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1.
采用镍锍火试金法结合ICP-MS分析了12个北大别白垩纪镁铁-超镁铁岩样品的Ir,Ru,Rh,Pt和Pd的含量,结果显示铂族元素（PGE）的含量较低,原始地幔标准化后的PGE分布模式呈正斜率型,PPGE相对原始地幔略微亏损,而IPGE强烈亏损,Pd/Ir值远高于相应的地幔比值。这些镁铁-超镁铁岩中PGE的强烈分异是地幔低程度的部分熔融过程中,PPGE主要受硫化物控制,而Ir则存在于非硫化物相如尖晶石,可能还有合金之中造成的。同时,铂族元素的分布特征表明这些镁铁-超镁铁岩是岩浆结晶分异的产物。 相似文献
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金川超大型铜镍硫化物矿床的铂族元素地球化学特征 总被引：21，自引：2，他引：19
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。 相似文献
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稀有气体被广泛用作地球化学示踪剂,本文对塔里木大火成岩省西北缘瓦吉里塔格霞石岩中的橄榄石和辉石单矿物进行了稀有气体同位素测定。结果表明,瓦吉里塔格霞石岩中的橄榄石和辉石单矿物具有较低的~3He/~4He值(分别为2.0~2.4 Ra和0.65~0.85 Ra)和略高于大气值的~(40)Ar/~(36)Ar值(342.3~651.7),反映了由古板块俯冲导致的较低的He、Ar同位素比值特征。研究表明,早中古生代南天山洋向南俯冲到塔里木板块之下,将富U或富~4He以及含有大气组分的流体带入到深部地幔,在塔里木地幔柱的作用下地幔源区发生低程度部分熔融产生霞石岩岩浆。 相似文献
4.
新疆哈密白石泉含铜镍镁铁-超镁铁质岩体铂族元素特征 总被引：7，自引：1，他引：7
新疆哈密白石泉镁铁-超镁铁质岩体的铂族元素研究表明,岩体的铂族元素总含量较低,原始地幔标准化模式具镁铁质岩石的特征,并具Pt 正异常,且铂族元素的分异主要受结晶分异作用的影响.岩体的Cu/Pd、Se/S、Ti/Pd值表明其发生过硫化物的熔离作用.Pd/Ir、Ni/Cu特征表明了岩体系高镁玄武岩岩浆的产物.铂族元素特征揭示了白石泉岩体硫化物的熔离作用是由原始岩浆结晶分异导致的,岩体的形成是原始岩浆发生橄榄石等的结晶,导致硫化物的熔离作用后,其残余岩浆演化的结果. 相似文献
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华北克拉通北缘中段大同地区发育呈岩墙形式产出的煌斑岩,该煌斑岩为超钾质碱性岩,极度低硅低钠高镁高钙高钾,且富H_2O和CO_2等流体组分。本文利用镍锍试金-电感耦合等离子体质谱法测定了这套煌斑岩的铂族元素组成,获得了其形成及演化过程的一些信息。大同煌斑岩铂族元素含量极低,∑PGE=2.14×10~(-9)~4.50×10~(-9),原始地幔标准化铂族元素配分型式为左倾型,亏损Ir亚组(IPGE),富集Pd亚组(PPGE),(Pd/Ir)_N=3.48~10.43。低铂族元素含量、高Cu/Ni比值(48101~90926)和高(Pd/Ir)_N比值指示大同煌斑岩形成于地幔低程度部分熔融(1%~13%),熔体形成时仍有部分硫化物残留于源区。岩浆演化过程中,未发生明显的结晶分异作用和地壳混染作用,硫未达到饱和-过饱和,未发生硫化物熔离作用。计算获得铂族元素在原始地幔与煌斑岩熔体间的分配系数分别为D_(Os)=35~124,D_(Ir)=13~35,D_(Ru)=34~91,D_(Rh)=5.8~10,D_(Pt)=3.1~9.7,D_(Pd)=2.2~4.5;PPGE较IPGE明显更不相容。与峨眉山大火成岩省玄武岩对比研究发现,岩浆岩中的铂族元素含量主要受源区地幔部分熔融程度和演化过程中硫化物熔离作用共同影响;而铂族元素之间的分异受源区部分熔融程度和岩浆分离结晶作用共同影响。 相似文献
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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。 相似文献
7.
