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1.
对富铝型豆荚状铬铁矿矿床成因的新认识一一以新疆萨尔托海铬铁矿矿床为例 总被引：2，自引：0，他引：2
萨尔托海铬铁矿矿床产于萨尔托海蛇绿岩块的地幔橄榄岩中,属于富铝型豆荚状铬铁矿床。该矿床与一套橄长岩和辉长岩类岩石紧密伴生,矿体周围常被一薄的绿泥石壳所包裹。本区铬铁矿的形成包括两个阶段:第一阶段是原始地幔岩经高度熔融形成富铬铬铁矿;第二阶段形成富铝铬铁矿。交代作用伴随着新生单斜辉石和斜长石的形成。原始地幔岩的高度熔融以及基性熔体在地幔橄榄岩中的形成和存在是萨尔托海铬铁矿形成的先决条件。 相似文献
2.
萨尔托海铬铁矿中的矿物包体研究 总被引：1，自引：0，他引：1
铬铁矿中矿物包体的研究对于探索铬铁矿的成因具有重要的指示意义。通过薄片扫描电镜背散射结合电子探针分析,在萨尔托海高铝铬铁矿中发现了大量矿物包体,包括:单斜辉石、斜方辉石、橄榄石、钠-金云母、钠-铬韭闪石、出溶的单斜辉石等,这些矿物呈单相或多相产出,在铬尖晶石结晶时被包裹。含水矿物钠-金云母,钠-铬韭闪石的大量出现指示含水环境,表明铬铁矿形成于含水的母岩浆中,可能形成于受俯冲流体/熔体影响的弧后扩张背景。结合之前在萨尔托海铬铁矿中发现的超高压矿物金刚石,认为萨尔托海铬铁矿的形成可能经历了深部地幔和浅部含水大洋岩石圈两个阶段。 相似文献
3.
西藏罗布莎不同类型铬铁矿的特征及成因模式讨论 总被引：6，自引：2，他引：4
蛇绿岩地幔橄榄岩中产出的豆荚状铬铁矿是铬的主要来源。已有的研究表明,豆荚状铬铁矿形成于洋中脊或俯冲带的浅部地幔环境。但随着近些年在豆荚状铬铁矿及围岩地幔橄榄岩中不断发现金刚石等深部矿物,人们也开始质疑豆荚状铬铁矿的浅部成因理论。本文系统研究了西藏雅鲁藏布江蛇绿岩带东段的罗布莎豆荚状铬铁矿床,识别出两类铬铁矿,一类以方辉橄榄岩为围岩的致密块状铬铁矿(Cr1#),另一类是以纯橄岩壳为围岩的浸染状铬铁矿(Cr2#)。两类铬铁矿在铬尖晶石的矿物化学成分、PGE和Re-Os同位素特征上存在较大差别,属不同演化过程的结果。地幔橄榄岩的地球化学特征指示罗布莎橄榄岩中存在由低铬且轻稀土亏损和高铬且轻稀土富集的两类方辉橄榄岩。在此基础上,提出豆荚状铬铁矿为多阶段形成的新认识,经历了早期俯冲至地幔过渡带(410~660km)的陆壳和洋壳物质被脱水和肢解,过渡带产生的热和流体促成了地幔的熔融和Cr的释放和汇聚;铬铁矿浆在地幔柱/地幔对流驱动下,运移至过渡带顶部冷凝固结,并有强还原性的流体进入,后者携带了深部形成的金刚石、斯石英等高压矿物,并进入"塑性-半塑性地幔橄榄岩"中;随着物质向上移动,深度降低,早期超高压相矿物发生相变,如斯石英转变成柯石英,高压相的铬铁矿中出溶成柯石英和单斜辉石;在侵位过程和俯冲带环境,含水熔体与方辉橄榄岩反应形成了不含超高压矿物的规模相对较小的浸染状铬铁矿(Cr2#)及纯橄岩壳。 相似文献
4.
