Discrete Mineral Phases Research Articles

Application of LA-ICP-MS to process mineralogy: Gallium and germanium recovery at Kipushi copper-zinc deposit

In the field of process mineralogy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is a valuable tool that can complement other mineralogical techniques used to characterise orebodies and concentrator performance. Many economic metals are present at ultra-low levels as solid solution or as inclusions within minerals and require complex recovery techniques to separate them from the bulk ore. Understanding metal occurrence is necessary for implementing the proper recovery strategies. LA-ICP-MS is a cost-effective and versatile method of measuring precious-metals and other economic trace-elements in solid solution in various types of mineral phases while achieving low detection limits. To demonstrate the practical uses of LA-ICP-MS to process mineralogy, XPS has collected data from a sulphide-rich heavy liquid separation and shaking table concentrate from the Kipushi Cu-Zn deposit, Katanga, Democratic Republic of Congo. In addition to Cu and Zn, Kipushi Corporation SA (KICO) is currently investigating strategies for concentrating Ge and Ga. A combination of gravity separation and recovery of Ge and Ga through flotation of Zn and other base metal sulphides are being considered. The objective of the LA-ICP-MS analysis was to determine the proportion of Ge and Ga present in solid solution in sulphides and in discrete mineral phases. The results indicate that sphalerite carries Ga in solid solution (42.5 ppm, representing 54% of the Ga deportment) and chalcopyrite hosts Ge in solid solution (2462 ppm, representing 21% of the Ge deportment). Discrete phases host the remaining portions of Ga and Ge. The deportment information can be used to guide flowsheet development in order to optimize recovery.

Vibrational spectroscopic study of three Mg–Ni mineral series in white and greenish clay infillings of the New Caledonian Ni-silicate ores

Abstract. This study presents and discusses infrared spectroscopic data of well characterised, naturally occurring trioctahedral layer silicates of the serpentine (Srp), talc (Tlc), and sepiolite (Sep) mineral groups, which are found in reactivated faults and sequences of white and green clay veins (deweylite and garnierite) of the New Caledonian Ni-silicate ores. Bands assigned to the OH stretching vibrations of these 1:1 and 2:1 layer silicates in both the fundamental and first overtone regions of mid- and near-infrared (MIR and NIR) spectra, respectively, are compared to those reported in the literature for synthetic Mg–Ni series of the Srp and Tlc mineral groups. They are also presented according to the sequences of infillings recognised in the white and green veins of the Ni-silicate ores. The study reveals that serpentine-like (SL) minerals of the first sequences of clay infillings are residues of larger crystals of serpentines (lizardite, chrysotile, and antigorite) and that the newly formed talc-like (TL) minerals and Sep are the main Ni-bearing carriers of the Ni-silicate ores. Decreasing crystal size and order in serpentine species have major effects on vibrational bands. They favour the broadening of the OH stretching bands, the degradation of the signals assigned to the interlayer OH, and the enhancement of the signal related to weakly bound water molecules. The replacement of Mg by Ni in octahedral sites of the 2:1 layer silicates (TL, Sep) of the greenish clay infillings can be traced by specific OH stretching bands related to the Mg3OH, Mg2NiOH, MgNi2OH, and Ni3OH configurations in the fundamental (MIR) and first overtone (NIR) regions of the spectra. The dominance of the Mg3OH and Ni3OH configurations with respect to mixed configurations in the Mg–Ni mineral series of the clay infillings (mostly in the dominant TL minerals) suggests that Mg and Ni segregation is related to separate Mg-rich and Ni-rich mineral phases rather than to a cationic clustering within the individual particles. This segregation of Mg and Ni in discrete mineral phases is related to Mg–Ni oscillatory zoning patterns (banded patterns) and is reproduced at the scale of the Ni-silicate ores between the white (deweylite) and greenish (garnierite) veins of the reactivated faults.

