ABUNDANCE AND DISTRIBUTION OF PLATINUM-GROUP ELEMENTS (PGE) IN PERIDOTITE FROM THE DAGZHUKA OPHIOLITE IN TIBET:IMPLICATIONS FOR MANTLE METASOMATISM

ABUNDANCE AND DISTRIBUTION OF PLATINUM-GROUP ELEMENTS (PGE) IN PERIDOTITE FROM THE DAGZHUKA OPHIOLITE IN TIBET:IMPLICATIONS FOR MANTLE METASOMATISM     

阜新中生代火山岩的铂族元素特征——以碱锅和乌拉哈达为例

采用镍锍火试金法结合ICP—MS分析了碱锅玄武岩和乌拉哈达高镁安山岩样品中的Ir．Ru、Rh、Pt和Pd的含量。原始地幔标准化后的PGE分布模式呈正斜率型，Pd／Ir值高于相应的地幔比值，表明铂族元素发生了分异，这是由于在部分熔融过程中，Ir存在于地幔矿物相尖晶石和合金中，而Pd赋存于硫化物中造成的，乌拉哈达高镁安山岩中的铂族元素还可能在结晶分异过程中受到先期结晶的矿物相和合金的影响。阜新火山岩Pt的负异常可能是包含Pt的金属合金残留在地幔中造成。     

The behaviour of platinum-group elements in basalts from the East Greenland rifted margin

. The continental flood basalts of the East Greenland volcanic rifted margin were extruded during continental breakup above the ancestral Iceland mantle plume at 55 Ma. Three distinct magma types, the low-Ti, high-Ti and very high-Ti series (LTS, HTS and VHTS respectively), are found intercalated in the ~6-km-thick Plateau Lava sequence. Incompatible trace elements indicate that the LTS are derived from a more depleted mantle source compared to HTS and VHTS. The LTS is characterised by increasing Cu (105 to 248 ppm) and Pd (7 to 24 ppb), constant Cu/Pd ratio (~10,000), and decreasing Ir (1.1 to <0.05 ppb) and Ru (1.8 to <0.3 ppb) concentrations during magmatic differentiation (16 to 7 wt% MgO). The constant Cu/Pd ratio reflects silicate- and chromite-dominated fractionation without concurrent segregation of sulphide. S-undersaturated differentiation is also indicated in the HTS, which also displays increasing Pd (6-16 ppb) and decreasing Ir concentrations (1 to <0.05 ppb) during differentiation, and the Cu/Pd ratios for the entire series average 21,000. However, some HTS samples have elevated Cu/Pd ratios (up to 33,000). Cu/Pd ratios in the HTS do not correlate with MgO, and this is interpreted to reflect varying Cu/Pd ratios of HTS parental magmas rather than S-saturated differentiation. During S-undersaturated differentiation of the LTS and HTS, Pt/Pd ratios decrease from 1.3 to 0.11 and 1.1 to 0.2 respectively, which indicates that Pd is much more incompatible than Pt during S-undersaturated differentiation. The VHTS consists exclusively of highly evolved samples with low MgO (6.6-6.1 wt%) and Pd/Ir ratios 98-228. Here, Cu/Pd ratios increase from 17,500 to 35,000 with decreasing Cr concentrations which indicate that these magmas experienced silicate fractionation with concurrent segregation of sulphide. The LTS represent melting of a depleted source and show high PGE concentrations and constant Cu/Pd ratios during S-undersaturated differentiation. Melting of a normal depleted upper mantle source generates S-saturated melts (MORB), and the depleted LTS source is therefore considered an extraordinary S-poor component within the ancestral Iceland plume. Of the three series, the VHTS contain the largest contribution from enriched mantle portions. The VHTS have similar PGE but much higher Nb concentrations for instance compared to the most evolved LTS and HTS samples, indicating that the enriched source contributes Nb but not PGE.     

