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1.
The behaviour of PGE in a rainforest ecosystem were investigated in four lateritic profiles (Nkamouna, Napene, West and East Mada) developed on serpentinites in the Kongo–Nkamouna massif (Lomié region, South-East Cameroon). In serpentinites, the total PGE content attains 22 ppb whilst it ranges between 26 and 200 ppb in the weathering blanket. Amongst the analyzed elements (platinum, iridium, ruthenium, rhodium, palladium), platinum and ruthenium contents are high in the saprolite zone and in the hardened materials of some weathering profiles (40–66 ppb for platinum, 50–71 ppb for ruthenium). Apart from the hardened materials, the total PGE content decreases from the coarse saprolite towards the clayey surface soil. The Fe2O3-PGE diagram indicates a relatively similar behaviour in these iron-rich samples. The Pt–Ir, Pt–Pd, Pt–Ru, Pt–Rh diagrams portray positive correlations between platinum and other PGE. This fact is supported by the positive correlation noticed between IPGE and PPGE. The Pt/Ir, Pt/Pd, Pt/Ru and Pt/Rh values indicate that iridium, palladium, ruthenium and rhodium are more mobile than platinum. These data confirm the mobility of PGE in laterites and the positive correlation reveals that PGE might be accommodated in the interfaces of iron oxides. The mass balance assessment shows that PGE are strongly leached from the Kongo–Nkamouna weathering blanket except in the coarse saprolite of the Nkamouna profile.  相似文献   

2.
The emission of platinum group elements (PGE) from automobile catalytic converters has led to enrichment of PGE in road dusts and roadside soils in urban areas that are well above the natural background levels. This paper evaluates the source of contamination of all the PGE and Au in road dusts and roadside soils in the Pearl River Delta region, including three major cities, Shenzhen, Guangzhou and Hong Kong, South China. Samples were digested using Carius tube and analyzed by isotope dilution ICP-MS; Os was separated by distillation and other PGE by Te-coprecipitation. All samples have elevated PGE concentrations above the background values of uncontaminated soils and contain higher Pt, Pd and Rh than other PGE. The maximum values are 181 ng/g Pt, 514 ng/g Pd, 53 ng/g Rh and 1345 ng/g Au. There are clear positive correlations between Pt and Pd, Pt and Rh, and Pd and Rh, indicating that the main emitted of PGE from automobile catalyst are Pt, Pd and Rh. High concentrations of Au were also found in road dust samples from Hong Kong and Shenzhen. Dust samples with higher Os contents have lower 187Os/188Os ratios. Samples from Hong Kong show relatively high Pt/Rh ratios. Positive correlations between Pt and Ru, and Pt and Ir were found in Shenzhen and Hong Kong, but only positive correlations between Pt and Ir were found in Guangzhou. These different characteristics reflect different automobile catalytic systems used in Hong Kong and mainland China.  相似文献   

3.
The distribution of platinum group elements (PGEs) in massive sulfides and hematite–magnetite±pyrite assemblages from the recently discovered basalt-hosted Turtle Pits hydrothermal field and in massive sulfides from the ultramafic-hosted Logatchev vent field both on the Mid-Atlantic Ridge was studied and compared to that from selected ancient volcanic-hosted massive sulfide (VHMS) deposits. Cu-rich samples from black smoker chimneys of both vent fields are enriched in Pd and Rh (Pd up to 227 ppb and Rh up to 149 ppb) when compared to hematite–magnetite-rich samples from Turtle Pits (Pd up to 10 ppb, Rh up to 1.9 ppb). A significant positive correlation was established between Cu and Rh in sulfide samples from Turtle Pits. PGE chondrite-normalized patterns (with a positive Rh anomaly and Pd and Au enrichment), Pd/Pt and Pd/Au ratios close to global MORB, and high values of Pd/Ir and Pt/Ir ratios indicate mafic source rock and seawater involvement in the hydrothermal system at Turtle Pits. Similarly shaped PGE chondrite-normalized patterns and high values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides at Logatchev likely reflect a similar mechanism of PGE enrichment but with involvement of ultramafic source rocks.  相似文献   

