Source Of Platinum Group Elements Research Articles

Traffic-related metals in urban snow cover: A review of the literature data and the feasibility of filling gaps by field data collection

A literature search on traffic related metals in polluted urban snow revealed a significant volume of references representing a substantive knowledge base. The frequently studied metals in urban snow included Zn, Cu, Pb, Cd and Ni. However, comparing metal concentrations across studies proves to be a complex effort due to the variations in site-specific factors among studies, such as traffic intensity, pavement conditions, hydrometeorological conditions, and research method aspects, such as sampling equipment and frequency, and laboratory analytical methods. The literature review indicated that among the commonly studied metals, Zn and Cu indicated potential environmental concerns, and that there was a lack of data on the occurrence and accumulation in snow of antimony (Sb), tungsten (W), and platinum group elements (PGEs). To partly mitigate this knowledge gap, a field study of these elements was carried out by sampling urban roadside snow at six locations with various land use and traffic intensities, focusing on accumulation of these elements in snowbanks along roadways. The results indicated that traffic related activities are the sources of PGEs, W and Sb in roadside snowbanks, as the concentrations of these metals increased with increasing traffic intensity. The mean concentrations of the studied metals followed this descending order: W (0.4 (Reporting limit-RL)–987 μg/l) > Sb (0.1 RL–33.2 μg/l) > Pd (0.02 (RL)–0.506 μg/l) > Rh (0.02 (RL)–0.053 μg/l). In laboratory melted snow, both W and Sb were mostly in the particulate-bound phase, with <25 % in the dissolved phase. For sites with metal concentrations above the detection limit, the regression analysis indicated linear trends in unit area deposition rates of W with time (snow age), described by R2 = 0.94.

The temporal distribution of platinum group elements (PGEs) in PM2.5.

In this paper, Changji, Xinjiang, northwest China, was selected as the study area, and platinum group elements (PGEs) in PM2.5 were quantified by ICP-MS using microwave digestion. The results indicated that the average concentrations (and range) of Rh, Pd, and Pt in PM2.5 were 0.21 (n.d. -1.41) ng/m3, 8.09 (n.d. -59.50) ng/m3, and 0.12 (n.d. -0.83) ng/m3, respectively. The concentration of Pd was significantly higher than Rh and Pt. Moreover, the seasonal variations of Rh and Pd were the same: highest in summer and lower in other seasons. However, the seasonal variation of Pt was opposite to that of Rh and Pd: highest in winter and lower in other seasons. Seasonal differences in emission sources of PGEs and the climatic characteristics of arid regions played important roles in the seasonal changes of PGEs. Rh and Pd had a common source and similar diurnal variation. The major influencing factors were traffic volume and meteorological conditions. The diurnal variation regularity of Pt was different from Rh and Pd. The superimposed effect of vehicle exhaust emissions and coal-fired emissions was the main reason why the diurnal variation of Pt was more complicated than those of Rh and Pd. The diurnal concentration of Pt varied with the seasons. It is caused by seasonal coal combustion and meteorological conditions.

Platinum Group Elements in Geosphere and Anthroposphere: Interplay among the Global Reserves, Urban Ores, Markets and Circular Economy

Industrial and strategic significance of platinum group elements (PGEs)—Os, Ir, Ru, Rh, Pd, Pt—makes them irreplaceable; furthermore, some PGEs are used by investors as “safe heaven” assets traded in the commodity markets. This review analyzes PGEs from various aspects: their place in the geosphere, destiny in the anthroposphere, and opportunity in the economy considering interactions among the exploration, recycling of urban ores, trade markets, speculative rhetoric, and changes required for successful technological progress towards the implementation of sustainability. The global market of PGEs is driven by several concerns: costs for extraction/recycling; logistics; the demand of industries; policies of waste management. Diversity of application and specific chemical properties, as well as improper waste management, make the recycling of PGEs complicated. The processing approach depends on composition and the amount of available waste material, and so therefore urban ores are a significant source of PGEs, especially when the supply of elements is limited by geopolitical or market tensions. Recycling potential of urban ores is particularly important in a long-term view disregarding short-term economic fluctuations, and it should influence investment flows in the advancement of innovation.