新疆萨尔托海高Al型铬铁矿中几乎不含原生的铂族矿物(PGM)和贱金属硫化物(BMS)包体，显示出成矿岩浆贫硫的特征。BMS多产于铬铁矿铬粒间裂隙、基质及蚀变环带中，主要以赫硫镍矿和针镍矿为主，其次为辉铜矿、砷镍矿、硫砷镍矿、毒砂等。PGM以包体产于BMS或铬铁矿粒间缝隙中，以硫钌矿(RuS2)为主，还包括硫锇矿(OsS2)、硫镍锇矿\[(Os，Ni)S2\]、硫钌锇矿\[(Ru，Os)S2\]，锑钯矿(Pd5Sb2)和少量Cu、Pt、Au的硫化物。铬铁矿全岩ΣPGE含量50. 64×10-9~92. 00×10-9，较世界范围内蛇绿岩型铬铁矿低，且具有IPGE较PPGE富集的特点，PdN/IrN在0. 1~0. 9之间，具有Os相对Ir富集的特点。铬铁矿主量元素和原位微量元素显示出与菲律宾阿科杰高Al型铬铁矿以及MORB中尖晶石相似的地球化学特征。根据萨尔托海铬铁矿中PGM及BMS的种类、产出特征，结合铬铁矿全岩PGE及单矿物微量元素地球化学特征，认为铬铁矿的形成与贫硫的拉斑玄武质岩浆与地幔橄榄岩的熔体岩石反应有关。铬铁矿形成后的晚期岩浆阶段使得自形程度较高的PGM(如硫锇矿)和BMS(如赫硫镍矿)形成，随后向热液阶段转变的过程中，由于温压条件改变、热液蚀变，形成了萨尔托海铬铁矿中Fe- Ni- As- S和PGM矿物组合。 相似文献
5.
6.
富铝型豆荚状铬铁矿床的成矿模式 总被引：2，自引：0，他引：2
富铝型豆荚状铬铁矿床系指产于ＰＴＧ系列蛇绿岩套地幔橄榄岩中的矿石，以富铝（Ａｌ２Ｏ３＞２０％）、低铬（Ｃｒ２Ｏ３＜４５％）为特征的铬铁矿床。该类型矿床以萨尔托海、贺根山及洪古勒楞铬铁矿床为代表。含富铝型铬铁矿床的岩体以伴有丰富的基性分凝体、含长地幔橄榄岩的出现以及矿石四周发育绿泥石薄壳而区别于含富铬型铬铁矿床的岩体。作者的研究表明富铝型铬铁矿床是原始地幔岩不同程度部分熔融再造的产物。富铬矿浆代表高度部分熔融的最终残余。富铝型铬铁矿床的成矿模式有两种：一为原始地幔岩中低度部分熔融再造的产物，以缺失高熔杂岩带为特征，属中低熔再造成矿模式，以洪古勒楞矿床为代表；另一种为原始地幔岩高度熔融再造的产物，以发育高熔杂岩带为特征，基性熔体与富铬矿浆之间曾发生了再平衡作用，属高熔再造－再平衡成矿模式，以萨尔托海及贺根山矿床为代表。 相似文献
7.
豆荚状铬铁矿是十分重要的战略资源,目前学者对它们的成因尚未形成统一的认识。先前的研究主要从岩石学、地球化学和地质年代学等方面对铬铁矿的成因进行了约束,但对铬铁矿包裹体类型及其反映的地质过程还缺乏系统的总结和研究。通过对不同岩体的铬铁矿中矿物包裹体进行详细的研究,发现铬铁矿中含有丰富的矿物包裹体,分为5大类：(1)无水硅酸盐类矿物包裹体,包括橄榄石、斜方辉石、单斜辉石等;(2)含水矿物,包括角闪石、绿泥石、蛇纹石等;(3)含铂族元素矿物和硫化物,包括Os-Ir合金、Pt-Fe合金、自然Os和自然Ir,以及黄铁矿、黄铜矿、磁黄铁矿等;(4)壳源矿物,包括锆石、金红石、石英、钙铬榴石等;(5)异常矿物,包括金刚石、碳硅石、柯石英等超高压矿物,以及自然镍、自然铬、自然铁和自然钛等。通过对比研究,确定它们形成于不同期次,进而初步拟定豆荚状铬铁矿形成过程存在4个阶段,分别为地幔深部的地幔柱/地幔对流、大洋岩石圈中地幔橄榄岩的部分熔融/岩浆结晶分异、俯冲带环境中的岩石-熔体反应和后期的热液蚀变/流体改造。认为铬铁矿中矿物包裹体记录了铬铁矿成矿各个时期的环境条件,针对铬铁矿中包裹体的详细研究可以更加准... 相似文献
8.