4.
The 2.7 Ga Kambalda Sequence comprises a mafic to ultramafic dominated volcanic rock sequence of the Kalgoorlie Terrane, Yilgarn Craton, Western Australia. The Sequence is divided into Lower and Upper Units separated by the Kambalda Komatiite Formation. Five basalt suites of the Lower Unit are tholeiitic where MgO spans 5-10 wt.% MgO, with minor assimilation-fractional crystallization (AFC), whereas six volcanic suites identified in the Upper Unit are tholeiitic to komatiitic-basalts with MgO 24-5 wt.% having generally greater degrees of AFC. Upper suites plot at Al2O3/TiO2 (17-26) close to the primitive mantle ratio of 21, and Pt + Pd (19-31 ppb), whereas the PGE-depleted Lower basalts plot at generally lower Al2O3/TiO2 (<16) and Pt + Pd (<10 ppb). Most suites have an average Pt/Pd ratio of 1.11, despite large variations in MgO contents, broadly consistent with the Pt/Pd ratio in the primitive mantle. On primitive mantle-normalised PGE plots, Upper suites generally display less fractionated patterns of the IPGE (Os, Ir, Ru and Rh) from the PPGE (Pt and Pd) relative to the Lower basalts. Most suites exhibit patterns with positive slopes reflecting relative enrichment of Pd, Pt, Au and Cu relative to Ni and IPGE. In suites of both Units, the concentrations of Ir and Ru fall with decreasing MgO contents, indicating their broadly compatible behaviour during magmatic evolution that involved AFC. Platinum and Pd behave as incompatible elements in the high-MgO suites, whereas Pt and Pd behave compatibly during crystallisation of the Lower basalt magmas, an interpretation consistent with progressively higher Cu/Pt and Cu/Pd ratios at decreasing MgO contents, and with falling Pt/Ti, collectively due to sulphur saturation induced by AFC as recorded in an antivariance of Pd/Ir with Nb/Th, a monitor of AFC.Collectively, the data suggest that several of the Lower Basalt suites crystallised under sulphide-saturated conditions, whereas most of the Upper Basalt Sequences remained sulphur undersaturated during magmatic evolution. Alteration, and fractional crystallisation of silicate and oxide phases, can be ruled out as factors governing PGE distribution in these mafic-ultramafic suites. Instead, the data suggest that discrete PGE-bearing phase (s) fractionated from the magmas. Such phases could be platinum group minerals (PGM; e.g., laurite) and/or alloys, or discrete PGE-rich nuggets or sulphides.  相似文献   

5.
The major element relationships in ferromanganese (Fe-Mn) crusts from Afanasiy-Nikitin seamount (ANS), eastern equatorial Indian Ocean, appear to be atypical. High positive correlations (r = 0.99) between Mn/Co and Fe/Co ratios, and lack of correlation of those ratios with Co, Ce, and Ce/Co, indicate that the ANS Fe-Mn crusts are distinct from Pacific seamount Fe-Mn crusts, and reflect region-specific chemical characteristics. The platinum group elements (PGE: Ir, Ru, Rh, Pt, and Pd) and Au in ANS Fe-Mn crusts are derived from seawater and are mainly of terrestrial origin, with a minor cosmogenic component. The Ru/Rh (0.5–2) and Pt/Ru ratios (7–28) are closely comparable to ratios in continental basalts, whereas Pd/Ir ratios exhibit values (<2) similar to CI-chondrite (∼1). The chondrite-normalized PGE patterns are similar to those of igneous rocks, except that Pd is relatively depleted. The water depth of Fe-Mn crust formation appears to have a first-order control on both major element and PGE enrichments. These relationships are defined statistically by significant (r > 0.75) correlations between water depth and Mn/Co, Fe/Co, Ce/Co, Co, and the PGEs. Fractionation of the PGE-Au from seawater during colloidal precipitation of the major-oxide phases is indicated by well-defined linear positive correlations (r > 0.8) of Co and Ce with Ir, Ru, Rh, and Pt; Au/Co with Mn/Co; and by weak or no correlations of Pd with water depth, Co-normalized major-element ratios, and with the other PGE (r < 0.5). The strong enrichment of Pt (up to 1 ppm) relative to the other PGE and its positive correlations with Ce and Co demonstrate a common link for the high concentrations of all three elements, which likely involves an oxidation reaction on the Mn-oxide and Fe-oxyhydroxide surfaces. The documented fractionation of PGE-Au and their positive association with redox sensitive Co and Ce may have applications in reconstructing past-ocean redox conditions and water masses.  相似文献   

