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1.
铂族元素矿物共生组合(英文) 总被引：1，自引：2，他引：1
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? 相似文献
2.
Controls on variations of platinum-group element concentrations in the sulfide ores of the Jinchuan Ni-Cu deposit, western China 总被引：3，自引：0，他引：3
Ongoing underground exploration in the giant Jinchuan Ni-Cu sulfide deposit in western China is beginning to emphasize the
potential for Cu-, Pt-, and Pd-rich sulfide ores that may have formed by sulfide liquid fractionation. The success of such
an effort relies on whether or not fractional crystallization of sulfide occurred in the Jinchuan system. In this paper, we
used available PGE data to evaluate such a process. We found that about two thirds of the 126 samples analyzed to date exhibit
significant decoupling not only between Pt and Pd but also between Ru, Rh, and Ir. The best explanation for the decoupling
is postmagmatic hydrothermal alteration, which affected not only silicates but also sulfides. The effects of postmagmatic
alteration must be considered when using metal and isotopic ratios to evaluate primary mineralization. PGE variations in the
remaining one third of the samples with Ir/(Ir + Ru) = 0.3–0.7, Ir/(Ir + Rh) = 0.4–0.8, and Pt/(Pt + Pd) = 0.3–0.7 indicate
variable R-factors within individual ore bodies as well as the entire deposit, consistent with the interpretation that multiple
sulfide-bearing magmas from depth were involved in the formation of the Jinchuan deposit. The mantle-normalized PGE patterns
of the least-altered samples from the Jinchuan deposit are similar to the picrite-related Pechenga Ni-Cu sulfide deposit in
Russia. PGE variations that can be related to sulfide liquid fractionation are observed in orebody-1 and orebody-24 but not
in orebody-2 at Jinchuan. Exploration for Cu-, Pt-, and Pd-rich sulfide ores that may have been expelled into fractures in
the footwalls of orebody-1 and orebody-24 appears to be justified. 相似文献
3.
Hazel M. Prichard Robert D. Knight Peter C. Fisher Iain McDonald Mei-Fu Zhou Christina Y. Wang 《Mineralium Deposita》2013,48(6):767-786
The division of platinum-group elements (PGE) between those hosted in platinum-group minerals (PGM) versus those in solid solution in base metal sulfides (BMS) has been determined for ores from the PGE-bearing Ni-Cu-rich Jinchuan intrusion in northwest China. All the BMS are devoid of Pt and Ir, and magmatic BMS are also barren of Rh. These PGE may have been scavenged by arsenic to form PGM during magmatic crystallization of the BMS. Pd, Os, and Ru are recorded in BMS and Pd is predominantly in solid solution in pentlandite. Unlike the fresh magmatic ores, in altered or serpentinized ores, Pd-PGM are present. Froodite is hosted in magnetite, formed during alteration of BMS, accompanied by sulfur loss and liberation of Pd. Michenerite ([Pd,Pt]BiTe), sperrylite (PtAs2), and Au-bearing PGM are located in altered silicates. Irarsite (IrAsS) occurs mainly enclosed in BMS. Padmaite (PdBiSe), identified at the junctions of magnetite and BMS, was the last PGM to form and locally partially replaces earlier non-Se-bearing PGM. We propose that padmaite formed under oxidizing conditions during late local remobilization of Se from the BMS. Se-bearing PGM are rare and our review shows they are frequently associated with carbonate, suggesting that Pd and Se can be mobilized great distances in low pH oxidizing fluids and may be precipitated on contact with carbonate. S/Se ratios are used by researchers of magmatic Ni-Cu-PGE ores to determine sulfur loss, assuming Se is immobile and representative of magmatic sulfur content. This study shows that Se as well as S is potentially mobile and this should be considered in the use of S/Se ratios. 相似文献
4.
采用ICP—MS方法分析了煎茶岭和金川硫化镍矿床岩石、矿石的铂族元素含量，煎茶岭岩体蛇纹岩的Cu／Pd比值低于原生地幔岩浆，说明岩浆熔离作用较弱，矿石的Pd／Ir比值较小，指示其多数矿石属于岩浆型，以岩浆成矿作用为主；而金川岩体的平均Cu／Pd比值远大于原生地幔岩浆，表明岩浆熔离作用强，矿石的Pd／Ir比值较大，体现了钯族元素矿化及成矿物质以幔源为主的特征。煎茶岭在成矿过程中有壳源物质的混染，整体上岩石、矿石铂族元素含量较低，这与岩浆熔离作用弱、铂族元素成矿作用不发育等因素有关；金川在成岩成矿过程中也有少量地壳物质的混染，但岩石、矿石铂族元素含量较高，反映了以岩浆深部熔离成矿作用为主的特征。 相似文献
5.