全球多地蛇绿岩型地幔橄榄岩和铬铁矿中发现微粒金刚石，并在中国西藏南部和俄罗斯乌拉尔北部的蛇绿岩铬铁矿中发现原位产出的金刚石，认为是地球上金刚石的一种新的产出类型，不同于金伯利岩型金刚石和超高压变质型金刚石。它们与呈斯石英假象的柯石英、高压相的铬铁矿和青松矿等高压矿物以及碳硅石和单质矿物等强还原矿物伴生，指示蛇绿岩中的这些矿物组合形成于深度150~300 km或者更深的地幔。金刚石具有很轻的C同位素组成（δ13C-18‰~-28‰），并出现多种含Mn矿物和壳源成分包裹体。研究认为它们曾是早期深俯冲的地壳物质，达到>300 km深部地幔或地幔过渡带后，经历了熔融并产生新的流体，后者在上升过程中结晶成新的超高压、强还原矿物组合，通过地幔对流或地幔柱作用被带回到浅部地幔，由此建立了一个俯冲物质深地幔再循环的新模式。蛇绿岩型地幔橄榄岩和铬铁矿中发现金刚石等深部矿物，质疑了蛇绿岩铬铁矿形成于浅部地幔的已有认识，引发了一系列新的科学问题，提出了新的研究方向。 相似文献
9.
前人报道在西藏中生代和俄罗斯极地乌拉尔早古生代蛇绿岩地幔橄榄岩铬铁矿中发现了金刚石等深部地幔矿物,认为需重新考虑铬铁矿浅部成因的传统认识。为了查明不同造山带蛇绿岩的铬铁矿中金刚石等深部矿物的分布规律和豆荚状铬铁矿的成因,笔者开展了内蒙古贺根山晚古生代蛇绿岩中的铬铁矿床的人工重砂矿物学研究,本研究获得约2000 kg的内蒙古贺根山蛇绿岩铬铁矿石样品,对所采样品开展人工重砂选矿,表明该铬铁矿矿石样品中至少有金刚石、碳硅石及其他自然元素类、金属互化物类、氧化物类、硫化物类、硅酸盐类等30余种矿物。内蒙—大兴安岭造山带晚古生代的内蒙古贺根山蛇绿岩带铬铁矿石中,发现金刚石等深部地幔矿物表明,贺根山铬铁矿可能为深部成因。 相似文献
10.
西藏蛇绿岩地幔中的主要自然金属矿物 总被引：9，自引：0，他引：9
在西藏雅鲁藏布江蛇绿岩带的罗布莎蛇绿岩块的豆荚状铬铁矿床中 ,揭示出一个由 70～ 80种矿物组成的地幔矿物群 ,包括自然金属、合金、硫 (砷 )化物、氧化物和硅酸盐等。这些矿物呈包裹体或脉石产于铬铁矿石中 ,经人工重砂分析 ,自然元素矿物有自然硅、自然铁、自然锌、自然铅、自然铝、自然铬、自然锡、自然镍、自然钨、自然钛、自然锇、自然铱、自然钌、自然钯、石墨、金刚石、自然金和自然银等。文中选择一些自然元素矿物 ,探索这些地幔矿物特点以及蛇绿岩和铬铁矿的形成机制。根据共生矿物群以及罗布莎地幔橄榄岩为新鲜的未蛇纹石化的岩石 ,认为罗布莎自然元素矿物与蛇纹石化作用无关。它们可能是在地核形成时期滞留于地幔中的成核物质 ,抑或是核幔之间化学反应的产物 ,后来被铬铁矿矿浆捕获 ,并同铬铁矿一起由地幔柱作用和板块作用侵位于浅部并仰冲出露于地表。 相似文献
11.
