pentlandite, chalcopyrite, galena, sphalerite, cobaltite, a chlorite-group mineral and magnetite. Associated precious-metal minerals include another new mineral species, naldrettite (Pd2Sb), sperrylite, sudburyite, michenerite, Au-Ag alloy, altaite, petzite (Ag3AuTe4) and hessite (Ag2Te). Ungavaite occurs as rare anhedral grains with inclusions of Au-Ag alloy or with attached chalcopyrite and a chlorite-group mineral. Grains of ungavaite vary in size (equivalent circle diameter) from ca. 36 to 116 m, with an average of 73 m (n = 4). Neither cleavage nor fracture was observed. It is distinctly anisotropic, non-pleochroic, has weak birefl ectance and does not exhibit discernible internal refl ections. Ungavaite appears bright creamy white in association with pentlandite, pyrrhotite, the chlorite-group mineral
The hydroseparator embodies novel technology that can be of great benefit for the study of accessory minerals in rocks, ores, industrial products and materials of potential environmental concern. The technique is described and an example is provided of its application in the study of the platinum-bearing CHR-2 chromitite of the Niquelândia layered intrusion, central Goiás, Brazil.
The newly developed patented technology of hydroseparation [Rudashevsky, N.S., Garuti, G., Andersen, J.C.Ø., Kretser, Y.L., Rudashevsky, V.N., Zaccarini, F., 2002. Separation of accessory minerals from rocks and ores by hydroseparation (HS) technology: method and application to CHR-2 chromitite, Niquelândia, Brazil. Transactions of the Institution of Mining and Metallurgy (Section B: Applied Earth Science) 111, B87–B94] was applied to study two samples from the Skaergaard intrusion, Greenland (BS03-01 and BS03-04) to determine the nature of the precious metal minerals (PMM) and to provide guidance for mineral processing. Copper alloys of Au and Pd, which dominate the PMM, characterize both samples. BS03-01 has 596 PPM particles: 94.7 vol.% PdCu (average grain size 24.5 μm), ∼4.0 vol.% PGM, and 1 vol.% Au minerals. The average grain size for all 596 precious metal minerals measured in this sample is 21.9 ± 1.1 μm at 95% confidence (median = 21.5 μm). Also, nearly 90 vol.% of the PMM measured in the <125 μm fractions are either liberated or attached/included in BMS, which makes the ore amenable to sulphide flotation. BS03-04 has 478 PPM grains, consisting of 84.7 vol.% Au alloys and 15.3 vol.% PGM. The average grain size of all the PMM particles in the gold ore is 22.3 ± 0.9 μm at 95% confidence (median = 22.35 μm). Like the Pd ore, recovery of precious metals in this sample will be closely related to the liberation of BMS. The mineralogical data proved useful to the metallurgical testwork on the bulk samples.
Method for separating granular material and device for carrying out said method
- N S Rudashevsky
- V N Rudashevsky
Rudashevsky N.S., Rudashevsky, V.N., (2001). Method for separating
granular material and device for carrying out said method. Russian
patent #2165300. M. 2001.
Dreikop platinum pipe
- T Oberthü R
- N S Rudashevsky
- V N Rudashevsky
- L J Cabri
- H Kocks
- J Lodziak
- D Klosa
Oberthü r, T., Rudashevsky, N.S., Rudashevsky, V.N., Cabri, L.J., Kocks,
H., Lodziak, J., Klosa, D. (2007). Dreikop platinum pipe, Bushveld
Complex, South Africa, new insights. Goldschmidt Conference
Abstracts, pA28.
Device for separation of solid particles. Application for Russian patent #2007121079. Date of priority 06.06
- N S Rudashevsky
- V N Rudashevsky
Rudashevsky N.S., Rudashevsky V.N. Device for separation of solid
particles. Application for Russian patent #2007121079. Date of
priority 06.06.2007.
Hydraulic classifier. Russian patent. Invention No. 2281808
- N S Rudashevsky
- V N Rudashevsky
Rudashevsky, N.S., Rudashevsky, V.N. (2006). Hydraulic classifier.
Russian patent. Invention No. 2281808. M. 2006.