Concentrations of platinum group elements (PGE), Ag, As, Au, Bi, Cd, Co, Mo, Pb, Re, Sb, Se, Sn, Te, and Zn, have been determined
in base metal sulfide (BMS) minerals from the western branch (402 Trough orebodies) of the Creighton Ni–Cu–PGE sulfide deposit,
Sudbury, Canada. The sulfide assemblage is dominated by pyrrhotite, with minor pentlandite, chalcopyrite, and pyrite, and
they represent monosulfide solid solution (MSS) cumulates. The aim of this study was to establish the distribution of the
PGE among the BMS and platinum group minerals (PGM) in order to understand better the petrogenesis of the deposit. Mass balance
calculations show that the BMS host all of the Co and Se, a significant proportion (40–90%) of Os, Pd, Ru, Cd, Sn, and Zn,
but very little (<35%) of the Ag, Au, Bi, Ir, Mo, Pb, Pt, Rh, Re, Sb, and Te. Osmium and Ru are concentrated in equal proportions
in pyrrhotite, pentlandite, and pyrite. Cobalt and Pd (∼1 ppm) are concentrated in pentlandite. Silver, Cd, Sn, Zn, and in
rare cases Au and Te, are concentrated in chalcopyrite. Selenium is present in equal proportions in all three BMS. Iridium,
Rh, and Pt are present in euhedrally zoned PGE sulfarsenides, which comprise irarsite (IrAsS), hollingworthite (RhAsS), PGE-Ni-rich
cobaltite (CoAsS), and subordinate sperrylite (PtAs2), all of which are hosted predominantly in pyrrhotite and pentlandite. Silver, Au, Bi, Mo, Pb, Re, Sb, and Te are found predominantly
in discrete accessory minerals such as electrum (Au–Ag alloy), hessite (Ag2Te), michenerite (PdBiTe), and rhenium sulfides. The enrichment of Os, Ru, Ni, and Co in pyrrhotite, pentlandite, and pyrite
and Ag, Au, Cd, Sn, Te, and Zn in chalcopyrite can be explained by fractional crystallization of MSS from a sulfide liquid
followed by exsolution of the sulfides. The early crystallization of the PGE sulfarsenides from the sulfide melt depleted
the MSS in Ir and Rh. The bulk of Pd in pentlandite cannot be explained by sulfide fractionation alone because Pd should have
partitioned into the residual Cu-rich liquid and be in chalcopyrite or in PGM around chalcopyrite. The variation of Pd among
different pentlandite textures provides evidence that Pd diffuses into pentlandite during its exsolution from MSS. The source
of Pd was from the small quantity of Pd that partitioned originally into the MSS and a larger quantity of Pd in the nearby
Cu-rich portion (intermediate solid solution and/or Pd-bearing PGM). The source of Pd became depleted during the diffusion
process, thus later-forming pentlandite (rims of coarse-granular, veinlets, and exsolution flames) contains less Pd than early-forming
pentlandite (cores of coarse-granular). 相似文献
6.
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
7.
论金川硫化铜镍矿床中贵金属元素的分带机制 总被引：3，自引：1，他引：3
在金川硫化铜镍矿床最大的寓矿体内,贵金属元素存在明显分带:Pt、Pd、Au、Ag含量在边部较低,向中心部位逐渐增高;Os、Ir、Ru、Rh含量在中心部位较低,向边部逐渐增高。通过对实际资料的分析,认为这种分带特征是硫化物液相结晶分异作用造成的。 相似文献
8.
金川铜镍硫化物矿床的成因及侵位机制尤其是块状矿石和铂钯富集体成因一直存在较大争议,本文通过对金川矿石的空间关系、地球化学特征研究,指出金川矿床遭受构造及热液蚀变作用影响明显,块状矿石相对富集Os、Ir、Ru、Rh,铂钯富集体相对富集Pt、Pd、Au、Cu.研究认为,块状矿石是晚期纯硫化物矿浆上升贯入后经单硫化物固溶体结晶堆积而成,残余熔浆形成初始铂族矿物,后期矿体遭受热液蚀变及构造剪切-热液作用,使Pt、Pd、Cu、Au迸一步富集形成铂钯富集体,并在有利于成矿的空间聚集成矿.块状矿石与铂钯富集体关系密切,据此推测2 #矿体、24#矿体深边部裂隙中具有良好的勘探前景. 相似文献
9.