《International Geology Review》2012,54(7):678-686
Podiform chromitites include both high-Cr and high-Al varieties with distinctly different geochemical characteristics. A comparison of high-Cr and high-Al deposits in western China has demonstrated that both varieties are magmatic in origin and that chromite compositions reflect the degree of partial melting in the mantle source area. The chromitites of the Sartohay ophiolite of Xinjiang Province have chromites with low Cr numbers (<70) and are hosted in highly depleted harzburgites. In both deposits melt/wall rock interaction has produced highly depleted dunite envelopes around the chromitites. In Sartohay, high-Al magmas reacted with lherzolites to produce high-Al dunites and harzburgites, whereas in Luobusa the reaction between more refractory melts and depleted harzburgites yielded only highly depleted dunite envelopes. This study suggests that high-Al deposits can occur in weakly depleted mantle sequences (lherzolite ophiolite type or transitional type) that are locally depleted by melt/rock reaction in the immediate vicinity of the chromitite pods. 相似文献
12.
豆荚状铬铁矿是蛇绿岩中特有的一类矿产，按其化学成分可分为高Cr型和高Al型两种。其中的PGE主要以RuS2和Os、Ir、Ru合金等包体形式存在，或以类质同像形式进入铬铁矿晶格。两种类型的铬铁矿均表现出负倾斜型PGE配分模式，其Pt、Pd含量相近；与高Al型铬铁矿相比，高Cr型铬铁矿有更高的Os、Ir、Ru含量，部分豆荚状铬铁矿表现出Pt、Pd相对富集的平坦到正倾斜型PGE配分模式。目前对豆荚状铬铁矿PGE含量及配分模式还缺少一个统一的解释，但其PGE地球化学可为豆荚状铬铁矿的成因及构造背景解释提供更多的信息。 相似文献
13.
İbrahim Uysal Mahmud Tarkian M. Burhan Sadiklar Federica Zaccarini Thomas Meisel Giorgio Garuti Stefanie Heidrich 《Contributions to Mineralogy and Petrology》2009,158(5):659-674
Ultramafic rocks around the city of Muğla in SW Turkey are represented by mantle peridotites depleted to various degrees,
ranging from cpx-rich harzburgites to depleted harzburgite and dunite. Cpx-rich harzburgites are thought to be the residua
left after extraction of MORB-type basalt, from which high-Al chromitite [49.2 < Cr# = 100 × Cr/(Cr + Al) < 53.5] crystallised
with a higher proportion of 187Os/188Os (average of 0.1361). However, depleted harzburgites are assumed to be the residua left after extraction of hydrous boninitic
melt produced by second stage partial melting of already depleted mantle due to a subducting slab, from which high-Cr chromitites
(64.2 < Cr# < 85.9) with lower and heterogeneous 187Os/188Os ratio (average of 0.1324) were crystallised as a result of melt–rock interaction in a supra-subduction environment. Dunites
around the chromite deposits are considered to be the product of melt–peridotite interaction. Most of the chromitites contain
high-Cr chromite and display enrichment in IPGE (Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with PGE concentrations between 61 and
1,305 ppb. Consistently, laurite-erlichmanite series minerals with various Os concentrations are found to be the most abundant
PGM inclusions in chromite. Os–Ir–Ru alloy, irarsite, and kashinite, as well as Pt–Fe alloy and Pt-oxide, which are not common
in ophiolitic chromitites, were also detected as magmatic PGM inclusions. Pentlandite, millerite, and, rarely heazlewoodite
form the magmatic inclusions of base-metal sulphide. The presence of olivine and clinopyroxene, as well as hydrous silicate
inclusions such as amphibole and phlogopite, in high-Cr chromitite supports the idea that high-Cr chromitites were formed
in a supra-subduction environment. 相似文献
14.