Calibration of a QEM-EDS system for rapid determination of potassium concentrations of feldspar grains used in optical dating

Potassium (K)-rich feldspars are one of two mineral types typically used for optical dating. Feldspar grains can contain up to ~14 wt% K that gives rise to an internal dose rate component. This internal component can comprise a significant proportion of the total environmental dose rate to which a mineral grain is exposed. The environmental dose rate term—the denominator in the optical age equation—determines the rate at which electronic charge is transferred into the crystal lattice of a mineral grain over its period of burial. Not all feldspar grains have the same K concentration, so internal dose rates differ between individual grains. K concentrations can range from 0 to 14 wt% due to the variable compositions of feldspar phases, differing proportions of discrete feldspar phases and/or the presence of other mineral inclusions in grains. Numerous techniques are available for determining the K concentrations of individual grains, but are time-consuming, and either lack the spatial resolution to classify discrete mineral phases within multi-phase grains, or the coverage to obtain whole-of-grain average K concentrations. Quantitative evaluation of minerals using energy dispersive spectroscopy (QEM-EDS) is a time-efficient and automated mapping technique that has the spatial resolution to classify most mineral phases, as well as the coverage to determine their area proportions. QEM-EDS can also be used to determine elemental concentrations based on spectral matches to EDS reference spectra. It is, however, difficult to determine accurate elemental concentrations for minerals such as feldspars, where solid solutions exist. To overcome this, we establish a QEM-EDS calibration using EDS spectra from six feldspar reference standards to define five solid solution regions along the alkali and plagioclase feldspar series. We test this calibration through comparisons of the K concentrations of discrete phases of three feldspar varieties (orthoclase/microcline, albite and sanidine), derived using both QEM-EDS and wavelength dispersive spectroscopy (WDS). We assume that the WDS-derived K concentrations represent the ‘true’ K concentrations of the phases, and calculate, from a best-fit weighted regression of the two data sets, a correction and uncertainty estimate that can be applied to the QEM-EDS-derived K concentrations, taking into account instrument irreproducibility and any measurement bias. We also test alternative mapping step sizes to optimise efficiency, and apply this time-efficient technique to individual luminescent feldspar grains from two samples. We propose that QEM-EDS is capable of (1) classifying the range of mineral phases in grains, (2) determining the area proportions of each of these phases, and (3) obtaining accurate whole-of-grain average K concentrations of individual feldspar grains using the calibration and correction presented here.

Impact of image resolution on quantification of mineral abundances and accessible surface areas

Imaging has emerged as a valuable means of geological sample characterization and parameterizing reactive transport simulations where image analysis can provide porosity, mineral composition and mineral accessible surface area data, for example. Images can be collected using a variety of techniques and at a range of resolutions, yet the impact of image resolution on measured properties is largely unknown. In this work, the impact of 2D image resolution on the calculated mineral abundances, accessibilities and effective surface areas are examined for a sample from the Paluxy formation, Kemper County, Mississippi. Scanning electron microscopy (SEM) backscatter electron (BSE) images of thin sections were captured at resolutions ranging from 0.3 μm to 6 μm. Images were segmented into pores and discrete mineral phases using ImageJ and algorithms developed in MATLAB. Porosity, mineral abundances and mineral accessibilities were calculated by counting pore and mineral pixels in the segmented image where accessible minerals were deemed as those adjacent to the pore space. A 3D X-ray computed tomography (CT) image of a core sample was collected, segmented, and analyzed to evaluate the 3D connected porosity. Cuboids with the same total area as the 2D image were randomly sampled and used to calculate the 3D connected surface area. This was then multiplied by mineral accessibility to calculate accessible mineral surface areas for non-clay minerals. Minimum variations were observed for mineral abundances calculated from images with varying resolutions. For high resolution images, 0.3 μm to 1 μm, mineral accessibilities agreed relatively well. For images with resolutions from 1 μm to 6 μm, the calculated accessibility of smectite/illite decreased with decreasing resolution while quartz accessibility increased. This in turn resulted in higher effective surface areas for quartz with decreasing resolution. No significant variations were observed for calcite, siderite and K-feldspar.