The source of platinum group elements in basalts of the ophiolite complex of the Kamchatsky Mys Peninsula (Eastern Kamchatka)

Contents of platinum group elements (PGE—Os, Ir, Ru, Rh, Pt, and Pd) and rhenium in basalts of different geochemical types from the ophiolite complex of the Kamchatsky Mys Peninsula have been determined by the isotope dilution-mass spectrometry method. The total contents of PGE in different basalts are commensurate (1.4-3.6 ppb), but the element ratios vary considerably. A specific feature of the rocks is the low degree of PGE fractionation (Pd/Ir = 0.9-6.6, Pt/Pd = 1.0-7.3), which makes them similar to the Hawaiian tholeiitic basalts and picrites. The most fractionated PGE pattern is observed for alkali basalt (Pd/Ir = 6.6), and the least fractionated one, for E-MORB (Pd/Ir = 1.7). The similarity of the PGE patterns of basalts of different geochemical types suggests their similar mantle sources. We propose a model explaining the geochemical features of the basalts of the Kamchatsky Mys ophiolite complex by an impurity of the Earth’s core material in the plume source. The Ir/Pd-Ru/Pd and Pd/10-Ir-Ru discrimination diagrams can be used to identify enriched (plume) basalts based on their PGE content.

Seasonal properties on PM1 and PGEs (Rh, Pd, and Pt) in PM1

Vehicle exhaust converters (VECs) are considered the sources of platinum group element (PGEs) to environment, but PGEs emitted from coal combustion in heating period in winter are ignored by researchers. Snow affecting on PM1 and PGEs in PM1 are given little attention either. A detailed examination of the concentrations of PM1 and its platinum group element (PGEs) components in Changji (Xinjiang, Northwest in China) has revealed their seasonal variations and influencing mechanisms. Each sample was continuously collected for 24 h using a medium flow rate intelligent total suspended particulate (TSP) sampler, then digested via an HNO3-HCl-HF system and analyzed by inductively coupled plasma-mass spectrometry (ICP-MS). The mean concentration of PM1 was 0.10 (0.04–0.41) mg m−3, and the concentrations of Rh, Pd and Pt in PM1 were 0.06 (n.d.–0.21) ng m−3, 1.99 (n.d.–10.77) ng m−3, and 0.05 (n.d.–0.19) ng m−3, respectively. Among the PGEs components, Pd had the highest concentration, while the concentrations of Pt and Rh were low. PM1 in winter is two or three times comparison than the other seasons, due to its major emission from coal combustion during the heating period. But the Rh, Pd, and Pt concentrations were lower in winter than in the other seasons. Rh, Pd, and Pt also had similar seasonal variations, their variation was different from the variation of PM1, and this different variation is attributed to the strongly scavenging effect of snow. The PGEs emissions from coal combustion were incline to enriched in large particles with a high degree of selectivity and the content of PGEs in PM1 was not strongly influenced by coal combustion. Therefore seasonal variations of TSP, PM2.5, and PGEs in PM1 were obviously different. The common source of PGEs in PM1 is vehicle exhaust converters (VECs), but VECs were not the sole source of Pt, which was also rarely emitted from coal combustion.

Platinum group elements in terrestrial oil shale from the Lunpola Basin, northern Tibet, China

ABSTRACTThe Lunpola oil shale is the largest oil shale resource in Tibet. Twenty-four samples were collected from this deposition to determine the platinum group element (PGE) characteristics. The total PGE contents in terrestrial oil shale are low (average 2.386 ng/g). The PGEs are enriched in the oil shale samples near the boundary between the oil shale and its underlying strata. The PGE enrichment may be the result of a change of oxic–anoxic conditions. The individual PGEs of oil shale samples from the Lunpola oil shale exhibit similar modes of occurrence, and their distributions are controlled mainly by Fe-bearing minerals (pyrite). The source of PGEs in the Lunpola oil shale is probably related to water chemistry and terrigenous supply.