Platinum-Group Element Geochemical Characteristics of the Picrites and High-Ti Basalts in the Binchuan Area,Yunnan Province

The Binchuan area of Yunnan is located in the western part of the Emeishan large igneous province in the western margin of the Yangtze Block.In the present study,the Wuguiqing profile in thickness of about 1440 m is mainly composed of high-Ti basalts,with minor picrites in the lower part and andesites,trachytes,and rhyolites in the upper part.The picrites have relatively higher platinum-group element（PGE） contents（ΣPGE=16.3-28.2 ppb）,with high Cu/Zr and Pd/Zr ratios,and low S contents（5.03-16.9 ppm）,indicating the parental magma is S-unsaturated and generated by high degree of partial melting of the Emeishan large igneous province（ELIP） mantle source.The slightly high Cu/Pd ratios（11 000-24 000） relative to that of the primitive mantle suggest that 0.007%sulfides have been retained in the mantle source.The PGE contents of the high-Ti basalts exhibit a wider range（ΣPGE=0.517-30.8 ppb）.The samples in the middle and upper parts are depleted in PGE and haveε_Nd（260 Ma） ratios ranging from -2.8 to -2.2,suggesting that crustal contamination of the parental magma during ascent triggered sulfur saturation and segregation of about 0.446%-0.554% sulfides,and the sulfide segregation process may also provide the ore-forming material for the magmatic Cu-Ni-PGE sulfide deposits close to the studied basalts.The samples in this area show Pt-Pd type primitive mantle-normalized PGE patterns,and the Pd/Ir ratios are higher than that of the primitive mantle（Pd/Ir=1）,indicating that the obvious differentiation between Ir-group platinum-group elements（IPGE） and Pd-group platinum-group elements（PPGE） are mainly controlled by olivine or chromites fractionation during magma evolution.The Pd/Pt ratios of most samples are higher than the average ratio of mantle（Pd/Pt=0.55）,showing that the differentiation happened between Pt and Pd.The differentiation in picrites may be relevant to Pt hosted in discrete refractory Pt-alloy phase in the mantle;whereas the differentiation in the high-Ti basalts is probably associated with the fractionation of Fe-Pt alloys,coprecipitating with Ir-Ru-Os alloys.Some high-Ti basalt samples exhibit negative Ru anomalies,possibly due to removal of laurite collected by the early crystallized chromites.     

Platinum-group elemental geochemistry of mafic and ultramafic rocks from the Xigaze ophiolite, southern Tibet

The Xigaze ophiolite in the central part of the Yarlung–Zangbo suture zone, southern Tibet, has a well-preserved sequence of sheeted dykes, basalts, cumulates and mantle peridotites at Jiding and Luqu. Both the basalts and diabases at Jiding have similar compositions with SiO₂ ranging from 45.9 to 53.5 wt%, MgO from 3.1 to 6.8 wt% and TiO₂ from 0.87 to 1.21 wt%. Their Mg^#s [100Mg/(Mg + Fe)] range from 40 to 60, indicating crystallization from relatively evolved magmas. They have LREE-depleted, chondrite-normalized REE diagrams, suggesting a depleted mantle source. These basaltic rocks have slightly negative Nb- and Ti-anomalies, suggesting that the Xigaze ophiolite represents a fragment of mature MORB lithosphere modified in a suprasubduction zone environment. The mantle peridotites at Luqu are high depleted with low CaO (0.3–1.2 wt%) and Al₂O₃ (0.04–0.42 wt%). They display V-shaped, chondrite-normalized REE patterns with (La/Gd)_N ratios ranging from 3.17 to 64.6 and (Gd/Yb)_N from 0.02 to 0.20, features reflecting secondary metasomatism by melts derived from the underlying subducted slab. Thus, the geochemistry of both the basaltic rocks and mantle peridotites suggests that the Xigaze ophiolite formed in a suprasubduction zone.Both the diabases and basalts have Pd/Ir ratios ranging from 7 to 77, similar to MORB. However, they have very low PGE abundances, closely approximating the predicted concentration in a silicate melt that has fully equilibrated with a fractionated immiscible sulfide melt, indicating that the rocks originated from magmas that were S-saturated before eruption. Moderate degrees of partial melting and early precipitation of PGE alloys explain their high Pd/Ir ratios and negative Pt-anomalies. The mantle peridotites contain variable amounts of Pd (5.99–13.5 ppb) and Pt (7.92–20.5 ppb), and have a relatively narrow range of Ir (3.47–5.01 ppb). In the mantle-normalized Ni, PGE, Au and Cu diagram, they are relatively rich in Pd and depleted in Cu. There is a positive correlation between CaO and Pd. The Pd enrichment is possibly due to secondary enrichment by metasomatism. Al₂O₃ and Hf do not correlate with Ir, but show positive variations with Pt, Pd and Au, indicating that some noble metals can be enriched by metasomatic fluids or melts carrying a little Al and Hf. We propose a model in which the low PGE contents and high Pd/Ir ratios of the basaltic rocks reflect precipitation of sulfides and moderate degrees of partial melting. The high Pd mantle peridotites of Xigaze ophiolites were formed by secondary metasomatism by a boninitic melt above a subduction zone.     

