Levels Of Platinum Group Elements Research Articles

Palladium release from catalytic converter materials induced by road de-icer components chloride and ferrocyanide.

Environmental levels of platinum group elements (PGEs) are rising due to emissions of vehicle catalytic converter (VCC) materials containing palladium, platinum and rhodium. When these PGE-containing VCC materials are exposed to soil and water, coordination complex formation with ligands present in the environment may mobilize PGEs into solution, particularly Pd. Road de-icing salt contains two ligands with high affinities for Pd2+: chloride (Cl-) from NaCl and cyanide (CN-) from ferrocyanide (Fe(CN)64-) anti-caking agents. Batch leaching studies of VCC materials were conducted with solutions representative of de-icer-contaminated road runoff at pH 8 and room temperature for 48h. Ferrocyanide (FC) concentrations of 0μM, 1μM, 2μM and 10μM were tested with background electrolyte concentrations of 0.028M NaCl (1000mg/L Cl-) or 0.028M NaClO4. Palladium release increased with FC concentration, ranging from 0.014±0.002μMPd without FC to 5.013±0.002μMPd at 10μM FC. At 0μM, 1μM and 2μM FC, chloride induced further Pd release, but had no effect at 10μM FC. PHREEQC modeling predicted that the predominant species present in equilibrium with Pd(OH)2(s) were Pd(OH)20 and Pd(CN)42-, and that PdClx2-x complexes had only a minor effect on the total concentration of dissolved palladium. The effect of FC on Pd release was predicted but not the effect of Cl-, indicating possible kinetic control. Platinum was measured above limits of detection (LODs) only at 10μM FC, and rhodium levels were below LODs, consistent with their slower complexation kinetics.

Enhanced release of palladium and platinum from catalytic converter materials exposed to ammonia and chloride bearing solutions.

The environmental levels of platinum group elements (PGEs) are steadily rising, primarily due to exhaust emissions of vehicle catalytic converter (VCC) materials containing solid PGEs. Once these VCC materials reach soil and water, the PGEs may be transported in the form of nanoparticles (dimensions 1-100 nm) or they may be mobilized by forming coordination complexes with ligands in the environment. Chloride (Cl-) and ammonia (NH3) are two ligands of particular concern due to their ubiquity as well as their potential to form the chemotherapy drug cisplatin (Pt(NH3)2Cl2) or other potentially bioactive complexes. This initial study examines the release of Pd and Pt into solutions exposed to VCC materials at pH 8 and 25 °C, using elemental analysis of metal content in post-exposure extracts. The solutions had total ammonia nitrogen concentrations (TAN, [NH4+] + [NH3]) of 0 μM, 5.56 μM, 55.6 μM and 1.13 × 105 μM (0 ppm, 0.1 ppm, 1 ppm, and 2147 ppm). The former three represent background environmental levels had a minimal effect on release. However, when combined with 1.13 × 105 μM Cl- (4000 ppm Cl-), 55.6 μM TAN induced a marked increase in metal release (∼41× for Pd). High TAN solutions induced more Pd and Pt release than equimolar NaCl solutions. Materials characterization revealed that ∼4 nm palladium-containing nanoparticles were present, spatially associated with nanoparticles of γ-Al2O3; ceria-zirconia nanoparticles were also present but did not have any metal associated with them. Platinum-containing nanoparticles were not observed.

Koncentracije Pt, Pd i Rh u tlu i vegetaciji: Pregledni rad

Automotive catalysts play an important role in the work of exhaust systems, reducing emissions of gaseous pollutants such as carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbons (HC) by more than 75%. However, hot exhaust gases that pass through the automotive catalyst cause platinum (Pt), palladium (Pd) and rhodium (Rh) emissions into the environment. Platinum group elements (PGE) and their complex salts represent a potential risk to human health, causing serious health problems (asthma, allergies). Previous research in the world related to the levels of PGE in the environment shows that these elements can be found in all components of the environment (air, water, soil, plants, road dust, ash, sewage sludge and shellfish). So far there is no data about levels of the mentioned metals in other environmental matrices (vegetation and soil) in our country, except in the air. The results of studies conducted in other countries indicate that Pt, Pd and Rh occur in elevated concentrations in the soil in urban areas (along the road) in relation to their naturally present proportion in the lithosphere. It has also been found that plant species due to emission sources accumulate these elements in their tissue and can translocate them into their upper organs. This review will give an insight into the state of platinum group elements worldwide in soil and vegetation.