6.
Platinum-group element (PGE) geochemistry combined with elemental geochemistry and magnetite compositions are reported for the Mesoproterozoic Zhuqing Fe–Ti–V oxide ore-bearing mafic intrusions in the western Yangtze Block, SW China. All the Zhuqing gabbros display extremely low concentrations of chalcophile elements and PGEs. The oxide-rich gabbros contain relatively higher contents of Cr, Ni, Ir, Ru, Rh, and lower contents of Pt and Pd than the oxide-poor gabbros. The abundances of whole-rock concentrations of Ni, Ir, Ru, and Rh correlate well with V contents in the Zhuqing gabbros, implying that the distributions of these elements are controlled by magnetite. The fractionation between Ir–Ru–Rh and Pt–Pd in the Zhuqing gabbros is mainly attributed to fractional crystallization of chromite and magnetite, whereas Ru anomalies are mainly due to variable degrees of compatibility of PGE in magnetite. The order of relative incompatibility of PGEs is calculated to be Pd?<?Pt?<?Rh?<?Ir?<?Ru. The very low PGE contents and Cu/Zr ratios and high Cu/Pd ratios suggest initially S-saturated magma parents that were highly depleted in PGE, which mainly formed due to low degrees of partial melting leaving sulfides concentrating PGEs behind in the mantle. Moreover, the low MgO, Ni, Ir and Ru contents and high Cu/Ni and Pd/Ir ratios for the gabbros suggest a highly evolved parental magma. Fe–Ti oxides fractionally crystallized from the highly evolved magma and subsequently settled in the lower sections of the magma chamber, where they concentrated and formed Fe–Ti–V oxide ore layers at the base of the lower and upper cycles. Multiple episodes of magma replenishment in the magma chamber may have been involved in the formation of the Zhuqing intrusions.  相似文献   

7.
The contents of the platinum-group elements (PGEs: Os, Ir, Ru, Rh, Pt, Pd) in the Abulangdang ultramafic intrusion have been determined using ICP-MS after nickel sulfide fire assay preconcentration. Different samples show significant differences in absolute PGE abundance. They display a pronounced negative incline in mantle-normalized patterns which are characterized by strong enrichment in IPGEs (Os, Ir, Ru) and depleting to slight enrichment in PPGEs (Rh, Pt, Pd). The characteristics of PGE distribution in the Abulangdang rocks are due to the combined action of sulfide and non-sulfide (spinel/chromite or alloy or micro-granular aggregation of metals). In comparison with the mafic-ultramafic rocks which host Ni-Cu-PGE deposits in the Emeishan Large Igneous Province (ELIP), it is assumed that the Abulangdang ultramafic intrusion may be the product of early-stage magma activity in the ELIP.  相似文献   

8.
Sorption isotherms, time-dependent adsorption and surface complexation modeling studies were used to investigate the post-depositional mobility of three of the platinum group-elements (Pd, Rh, and Pt) in semi-arid soil and sediment samples with varying surface properties. The acidity constants (Log Ka1 and Log Ka2), optimized from batch titration data, ranged from 4.69 to 5.34 for Log Ka1 and from −6.51 to −7.61 for Log Ka2, suggesting the occurrence of both protonation and deprotonation reactions on the solid surfaces. Partition coefficients and removal rates of the metals had a general trend of Pd > Pt > Rh. The sediment sample, with the highest clay content and exchangeable cation concentrations, also had the highest affinity for the metals. The times required for sediment to adsorb 63% of the metals were 2.63 h, 4.08 h and 10.64 h for Pd, Pt and Rh, respectively. The FITEQL program successfully optimized the conditional binding constants of the metals on the solids from batch adsorption data. The constants decreased in the order of Pd > Rh > Pt, which was consistent with the observed high affinity of the solids for Pd. The modeling results also showed that aqueous Pd was the least sensitive to pH followed by Rh and Pt. However, metal adsorption below the points of zero net proton charges (ca. pH 6.7) is attributable to the involvement of permanent negatively charged binding sites in the adsorption process. Notably, partition coefficients, removal rates and conditional binding constants all showed a high affinity of Pd for the solids. A similarity between the model outputs and the batch adsorption data indicates the suitability of the model for describing the mobility and retention of the three metals in semi-arid soils and sediments.  相似文献   