Spatial and temporal distribution of platinum group elements (PGEs) in roadside soils from Shanghai and Urumqi, China

Purpose The aims of this study are to elucidate the temporal trend, spatial distribution and the source of platinum group elements(PGEs) in roadside soil from Shanghai and Urumqi.

Complex Anthropogenic Sources of Platinum Group Elements in Aerosols on Cape Cod, USA

Platinum group elements (PGE) of anthropogenic origin have been reported in rainwater, snow, roadside soil and vegetation, industrial waste, and urban airborne particles around the world. As recent studies have shown that PGE are bioavailable in the environment and pose health risks at chronic levels, the extent of PGE pollution is of global concern. In this study, we report PGE concentrations and osmium isotope ((187)Os/(188)Os) ratios of airborne particles (particulate matter, PM10) collected in Woods Hole, a small coastal village on Cape Cod, Massachusetts, U.S.A. The sampling site is more than 100 km away from the nearest urban centers (Boston, Providence) and has no large industrial emission center within a 30 km radius. The study reveals that, although PGE concentrations in rural airborne particulate matter are orders of magnitude lower than in urban aerosols, 69% of the total osmium is of anthropogenic origin. Anthropogenic PGE signatures in airborne particles are thus not restricted to large cities with high traffic flows and substantial industries; they can also be found in rural environments. We further conclude that the combination of Pt/Rh concentration ratios and (187)Os/(188)Os composition can be used to trace PGE sources. The Pt/Rh and (187)Os/(188)Os composition of Woods Hole aerosols indicate that the anthropogenic PGE fraction is primarily sourced from ore smelting processes, with possible minor contributions from fossil fuel burning and automobile catalyst-derived materials. Our results further substantiate the use of (187)Os/(188)Os in source apportionment studies on continental scales.

Leaching of Ni–Cu–Fe–S converter matte at varying iron endpoints; mineralogical changes and behaviour of Ir, Rh and Ru

The Bushveld Igneous Complex in South Africa is a rich source of platinum group elements (PGEs), as well as base metal sulphides. Typical beneficiation routes entail milling and flotation, smelting, matte converting and hydrometallurgical processing of converter matte to selectively recover metal values. The primary focus is on PGE recovery, with the secondary objective of base metals recovery. At the Western Platinum Pty. Ltd. Base Metals Refinery, converter matte typically contains 48% Ni, 29% Cu, 21% S and 0.6–5% Fe by weight, and the major mineral phases have compositions approaching heazlewoodite (Ni3S2), chalcocite (Cu2S) and a Ni–Cu alloy. It has been observed that the iron content of converter matte can have a significant impact on performance of the first stage atmospheric leach, in which the primary goal is to precipitate copper and PGEs from spent electrolyte (via metathesis and cementation reactions) and the secondary goal is the dissolution of nickel. In this work, laboratory scale batch leach tests were carried out with samples of converter matte with varying Fe-endpoints (0.53%, 0.83% and 5.72%), under oxygenated and non-oxygenated conditions, to improve understanding of the effect of the Fe-endpoint. X-ray diffraction and scanning electron microscopy techniques were employed to understand mineralogical changes that take place during leaching. Matte with a higher iron content was characterised by a lower Ni–Cu alloy content than matte with a lower iron content, and the presence of relatively inert pentlandite (NiFe)9S8. Under oxygenated conditions, nickel was leached more readily from low iron matte and copper and PGEs were precipitated more readily onto low iron matte than high iron matte. Under non-oxygenated conditions, copper was precipitated more readily onto the low iron matte and more nickel was leached from a low-iron matte than high iron matte, this can probably be attributed to the presence of the alloy phase in the low iron matte, which galvanically inhibits the metathesis reaction.