Mineralogy and mixing state of north African mineral dust by online single-particle mass spectrometry

Abstract. The mineralogy and mixing state of dust particles originating from the African continent influences climate and marine ecosystems in the North Atlantic due to its effect on radiation, cloud properties and biogeochemical cycling. However, these processes are difficult to constrain because of large temporal and spatial variability, and the lack of in situ measurements of dust properties at all stages of the dust cycle. This lack of measurements is in part due to the remoteness of potential source areas (PSAs) and transport pathways but also because of the lack of an efficient method to report the mineralogy and mixing state of single particles with a time resolution comparable to atmospheric processes, which may last a few hours or less. Measurements are equally challenging in laboratory simulations where dust particles need to be isolated and characterised in low numbers whilst conditions are dynamically controlled and monitored in real time. This is particularly important in controlled expansion cloud chambers (CECCs) where ice-nucleating properties of suspended dust samples are studied in cold and mixed phase cloud conditions. In this work, the mineralogy and mixing state of the fine fraction (<2.5 µm) in laboratory-suspended dust from PSAs in north Africa were made using novel techniques with online single-particle mass spectrometry (SPMS) and traditional offline scanning electron microscopy (SEM). A regional difference in mineralogy was detected, with material sourced from Morocco containing a high number fraction of illite-like particles in contrast to Sahelian material which contains potassium- and sodium-depleted clay minerals like kaolinite. Single-particle mixing state had a much greater local variation than mineralogy, particularly with respect to organic–biological content. Applying the same methods to ambient measurement of transported dust in the marine boundary layer at Cabo Verde in the remote North Atlantic enabled the number fractions of illite/smectite clay mineral (ISCM), non-ISCM and calcium-containing particles to be reported at a 1 h time resolution over a 20-day period. Internal mixing of silicate particles with nitrate, chlorine and organic–biological material was also measured and compared to that in the suspended soils. The results show SPMS and SEM techniques are complementary and demonstrate that SPMS can provide a meaningful high-resolution measurement of single-particle mineralogy and mixing state in laboratory and ambient conditions. In most cases, the differences in the mineralogical composition between particles within a soil sample were small. Thus, particles were not composed of discrete mineral phases. In ambient measurements, the ISCM and nitrate content was found to change significantly between distinct dust events, indicating a shift in source and transport pathways which may not be captured in offline composition analysis or remote sensing techniques.

Tungsten Speciation and Solubility in Munitions-Impacted Soils.

Considerable questions persist regarding tungsten geochemistry in natural systems, including which forms of tungsten are found in soils and how adsorption regulates dissolved tungsten concentrations. In this study, we examine tungsten speciation and solubility in a series of soils at firing ranges in which tungsten rounds were used. The metallic, mineral, and adsorbed forms of tungsten were characterized using X-ray absorption spectroscopy and X-ray microprobe, and desorption isotherms for tungsten in these soils were used to characterize its solid-solution partitioning behavior. Data revealed the complete and rapid oxidation of tungsten metal to hexavalent tungsten(VI) and the prevalence of adsorbed polymeric tungstates in the soils rather than discrete mineral phases. These polymeric complexes were only weakly retained in the soils, and porewaters in equilibrium with contaminated soils had 850 mg L-1 tungsten, considerably in excess of predicted solubility. We attribute the high solubility and limited adsorption of tungsten to the formation of polyoxometalates such as W12SiO404-, an α-Keggin cluster, in soil solutions. Although more research is needed to confirm which of such polyoxometalates are present in soils, their formation may not only increase the solubility of tungsten but also facilitate its transport and influence its toxicity.

Geochemical Characterization of Trace MVT Mineralization in Paleozoic Sedimentary Rocks of Northeastern Wisconsin, USA

Disseminated Mississippi Valley-type (MVT) mineralization occurs throughout northeastern Wisconsin, USA, and is recognized as the source of regionally extensive natural groundwater contamination in the form of dissolved arsenic, nickel, and other related metals. Although considerable attention has been given to arsenic contamination of groundwater in the region, limited attention has been focused on characterizing the bedrock sources of these and other metals. A better understanding of the potential sources of groundwater contamination is needed, especially in areas where groundwater is the dominant source of drinking water. This article describes the regional, stratigraphic, and petrographic distribution of MVT mineralization in Paleozoic rocks of northeastern Wisconsin, with a focus on sulfide minerals. Whole-rock geochemical analysis performed on 310 samples of dolomite, sandstone, and shale show detectable levels of arsenic, nickel, cobalt, copper, lead, zinc, and other metals related to various sulfide mineral phases identified using scanning electron microscopy. MVT minerals include pyrite, marcasite, sphalerite, galena, chalcopyrite, fluorite, celestine, barite, and others. We describe the first nickel- and cobalt-bearing sulfide mineral phases known from Paleozoic strata in the region. Arsenic, nickel, and cobalt are sometimes present as isomorphous substitutions in pyrite and marcasite, but discrete mineral phases containing nickel and cobalt elements are also observed, including bravoite and vaesite. Locally abundant stratigraphic zones of sulfide minerals occur across the region, especially in the highly enriched Sulfide Cement Horizon at the top of the Ordovician St. Peter Sandstone. Abundant quantities of sulfides also appear near the contact between the Silurian Mayville Formation and the underlying Maquoketa and Neda formations in certain areas along and east of the Niagara escarpment. This article illustrates how a detailed geochemical and mineralogical investigation can yield a better understanding of groundwater quality problems.