9.
Summary The Jinchuan deposit is a platinum group element (PGE)-rich sulfide deposit in China. Drilling and surface sampling show that three categories of platinum group element (PGE) mineralization occur; type I formed at magmatic temperatures, type II occurs in hydrothermally altered zones of the intrusion, and type III in sheared dunite and lherzolite. All ore types were analyzed for Os, Ir, Ru, Rh, Pd, Pt and Au, as well as for Cu, Ni, Co and S. Type I ore has (Pt + Pd)/(Os + Ir + Ru + Rh) ratios of <7 and relatively flat chondrite-normalized noble metal patterns; the platinum group minerals (PGM) are dominated by sperrylite and moncheite associated with chalcopyrite, pyrrhotite and pentlandite. Type II has (Pt + Pd)/(Os + Ir + Ru + Rh) ratios from 40 to 330 and noble metal distribution patterns with a positive slope; the most common PGM are sperrylite and Pd bismuthotelluride phases concentrated mostly at the margins of base metal sulfides. Type III ores have the highest (Pt + Pd)/(Os + Ir + Ru + Rh) ratios from 240 to 710; the most abundant PGM are sperrylite and phases of the Pt–Pd–Te–Bi–As–Cl system. It is concluded that the Jinchuan deposit formed as a result of primary magmatic crystallization followed by hydrothermal remobilization, transport, and deposition of the PGE.  相似文献   

10.
Fourteen peridotite xenoliths collected in the Massif Central neogene volcanic province (France) have been analyzed for platinum-group elements (PGE), Au, Cu, S, and Se. Their total PGE contents range between 3 and 30 ppb and their PGE relative abundances from 0.01 to 0.001 × CI-chondrites, respectively. Positive correlations between total PGE contents and Se suggest that all of the PGE are hosted mainly in base metal sulfides (monosulfide solid solution [Mss], pentlandite, and Cu-rich sulfides [chalcopyrite/isocubanite]). Laser ablation microprobe-inductively coupled plasma mass spectrometry analyses support this conclusion while suggesting that, as observed in experiments on the Cu-Fe-Ni-S system, the Mss preferentially accommodate refractory PGEs (Os, Ir, Ru, and Rh) and Cu-rich sulfides concentrate Pd and Au. Poikiloblastic peridotites pervasively percolated by large silicate melt fractions at high temperature (1200°C) display the lowest Se (<2.3 ppb) and the lowest PGE contents (0.001 × CI-chondrites). In these rocks, the total PGE budget inherited from the primitive mantle was reduced by 80%, probably because intergranular sulfides were completely removed by the silicate melt. In contrast, protogranular peridotites metasomatized by small fractions of volatile-rich melts are enriched in Pt, Pd, and Au and display suprachondritic Pd/Ir ratios (1.9). The palladium-group PGE (PPGE) enrichment is consistent with precipitation of Cu-Ni-rich sulfides from the metasomatic melts. In spite of strong light rare earth element (LREE) enrichments (Ce/YbN < 10), the three harzburgites analyzed still display chondrite-normalized PGE patterns typical of partial melting residues, i.e., depleted in Pd and Pt relative to Ir and Ru. Likewise, coarse-granular lherzolites, a common rock type in Massif Central xenoliths, display Pd/Ir, Ru/Ir, Rh/Ir, and Pt/Ir within the 15% uncertainty range of chondritic meteorites. These rocks do not contradict the late-veneer hypothesis that ascribes the PGE budget of the Earth to a late-accreting chondritic component; however, speculations about this component from the Pd/Ir and Pt/Ir ratios of basalt-borne xenoliths may be premature.  相似文献   