The effects on soil/water/plant/animal systems by platinum group elements

Abstract Emissions of toxic substances such as oxides of carbon, nitrogen, sulphur, and, in addition, aromatic hydrocarbons, aldehydes and heavy metals are the most serious problem of road traffic affecting landscape. Platinum group elements (PGE), which are the main component of the catalyst, are one of the main sources of heavy metals in the environment. Here, we review the way by which emissions and forms of the emitted PGE end up in the environment especially to the soil-water-plant-animal system. The major points discussed are the following: 1) the main sources of PGE emission are automobile exhaust catalysts; 2) hospitals, where platinum is widely used to treat malignant neoplasm, and urban waste water belonging to other important sources of PGE in the environment; 3) soil is one of the most important components of the environment that may be contaminated with platinum metals; 4) phytotoxicity of PGE depends on the following conditions: the concentration of metals in the soil, time of exposure, the chemical form of metal, the chemical composition of exposed soil and plant species; 5) animals are also endangered by the increasing concentration of PGE in the environment. Moreover, we pay our attention to thiol-based mechanisms of how an organism protects itself against platinum group elements.

Health Risk of Platinum Group Elements from Automobile Catalysts

Platinum group elements (PGE) are widely used in industries with an increasing number, and their emissions are resulting in elevated environmental concentrations of these rare metals. Automobile catalyst, which uses Pd, Pt, and Rh as active components, is the most important application field of PGE, and is becoming the main source of PGE emitted into the environments, contributing to a global increase in PGE concentrations. The paper reports the emitted PGE concentrations and distribution found in urban air and accumulated on the road surface and in roadside soil, plant, and their contamination of aquatic environments. The bioavailability, potential uptake into the biosphere, potential risks for humans and the environment are discussed.

Initial Os-isotopic composition of Os-Ir-Ru alloys from ultramafic massifs of the Polar Siberia

This study firstly presents chemical and initial Os-isotopic compositions of Os-Ir-Ru minerals of two ultramafic formations of Polar Siberia, which are exemplified by Guli clinopyroxene-dunite massif of the Maimecha-Kotui Province and the Kunar dunite-harzburgite massif from the Chelyuskin ultramafic belt of the Taimyr Peninsula. The study employed a range of methods, including electron microprobe analysis, negative thermal ionization mass spectrometry (N-TIMS) and laser ablation attached to an inductively coupled plasma mass spectrometry (LA MC-ICP-MS). The majority of platinum-group minerals (PGM) from the Guli massif are Os-(Ir-Ru) solid solutions or Os-rich minerals. At Kunar, minerals of Ru-Os-Ir system (i.e., osmium, ruthenium, iridium and rutheniridosmine) dominate the PGM assemblage. The ruthenium trend in the mineral compositions is due to the formation of these minerals under high pressures and temperatures at considerable depths. The 187Os/188Os values of Os-rich minerals from the Guli massif range from 0.12309 ± 0.00002 to 0.12606 ± 0.00003 (n = 168). The initial Os-isotopic composition of PGM from the central block of the Guli massif is characterized by the 187Os/188Os values, varying in the range 0.12404–0.12606. Osmiumrich minerals from the southwestern block of the Guli massif are characterized by the least “radiogenic” 187Os/188Os values (i.e., 0.12309–0.12341). Low relative to the chondritic universal reservoir (CHUR) 187Os/188Os values are indicative of a near-to-chondritic source of platinum-group elements (PGE). The most “productive” stage of PGM formation at Guli (n = 121) is recorded in the time interval of 545–615 Ma. The older model 187Os/188Os ages of osmium minerals are characteristic of the southwestern block of the Guli massif (e.g., 745–760 Ma). The results of the initial Os-isotopic composition for Os-rich alloys are consistent with a model, in which PGM were formed during multi-stage melt depletion events in the mantle. This agrees well with the suggestion that the Guli massif consists of heterogeneous blocks of ultramafic rocks. The 187Os/188Os ratio in the investigated PGM from the Kunar massif varies in a wider range (0.1094–0.1241, n = 28). For the dominant set of PGM samples (n = 25), regardless of their chemical composition, four groups of the initial osmium isotopic compositions can be estimated, with average 187Os/188Os values of 0.1217 ± 0.0002 (n = 7), 0.1223 ± 0.0002 (n = 7), 0.1230 ± 0.0002 (n = 6) and 0.1238 ± 0.0003 (n = 6), respectively. The average model Re-Os ages for the defined groups of the Kunar massif are consistent with Late Riphean age interval (e.g., 975 ± 42 Ma, 892 ± 42 Ma, 791 ± 28 Ma and 681 ± 42 Ma, respectively). Significant variations in the 187Os/188Os values and model ages for Ru-Os-Ir alloys at Kunar are close to those from other duniteharzburgite massifs of the Earth, pointing out for their prolonged multi-stage evolution within the upper mantle.