Potentially toxic elements in bottom ash from hazardous waste incinerators: an integrated approach to assess the potential release in relation to solid-phase characteristics

Understanding the chemical and mineralogical characteristics of bottom ash (BA) containing Potentially Toxic Elements (PTEs, e.g., As, Cd, Co, Cu, Cr, Mo, Ni, Pb and Zn) is necessary because it provides information to the potential environmental impacts and possible management options. In this study, we used an integrated approach, combining solid phase characterization [by X-ray diffraction (XRD) and Field Emission Gun Electron Probe Micro Analysis (FEG-EPMA)] and leaching tests. XRD analysis for mineralogical characterization was used but turned out not always to allow detecting discrete mineral phases containing PTEs. Therefore, FEG-EPMA, which is less often used for waste characterization, was used to provide information on the elemental associations focusing on some PTE retaining phases. This allowed direct solid phase characterization and investigation of the relationship between discrete and bulk solid-phase characteristics and PTE leaching behavior from BA. Some environmental scenarios related to PTE release were also assessed. Liming can reduce the PTE concentrations in the leachates to a desirable level, but the release of Mo from one of the BA samples would still be of concern. Our results indicated that attention should be paid to the safe disposal of this BA to avoid leaching of Mo and contamination to environment.

Low-crystallinity products of trace-metal precipitation in neutralized pit-lake waters without ferric and aluminous adsorbent: Geochemical modelling and mineralogical analysis

AbstractThe removal of dissolved trace metals during neutralization of acid mine drainage has usually been described and modelled as a progressive, pH-dependent sorption onto standard ferric or aluminous adsorbent. In the absence of adsorbent mineral surfaces, trace metals tend to form amorphous to low-crystallinity compounds which are often difficult to characterize. Here, we study the behaviour of the more soluble metals (Cu2+, Zn2+, Mn2+, Co2+, Ni2+, Cd2+) in the absence of ferric and aluminous adsorbent by neutralization experiments with waters from two acidic pit lakes. The objectives of our study were to identify the mineral products formed by trace-metal precipitation and the pH ranges at which these metals are removed from the solutions. Both geochemical modelling and detailed mineralogical and chemical analyses (XRD, SEM, TEM, XRF, ICP-AES) were undertaken to characterize the products. The schwertmannite and hydrobasaluminite colloids formed in the initial neutralization stages were removed from the waters at pH 3.5 and 5.1, respectively. These two minerals had previously adsorbed the Cr3+and Pb2+initially present in the solutions. The Cu precipitates were amorphous to X-rays, though chemical and modelling data suggest that Cu probably precipitated as a precursor of brochantite (Cu4(SO4)(OH)6·2H2O) at pH >6.0, together with minor quantities of other Cu hydroxysulfates (langite, antlerite) and Cu(OH)2. At higher pH, other divalent metals (Zn2+, Mn2+) precipitated as silicates, carbonates and/or (possibly) minor oxides and (oxy)hydroxides. The high concentration of aqueous SiO2in the solutions allowed Zn to precipitate as willemite (Zn2SiO4) at pH >7.0. Similarly, the presence of inorganic carbon (originally as CO2(aq.)) greatly influenced the nature of the corresponding precipitate of Mn. This metal was initially present as Mn2+and experienced a partly oxidative precipitation forming, in combination with Mg2+, the hydroxyl carbonate desautelsite (Mg6Mn2(CO3)(OH)16·4H2O) at pH 9.0–10.0. The formation of Mn3+/Mn4+oxides and hydroxides (hausmannite, manganite, birnessite) could not be demonstrated, although geochemical calculations support their subordinate formation. Other metallic cations such as Co2+, Ni2+and Cd2+did not form discrete mineral phases but were totally removed by sorption onto and/or incorporation into the cited Zn and Mn compounds. The discrepancies between theoretical and demonstrated mineralogy and the significance of these minerals for future pit-lake remediation initiatives are discussed.