中国铬铁矿的铂族元素分布特征

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。     

Platinum group element (PGE) geochemistry to understand the chemical evolution of the Earth’s mantle

Platinum group elements (PGE: Os, Ir, Ru, Rh, Pt, Pd) are important geochemical and cosmochemical tracers. Depending on physical and chemical behaviour the PGEs are divided into two subgroups: IPGE (Ir, Os, Ru) and PPGE (Pd, Pt, Rh). Platinum group elements show strong siderophile and chalcophile affinity. Base metal sulfides control the PGE budget of the Earth’s mantle. Mantle xenoliths contain two types of sulfide populations: (1) enclosed within silicate minerals, and (2) interstitial to the silicate minerals. In terms of PGE characters the included variety shows IPGE enriched patterns — similar to the melt-depleted mantle harzburgite, whereas the interstitial variety shows PPGE enriched patterns — resembling the fractionated PGE patterns of the basalt. These PGE characters of the mantle sulfides have been interpreted to be representative of multi-stages melting process of the mantle that helped to shape the chemical evolution of the Earth.     

Platinum-group element constraints on source composition and magma evolution of the Kerguelen Plateau using basalts from ODP Leg 183

Seventeen basalts from Ocean Drilling Program (ODP) Leg 183 to the Kerguelen Plateau (KP) were analyzed for the platinum-group elements (PGEs: Ir, Ru, Rh, Pt, and Pd), and 15 were analyzed for trace elements. Relative concentrations of the PGEs ranged from ∼0.1 (Ir, Ru) to ∼5 (Pt) times primitive mantle. These relatively high PGE abundances and fractionated patterns are not accounted for by the presence of sulfide minerals; there are only trace sulfides present in thin-section. Sulfur saturation models applied to the KP basalts suggest that the parental magmas may have never reached sulfide saturation, despite large degrees of partial melting (∼30%) and fractional crystallization (∼45%).First order approximations of the fractionation required to produce the KP basalts from an ∼30% partial melt of a spinel peridotite were determined using the PELE program. The model was adapted to better fit the physical and chemical observations from the KP basalts, and requires an initial crystal fractionation stage of at least 30% olivine plus Cr-spinel (49:1), followed by magma replenishment and fractional crystallization (RFC) that included clinopyroxene, plagioclase, and titanomagnetite (15:9:1). The low Pd values ([Pd/Pt]_pm < 1.7) for these samples are not predicted by currently available K_d values. These Pd values are lowest in samples with relatively higher degrees of alteration as indicated by petrographic observations. Positive anomalies are a function of the behavior of the PGEs; they can be reproduced by Cr-spinel, and titanomagnetite crystallization, followed by titanomagnetite resorption during the final stages of crystallization. Our modeling shows that it is difficult to reproduce the PGE abundances by either depleted upper or even primitive mantle sources. Crustal contamination, while indicated at certain sites by the isotopic compositions of the basalts, appears to have had a minimal affect on the PGEs. The PGE abundances measured in the Kerguelen Plateau basalts are best modeled by melting a primitive mantle source to which was added up to 1% of outer core material, followed by fractional crystallization of the melt produced. This reproduces both the abundances and patterns of the PGEs in the Kerguelen Plateau basalts. An alternative model for outer core PGE abundances requires only 0.3% of outer core material to be mixed into the primitive mantle source. While our results are clearly model dependent, they indicate that an outer core component may be present in the Kerguelen plume source.     