Levels of platinum group elements and rare-earth elements in wild mushroom species growing in Poland

Due to limited data-describing abilities of mushrooms to accumulate platinum group elements (PGEs) and rare-earth elements (REEs), the aim of this study was to determine, by inductively coupled plasma optical emission spectrometry followed by microwave-assisted sample digestion by nitric acid, the content of these elements in 20 mushroom species (10 above ground and 10 growing on wood), mostly edible, collected near a busy trunk road. The highest content of PGEs in above-ground mushroom species was observed in Lepista gilva and Suillus bovinus fruit bodies (0.38 ± 0.05 and 0.37 ± 0.03 mg kg−1 DW, respectively), while in mushrooms growing on wood, the highest content was observed in Pleurotus ostreatus (0.35 ± 0.04 mg kg−1 DW). The mean content of PGEs for both these groups was 0.23 ± 0.08 and 0.26 ± 0.07 mg kg−1 DW, respectively. The highest content of REEs in Suillus luteus and Tricholoma equestra was 5.03 ± 0.50 and 2.18 ± 0.56 mg kg−1 DW, respectively, but within mushrooms growing on wood in Ganoderma applanatum fruiting bodies it was 4.19 ± 0.78 mg kg−1 DW. Mean contents of REEs were 1.39 ± 1.21 and 1.61 ± 0.97 mg kg−1 DW in above-ground species and species growing on wood, respectively. Generally, the group of mushroom species growing on wood was capable of slightly higher accumulation of both REEs and PGEs. No limits have been established for both the groups until now.

The metallobiochemistry of ultratrace levels of platinum group elements in the rat.

The use of platinum, palladium and rhodium (Platinum Group Elements - PGEs) and the possibility of exposure to their ultratrace levels is increasing. In fact, the exponential development of metallic PGE-based nanoparticles (<100 nm in size) opens extraordinary perspectives in the areas of electrocatalysts and catalytic converters, magnetic nanopowders, polymer membranes, cancer therapy, coatings, plastics, nanofibres and textiles. Like other metal-based nanoparticles, exposure to PGEs nanoparticles may result in a release of ultratrace amounts of Pt, Pd, Rh ions in the body whose metabolic fate and toxicity still need to be evaluated. Furthermore, PGEs can act as allergic sensitizers by acting as haptens and inducing both type I and IV allergic reactions. In this work we studied the in vivo metabolic patterns of ultratrace levels of potent allergens and sensitizers PGE halogenated salts. (191)Pt, (103)Pd and (101m)Rh radioisotopes were prepared via cyclotron irradiation and used for radiolabelling Na2(191)PtCl4, Na2(103)PdCl4 and Na2(101m)RhCl6 salts. These anionic chlorocomplexes were intraperitoneally injected into rats (114 ng Pt kg(-1) bodyweight; 24 ng Pd kg(-1) b.w.; 16 ng Rh kg(-1) b.w.). At 16 h post-exposure, PGEs were poorly but significantly retained in all tissues analysed. Kidneys, spleen, adrenal gland, liver, pancreas and small intestine were the organs with the highest Pt, Pd, Rh concentrations. In the blood 30-35% of (103)Pd and (191)Pt and 10% of (101m)Rh were recovered in the plasma, mainly bound to albumin and to a less extent to transferrin. The hepatic and renal intracellular distribution showed the highest recovery of (191)Pt, (103)Pd and (101m)Rh in the nuclear fraction (liver) and in the cytosol (kidney). Chromatographic separation and ultrafiltration experiments on kidney and liver cytosols showed the strong ability of biochemical macromolecules to bind (191)Pt, (103)Pd and (101m)Rh, and being responsible for the retention of the three elements in the body. The link to macromolecules is the basis for the sensitizing capacity of PGEs.

Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)

Evidence of Increased Anthropogenic Emissions of Platinum in Coastal Systems from Time-Series Analysis of Mussels Samples (1991-2011)

Analytical Determination and Bio-Monitoring of Platinum Group Elements in Roadside Grass Using Microwave Assisted Digestion and Electrothermal Atomic Absorption Spectrometry

The analytical conditions that enable the determination of traffic related platinum group elements (PGEs) in roadside grass using microwave digestion and electrothermal atomic absorption spectrometry were evaluated as an alternative to the biomonitoring of traffic related PGEs and Pb levels in urban areas. To optimize the analytical conditions and account for matrix effects that could import error in the analysis, method optimization was based on matrix simulation through analyte recovery from spiked unpolluted samples against a matrix blank. A mixture of nitric and hydrofluoric acid under progressively increasing microwave irradiation was optimized to afford the quantitative extraction of platinum group elements from plant matrix. Due to the low levels of platinum group elements in real samples, preconcentration was accomplished using sample evaporation followed by dissolution in dilute nitric acid prior to deliverance to the atomic detector. Quantitation limits below 1 ng g−1 for Pd and Rh and lower than 2 ng g−1 for Pt, were accomplished, enabling the monitoring of platinum group elements bioaccumulation in roadside grass with satisfactory recoveries, as determined from the analysis of spiked samples. The results from method application in an annual monitoring survey of PGEs and Pb levels in urban flora and other roadside media are presented and discussed.

Eastern Wrangellia – A New Ni-Cu-PGE Metallogenic Terrane in North America

Triassic ultramafic-mafic intrusive complexes along the eastern margin of ``Wrangellia' adjacent the Denali fault from east-central Alaska to northern British Columbia constitutes a newly recognized Ni-Cu-PGE metallogenic terrane that can be traced for at least 600 km. These sill- like intrusive centres acted as subvolcanic magma chambers that fed the extensive thick, overlying basalts and locally picritic pyroclastcs of the Nikolai Group in an oceanic plateau flood basalt setting. Confinement of the olivine-rich ultramafic sills, Ni-Cu-PGE mineralization, and more primitive coeval basalts and picrites exclusively to the eastern portion of Wrangellia is believed to be the product of melts forming in closer proximity to the hotter mantle plume tail or ``axial jet' relative to the cooler more distal portions. The recent discovery of proximal, picritic volcanics with some of the larger mineralized ultramafic bodies in Alaska finally concludes the past paradox oftholeiitic parental magmas and primitive Ni-Cu-PGE ores in this terrane. The unprecedented levels of platinum group elements, the vast extent of this mineralized terrane, the temporal association with Siberian Trap magmatism, and the accompanying Noril'sk mineralizing event, suggest that mantle plume activity during the Permo-Triassic was unique with respect to the Phanerozoic record.