Li Shengrong 《中国地质大学学报(英文版)》1999,10(1):2
ＩＮＴＲＯＤＵＣＴＩＯＮＬｏｗｅｒＣａｍｂｒｉａｎｂｌａｃｋｒｏｃｋｓｅｒｉｅｓｅｘｉｓｔｓｂｒｏａｄｌｙｉｎｍｏｒｅｔｈａｎ１０ｐｒｏｖｉｎｃｅｓｉｎＳｏｕｔｈＣｈｉｎａ（Ｃｈｅｎｅｔａｌ．,１９９０）．Ｔｈｅｂｏｔｏｍｏｆｔｈｅｓｅｒｉｅｓｓｐｏ... 相似文献
10.
金川铜镍硫化物矿床岩浆通道型矿体地质地球化学特征 总被引：7，自引：0，他引：7
金川铜镍硫化物矿床6行富铜（铂族）矿体曾因Cu、Pt、Pd等含量明显高于相邻其它矿体而被认为是岩浆期后热液叠加作用的产物,研究发现,空间上该矿体受断层构造控制,在矿石组构、矿物组成和硫同位素组成方面与相邻岩浆融离型1号矿体一致,显示了该矿体岩浆成矿作用的特征。在元素地球化学方面,6行富铜（铂族）矿体的Cu、Ni、Pt、Pd含量及Cu/Ni比值明显高于1号主矿体,而Os、Ir、Rh、Ru却明显低于后者,同时,前者相对富含LREE,轻、重稀土分异程度高于后者。根据硫化物结晶分异过程中金属元素分配规律及稀土元素特征,阐明了6行富铜（铂族）矿体为岩浆通道型矿体,是岩浆硫化物晚期结晶的产物。矿区中西部存在的Cu、Ni、Pt、Pd、Au等含量高,而Os、Ir、Rh、Ru含量低的部位,是寻找岩浆通道型矿体的有利部位。 相似文献
11.
方解石作为木落稀土矿床常见的脉石矿物,其中的铂族元素(简称PGE)地球化学特征有可能记录了地质流体的性质。采用ICP-MS分析木落方解石中PGE的含量,并对铂族元素的分布、相关性、成因进行了探讨。木落方解石可以分为两类:I型方解石和Ⅱ型方解石。I型方解石中∑PGE(不含Os)0.62～1.33ng/g,具相对低的Pd/Pt、Pd/Rh、Pd/Ru、Pd/Ir比值,不太显著的Pt-Pd分配模式,为岩浆成因方解石,与成矿作用密切相关;Ⅱ型方解石中∑PGE(不含Os)1.85～2.97ng/g,具相对高的Pd/Pt、Pd/Rh、Pd/Ru、Pd/Ir比值和显著的Pt-Pd分配模式,为热液成因方解石,代表了成矿作用后的一期地质流体作用,与成矿关系不大,仅局部地区存在改造前次流体作用形成的稀土矿体。富CO2热液具有携带PGE的能力,并能够导致PGE的分异,与富CO2岩浆相比,富CO2热液对铂族元素具有一定程度的富集作用。 相似文献
12.
青海化隆地区拉水峡铜镍矿床地质、
地球化学特征及成因 总被引：3，自引：1，他引：2
拉水峡铜镍矿床位于化隆基性—超基性岩带中,岩体几乎全岩发生铜、镍硫化物矿化,且已遭受强烈蚀变,以角闪岩为主。岩浆期主要金属硫化物矿物组合为磁黄铁矿、黄铜矿、镍黄铁矿;热液蚀变期主要有紫硫镍矿、黄铁矿、黄铜矿、针镍矿等;氧化表生期主要为含镍高岭石、含镍绿泥石、孔雀石等。矿石轻稀土元素富集和负Eu异常明显,说明岩浆演化过程中发生了大量斜长石等的分离结晶作用。∑PGE含量平均为2460.46×10-9,(Pd+Pt)/(Os+Ir+Ru)值为0.40~2.00,表明铂族元素与岩浆深部熔离作用密切相关;但Pt/Pd(0.01~2.62)、Pd/Ir(0.91~8.77)说明热液作用对铂族元素具有一定的富集作用。S同位素组成变化范围很小,δ34S平均值为2.24‰,硫化物中的S以地幔S为主。拉水峡矿床的形成经历了岩浆融离贯入、热液叠加改造及表生氧化作用3个阶段。 相似文献
13.