云南鸡街碱性超基性岩铂族元素地球化学特征

本文首次报道了攀西裂谷南段云南省鸡街碱性超基性岩中铂族元素(PGE)的地球化学特征。采用改进的Carius管法测定了霞霓钠辉岩、霓霞岩和磷霞岩中的低含量PGE。PPGE与IPGE呈现强烈分馏,推断幔源岩在低程度部分熔融过程中Pt、Pd表现为相似的不相容性,而Ir、Ru表现为相容性,这种分馏效应随着结晶分异作用的进行而逐渐增强。3种岩石均出现Ru的负异常及Pt、Pd的解耦,说明母岩浆经历了早期的橄榄石晶出,在结晶分异过程中Pd较Pt更不相容。由于岩浆上升过程中的压力减小和结晶分异作用导致的成份变化使岩浆可以达到硫的局部饱和而熔离,表现为部分样品中Cu/Pd远高于原始地幔值。本文通过碱性超基性岩与金伯利岩、煌斑岩和邻区碱性、过碱性玄武岩PGE特征的对比,探讨了其岩浆源区及演化特征。     

Behaviour of Ni-PGE-Au-Cu in mafic-ultramafic volcanic suites of the 2.7 Ga Kambalda Sequence, Kalgoorlie Terrane, Yilgarn Craton

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.     

Composition and evolution of PGE mineralization in chromite ores from the Il’chir ophiolite complex (Ospa–Kitoi and Khara-Nur areas,East Sayan)

Data are presented on chromitites from the northern and southern sheets of the Il’chir ophiolite complex (Ospa–Kitoi and Khara-Nur (Kharanur) massifs). The new and published data are used to consider similarities and differences between ore chrome-spinel from the chromitites of the northern and southern ophiolite sheets as well as the species diversity of PGE minerals and the evolution of PGE mineralization. Previously unknown PGE minerals have been found in the studied chromitites.Ore chrome-spinel in the chromitites from the northern sheet occurs in medium- and low-alumina forms, whereas the chromitites from the southern sheet contain only medium-alumina chrome-spinel. The PGE minerals in the chromitites from the southern sheet are Os–Ir–Ru solid solutions as well as sulfides and sulfoarsenides of these metals. The chromitites from the northern sheet contain the same PGE minerals and diverse Rh–Pt–Pd mineralization: Pt–Ir–Ru–Os and isoferroplatinum with Ir and Os–Ir–Ru lamellae. Areas of altered chromitites contain a wide variety of low-temperature secondary PGE minerals: Pt–Cu, Pt–Pd–Cu, PdHg, Rh2SnCu, RhNiAs, PtAs2, and PtSb2. The speciation of the PGE minerals is described along with multiphase intergrowths. The relations of Os–Ir–Ru solid solutions with laurite and irarsite are considered along with the microstructure of irarsite–osarsite–ruarsite solid solutions. Zoned Os–Ir–Ru crystals have been found. Zone Os82–99 in these crystals contains Ni3S2 inclusions, which mark off crystal growth zones. Different sources of PGE mineralization are presumed for the chromitites from the northern and southern sheets.The stages of PGE mineralization have been defined for the chromitites from the Il’chir ophiolite belt. The Pt–Ir–Ru–Os and (Os, Ru)S2 inclusions in Os–Ir–Ru solid solutions might be relics of primitive-mantle PGE minerals. During the partial melting of the upper mantle, Os–Ir–Ru and Pt–Fe solid solutions formed syngenetically with the chromitites. During the late-magmatic stage, Os–Ir–Ru solid solutions were replaced by sulfides and sulfarsenides of these metals. Mantle metasomatism under the effect of reduced mantle fluids was accompanied by PGE remobilization and redeposition with the formation of the following assemblage: garutiite (Ni,Fe,Ir), zaccariniite (RhNiAs), (Ir,Ni,Cu)S3, Pt–Cu, Pt–Cu–Fe–Ni, Cu–Pt–Pd, and Rh–Cu–Sn–Sb. The zoned Os–Ir–Ru crystals in the chromitites from the northern sheet suggest dissolution and redeposition of Os–Ir–Ru primary-mantle solid solutions by bisulfide complexes. Most likely, the PGE remobilization took place during early serpentinization at 450–600 ºC and 13–16 kbar.During the crustal metamorphic stage, tectonic movements (obduction) and a change from reducing to oxidizing conditions were accompanied by the successive transformation of chrome-spinel into ferrichromite–chrome-magnetite with the active participation of a metamorphic fluid enriched in crustal components. The orcelite–maucherite–ferrichromite–sperrylite assemblage formed in epidote-amphibolitic facies settings during this stage.The PGE mineral assemblage reflects different stages in the formation of the chromitites and dunite-harzburgite host rocks and their transformation from primitive mantle to crustal metamorphic processes.     