QUANTITATIVE MASS BALANCE OF PLATINUM GROUP ELEMENTS IN THE KELLY LAKE Ni-Cu-PGE DEPOSIT, COPPER CLIFF OFFSET, SUDBURY

A mineralogical mass balance has been calculated for the fraction of platinum group elements (PGE) incorporated as solid solution in sulfides and sulfarsenides and the fraction that occurs as major constituents in platinum group minerals (PGM) in the Kelly Lake Ni-Cu-PGE sulfide deposit in the Copper Cliff offset, Sudbury. Low levels of PGE in sulfides were determined quantitatively for the first time in Sudbury ores by laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS), providing significantly more accurate data on the inventory and mineralogical distribution of the PGE than in previous studies. The majority of the Pt (98%), Rh (97%), and Ir (86–91%), and lesser but still large fractions of Pd (77–87%) and Ru (67–71%), occur as discrete PGM with the remainder occurring (in decreasing abundance) in solid solution in gersdorffite (1,700 ppm ∑PGE), pentlandite (1.35 ppm), chalcopyrite (0.5 ppm), and pyrrhotite (0.3 ppm). Although the PGE are present in low concentrations in sulfides, the abundances of these phases can be high enough to constitute a significant fraction of the total PGE. In particular, significant proportions of the Pd (14–23%) and Ru (~30%) in the Kelly Lake samples are hosted by sulfides and sulfarsenides. This has important implications for the genesis of the PGE, for the redistribution of the PGE during cooling and hydrothermal alteration, and for metal recovery during ore beneficiation.

Monitoring Pt and Rh in urban aerosols from Buenos Aires, Argentina

Vehicular traffic is the main source of platinum group elements (PGEs) in highly populated urban areas like Buenos Aires where a traffic density of 1,500,000 vehicles day −1 (corresponding to 7500 vehicles km −2) is estimated. Since there is no information on the levels of PGEs in Buenos Aires, a pilot study was undertaken to ascertain the amount of two major PGEs, namely Pt and Rh, in the atmosphere of this city. To this end, 49 samples of PM-10 particulate matter were collected during 7 days in seven representative sampling sites located downtown Buenos Aires and spread over an area of about 30 km 2. The collection of particulate matter was performed on ash-free glass-fiber filters using high volume samplers with PM-10 sampling heads. Filters loaded with the particulate matter were subjected to microwave (MW)-assisted acid digestion using a combination of HNO 3, HF and HClO 4. The resulting solutions were evaporated and then diluted with 0.1 mol l −1 HCl. Analyses were performed by sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) and special attention was paid to the control of mass interferences. Statistical analysis was performed on the experimental data obtained for the element concentrations taking also into account local meteorological data for the monitored period. The highest concentrations of Pt and Rh were detected at two sites (Hospital Alemán and Casa Rapallini) located in streets with traffic consisting mostly of passenger cars. The Pt content (in pg m −3) in airborne particulate matter was found to vary from 2.3 to 47.7, with a mean value of 12.9 ± 7, and that of Rh from 0.3 to 16.8, with a mean value of 3.9 ± 2.8. These concentrations are by far below the levels for which adverse health effects might be expected to occur, i.e., around 100 ng m −3. On the other hand, monitoring of PGEs should be carried out in a systematic fashion to detect possible dramatic increases from today's levels.

Determination of platinum group elements (PGE) in environmental samples by ICP-MS: a critical assessment of matrix separation for the mitigation of interferences

The accurate determination of Pt, Pd and Rh (platinum group elements, PGE) in environmental samples by inductively coupled plasma–mass spectrometry (ICP-MS) is complicated by molecular ion and doubly charged ion interferences (e.g. CuAr+, HfO+, SrO+, YO+ and Pb2+). Two matrix separation techniques, tellurium coprecipitation and ion exchange, are compared in terms of PGE recovery and separation efficiency by application to standard solutions and the new reference material BCR-723, a road dust material collected from the Tanzenberg Tunnel in Austria. Ion exchange using Dowex AG50W-X8 strong cation exchange resin is highly effective in terms of both separation efficiency (&gt;99.7%) and PGE recovery (93.8 to 101.6%) and allows accurate, interference-free determination of PGEs. PGE recoveries by Te coprecipitation are incomplete, ranging between 84 and 93%. Significant amounts of copper (up to c. 30%) are also recovered, which, due to CuAr + formation, causes interferences on both 103 Rh (monoisotopic) and 105 Pd. The generally high levels of interferent elements in environmental matrices (e.g. Cu, Pb etc.) and the magnitude of Cu recovery by Te coprecipitation limit the applicability of data correction using interference equations. Reductions in Cu yield by Te coprecipitation, to &lt;4%, can be achieved through the addition of potassium iodide prior to matrix separation. However, due to the incomplete recovery of PGEs, ion exchange provides a more robust method for the determination of low levels of PGEs.