金川铜镍硫化物矿床铂族元素的赋存状态及分布规律 总被引：17，自引：3，他引：14
金川铜硫化物矿床铂族元素球粒陨石标准化型式属于Ｐｔ－Ｐｄ配分类型,Ｐｔ、ｐｄ〉Ｏｓ、Ｉｒ、Ｒｕ、Ｒｈ,存在３种不同形式的图形;ＰＧＥ（铂族元素）在熔离和深熔－－贯入型岩矿体中,ＰＧＥ含量从非含矿岩石→ＳＮ－Ｂ→ＳＮ－Ａ２→ＳＮ－Ａ１依次增加,显示与金属硫化物含量具有正消长关系;矿石中８０％以上的铂和７０Ｔ以上的钯呈矿物相存在;ＰＧＥ富集体主要分布在富矿体膨大处的中、下部。 相似文献
14.
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
15.
The peridotites of the Manipur Ophiolite Complex (MOC) have been examined based on mineral chemistry, major elements and PGE
contents. They represent high-magnesian cumulates with Mg# > 0.90 (Mg/Mg+Fe) in olivine and Cr# > 0.12 (Cr/Cr+Al) in spinel.
High Mg* contents of the olivine show that these rocks are most likely derived from partial melting of the residual upper
mantle. The peridotites contain higher concentration of Palladium Group PGE (PPGE) (Rh=4.4−6.6ppb; Pd=336−458ppb and Pt=14.6−36.4ppb)
than the Iridium Group PGE (IPGE) (Os=2.4−5.8ppb; Ir=3.2−4.16ppb and Ru=5.2−7ppb). These are characterized by overall enrichment
of PGE concentration (σPGE=365.8 − 516.6 ppb) and high ratio of (Pt+Pd)/(Os+Ir+Ru). This suggests that the rocks are formed
by partial melting and crystal fractionation of olivine-rich (picritic) magma. 相似文献
16.
The paper presents concentrations of the platinum-group and chalcophile elements in the base metal sulfides (BMS) from the Jinchuan Ni–Cu sulfide deposit determined by laser ablation-inductively coupled plasma-mass spectrometry. Mass balance calculations reveal that pentlandite hosts a large proportion of Co, Ni and Pd (> 65%), and that pentlandite and pyrrhotite accommodate significant proportions of Re, Os, Ru, Rh, and Ag (~ 35–90%), whereas chalcopyrite contains a small amount of Ag (~ 10%) but negligible platinum-group elements. Iridium and Pt are not concentrated in the BMS and mostly occur in As-rich platinum-group minerals. The enrichments of Co, Ni, Re, Os, Ru, and Rh in pentlandite and pyrrhotite, and Cu in chalcopyrite are consistent with the fractionation of sulfide liquid and exsolution of pentlandite and pyrrhotite from the mono-sulfide solid solution (MSS). The Ir-bearing minerals exsolved from the MSS, depleting pentlandite and pyrrhotite in Ir, whereas sperrylite exsolved from the residual sulfide liquid on cooling. Diffusion of Pd from residual sulfide liquid into pentlandite during its exsolution from the MSS and crystallization of Pt-bearing minerals in the residual sulfide liquid resulted in the enrichment of Pd in pentlandite and decoupling between Pd and Pt in the Jinchuan net-textured and massive ores. 相似文献
17.
Liang Qi Mei-Fu Zhou Zheng Zhao Jing Hu Yan Huang 《Environmental Earth Sciences》2011,64(6):1683-1692
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
18.
M. A. E. Huminicki P. J. Sylvester R. Lastra L. J. Cabri D. Evans-Lamswood D. H. C. Wilton 《Mineralogy and Petrology》2008,92(1-2):129-164
Summary This study reports the first documented occurrence of platinum group-minerals (PGM) in the vicinity of the Voisey’s Bay magmatic
sulfide ore deposit. The PGM are present in a sulfide poor, hornblende gabbro dyke in the Southeast Extension Zone of the
massive sulfide Ovoid deposit. The dyke has somewhat elevated concentrations of platinum-group elements (PGE) and gold (up
to 1.95 g/t Pt, 1.41 g/t Pd, and 6.59 g/t Au), as well as Cu, Pb, Ag, Sn, Te, Bi and Sb. The PGM formed by magmatic processes
and were little disturbed by subsequent infiltration of an externally-supplied hydrothermal fluid. To date, no similar PGM
occurrences have been discovered in the Ovoid deposit itself.
Whole rock REE patterns indicate that the dyke is geochemically related to the main conduit troctolites, which carry the bulk
of the massive sulfide mineralization at Voisey’s Bay. The PGE mineralization is Pt- and Pd-rich, where the Pt and Pd occur
predominantly as discrete PGM with minor Pd in solid solution in galena (average=1.8 ppm) and pentlandite (average=2 ppm).