金宝山和白马寨铜镍硫化物矿床均主要赋存在峨眉山大火山岩省中,但其矿化特征存在许多不同。本文着重对比了金宝山铂钯矿床和白马寨铜镍矿床的铂族元素(PGE)地球化学特征,发现前者表现为高ΣPGE及低的(Cu Ni)、Pd/Ir(3.84~26.49)、Cu/Pd(46.91~1309.58)值和Au/Pd值,相反,后者表现为低ΣPGE、高(Cu Ni)、Pd/Ir(4.72~297.2)、Cu/Pd(10875.13~974788.55)值和较高的Au/Pd值。金宝山和白马寨PGE原始地幔标准化配分模式均主要表现为左倾型,但二者表现为镜像关系。金宝山较白马寨的PGE间相关性好,可能说明白马寨母岩浆经历了较为复杂的地质过程,其铂族元素体系因此受到较大的扰动。结合前人有关杨柳坪铜镍铂族元素矿床的铂族元素数据,认为峨眉地幔柱形成铜镍铂族元素矿床大致可以分成3个阶段:1金宝山阶段:即为S的低度饱和阶段,为峨嵋地幔柱上升初期,吸收少量壳源物质,由于PGE在硫化物中很高的分配系数,导致少量硫化物熔体从硅酸盐中萃取大量PGE和少量Cu-Ni熔离出来,与铬铁矿、橄榄石和辉石等,于高温下结晶分异堆积而成金宝山岩体,形成独立铂钯矿床。... 相似文献
8.
大别造山带祝家铺辉长岩的铂族元素特征 总被引：8，自引：2，他引：8
采用镍锍火试金法结合ICP-MS分析了祝家铺14个辉长岩样品中的Ir，Ru，Rh，Pt和Pd的含量。结果显示其PGE的含量较低，原始地幔标准化后的PGE分布模式呈正斜率型，PPGE相对原始地幔略微亏损，而IPGE强烈亏损，Pd／Ir值(22—138)远高于相应的地幔比值，表明铂族元素发生了分异。对祝家铺辉长岩的铂族元素研究表明，在其源区发生过硫化物的分异作用，地壳的混入可能促进了硫化物的饱和。祝家铺辉长岩中铂族元素的分异是因为在地幔部分熔融和岩浆演化过程中，PPGE主要受硫化物控制，而Ir则存在于非硫化物相如尖晶石、可能还有合金之中。 相似文献
9.
本文对塔里木盆地二叠纪大火成岩省中瓦吉里塔格地区超镁铁质隐爆角砾岩进行了铂族元素(PGE)和主、微量及稀土元素分析和研究。结果显示,隐爆角砾岩中Os、Ir、Ru、Rh、Pt和Pd含量分别为0.36×10-9～1.08×10-9、0.23×10-9～0.44×10-9、0.29×10-9～0.92×10-9、0.11×10-9～0.18×10-9、1.88×10-9～3.16×10-9和1.39×10-9～3.52×10-9,均低于原始地幔,与夏威夷苦橄岩相似。该岩石的Pd/Ir比值在3.6～11.9之间,PGE分配模式呈一条正倾斜的曲线,表现出一定程度的分异,具有非俯冲背景下产生的基性-超基性岩的PGE配分特点。略高于原始地幔但变化较小的Cu/Pd比值(5.1×104～12.1×104)表明其岩浆在上升侵位过程中并没有发生明显的饱和硫化物熔离作用,而岩浆源区在部分熔融过程中可能有少量残留的硫化物存在。隐爆角砾岩全岩的IPGE元素与MgO之间基本上呈正相关,而PPGE元素与MgO之间则略成负相关或无明显相关性,指示PGE的分异主要受到橄榄石结晶分异作用的控制。地球化学特征显示隐爆角砾岩的稀土元素总量高度富集(964.1×10-6～1299×10-6)和轻、重稀土强烈分馏((La/Yb)N=45.88～64.90),且微量元素蛛网图上大离子亲石元素富集和Nb、Ta的轻微亏损以及Zr、Hf的明显贫化,表明岩石可能遭受一定程度的地幔交代作用影响。但是,角砾与胶结物具有相近的PGE特征表明交代作用对PGE的影响并不大,暗示PGE可能主要赋存于禁锢在硅酸盐矿物内的硫化物包裹体中。 相似文献
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WANG Ruiting MAO Jingwen HE Ying WANG Dongsheng TANG Zhongli 《大地构造与成矿学(英文版)》2005,29(2):152-163
The platinum-group element geochemistry of rocks and ores from Jinchuan super-large copper-nickel sulfide deposit is systemically studied in this paper. The Cu/Pd mean ratio of Jinchuan intrusion is lower than that of original mantle magma, which indicates that these ultrabasic rocks were crystallized from magma that lost Pd in the form of melting segregation of sulfides. The PGE of the rocks show trend of partial melting, similar to that of mantle peridotite, which shows that magma formation occurs during rock-forming and ore-forming processes. The chondrite normalized PGE patterns of the rocks and ores are well related to each other, which signifies the signatures of multi-episode magmatic intrusion, melting and differentiation in the formation processes of rocks and ores. In addition, analyses