G. N. Savelieva V. G. Batanova N. A. Berezhnaya S. L. Presnyakov A. V. Sobolev S. G. Skublov I. A. Belousov 《Geotectonics》2013,47(3):167-179
The paper presents new determinations of the U-Pb zircon age of high-Al chromitite from dunite of the mantle section of the Voikar-Synya massif at the Kershor site in the boundary zone with rocks of the dunite-wehrlite-clinopyroxenite complex. The high-Cr chromitite from dunite in the central part of the same massif contains zircon dated at ca. 0.6 Ga [10]. It is suggested that Paleoproterozoic (2.0?1.9 Ga) zircons from chromitites of the mantle section near the petrological Moho boundary were formed in the course of partial melting of peridotites and/or their interaction with migrating MORB-type melts. The occurrence of Vendian and Paleoproterozoic zircons in chromitites from different parts of the mantle section, as well as previously published petrological, geochemical, and geological data [2, 11, 22] allow us to suggest a complex multistage evolution of the mantle section in ophiolites. The arguments stated below show that chromitites and host dunites could have been formed at different times and were probably related to different processes. Thus, not only various complexes of the pre-Paleozoic oceanic crust reworked in the suprasubduction setting differ in age, but also the mantle rock of similar petrography, vary in the time of their formation. 相似文献
15.
On the basis of their mineral chemistry, podiform chromitites are divided into high-Al (Cr# = 20–60) (Cr# = 100 1 Cr/(Cr + Al)) and high-Cr (Cr# = 60–80) varieties. Typically, only one type occurs in a given peridotite massif, although some ophiolites contain several massifs that can have different chromitite compositions. We report here the occurrence of both high-Cr and high-Al chromitite in a single massif in China, the Dongbo mafic-ultramafic body in the western Yarlung-Zangbo suture zone of Tibet. This massif consists mainly of mantle peridotites, with lesser pyroxenite and gabbro. The mantle peridotites are mainly composed of harzburgites and minor lherzolites; a few dike-like bodies of dunite are also present. Seven small, lenticular bodies of chromitite ores have been found in the harzburgites, with ore textures ranging from massive through disseminated to sparsely disseminated; no nodular ore has been observed. Individual chromitite pods are 1–3 m long, 0.2–2 m wide and strike NW, parallel to the main trend of the peridotites. Chromitite pods 3, 4, and 5 consist of high-Al chromitite (Cr# = 12–47), whereas pods 1 and 2 are high-Cr varieties (Cr# = 73 to 77). In addition to chromian spinel, all of the pods contain minor olivine, amphibole and serpentine. Mineral structures show that the peridotites experienced plastic deformation and partial melting. The mineralogy and geochemistry of the Dongbo peridotites suggest that they formed originally at a mid-ocean ridge (MOR), and were later modified by suprasubduction zone (SSZ) melts/fluids. We interpret the high-Al chromitites as the products of early mid-ocean ridge basalt (MORB) or arc tholeiite magmas, whereas the high-Cr varieties are thought to have been generated by later SSZ melts. 相似文献
16.
Argirios Kapsiotis Tassos A. Grammatikopoulos Basilios Tsikouras Konstantin Hatzipanagiotou Federica Zaccarini Giorgio Garuti 《Mineralogy and Petrology》2011,101(1-2):129-150
The Pindos ophiolite complex, located in the northwestern part of continental Greece, hosts various chromite deposits of both metallurgical (high-Cr) and refractory (high-Al) type. The Pefki chromitites are banded and sub-concordant to the surrounding serpentinized dunites. The Cr# [Cr/(Cr?+?Al)] of magnesiochromite varies between 0.75 and 0.79. The total PGE grade ranges from 105.9 up to 300.0?ppb. IPGE are higher than PPGE, typical of mantle hosted ophiolitic chromitites. The PGM assemblage in chromitites comprises anduoite, ruarsite, laurite, irarsite, sperrylite, hollingworthite, Os-Ru-Ir alloys including osmium and rutheniridosmine, Ru-bearing oxides, braggite, paolovite, platarsite, cooperite, vysotskite, and palladodymite. Iridarsenite and omeiite were also observed as exsolutions in other PGM. Rare electrum and native Ag are recovered in concentrates. This PGM assemblage is of great petrogenetic importance because it is significantly different from that commonly observed in podiform mantle-hosted and banded crustal-hosted ophiolitic chromitites. PGE chalcogenides of As and S are primary, and possibly crystallized directly from a progressively enriched in As boninitic melt before or during magnesiochromite precipitation. The presence of Ru-bearing oxides implies simultaneous desulfurization and dearsenication processes. Chemically zoned laurite and composite paolovite-electrum intergrowths are indicative of the relatively high mobility of certain PGE at low temperatures under locally oxidizing conditions. The PGM assemblage and chemistry, in conjunction with geological and petrologic data of the studied chromitites, indicate that it is characteristic of chromitites found within or close to the petrologic Moho. Furthermore, the strikingly different PGM assemblages between the high-Cr chromitites within the Pindos massif is suggestive of non-homogeneous group of ores. 相似文献
17.