MINERALOGY OF RARE OCCURRENCES OF PRECIOUS-METAL-ENRICHED MASSIVE SULFIDE IN THE VOISEY'S BAY Ni-Cu-Co OVOID DEPOSIT, LABRADOR, CANADA

The Voisey’s Bay Ovoid Ni–Cu–Co magmatic sulfide deposit, Labrador, is generally poor in precious metals (Pt, Pd, Ag, Au), but unusual occurrences with elevated levels (Pt + Pd > 0.5 ppm) are present. We present a quantitative description of the precious-metal mineralogy of four such occurrences within massive sulfides. The four samples, all from near the center of the Ovoid, were examined by SEM-based Mineral Liberation Analysis for characterization of precious-metal minerals. Distributions of precious metals among the major sulfide minerals were estimated using mass-balance calculations based on bulk assays of the samples and the proportions and compositions of the minerals. The results indicate that the majority of precious metals are present as discrete mineral phases including sperrylite, froodite, michenerite, Au–Ag alloy, volynskite, stutzite and acanthite, whereas minor to moderate amounts of Pt, Pd, Ag and Au are found in solid solution in pyrrhotite, pentlandite, chalcopyrite and galena. The precious-metal minerals are normally associated with pentlandite, galena, chalcopyrite, pyrrhotite and magnetite, and rarely with breithauptite (NiSb), altaite (PbTe), other precious-metal minerals and native bismuth. With the exception of sperrylite, which is coarse grained and liberated easily by electric pulse disaggregation, the precious-metal minerals are most commonly found as fine inclusions in pentlandite and galena, and less so as larger attachments. The associations are consistent with previously reported precious-metal mineral data from a hornblende gabbro dyke of the Southeast Extension Zone at Voisey’s Bay, demonstrating similar modes of crystallization, which are likely related to crystallization of a highly differentiated sulfide magma in both areas. Processing of Pt from sperrylite and perhaps Pd from froodite could be achieved in ores with a mineralogy similar to the samples described here by grinding, and gravity or flotation methods, but the Au–Ag alloy, volynskite and stutzite would likely be too fine to recover as discrete grains for Ag and Au concentration. Instead, the Ag and Au could be recovered as a by-product of Ni–Cu–Co processing of the pentlandite and chalcopyrite, which are the major hosts of the Ag and Au minerals.

Distribution, speciation and bioavailability of arsenic in a shallow-water submarine hydrothermal system, Tutum Bay, Ambitle Island, PNG

Shallow-water hydrothermal vent systems can introduce large amounts of potentially toxic elements, such as arsenic (As), into coastal marine environments. The first step in understanding and describing the potential impact of these elements throughout hydrothermally influenced coastal ecosystems is to determine the element's distribution and speciation, which in turn influences the availability of the toxin for biological uptake. Shallow submarine hot springs near Ambitle Island, Papua New Guinea, are discharging as much as 1.5 kg per day of arsenic directly into a coral-reef ecosystem. We have investigated the bioavailability of the As throughout Tutum Bay by studying vent fluid, seawater, pore water, precipitates, and sediments. In addition to measuring As abundance, As speciation (As(III), As(V), and the methylated species DMA and MMA) was determined in various waters. The As concentration for discrete mineral phases in vent precipitates and sediments was determined by sequentially extracting arsenic from the easily extractable, carbonate, Fe-oxyhydroxide or hydrous ferric oxide (HFO), and residual fractions, each of which have a different bioavailability. Diffuse venting seems to play a critical role on the distribution of As throughout Tutum Bay surface sediments, which have a mean As concentration of 527 ppm while excluding the vent precipitates (range = 1483 to 52 ppm). Up to 54 ppm As were extracted from the easily extractable fraction of surface sediments (mean = 19.7 ppm), using a K 2HPO 4/KH 2PO 4 buffer at pH = 7.2. Arsenic from this fraction is considered to be the most available for biological processes, and therefore the most dangerous for biota. However, sequential extraction shows that 98.6% of the As in vent precipitates, and a mean of 93.3% in surface sediments (range = 88.2% to 96.3%), is coprecipitated with the hydrous ferric oxide (HFO) fraction. Thus, the bulk of the As being discharged into Tutum Bay is scavenged by the HFO, and should remain stable unless the physicochemical conditions surrounding the oxides change. In surface seawaters of Tutum bay, we found as much as four times the average seawater concentration of As (8.4 μg/L compared to ∼2 μg/L). The abundance of As in seawater just above the sediment/water interface is near normal, although As(III) in both surface and bottom seawater throughout Tutum Bay is substantially enriched compared to average seawater. Hydrothermal venting therefore provides bioavailable As by two major pathways throughout Tutum Bay: 1) easily-exchangeable As from hydrothermally influenced sediments to as far away as 200 m from focused venting, and 2) in surface seawaters, which may allow for biological uptake by phytoplankton and transfer up the food web.