11.
Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure distributions of the siderophile elements V, Fe, Co, Ni, Mo, Ru, Rh, Pd, W, Re, Os, Ir, Pt, and Au in Fremdlinge with a spatial resolution of 15 to 25 μm. A sulfide vein in a refractory inclusion in Allende (CV3-oxidized) is enriched in Rh, Ru, and Os with no detectable Pd, Re, Ir, or Pt, indicating that Rh, Ru, and Os were redistributed by sulfidation of the inclusion, causing fractionation of Re/Os and other siderophile element ratios in Allende CAIs. Fremdlinge in compact Type-A inclusions from Efremovka (CV3-reduced) exhibit subsolidus exsolution into kamacite and taenite and minimal secondary formation of V-magnetite and schreibersite. Siderophile element partitioning between taenite and kamacite is similar to that observed previously in iron meteorites, while preferential incorporation of the light PGEs (Ru, Rh, Pd) relative to Re, Os, Ir, and Pt by schreibersite was observed. Fremdling EM2 (CAI Ef2) has an outer rim of P-free metal that preserves the PGE signature of schreibersite, indicating that EM2 originally had a phosphide rim and lost P to the surrounding inclusion during secondary processing. Most Fremdlinge have chondrite-normalized refractory PGE patterns that are unfractionated, with PGE abundances derived from a small range of condensation temperatures, ∼1480 to 1468 K at Ptot = 10−3 bar. Some Fremdlinge from the same CAI exhibit sloping PGE abundance patterns and Re/Os ratios up to 2 × CI that likely represent mixing of grains that condensed at various temperatures.  相似文献   

12.
Highly siderophile element concentrations (HSE: Re and platinum-group elements (PGE)) are presented for gabbros, gabbroic eclogites and basaltic eclogites from the high-pressure Zermatt-Saas ophiolite terrain, Switzerland. Rhenium and PGE (Os, Ir, Ru, Rh, Pt, Pd) abundances in gabbro- and eclogite-hosted sulphides, and Re-Os isotopes and elemental concentrations in silicate phases are also reported. This work, therefore, provides whole rock and mineral-scale insights into the PGE budget of gabbroic oceanic crust and the effects of subduction metamorphism on gabbroic and basaltic crust.Chondrite-normalised PGE patterns for the gabbros are similar to published mid-ocean ridge basalts (MORB), but show less inter-element fractionation. Mean Pt and Pd contents of 360 and 530 pg/g, respectively, are broadly comparable to MORB, but gabbros have somewhat higher abundances of Os, Ir and Ru (mean: 64, 57 and 108 pg/g). Transformation to eclogite has not significantly changed the concentrations of the PGE, except Pd which is severely depleted in gabbroic eclogites relative to gabbros (∼75% loss). In contrast, basaltic eclogites display significant depletion of Pt (?60%), Pd (>85%) and Re (50-60%) compared with published MORB, while Os, Ir and Ru abundances are broadly comparable. Thus, these data suggest that only Pt, Pd and Re, and not Os, Ir and Ru, may be significantly fluxed into the mantle wedge from mafic oceanic crust. Re-Os model ages for gabbroic and gabbroic eclogite minerals are close to age estimates for igneous crystallisation and high-pressure metamorphism, respectively, hence the HSE budgets can be related to both igneous and metamorphic behaviour. The gabbroic budget of Os, Ir, Ru and Pd (but not Pt) is dominated by sulphide, which typically hosts >90% of the Os, whereas silicates account for most of the Re (with up to 75% in plagioclase alone). Sulphides in gabbroic eclogites tend to host a smaller proportion of the total Os (10-90%) while silicates are important hosts, probably reflecting Os inheritance from precursor phases. Garnet contains very high Re concentrations and may account for >50% of Re in some samples. The depletion of Pd in gabbroic eclogites appears linked, at least in part, to the loss of Ni-rich sulphide.Both basaltic and gabbroic oceanic crust have elevated Pt/Os ratios, but Pt/Re ratios are not sufficiently high to generate the coupled 186Os-187Os enrichments observed in some mantle melts, even without Pt loss from basaltic crust. However, the apparent mobility of Pt and Re in slab fluids provides an alternative mechanism for the generation of Pt- and Re-rich mantle material, recently proposed as a potential source of 187Os-186Os enrichment.  相似文献   