Autocatalyst-derived platinum, palladium and rhodium (PGE) in infiltration basin and wetland sediments receiving urban runoff

The emission of platinum group elements (PGE) from automobile catalytic converters has led to rapid increases in Pt, Pd and Rh concentrations in roadside media. Significant quantities of the PGE may enter and accumulate in fluvial systems via road runoff. This paper examines the occurrence and spatial distribution of autocatalyst-derived PGE in surface sediments of infiltration basin and wetland sediments receiving road-runoff in Perth, Western Australia. Samples were analysed by ICP-MS following microwave digestion and cation exchange. PGE concentrations ranged between 1.5–17.2 Rh, 5.4–61.2 Pd and 9.0–103.8 ng g −1 Pt. The highest levels of PGE were generally found at basin topographic low points and these concentrations were found to be strongly related to the area of road surface drained and the traffic volume. PGE ratios in infiltration basin and wetland sediments were within the typical range of catalytic converter compositions. However, comparisons of PGE ratios between parent road dusts and infiltration basin sediments revealed a systematic shift in Pt/Pd ratios, suggesting that PGE fractionation can occur during transport through the drainage system and that a small portion of Pd in road dust may be solubilised under natural conditions.

P81 Occupational hypersensitivity to platinum group elements

Objective: the increasing industrial use of platinum–group elements (PGEs), namely Ir, Pd, Pt and Rh and related hypersensitivity such as respiratory symptoms, urticaria and contact dermatitis, have led to a growing need to monitor selected populations of exposed workers. Our aim is to determine the prevalence and the clinical characteristics of hypersensitivity to the platinum‐group elements; the levels of PGE measured in indoor airborne particulate matter and in biological samples (serum, urine and hair) taken from of employees in a platinum refining and catalyst manufacture; to correlate environmental exposure role and platinum salts concentrations in biological samples in the onset of allergy.Material and methods: 132 subjects variable exposed were informed about the purpose of this study and gave their consent. The examination consisted of a work exposure and medical questionnaire, physical examination, skin prick test to platinum salts and to other common allergens and patch test to platinum salts. Airborne PGEs was collected by personal and area samples. Biological samples (serum, urine and hair) were collected. Analitical procedure based on sector field inductively coupled plasma mass spectometry (SP‐ICP‐MS) for the analysis of airborne filter, serum, urine and hair was used. Results: positive prick test to platinum salts were found in 18 workers, 4 out 14 gave simultaneous positive reactions to Pt, Rh and Ir. 2 out 14 gave a positive reaction to Pt and Pd. Positive patch test reactions to Pt were found in 2 subjects, 1 out 2 gave positive reaction also to PdConclusion: the preliminary results of the investigation indicate that Pt‐salts are important allergens in catalyst industry and that the clinical manifestation involves both the respiratory system and the skin

Development of an analytical method for monitoring worker populations exposed to platinum-group elements

The increasing industrial use of platinum-group elements (PGEs), namely Ir, Pd, Pt and Rh, and related allergies such as rhinitis, conjunctivitis, asthma, urticaria and contact dermatitis, have led to a growing need to monitor selected populations of exposed workers. In this study, the levels of PGEs were measured in indoor airborne particulate matter and in biological samples taken from employees of a plant where car catalytic converters are produced and precious metals are recovered from spent carbon catalysts. The development of an analytical procedure based on quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) for the analysis of PGEs in airborne particulate matter and on sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) for the analysis of PGEs in blood, serum, urine and hair is described. For airborne particulate matter deposited on filters, the limits of detection (LoDs) were found to be 0.006 ng m −3, 0.020 ng m −3, 0.018 ng m −3 and 0.006 ng m −3 for Ir, Pd, Pt and Rh, respectively. Repeatability of measurements ranged from 1.8 to 8.5%, while recovery was in the range from 92 to 102%. For biological samples LoDs in blood, serum, urine and hair ranged from (in ng l −1) 0.2–0.6 for Ir, 5–10 for Pd, 1–3 for Pt and 2–3 for Rh. For all biological materials, the repeatability varied from 1.1 to 12% for the four elements. Recovery data for the determination of PGEs in biological matrices were found to range from 84.0 to 107.8%. The method was applied to the determination of either total or respirable airborne PGEs collected from five different work areas in the plant. The difference between areas with high and low exposure correlates closely with metal levels in hair, blood and urine. The correlation coefficients between Pt in airborne particulate matter and Pt in biological materials was 0.994, 0.991 and 0.970 for blood, hair and urine, respectively.