Contaminant bioavailability in soils, sediments, and aquatic environments.

The aqueous concentrations of heavy metals in soils, sediments, and aquatic environments frequently are controlled by the dissolution and precipitation of discrete mineral phases. Contaminant uptake by organisms as well as contaminant transport in natural systems typically occurs through the solution phase. Thus, the thermodynamic solubility of contaminant-containing minerals in these environments can directly influence the chemical reactivity, transport, and ecotoxicity of their constituent ions. In many cases, Pb-contaminated soils and sediments contain the minerals anglesite (PbSO4), cerussite (PbCO3), and various lead oxides (e.g., litharge, PbO) as well as Pb2+ adsorbed to Fe and Mn (hydr)oxides. Whereas adsorbed Pb can be comparatively inert, the lead oxides, sulfates, and carbonates are all highly soluble in acidic to circumneutral environments, and soil Pb in these forms can pose a significant environmental risk. In contrast, the lead phosphates [e.g., pyromorphite, Pb5(PO4)3Cl] are much less soluble and geochemically stable over a wide pH range. Application of soluble or solid-phase phosphates (i.e., apatites) to contaminated soils and sediments induces the dissolution of the "native" Pb minerals, the desorption of Pb adsorbed by hydrous metal oxides, and the subsequent formation of pyromorphites in situ. This process results in decreases in the chemical lability and bioavailability of the Pb without its removal from the contaminated media. This and analogous approaches may be useful strategies for remediating contaminated soils and sediments.

Soil Solution Chemistry of Sewage-Sludge Incinerator Ash and Phosphate Fertilizer Amended Soil

The chemical composition of the soil solution provides useful information on the feasibility of amending agricultural land with municipal and industrial waste, because the soil solution is the medium for most soil chemical reactions, the mobile phase in soils, and the medium for mineral absorption by plant roots. The soil solutions studied in this research were from plots in a 4-yr field experiment conducted to evaluate the effects of the trace metals and P in sewage-sludge incinerator ash. Treatments compared ash with equivalent P rates from triple-superphosphate fertilizer and a control receiving no P application. Ash and phosphate fertilizer were applied annually at rates of 35, 70, and 140 kg citrate-soluble P ha−1. Cumulative ash applications during 4 yr amounted to 3.6, 7.2, and 14.4 Mg ash ha−1. Soil solutions were obtained by centrifugation-immiscible liquid displacement using a fluorocarbon displacing agent. Following chemical analysis, a chemical speciation model was used to determine possible solubility-controlling minerals for trace metals and P, and correlations between solution composition and plant uptake were analyzed. Ash increased soil solution pH, Cd, and Zn, but had no significant effect on solution concentrations of other trace metals. Ash increased soil solution P and S, but P increases were less than those from equivalent citrate-soluble P rates of phosphate fertilizer. Soil solution Ba appeared to be in equilibrium with barite (BaSO4). Solubility data did not indicate that any discrete mineral phases controlled Cd, Zn, Cu, Ni, Ph, or P solubility. Soil solution P concentration was strongly correlated (r = 0.92) with P accumulation in sweet corn (Zea mays L.) plants, but solution trace metal concentrations were either weakly correlated (r = 0.49 for Zn and 0.36 for Cd) or not signilicantly correlated (r = 0.09 for Ni and −0.25 for Cu) with plant accumulation.