《International Geology Review》2012,54(6):494-507
The Jurassic Mayari-Baracoa ophiolite belt and associated Cretaceous volcanic rocks form the Zaza zone of eastern Cuba. This zone has been traditionally considered allochthonous and overrides a passive continental margin, the Cuban foreland. The ophiolites consist of mantle tectonites and cumulates, overlain by a volcanicarc sequence including porphyritic basalts and andesitic lavas. These are, in turn, overlain by a sequence of tuffs and epiclastic sedimentary rocks. There are two ophiolitic massifs in the belt, the Mayari-Cristal Massif (MCM) and the Moa-Baracoa Massif (MBM). The MCM consists of harzburgites and dunites with abundant high-Cr podiform chromitites and dikes of gabbro and pyroxenite. The MBM, on the other hand, is composed of harzburgites with abundant high-Al podiform chromitites, cut by troctolite dikes. The two ophiolitic massifs have different REE and PGE patterns and contents. The mantle sequence in the MCM is more depleted than that in the MBM. We suggest that the MCM formed beneath a volcanic island arc and the MBM beneath a nascent spreading center in a back-arc basin. The two massifs form a paired ophiolite belt. 相似文献
18.
Petrological characteristics of podiform chromitites and associated peridotites of the Pan African Proterozoic ophiolite complexes of Egypt 总被引：10，自引：0，他引：10
Mafic-ultramafic fragments of a dismembered ophiolite complex are abundant in the late Precambrian Pan African belt of the
Eastern Desert of Egypt and north-east Sudan. The ultramafic bodies in the Eastern Desert of Egypt are mostly characterised
by the harzburgite–dunite–chromitite association. Because of their severe metamorphism, almost all primary silicates were
converted to secondary minerals and we use the chrome spinel as a reliable petrogenetic indicator. The podiform chromitite
deposits are common as small and irregularly shaped masses in the central and southern parts of the Eastern Desert. They strongly
vary in texture, degree of alteration and chemical composition of chrome spinel. The podiform chromitites exhibit a wide range
of composition from high Cr to high Al varieties. The Cr of chrome spinel ranges from 0.65 to 0.85 in dunite, quite similar
in the high-Cr chromitite, whereas it is around 0.5 in harzburgite. Primary hydrous mineral inclusions, amphibole and phlogopite,
in chrome spinel are reported for the first time from the Pan African Proterozoic podiform chromitites. The petrological characteristics
of Pan African podiform chromitites and associated peridotites of Egypt are similar to those of Phanerozoic ophiolites. The
Proterozoic podiform chromitites may have formed in the same way as the Phanerozoic ones, namely by melt-harzburgite reaction
and subsequent melt mixing. The similarity of the mantle section of the late Proterozoic and the Phanerozoic ophiolites suggests
that the thermal conditions controlling genesis of the crust–mantle system basically have not changed since the late Proterozoic
era. The Pan African harzburgite is very similar to abyssal peridotite at fast-spreading ridges, and the high-Cr, low-Ti character
of spinel in chromitite and dunite indicates a genetic link with a supra-subduction zone setting. The late Proterozoic ophiolites
of Egypt are possibly a fragment of oceanic lithosphere modified by arc-related magmatic rocks, or a fragment of back-arc
basin lithosphere.
Received: 26 October 1999 / Accepted: 28 June 2000 相似文献