An accurate procedure for the determination of low levels of platinum group elements in standard materials by neutron activation analysis

The paper describes a destructive neutron activation procedure for the determination of all platinum group elements (PGE). Only a few steps are required after irradiation, namely sample dissolution, osmium and ruthenium separation by solvent extraction, anion exchange separation of remaining noble metals and counting. The chemical yield is evaluated. The method has been used for the determination of noble metals in a large variety of standard reference materials, mainly of geological and technological origin. The results, given as the average of four independent analyses are reported and discussed. Average precision for the whole procedure is usually below 8% and sensitivities are adequate to meet the analysis requirements of terrestrial PGE- and Au-poor materials.

Acraman impact ejecta and host shales: Evidence for low-temperature mobilization of iridium and other platinoids

Research Article| February 01, 1990 Acraman impact ejecta and host shales: Evidence for low-temperature mobilization of iridium and other platinoids Malcolm W. Wallace; Malcolm W. Wallace 1Department of Geology and Geophysics, University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001, Australia Search for other works by this author on: GSW Google Scholar Victor A. Gostin; Victor A. Gostin 1Department of Geology and Geophysics, University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001, Australia Search for other works by this author on: GSW Google Scholar Reid R. Keays Reid R. Keays 2Department of Geology, University of Melbourne, Parkville, Victoria 3052, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information Malcolm W. Wallace 1Department of Geology and Geophysics, University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001, Australia Victor A. Gostin 1Department of Geology and Geophysics, University of Adelaide, G.P.O. Box 498, Adelaide, South Australia 5001, Australia Reid R. Keays 2Department of Geology, University of Melbourne, Parkville, Victoria 3052, Australia Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1990) 18 (2): 132–135. https://doi.org/10.1130/0091-7613(1990)018<0132:AIEAHS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Malcolm W. Wallace, Victor A. Gostin, Reid R. Keays; Acraman impact ejecta and host shales: Evidence for low-temperature mobilization of iridium and other platinoids. Geology 1990;; 18 (2): 132–135. doi: https://doi.org/10.1130/0091-7613(1990)018<0132:AIEAHS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Geochemical investigations of a widely dispersed Late Proterozoic impact ejecta horizon and its host shales (Bunyeroo Formation, Australia) have provided strong evidence for low-temperature mobilization of the platinum group elements (PGE), including Ir. PGE anomalies are associated with both the ejecta horizon (Ir up to 2.0 ppb, Pt up to 270 ppb) and the green shales that envelop it. Several PGE anomalies (0.073-0.45 ppb Ir, 3.11-314 ppb Pt) also occur in thin green shale beds at other stratigraphic levels within a predominantly red shale sequence (average red shale background of 0.019 ppb Ir and 0.89 ppb Pt). All green shale horizons analyzed, regardless of their stratigraphic position, have relatively high levels of Ir and other PGE. The nonextraterrestrial, postdepositional origin of the PGE at other stratigraphic levels away from the impact ejecta horizon is indicated by their occurrence in thin, permeable, green beds in a predominantly red shale sequence, their association with enrichments in Cu-V-Zn-Ni, and their nonchondritic PGE interelement ratios. The impact ejecta horizon has a more chondritic PGE geochemistry consistent with a meteoritic origin. A redox precipitation model similar to that invoked for redbed Cu-U-V deposits is proposed to explain the PGE anomalies in the green shales. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Petrology of the St. Stephen Intrusion and the genesis of related nickel-copper sulfide deposits