13.
Ultramafic xenoliths from a veined mantle wedge beneath the Kamchatka arc have non-chondritic, fractionated chondrite-normalized platinum-group element (PGE) patterns. Depleted (e.g., low bulk-rock Al2O3 and CaO contents) mantle harzburgites show clear enrichment in the Pd group relative to the Ir group PGEs and, in most samples, Pt relative to Rh and Pd. These PGE signatures most likely reflect multi-stage melting which selectively concentrates Pt in Pt–Fe alloys while strongly depleting the sub-arc mantle wedge in incompatible elements. Elevated gold concentrations and enrichment of strongly incompatible enrichment (e.g., Ba and Th) in some harzburgites suggest a late-stage metasomatism by slab-derived, saline hydrous fluids. Positive Pt, Pd, and Au anomalies coupled with Ir depletions in heavily metasomatized pyroxenite xenoliths probably reflect the relative mobility of the Pd and Ir groups (especially Os) during sub-arc metasomatism which is consistent with Os systematics in arc mantle nodules. Positive correlations between Pt, Pd, and Au and various incompatible elements (Hf, U, Ta, and Sr) also suggest that both slab-derived hydrous fluids and siliceous melts were involved in the sub-arc mantle metasomatism beneath the Kamchatka arc.  相似文献   

14.
This paper presents the first study of accessing the Pt, Pd and Rh levels in road dusts collected from Hyderabad city, India, as these metals, emitted from automobile catalytic converters, are accumulating in the environment causing concern about human health and ecological risks. Samples were analyzed by ICP-MS following preconcentration by NiS-fire assay and Te coprecipitation. Pt (1.5–43 ng/g), Pd (1.2–58 ng/g) and Rh (0.2–14.2 ng/g) concentrations obtained were above upper crust values, but were lower when compared with several other cities around the world. Dust samples from road junctions and traffic signals with heavy and erratic traffic flow showed higher PGE levels than those from roads with low and free flow traffic suggesting that traffic flow conditions greatly influenced emission of PGE from the catalyst. Significant correlation of Pt, Pd and Rh indicate a common source for these metals. PGE were also positively correlated with Ce, Zr, Hf and Y. These positive inter-element correlations identified traffic as the main source of PGE emission to the roadway environment. The results obtained indicate to an appreciable increase in auto catalyst-derived PGE. In consideration of the adverse effects of PGE, monitoring their level and transformation paths is of prime importance.  相似文献   

15.
中国铬铁矿的铂族元素分布特征   总被引：2，自引：0，他引：2  
周美付  白文吉 《矿物学报》1994,14(2):157-163
用NiS溶解和Te沉淀方法富集铂族元素（PGE），制成镍扣，再溶解于浓HCl中，使PGE和Te一起沉淀。制备的样品溶液在ELAN－5000型电感耦合等离子质谱仪（ICP－MS）上分析PGE。中国铬铁矿矿石，包括蛇绿岩套中的豆荚状铬铁矿床、非层状侵入体铬铁矿，计13个矿床（化）样品，其PGE模式表明，主要呈RU正异常模式，个别不同模式是由母岩不同以及铂族元素矿化叠加引起的。铬铁矿的PGE模式不取决于铬铁矿的化学成分，而取决于其母岩性质以及形成温度和铂族元素的熔点。  相似文献   