Geochemistry of platinum group elements in marine oil shale from the Changshe Mountain area (China): Implications for modes of occurrence and origins

Abstract The Shengli River–Changshe Mountain oil shale zone, located in the North Qiangtang depression, northern Tibet plateau, represents a potentially largest marine oil shale resource in China. Eighteen samples, including oil shale and micritic limestone, were collected from the Changshe Mountain oil shale to determine the concentrations, the modes of occurrence, and origins of platinum group elements (PGEs) in marine oil shale. The oil shale samples from the Changshe Mountain area exhibit low total PGE contents ranging from 3.196 to 8.071 ng/g with a weighted mean value of 5.383 ng/g, while the micritic limestone samples from the Changshe Mountain area exhibit a little lower ranging from 0.471 to 5.669 ng/g. PGEs in oil shale samples are characterized by high contents in Pd (3.23 ng/g), Pt (1.60 ng/g), and Os (0.32 ng/g), as compared to Rh (0.083 ng/g), Ru (0.112 ng/g), and Ir (0.043 ng/g). The individual PGEs of oil shale samples from the Changshe Mountain area exhibit various modes of occurrence. Ru and Ir are mainly controlled by clay minerals and partly present as sulfide. Rh is mainly associated with sulfide and possibly present as clay minerals. Pt is associated with clay minerals and sulfide, and Pd is controlled by organic matter and pyrite, while Os is mainly present in organic matter. Three possible sources of PGEs were identified in oil shale seams in the Changshe Mountain area. Ru and Ir are mainly terrigenous inputs. Rh and Pt are derived from mixed sources (seawater and terrigemnous supply), while Pd and Os are mainly derived from seawater. The terrestrial source of the oil shale seams in the Changshe Mountain oil shale was the Suowa Formation limestone and the Nadi Kangri felsic volcanic rocks.

Assessing the potential involvement of an early magma staging chamber in the generation of the Platreef Ni–Cu–PGE deposit in the northern limb of the Bushveld Complex: a pilot study of the Lower Zone Complex at Zwartfontein