The St. Stephen intrusion is a tholeiitic mafic-ultramafic intrusion of Devonian age occurring in the Gander terrane of the Appalachian orogen. The intrusion is dominated by olivine-plagioclase cumulates, olivine cumulates, and plagioclase cumulates. Olivine ranges in composition from Fo 61 to Fo 85 and plagioclase from An 43 to An 89 . Variations in the compositions of clinopyroxene and orthopyroxene are within Wo (sub 42-47) En (sub 37-50) Fs (sub 6-18) and Wo (sub 3-3) En (sub 50-71) Fs (sub 26-47) respectively. The Cr/Cr + Al and Mg/Mg + Fe (super +2) ratios of chromites range from 0.25 to 0.75 and 0.01 to 0.65, respectively. This appears to have resulted from the changes in the composition of the melt from which chromites were crystallized and reaction of the early formed cumulus chromites with the intercumulus melt. The observed crystallization sequence olivine (+ chromite), olivine + plagioclase, olivine + plagioclase + clinopyroxene, plagioclase + clinopyroxene + orthopyroxene (+ olivine), plagioclase + orthopyroxene (+ clinopyroxene), plagioclase + clinopyroxene appears to have resulted from simple fractional crystallization of a common tholeiitic parent magma. The composition of the parent magma seems to have an affinity to the mid-ocean ridge basalts.The intrusion contains numerous zones of significant Ni-Cu sulfide mineralization. The principal sulfide minerals are those typical of magmatic assemblages: pyrrhotite, pentlandite, and chalcopyrite. Ni and Cu concentrations reach 2.40 and 3.90 percent, respectively. Platinum-group element concentrations are generally low, with maximum abundances in massive sulfides, for example, not exceeding 62 ppb. Attainment of sulfur saturation in the St. Stephen magma during the early stages of the differentiation corresponds to the appearance of plagioclase on the liquidus following crystallization of about 10 percent of the olivine. The nickel-depleted nature of olivines at this interval can be explained by fractional crystallization of olivine and sulfide in the proportion of 50:1. An earlier segregation of sulfide from the parental magma seems to be responsible for the very low levels of platinum-group elements in the interstitial sulfides associated with the olivine cumulates. Preferential assimilation of the sulfide-rich portions of the country-rock metasediments and attainment of sulfide-silicate equilibrium on a local scale are believed to have played important roles in the formation of large pyrrhotite-rich sulfide bodies.

Determination of trace and ultra-trace amounts of noble metals in geological and related materials by graphite-furnace atomic-absorption spectrometry after separation by ion-exchange or co-precipitation with tellurium

Two methods for determining μg/g and ng/g levels of the noble metals, except for osmium, in ores, concentrates, mattes, and silicate and iron-formation rocks are described. After sample decomposition with hydrofluoric acid and aqua regia, followed by fusion of any insoluble residue with sodium peroxide, the noble metals are separated from the matrix elements by either cation-exchange or co-precipitation with tellurium. The resulting eluate, or the solution obtained after dissolution of the tellurium precipitate, is evaporated to dryness and the noble metals are ultimately determined in a 1 M hydrochloric acid medium by graphite-furnace atomic-absorption spectrometry. The ion-exchange method is recommended for the determination of μg/g levels of gold, silver and platinum-group elements, whilst the tellurium co-precipitation method is recommended for ng/g levels of platinum-group elements. The latter method is not recommended for the determination of ng/g levels of silver and gold in rocks, because of interference from tellurium during atomization in the furnace. Results obtained by these methods for 15 international reference samples, including four Canadian iron-formation rocks, are compared with other published data.