The discrete PGM are predominantly hosted by disseminated base-metal sulfides (bornite, chalcopyrite, and galena) (56 vol%)
and are associated with other precious metal minerals (13 vol%) with only ∼3 vol% of the PGM hosted by silicate minerals.
In whole rock samples, the PPGE (Pt, Pd, and Rh) correlate with abundances of chalcopyrite, bornite, galena, and other precious
metal minerals (PMM), whereas the IPGE (Ir, Ru, and Rh) correlate with pyrrhotite and pentlandite. There are no correlations
of the PGE with chlorine. Lead isotope compositions of galena associated with the PGE mineralization in the Southeast Extension
Zone are broadly similar to those for galena in the Ovoid. The lead isotope compositions are much different from those in
the Voisey’s Bay Syenite, which is a potential external hydrothermal fluid source.
The observed Cu-rich, Pb-rich sulfide compositions and associated Pt-Pd-Au-Ag-Sn-Te-Bi-Sb assemblage in the dyke can be produced
magmatically as late ISS differentiates (e.g., Prichard et al., 2004). Melting temperatures of the PGM are also consistent with a magmatic origin. Following crystallization of PGM
from magmatic sulfide, an external REE-enriched hydrothermal fluid was introduced to the system, producing secondary amphibole
and locally remobilizing the Pb and Sn from the sulfides hosting the PGM.
Author’s address: M. A. E. Huminicki, Department of Earth Sciences, Memorial University of Newfoundland, St. John’s, NL, Canada A1B 3X5 相似文献
19.
Summary ?We report, for the first time, the occurrence of five palladium-rich, one palladium bearing and two gold-silver minerals
from podiform chromitites in the Eastern Alps. Minerals identified include braggite, keithconnite, stibiopalladinite, potarite,
mertieite II, Pd-bearing Pt-Fe alloy, native gold and Ag-Au alloy. They occur in heavy mineral concentrates produced from
two massive podiform chromitite samples (unaltered and highly altered) of the Kraubath ultramafic massif, Styria, Austria.
Distribution patterns of platinum-group elements (PGE) in these chromitites show considerable differences in the behaviour
of the less refractory PGE (PPGE-group: Rh, Pt, Pd) compared to the refractory PGE (IPGE-group: Os, Ir, Ru). PPGE are more
enriched in chromitite showing pronounced alteration features. The unaltered chromitite displays a negatively sloped chondrite-normalised
PGE pattern similar to typical ophiolitic-podiform chromitite.
Except for the Pd- and Au-Ag minerals that are generally rare in ophiolites, about 20 other platinum-group minerals (PGM)
have been discovered. They include PGE-sulphides (laurite, erlichmanite, kashinite, bowieite, cuproiridsite, cuprorhodsite,
unnamed Ir-rich variety of ferrorhodsite, unnamed Ni-Fe-Cu-Rh- and Ni-Fe-Cu-Ir-Rh monosulphides), PGE alloys (Pt-Fe, Ir-Os,
Os-Ir and Ru-Os-Ir), PGE-sulpharsenides (irarsite, hollingworthite, platarsite, ruarsite and a number of intermediate species),
sperrylite and a Ru-rich oxide (?). Three PGM assemblages have been recognised and attributed to different processes ranging
from magmatic to hydrothermal and weathering-related.
Pd-rich minerals are characteristic of both chromitite types, although their chemistry and relative proportions vary considerably.
Keithconnite, braggite and Pd-bearing ferroan platinum, together with a number of PGE-sulphides (mainly laurite-erlichmanite)
and alloys, are typical only of the unaltered podiform chromitite (assemblage I). Euhedral mono- and polyphase PGM grains
in the submicron to 100 μm range show features of primary magmatic assemblages. The diversity of PGM in these assemblages
is unusual for ophiolitic environments. In assemblage II, laurite-erlichmanite is intergrown with and overgrown by PGE-sulpharsenides;
other minerals of assemblage I are missing. Potarite, stibiopalladinite, mertieite II, native gold and Ag-Au alloys, as well
as PGE-sulpharsenides, sperrylite and base metal arsenides and sulphides are characteristic for the highly altered chromitite
(assemblage III). They occur either interstitial to chromite in association with metamorphic silicates, in chromite rims or
along cracks, and are thus interpreted as having formed by remobilization of PGE by hydrothermal processes during polyphase
regional metamorphism.
Received August 3, 2000;/revised version accepted December 28, 2000 相似文献
20.
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