The Platreef of the northern limb of the Bushveld Complex is one of the world's most significant deposits of platinum-group elements (PGE) with associated Ni and Cu. The origin of the Platreef is controversial. Some workers suggest that it is a northern facies of the Merensky Reef or part of the Upper Critical Zone, while others have suggested that the Platreef formed by processes entirely contained within the northern limb, unrelated to mineralisation events elsewhere in the complex. The northern limb is separated from the rest of the complex by the Thabazimbi–Murchison Lineament (TML) and the effect that this structure had on the intrusion of Bushveld magmas is debated. The presence of chilled rocks and cross-cutting relationships between the Platreef and its hangingwall gabbronorites would seem to preclude the magma that formed the hangingwall also acting as a source of PGE to the Platreef. The base metal sulphides in the Platreef carry very high PGE tenors (comparable with the Merensky Reef) indicating that the PGE must have been concentrated from a large volume of magma, but the source of that magma has not been established. In order to solve this PGE mass balance paradox, McDonald and Holwell have suggested that the magmas that formed the (pre-Platreef) Lower Zone may have been the source of PGE. At present, other models do not involve any significant role for the Lower Zone magmas in forming the Platreef. The data presented in this pilot study of the Lower Zone intrusion at Zwartfontein test some of the predictions arising from the McDonald and Holwell model. They highlight some important first order differences between Lower Zone intrusions in the northern limb compared with the rest of the Bushveld Complex. The enrichment in Th and LREE that characterizes the Lower Zone rocks in the eastern and western Bushveld appears to be missing in the northern limb. The lithophile element signatures of the different types of Lower Zone are suggested to result from mafic magmas intruding north and south of the TML and being contaminated by these different types of crust. Most significantly, the study has also revealed strong depletion of chalcophile elements (Ni, Cu and PGE) in the Lower Zone intrusion at Zwartfontein. The results are consistent with the depleted products expected from the processing of pre-Platreef magma(s) by interactions with sulphides at a deeper level within the magmatic plumbing system. The results provide a positive first test of one of the predictions arising from the McDonald and Holwell Platreef model. The existence of a system capable of removing PGE and producing a large volume of depleted ultramafic cumulates, in close proximity to the most highly mineralised sector of the Platreef, is suggested to be highly significant.

Environmental Relevance of the Platinum-Group Elements

Platinum-group elements (PGE) are used in an increasing number of applications, and emissions are resulting in elevated environmental concentrations of these normally rare metals. Automobile exhaust catalysts, which use Pd, Pt, and Rh as active components, are the main source of PGE emitted into urban and roadside environments, and they contribute to a global increase in PGE concentrations. Emitted PGE are found in urban air and accumulate on the road surface and in roadside soil. Transport of PGE via stormwater is resulting in contamination of aquatic environments. There is now mounting evidence that a fraction of PGE in the environment is bioavailable, and potential uptake into the biosphere is raising concern over potential risks for humans and the environment.

Platinum-group elements of the Meishan Permian–Triassic boundary section: Evidence for flood basaltic volcanism

Permian–Triassic boundary sections record the most severe mass extinction event in geological history. However, there is a long-standing controversy of whether bolide impact and/or basaltic flood volcanism triggered the mass extinction. Platinum-group elements (PGEs) are enriched in most extraterrestrial materials, but highly depleted in the terrestrial crust materials. We analyzed Ir, Ru, Rh, Pt and Pd in a set of samples from the global stratotype section and point (GSSP) of the Permian–Triassic boundary at Meishan, China, using isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) and nickel sulfide fire assay (NiS-FA) combined with Te coprecipitation. The samples have no Ir anomaly (5–53 pg/g), and their PGE patterns normalized to chondrites are highly fractionated with Ir/Pd ratios of 0.02–0.03 × CI, distinct from most extraterrestrial materials. In contrast, these patterns are closely parallel to those of the Siberian and probably Emeishan flood basalts, suggestive of possible sources of PGEs from the basalts. The abundances of PGEs increase in order of the pyrite lamina on the top of bed 24, bed 25 and bed 26, and then decrease to bed 28, probably indicative of a maximum eruption of the flood basalts during deposition of bed 26. The new data favor massive volcanism, rather than extraterrestrial impact, as a major cause of the Permian–Triassic boundary mass extinction.