about the relation between PGE and S, and study on Re-Os isotopes indicate that few contamination of the crustal substances occurred during the magmatic intrusion and the formation of deposit. However, contamination by crustal substances helps to supply part of the S for the enrichment of PGE. Meanwhile, the hydrothermal process is also advantageous for the enrichment of PGE, especially lbr Pt and Pd, due to deep melting segregation. The characteristic parameters （such as Pt/（Pt＋Pd）, （Pt＋Pd）/（Ru＋Ir＋Os）, Pd/Ir, Cu/（Ni＋Cu）, and so on.） for platinum-group elements for Jinchuan sulfide copper-nickel deposit show the same features as those for sulfide copper-nickel deposit related to basic magma, which also illustrates its original magma property representative of Mg-high tholeiite. Therefore, it is the marie （not ultramafic） magma that resulted in the formation of the superlarge sulfide copper-nickel deposit enriched in Cu and PGE. To sum up, the geochemical characteristics of platinum-group elements in rocks and ores from Jinchuan copper-nickel sulfide deposit are constrained by the continental rift tectonic environment, the parent magma features, the enriched mantel magma source, the complex metallogenesis and PGE geochemical signatures, and this would be rather significant for the study about the genetic mechanism of copper-nickel sulfide deposits. 相似文献
12.
云南鸡街碱性超基性岩铂族元素地球化学特征 总被引：1，自引：1，他引：0
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。 相似文献
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核桃树富铂岩浆硫化物矿床位于四川会理县小关河地区,是峨眉山大火成岩省中含较高铂族元素含量的岩浆硫化物矿床之一。本文通过对核桃树岩体及部分硫化物矿石主量元素、微量元素及铂族元素的系统分析,讨论了该岩体的岩浆源区及母岩浆性质、地幔部分熔融程度,并探讨了其成因机制。研究认为,核桃树含矿岩体属拉斑玄武岩成因系列,具有与峨眉山玄武岩相似的微量元素组成特征,是峨眉山大火成岩省构造-岩浆活动的产物;铂族元素的原始地幔标准化配分型式与金宝山铂钯矿相似,没有PGE相对于Ni和Cu的明显亏损,Pt和Pd相对Os、Ir、Ru和Rh富集,为PPGE富集的左倾型式,Pd/Ir=1.5~13.1,低于一般大陆拉斑玄武岩,与原始地幔接近。通过岩石地球化学及模拟分析表明,成矿母岩浆MgO约为11.93%、SiO_2约为49.88%、FeOT约为13.71%、TiO_2约为2.61%,为高Mg拉斑玄武质岩浆,是由类似于洋岛玄武岩岩浆源区成分的地幔经过较高程度(约20.17%)的部分熔融形成的苦橄质岩浆演化而来。与小关河地区主要的几类岩浆硫化物矿床的镍铜铂族元素组成及硫化物熔离模式对比分析发现,核桃树高的PGE含量和低的Cu/Pd比值说明了该矿床的硫化物是从PGE不亏损的玄武质岩浆中熔离出来的,类似金宝山矿床。成岩成矿机制分析认为,部分熔融形成的苦橄质岩浆在上升的过程中,发生了以橄榄石(约12.7%)为代表的镁铁质矿物堆积,并形成残余髙镁玄武质岩浆;部分残余髙镁玄武质岩浆向浅部运移过程中,由于温度降低、混染等因素的影响,导致岩浆S饱和,触发硫化物熔离作用的发生(R值为2000~50000),熔离出硫化物熔体与岩浆通道内晶出的橄榄石构成含矿"晶粥",在构造挤压作用下,在浅部岩浆房中由于重力影响发生堆积作用形成具有较富PGE的含矿岩体,R值较大变化正好与PGE含量较大变化相对应。 相似文献
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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 haveεNd（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. 相似文献
15.