16.
The Palaeoproterozoic Ni–Cu sulphide deposits of the PechengaComplex, Kola Peninsula, occur in the lower parts of ferropicriticintrusions emplaced into the phyllitic and tuffaceous sedimentaryunit of the Pilgujärvi Zone. The intrusive rocks are comagmaticwith extrusive ferropicrites of the overlying volcanic formation.Massive lavas and chilled margins from layered flows and intrusionscontain <3–7 ng/g Pd and Pt and <0·02–2·0ng/g Ir, Os and Ru with low Pd/Ir ratios of 5–11. Theabundances of platinum group elements (PGE) correlate with eachother and with chalcophile elements such as Cu and Ni, and indicatea compatible behaviour during crystallization of the parentalmagma. Compared with the PGE-depleted central zones of differentiatedflows (spinifex and clinopyroxene cumulate zones) the olivinecumulate zones at the base contain elevated PGE abundances upto 10 ng/g Pd and Pt. A similar pattern is displayed in intrusivebodies, such as the Kammikivi sill and the Pilgujärvi intrusion.The olivine cumulates at the base of these bodies contain massiveand disseminated Ni–Cu-sulphides with up to 2 µg/gPd and Pt, but the PGE concentrations in the overlying clinopyroxenitesand gabbroic rocks are in many cases below the detection limits.The metal distribution observed in samples closely representingliquid compositions suggests that the parental magma becamesulphide saturated during the emplacement and depleted in chalcophileand siderophile metals as a result of fractional segregationof sulphide liquids. Relative sulphide liquid–silicatemelt partition coefficients decrease in the order of Ir >Rh > Os > Ru > Pt = Pd > Cu. R-factors (silicate-sulphidemass ratio) are high and of the order of 104–105, andthey indicate the segregation of only small amounts of sulphideliquid in the parental ferropicritic magma. In differentiatedflows and intrusions the sulphide liquids segregated and accumulatedat the base of these bodies, but because of a low silicate–sulphidemass ratio the sulphide liquids had a low PGE tenor and Pt/Irand Cu/Ir ratios similar to the parental silicate melts. Duringcooling the sulphide liquid crystallized 40–50% of monosulphidesolid solution (mss) and the residual sulphide liquid becameenriched in Cu, Pt and Pd and depleted in Ir, Os and Ru. TheCu-rich sulphide liquid locally assimilated components of thesurrounding S-rich sediments as suggested by the radiogenicOs isotopic composition of some sulphide ores (  相似文献   

17.
吉林省油页岩中铂族元素的化学牲及分配规律研究   总被引：2，自引：0，他引：2  
采用电感耦合等离子体发射质谱仪(ICP-MS)测定了吉林省油页岩中铂族元素的含量,并对油页岩中铂族元素的化学特征、与无机组分的相关性及其分布模式等进行了分析和阐述.通过油页岩中铂族元素的含量与地壳和中国东部出露地壳中铂族元素丰度的比较表明,Rh、Ru、Ir等元素相对富集,其中松原油页岩中Rh、Ir的含量约为地壳平均值的10倍.研究区油页岩中铂族元素以Pt-Pd分配模式为典型特征,一般Pt的丰度大于Pd.油页岩中铂族元素与无机组成相关分析的结果表明,油页岩中铂族元素可能呈吸附态存在于高岭石、伊利石等粘土矿物中.  相似文献   

18.
吉林省油页岩中铂族元素的化学特征及分配规律研究   总被引：2，自引：0，他引：2  
采用电感耦合等离子体发射质谱仪(ICP MS)测定了吉林省油页岩中铂族元素的含量,并对油页岩中铂族元素的化学特征、与无机组分的相关性及其分布模式等进行了分析和阐述。通过油页岩中铂族元素的含量与地壳和中国东部出露地壳中铂族元素丰度的比较表明,Rh、RuI、r等元素相对富集,其中松原油页岩中RhI、r的含量约为地壳平均值的10倍。研究区油页岩中铂族元素以Pt Pd分配模式为典型特征,一般Pt的丰度大于Pd。油页岩中铂族元素与无机组成相关分析的结果表明,油页岩中铂族元素可能呈吸附态存在于高岭石、伊利石等粘土矿物中。  相似文献   