Highly siderophile element behaviour accompanying subduction of oceanic crust: Whole rock and mineral-scale insights from a high-pressure terrain

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.     

铂族元素矿物共生组合(英文)

由于铂族元素能有效地降低汽车尾气的污染 ,其需求量日益增加 ,对铂族元素矿床的寻找已是当务之急。着重从矿物矿床学角度对铂族元素的矿物共生特点进行了探讨。铂族元素可呈独立矿床产出 ,主要产于基性超基性层状侵入体、蛇绿岩套及阿拉斯加式侵入体中。铂族元素也伴生于铜镍矿床中 ,该类铜镍矿床主要与苏长岩侵入体、溢流玄武岩及科马提岩有关。产于基性超基性层状侵入体中的铂族矿物有铂钯硫化物、铂铁合金、钌硫化物、铑硫化物、铂钯碲化物、钯砷化物及钯的合金。这些铂族矿物可与硫化物矿物共生 ,也可与硅酸盐矿物共生 ,还可与铬铁矿及其他氧化物矿物共生。产于蛇绿岩套中的铂族矿物主要是钌铱锇的矿物 ,而铂钯铑的矿物则较少出现 ,这些铂族矿物可呈合金、硫化物、硫砷化物以及砷化物 4种形式出现。产于阿拉斯加式侵入体中的铂族矿物主要有铂铁合金、锑铂矿、硫铂矿、砷铂矿、硫锇矿及马兰矿等少数几种 ,其中铂铁合金与铬铁矿及与其同时结晶的高温硅酸盐矿物共生 ,而其他的铂族矿物则与后来的变质作用及蛇纹岩化作用中形成的多金属硫化物及砷化物共生。产于铜镍矿床中的铂族矿物主要是铂和钯的矿物。产于基性超基性层状侵入体、蛇绿岩套及阿拉斯加式侵入体中的铂族矿物的共同特点是它们均与铬铁矿?     

攀西地区水系沉积物铂、钯地球化学异常特征及找矿远景预测

水系沉积物地球化学测量表明,攀枝花-西昌地区存在一个与峨眉山玄武岩分布范围基本吻合的P t,Pd区域地球化学异常,玄武岩中铂族元素丰度值普遍较高是一种正常的高背景现象,而峨眉山玄武岩中P t,Pd严重亏损或正异常显著的局部地区则显示出一定程度的成矿潜力。研究根据水系沉积物下伏基岩性质的不同,确定了不同地层单元和侵入岩类的P t,Pd背景值和异常下限,在研究区圈出多处P t,Pd衬值异常。结合有关铂族矿床以及同源玄武岩地球化学特征的认识,通过对水系沉积物P t,Pd综合异常的筛选,初步优选出铂族元素找矿远景区10个。     

滇西金宝山富铂钯岩体岩浆源区研究：铂族元素和Sr-Nd同位素约束

金宝山杂岩体位于扬子板块西缘,毗邻哀牢山造山带北段,岩体中蕴含丰富的铂钯资源,是峨眉山大火成岩省(ELIP)中大型岩浆型铂族元素矿床。岩体的主要组成为辉石橄榄岩,矿体以似层状、透镜状产出于辉石橄榄岩中。地幔是镍矿床和铂族元素矿床最重要的源区,因而对Ni、Cu及PGE等元素行为的研究,是剖析岩浆型Ni-Cu-PGE矿床源区特征的一个重要研究方向。该研究获得金宝山岩体中辉橄岩铂族元素及Sr-Nd同位素数据,结合前人对ELIP中不同类型岩石系列PGE成分研究及Ni、Cu、PGE等元素在岩浆和硫化物中的分配系数,半定量模拟得到金宝山原始岩浆的形成源于地幔中高度部分熔融(25%~40%)形成的富PGE岩浆(含12.8×10-9 Pd,9.8×10-9 Pt,0.6×10-9 Rh和0.7×10-9 Ir),其铂族元素成分与ELIP苦橄岩成分相当,并且岩浆在演化的过程中遭受了10%~20%地壳混染作用。利用批式部分熔融公式及各铂族元素在硅酸盐矿物和熔体之间的分配系数反演计算得到产生金宝山熔体的地幔约含有5.3×10-9 Pd,7.5×10-9 Pt,0.75×10-9 Rh和1.5×10-9 Ir,相比原始地幔而言并没有表现出明显富集PGE的特征。这表明地幔中高度部分熔融+大量岩浆与硫化物的充分反应是形成大型岩浆型铂族元素矿床的一种可具备的条件。     