The Qingkuangshan Ni-Cu-PGE deposit, located in the Xiaoguanhe region of Huili County, Sichuan Province, is one of several Ni-Cu-PGE deposits in the Emeishan Large Igneous Province (ELIP). The ore-bearing intrusion is a mafic-ultramafic body. This paper reports major elements, trace elements and platinum-group elements in different types of rocks and sulfide-mineralized samples in the intrusion. These data are used to evaluate the source mantle characteristics, the degree of mantle partial melting, the composition of parental magma and the ore-forming processes. The results show that Qingkuangshan intrusion is part of the ELIP. The rocks have trace element ratios similar to the coeval Emeishan basalts. The primitive mantle-normalized patterns of Ni-Cu-PGE have positive slopes, and the ratios of Pd/Ir are lower than 22. The PGE compositions of sulfide ores and associated rocks are characterized by Ru depletion. The PGE contents in bulk sulfides are slightly depleted relative to Ni and Cu, which is similar to the Yangliuping Ni-Cu-PGE deposit. The composition of the parental magma for the intrusion is estimated to contain about 14.65 wt% MgO, 48.66 wt% SiO2 and 15.48 wt% FeOt, and the degree of mantle partial melting is estimated to be about 20%. In comparison with other typical Ni-Cu-PGE deposits in the ELIP, the Qingkuangshan Ni-Cu-PGE deposit has lower PGE contents than the Jinbaoshan PGE deposit, but has higher PGE contents than the Limahe and Baimazhai Ni-Cu deposit, and has similar PGE contents to the Yangliuping Ni-Cu-PGE deposit. The moderate PGE depletions in the bulk sulfide of the Qingkuanghan deposit suggest that the parental magma of the host intrusion may have undergone minor sulfide segregation at depth. The mixing calculations suggests that an average of 10% crustal contamination in the magma, which may have been the main cause of sulfide saturation in the magma. We propose that sulfide segregation from a moderately PGE depleted magma took place prior to magma emplacement at Qingkuangshan, that small amounts of immiscible sulfide droplets and olivine and chromite crystals were suspended in the ascending magma, and that the suspended materials settled down when the magma passed trough the Qingkuangshan conduit. The Qingkuangshan sulfide-bearing intrusion is interpreted to a feeder of Emeishan flood basalts in the region. 相似文献
16.
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 总被引：5，自引：0，他引：5
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。 相似文献
17.
The behaviour of platinum-group elements in basalts from the East Greenland rifted margin 总被引：5，自引：0，他引：5
Peter Momme Christian Tegner Kent C. Brooks Reid R. Keays 《Contributions to Mineralogy and Petrology》2002,143(2):133-153
. 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. 相似文献
18.
MAIER WOLFGANG D.; ROELOFSE FREDERICK; BARNES SARAH-JANE 《Journal of Petrology》2003,44(10):1787-1804
We have analysed 18 samples of komatiite from five consecutivelava flows of the Komati Formation at Spinifex Creek, BarbertonMountain Land. Our samples include massive komatiite, varioustypes of spinifex-textured komatiite, and flow-top breccias.The rocks have low platinum-group element (PGE) contents andPd/Ir ratios relative to komatiites from elsewhere, at 0·45–2ppb Os, 1–1·4 ppb Ir, <1–5 ppb Ru, 0·33–0·79ppb Rh, 1·7–6 ppb Pt, 1·6–6·1ppb Pd, and Pd/Ir 3·3. Pt/Pd ratios are c. 1·1.Platinum-group elements are depleted relative to Cu (Cu/Pd =15 300). They display a tendency to increase in the less magnesiansamples, suggesting that the magmas were S-undersaturated uponeruption and that all PGE were incompatible with respect tocrystallizing olivine. Komatiites from the Westonaria Formationof the Ventersdorp Supergroup and the Roodekrans Complex nearJohannesburg have broadly similar PGE patterns and concentrationsto the Komati rocks, suggesting that the PGE contents of SouthAfrican ultrabasic magmas are controlled by similar processesduring partial mantle melting and low-P magmatic crystallization.Most workers believe that the Barberton komatiites formed byrelatively moderate-degree batch melting of the mantle at highpressure. Based on the concentration of Zr in the Komati samples,we estimate that the degree of partial melting was between 26and 33%. We suggest that the low PGE contents and Pd/Ir ratiosof all analysed South African komatiites are the result of sulphideshaving been retained in the mantle source during partial melting.The difference in Pd/Ir between our samples and Al-undepletedkomatiites from elsewhere further suggests that the PGE arefractionated during progressive partial melting of the mantle.Thus, our data are in agreement with other recent studies showingthat the PGE are hosted by different phases in the mantle, withPd being concentrated by interstitial Cu-rich sulphide, andthe IPGE (Os, Ir, Ru) and Rh resting in monosulphide solid solutionincluded within silicates. Pt is possibly controlled by a discreterefractory phase, as Pt/Pd ratios of most komatiites worldwideare sub-chondritic. KEY WORDS: platinum-group elements; komatiites; Barberton; mantle melting; South Africa 相似文献