19.
The concentrations of platinum-group elements (PGE), Co, Re,Au and Ag have been determined in the base-metal sulphide (BMS)of a section of the Merensky Reef. In addition we performeddetailed image analysis of the platinum-group minerals (PGM).The aims of the study were to establish: (1) whether the BMSare the principal host of these elements; (2) whether individualelements preferentially partition into a specific BMS; (3) whetherthe concentration of the elements varies with stratigraphy orlithology; (4) what is the proportion of PGE hosted by PGM;(5) whether the PGM and the PGE found in BMS could account forthe complete PGE budget of the whole-rocks. In all lithologies,most of the PGE (65 up to 85%) are hosted by PGM (essentiallyPt–Fe alloy, Pt–Pd sulphide, Pt–Pd bismuthotelluride).Lesser amounts of PGE occur in solid solution within the BMS.In most cases, the PGM occur at the contact between the BMSand silicates or oxides, or are included within the BMS. Pentlanditeis the principal BMS host of all of the PGE, except Pt, andcontains up to 600 ppm combined PGE. It is preferentially enrichedin Pd, Rh and Co. Pyrrhotite contains, Rh, Os, Ir and Ru, butexcludes both Pt and Pd. Chalcopyrite contains very little ofthe PGE, but does concentrate Ag and Cd. Platinum and Au donot partition into any of the BMS. Instead, they occur in theform of PGM and electrum. In the chromitite layers the whole-rockconcentrations of all the PGE except Pd are enriched by a factorof five relative to S, Ni, Cu and Au. This enrichment couldbe attributed to BMS in these layers being richer in PGE thanthe BMS in the silicate layers. However, the PGE content inthe BMS varies only slightly as a function of the stratigraphy.The BMS in the chromitites contain twice as much PGE as theBMS in the silicate rocks, but this is not sufficient to explainthe strong enrichment of PGE in the chromitites. In the lightof our results, we propose that the collection of the PGE occurredin two steps in the chromitites: some PGM formed before sulphidesaturation during chromitite layer formation. The remainingPGE were collected by an immiscible sulphide liquid that percolateddownward until it encountered the chromitite layers. In thesilicate rocks, PGE were collected by only the sulphide liquid. KEY WORDS: Merensky Reef; Rustenburg Platinum Mine; sulphide; platinum-group elements; image analysis; laser ablation ICP-MS  相似文献   

20.
A set of platinum group element (PGE) analyses of about 120 samples from a 250-m continuous drill core through the Mount Keith komatiite-hosted nickel orebody, combined with Ni, Cu, Co, S, and major elements, reveals a complex trend of covariance between the original cumulus components of a thick sequence of nearly pure olivine–sulphide liquid adcumulates. The intersection is divided into informal chemostratigraphic zones, defined primarily by combinations of fine-scale cyclicity in original olivine composition, defined by Mg#, and sulphide composition, defined by Pt/S and Ni/S. Contents of Ni and PGE in 100% sulphides (tenors) were determined from linear regressions of the Ni–S and PGE–S covariance for each zone. Inferred olivine compositions range from about Fo92 to Fo94.6 and show a broad decrease from bottom to top of the sequence complicated by numerous reversals, revealing crystallisation in an open conduit system. Ni and PGE tenors of Mount Keith sulphide ores have typical values similar to the type I deposits of the Kambalda Dome. Mobility of S, at least on the scale of 2-m sample composites, is evidently relatively minor. Tenors for the various zones range 12–22% Ni, 370–1540?ppb Pt, 970–3670?ppb Pd, 100–460?ppb Ir, 170–460?ppb Rh, and 710–1260?ppb Ru. Pt, Pd, and Rh tenors are very strongly correlated, but the iridium group of platinum group elements (IPGEs; Ir and Ru) less so. Tenor variations are predominantly controlled by variations in magma/sulphide ratio R (100–350), with a minor component of variance from equilibrium crystallisation trends in the parent magma. PGE depletion in the silicate melt due to sulphide liquid extraction is limited by entrainment of sulphide liquid droplets and continuous equilibration with the transporting silicate magma. Ratios of the PGEs to one another are similar to those in the host komatiite magma, with the exception of Pt, which is systematically depleted in ores, relative to Rh and Pd and relative to host magma, by a consistent factor of about 2 to 2.5. This anomalous Pt depletion relative to PGE element ratios in unmineralized komatiitic rocks matches that observed in bulk compositions of many komatiite-hosted orebodies. The highly consistent nature of this depletion, and particularly the very strong correlation between Pt, Pd, and Rh in the Mount Keith deposit, argue that this depletion is a primary magmatic signal and not an artefact of alteration. Differential diffusion rates between Pt and the other PGEs, giving rise to a low effective partition coefficient for Pt into sulphide liquid, is advanced as a possible but not definitive explanation.  相似文献   

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