Platinum, Palladium, and Rhodium in Fresh Snow from the Aspe Valley (Pyrenees Mountains, France)

Platinum, palladium, and rhodium have been measured in fresh snow samples from 14 locations within the Aspe Valley (Pyrenees Mountains, France) during two winter seasons, February 2003 and March 2004. Ultraclean procedures were employed for the sampling, sample treatment, and analysis in order to reduce sample contamination. Possible spectral interferences on platinum group element (PGE) analysis by inductively coupled plasma mass spectrometry (ICP-MS) were controlled and corrected. The detection limits obtained were 0.05, 0.45, and 0.075 pg g(-1) for Pt, Pd, and Rh, respectively. PGE content in fresh snow from the Pyrenees Mountains range from 0.20 to 2.51 pg g(-1) for Pt, 1.45-14.04 pg g(-1) for Pd, and 0.24-0.66 pg g(-1) for Rh. The higher PGE concentration, generally measured in sites located close to road traffic, exhibit potential resuspension of PGE-enriched particles emitted locally from the car exhaust, although no direct relationship could be observed with the number of vehicles. Measured atmospheric synoptic conditions allowed identification of the origin of air masses reaching the Aspe Valley and therefore provided information about the possible sources of platinum group elements. Higher PGE concentrations measured in 2004 samples, compared to the ones collected in 2003, indicate the influence of atmospheric synoptic conditions on the studied area. Fresh snow samples collected in 2003 could not be linked to a specific source, whereas 2004 samples could be influenced by PGE emissions from European vehicle fleet and Russian PGE-containing mining activities.

Phoscorite-Carbonatite Pipe Complexes

The background to a project in Brazil is described that has found promising concentrations of platinum group elements (PGEs) in phoscorite-carbonatite complexes. Further geochemical and mineralogical research is underway to determine their potential as ore deposits. The well-established industrial demand and current level of prices for the platinum group metals have encouraged the exploration of geological environments other than the layered maficultramafic intrusions that provide the bulk of platinum metals. Environments, such as the Ural-Alaskan Type Complexes (U-ATCs) and the associated placer deposits were for many years the only known sources of the PGEs. This paper attempts to show a connection between platiniferous dunite-pyroxenite pipes in the Ural Platinum Belt and those on the eastern margin of the Bushveld Complex, both being significant PGE producers in the past, and phoscoritecarbonatite pipe (PCP) complexes. PCP complexes may be a promising source of PGEs. Four Brazilian PCP complexes are sampled (Salitre, Tapira, Ipanema and Catalão) as well as the Phalaborwa PCP complex in South Africa.

Observations on the relationship between the Platreef and its hangingwall

Observations on the nature of the contact between the Platreef and its hangingwall have revealed that not only were the hangingwall gabbronorites intruded after the Platreef igneous rocks and the development of platinum group element (PGE) mineralisation, but that there appears to have been a significant time-break separating the two intrusive events. The hangingwall gabbronorites truncate several features present within the Platreef pyroxenites but not in the hangingwall, such as shear zones and reef which has undergone alteration by Fe-rich fluids, implying that these features were formed prior to intrusion of the gabbronorites. A fine-grained leuconorite at the base of the hangingwall exhibits textures showing erosion of Platreef orthopyroxene by fine-grained cumulus plagioclase, suggesting intrusion of a hot magma over cooled Platreef. Xenoliths of reef pyroxenite are also found in the hangingwall. PGE mineralisation is present within basal zones of the hangingwall where the hangingwall overlies mineralised Platreef pyroxenite. We interpret the contact as a magmatic unconformity and, as the gabbronorites do not appear to be PGE-depleted, suggest that PGEs and S were scavenged or assimilated from the reef by the intruding magma, producing zones of orthomagmatic PGE mineralisation in topographic depressions at the base of the crystallising hangingwall. The presence of calc–silicate xenoliths in the hangingwall gabbronorites can be explained by footwall anticlines or diapirism which the relatively thin Platreef had not overtopped, allowing footwall dolomite to be exposed to the main influx of hangingwall magma. The identification of a time-break between Platreef and hangingwall intrusion, and the most likely source of basal hangingwall PGE mineralisation being the underlying Platreef, shows that the magma that formed the gabbronorites could not have been the source of PGE for the Platreef as previously thought.

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.