金川超大型铜镍硫化物矿床的铂族元素地球化学特征

对金川超大型铜镍岩浆硫化物矿床岩石、矿石的铂族元素地球化学特征研究表明 ,金川岩体的平均Cu/Pd值远大于原生地幔岩浆的Cu/Pd值 ,说明其岩石为因硫化物析离而失去Pd的岩浆所结晶 ;且岩石的PGE具有部分熔融趋势 ,与地幔橄榄岩接近 ,这些均指示存在岩浆熔离作用。该矿床岩石、矿石的PGE球粒陨石标准化分布模式比较对应 ,均可分为两种类型 ,反映了岩浆多次侵入、熔离分异同时成岩成矿的特征。另外 ,PGE S关系分析表明其成岩成矿过程中有少量地壳物质混染。PGE地球化学特征参数还指示了其高镁拉斑玄武质母岩浆的性质。     

A reconnaissance study of platinum group elements (PGE) contents from sulfide mineralization in pyroxenites in Faryab ophiolite of Iran

Platinum group elements (PGE) enrichment occurs in Zn–Cu and Ni-rich ophiolities in a number of geological settings. Platinum group elements (PGE) mineralization in Pyroxenite from the Faryab ophiolities of Zagros belt in south Iran was studied. The ophiolite rocks represent blocks of Tethyan oceanic crust that were emplaced on the continental margin during the late Cretaceous period. Much of lower ophiolitic section is composed of homogeneous harzburgite, while upper sections harzburgite interlayer with dunite and pyroxenite are included. This study focused on pyroxenite that includes most of sulfide mineralization in Faryab. More than 500 samples were investigated from polished thin sections; that cover all area of Faryab. The sulfide phases include pyrrhotite, pentlandite, millerite, violarite, smythite, and heazlewoodite. The results show that in almost all the samples Os is below the 2 ppb detection limit, Platinum values vary from <5 to 91 ppb and the light PGE (Ru, Rh, and Pd) relative to the heavy PGE (Os, Ir, and Pt) are more concentrated. Calculation showed that in pyroxenites Pd–Pt is occurring with orthopyroxenite and Rh–Os is occurring in clinopyroxenite. Ni/Pd ratios in Faryab vary between 7 and 356 and Pd/Ir ratio is 0.1–27. This indicates that in Faryab area partial melt of mantle occurred. Pd/Rh ratio in Faryab is 0.1–11, and Pd/Pt varies between 0.2 and 1.5. Pd/Ir ratio in Faryab decreases and shows that PGE in Faryab occurred.     

Preliminary Study on the PGE Geochemistry of the Permian Basalts in the Jinping Area

INTRODUCTIONIn comparison with studies on the geochemistryof the REE and trace elements of the Emeishan Per-mian basalts ,there has been onlyli mited research onthe platinum group elements ( PGE) . Preli minarystudies have been carried out on the PGE geochemis-try of the basalts in the Emeishan area ( QingyingPower Station profile) and Xinjie area (Zhang andLi ,1998) ,andinthe Shuicheng and Weining areasinGuizhou (Li et al .,2003) . There are no PGEanaly-sis data of the basaltsin…     

贵州西部红岩地区水系沉积物中Pt、Pd地球化学异常的识别及推断解释

与基性-超基性岩相比,我国的峨 眉山玄武岩具有高含量的Pt、Pd地球化学背景。从峨眉山玄武岩分布区分辨出与基性、超基性侵入岩有关的Pt、Pd地球化学异常,是我国Pt、Pd找矿获得重大突破的关键技术。在贵州西部开展的1∶5万 水系沉积物测量显示,采用岩石背景衬值法可有效区分岩性和矿致Pt、Pd异常。在红岩村附近茅口组灰岩与玄武岩接触带及北东向断层的复合部位圈出了浓度分度清晰的As、Sb、Hg、Pb、Cr、Ni、Pt、 Pd组合异常,推测在该组合异常下方可能存在一个赋存有Pt、Pd矿的隐伏基性-超基性含矿岩体(脉)。     

Abundance and distribution of PGE and Au in the island-arc mantle: implications for sub-arc metasomatism

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.