The influence of inorganic matter on the pyrolysis of Canadian lignite in a fluidized bed

In low rank coals much of the inorganic matter is present as cations associated with organic carboxyl groups in the coal rather than as discrete mineral phases. By treating the coal with acid the inorganic content is reduced by cation exchange, as well as by acid leaching of discrete minerals. Whole and acid treated samples of pulverized lignite were pyrolyzed in pilot scale (1 to 3 kg coal/h) and bench scale (60 to 100 g coal/h) fluidized bed reactors at atmospheric pressure, 0.45 second vapour-residence time, and temperatures ranging from 500 to 730°C. Yields of char, tar, water and light gases were determined. Removal of inorganic matter from a Saskatchewan lignite resulted in increased yields of tar and total volatile matter, with little effect on the yields of light gases. Increased yields of tar are largely a result of an increased asphaltene fraction in general and specifically of an increased catechol content. Char from acid-washed coal is less reactive to carbon dioxide than is char obtained from raw lignite.

The association of major, minor and trace inorganic elements with lignites. II. Minerals, and major and minor element profiles, in four seams

Abstract Inorganic elements in lignites may be present in carboxylate salts and organic coordination complexes as well as in discrete mineral phases. Moreover, organic matter can alter mineral phases in peats. The objectives of this study are to investigate how a number of important elements are held in some typical lignites and hence to document organic inorganic interactions of various kinds. Accordingly, detailed profiles of the distribution of 10 major and minor elements through four lignite seams have been made, including roof and floor rocks and any mineral partings. Elements extractable by 1.0 N ammonium acetate and by 1.0 N HCl and in the insoluble residue have been analyzed by plasma arc emission and atomic absorption spectrometry. Mineral phases were analyzed by x-ray diffraction and infrared spectrometry. Substanial proportions (40–90%) of the Ca, Mg, Sr, Ba, Na and Mn were extractable from the organic zones, but not the inorganic, by ammonium acetate, and were inferred to have been present in the organic matter as carboxylate salts. Much of the K and some Mg were present in clay minerals, but K-containing clays were depleted in the coal layers relative to roof and floor, probably because organic acids in the peat had leached the K out of illite, thus altering the clays. Part of the Mn was in the organic matter either complexed or dispersed as acid-soluble mineral (e.g. MnS, MnCO3). Acid-soluble Al and Ti were found to be quite abundant in the organic layers but not in the roof and floor; they probably are complexed with the organic matter. The principal conclusion is that the organic matter in peat and lignites has a profound influence, in many ways, on the suite of inorganic materials with which it becomes associated.

Platinum-group elements and gold in the komatiite-hosted Fe-Ni-Cu sulfide deposits at Kambalda, Western Australia

The concentrations of all platinum-group elements and gold in monthly composited samples of mined ores have been determined by neutron activation analysis. Average values from a typical medium Ni tenor ore shoot (10% Ni in 100% sulfides) are: Os, 480; Ir, 230; Ru, 980; Rh, 320; Pt, 1,650; Pd, 2,050; Au, 500 (all values are in ppb and are recalculated to 100% sulfides). These values are similar to those reported from other komatiite-hosted ores. Os, Ir, Ru, Rh, and Pd correlate strongly with Ni (r = 0.63 to 0.92) whereas Pt (r = 0.50) correlation with Ni is only moderate. Au does not correlate with Ni (r = -0.28).Geochemical profiles of platinum-group element values recalculated to 100 percent sulfides through typical ore zones show that Pt, Pd, and Au are lower in massive ore relative to overlying matrix and disseminated ores, whereas other platinum-group elements have a more uniform distribution through these ore types. Pt, Pd, and Au are strongly concentrated at the footwall metabasalt-massive ore contact and in small sulfide-filled fractures within the footwall metabasalt. Other platinum-group elements are concentrated to a lesser extent at this position. Some magnetite-rich selvedges immediately above massive ores are depleted in Os, Ir, and Ru.Pt, Pd, and Au largely occur in discrete mineral phases (Hudson and Donaldson, 1984) and Os, Ir, Ru, and Rh are interpreted to occur in solid solution in pentlandite. The present concentration of Pt, Pd, and Au at the base of massive ores in late fractures is attributed to metamorphic remobilization although this does not preclude an original magmatic concentration of platinum-group elements at the base of the massive ore. The variation in the platinum-group element content of bulk ore samples is similar to that of Ni, Cu, and Co and is controlled by a variation in Fe content at constant sulfur levels.

The distribution of uranium in kolm: Evidence from backscattered electron imagery

Abstract The distribution of uranium in kolm from Upper Cambrian alum shales has been studied using backscattered electron imagery, and found to be concentrated in discrete mineral phases. Authigenic minerals in kolm include pyrite, galena, and a cerium-bearing mineral referable to monazite. Uranium occurs within the monazite and generally shows a close relationship with phosphorus. Uranium bearing monazite has also been identified within the host alum shale.

Inorganic constituents in American lignites

Both the discrete mineral phases and the ion-exchangeable inorganic constituents of lignites from Texas, Montana, and North Dakota have been studied. The ion-exchangeable cations and the carboxyl groups with which they are associated were characterized by ion exchange methods utilizing ammonium acetate and barium acetate respectively. Na, K, Mg, Ca, Sr, and Ba were found to be present in all three coals, but significant variations in the relative and absolute concentrations of all the cations were observed. It was found that Ca and Mg were the most abundant cations and that 40–60% of the carboxyl groups in the raw coals were exchanged with cations. The discrete mineral phases in these lignites were studied by semi-quantitative X-ray diffraction and infrared spectroscopy. The importance of the cations in this analysis was shown when the mineralogical analyses of the low-temperature ash (LTA) of the coals with the cations removed and the raw coals were compared. Results show that up to 50% of the LTA of these raw coals can be attributed to the existence of metal cations and that fixation of sulphur, carbon, and oxygen to form carbonates and sulphates is the major reason for this contribution.

Uranium-enriched minerals in mesostasis areas of the Rhum layered pluton

The distribution of uranium in intercumulus minerals of the Rhum layered intrusion, Inner Hebrides, has been studied by the fission track technique. A striking feature was the frequent occurrence of intense fission track stars recorded on the organic solid state nuclear track detectors. The high uranium sources corresponding to such features were found to be small, discrete mineral phases, often not larger than 50 μm in size. The phases were identified as the zirconium- or phosphorus-bearing minerals zirconolite (essentially (CaFe)(Zr)(Ti)2O7), baddeleyite, zircon and apatite. Although zirconolite and baddeleyite frequently coexist in mesostasis areas of lunar mare basalts, baddeleyite has been only rarely observed, and zirconolite not yet reported in terrestrial basalts, with this being the first recorded occurrence of zirconolite and baddeleyite from a terrestrial ultrabasic cumulate. From estimated uranium concentrations, all of which exceed 50 p.p.m., the uranium values decrease in the order zirconolite, baddeleyite, zircon, apatite. The mesostasis areas in which these minerals occur, are to a certain extent determined by the pre-existing cumulus mineral morphologies. Branching, or “cup-shaped”, olivines provide small scale hollows in which residual magmatic fluids become trapped. Such fluids clearly concentrate those elements not incorporated into the cumulus phases, e.g. uranium, phosphorus, zirconium, etc., and crystallise to give uranium-enriched minerals.

Isotopic Evidence on the Origin of the Colorado Plateau Uranium Ores

Uranium-lead isotopic ages of the Colorado Plateau primary-uranium ores have been measured by the isotope-dilution method on discrete mineral phases. The ages obtained from Jurassic rocks range from 65 to 175 m.y. (million years) and from Triassic rocks 22–220 m.y.; it is unlikely that uranium was introduced into the Plateau during a single period. The U 238 -Pb 206 ages from one mine vary up to a factor of three. The U 238 -Pb 206 and U 235 -Pb 207 ages on the same sample commonly differ by more than the experimental error. Two hypotheses proposed to explain these problems are based on (1) subsequent loss of radiogenic lead and (2) incorporation of old radiogenic lead at the time of mineral formation. The new data present serious questions for the original radiogenic-lead hypothesis. The isotopic ages obtained from the three ratios U 238 /pb 206 , U 235 /Pb 207 , and Pb 207 /Pb 206 on Colorado Plateau samples are usually not concordant, and no direct relationship to the absolute geologic age can be obtained. Under the lead-loss hypothesis, however, the U 235 -Pb 207 ages are considered the most reliable, providing at all times a minimum age. The theory of origin of these deposits that is most probable and also consistent with the isotopic data involves deposition of uranium by ground water in H 2 S-rich locations. This generally occurs shortly after sedimentation but may also occur later, if circulatory conditions are favorable.