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1.
A. R. Cabral G. Beaudoin M. Choquette B. Lehmann J. C. Polônia 《Mineralogy and Petrology》2007,90(1-2):141-150
Summary The Córrego Bom Sucesso alluvial deposit near Serro, Minas Gerais, probably provided the specimens from which the element
palladium was first discovered. Its Pt–Pd nuggets are characteristically botryoidal, arborescent and coralloidal, and exhibit
an external halo with the composition of palladiferous platinum to virtually pure platinum. X-ray mapping of an arborescent
Pt–Pd nugget from the historical occurrence documents selective palladium depletion, similar to the high-fineness gold haloes
developed on detrital Au–Ag grains under supergene conditions. The Pd-depleted alteration zone truncates inclusions of crystals
stoichiometrically close to PdPt within the Pt–Pd aggregate. Selective metal leaching in the weathering environment can account
for the frequently observed Pt-enriched rims on alluvial platiniferous alloys which may lead to the formation of platinum
nuggets at an advanced degree of weathering.
Present address: Department of Geology: Exploration Geology Rhodes University PO Box 94, Grahamstown, 6140 South Africa 相似文献
2.
Keiko Hattori Louis J. Cabri Stanley R. Hart 《Contributions to Mineralogy and Petrology》1991,109(1):10-18
Osmium isotope ratios for two types of platinum group mineral (PGM) nuggets of eluvial (residual) origin, associated with the Freetown Layered Gabbro Complex, were determined in-situ using an ion microprobe. The values for erlichmanite nuggets are 1.08. Those for PGM inclusions in Pt–Fe alloy nuggets are higher, ranging from 1.2 to 2.1. Ratios of187Os/186Os vary between the nuggets, but they are consistent within individual nuggest. The data suggest early formation of the erlichmanite nuggets, prior to a postulated substantial contribution of crustal Os. The Pt–Fe alloy nuggets, on the other hand, were formed later in a residual melt which was contaminated by crustal Os due to the assimilation (<10%) or the gaseous/fluid transport of Os from Archaean host rocks into the magma. The lack of systematic mineralogical and chemical changes of the Complex and extensive granulitization in the adjacent host rocks and xenoliths may favor the latter process.The lack of high187Os/186Os ratios, consistent187Os/186Os values within individual nuggets and their textures and mineralogy suggest that the studied PGM nuggets were not formed during lateritization or in low-temperature depositional environments. 相似文献
3.
INAA of ten coarse-grained, melilite-spinel-bearing inclusions in the Allende meteorite for Ca, Sc, Hf, Ta, W, Os, Ir, Ru, La, Ce, Sm, Eu, Tb, Dy, Yb, Fe, Co, Cr and Au reveals that all of the refractory elements are enriched by a mean factor of 18.6 relative to their concentrations in Cl chondrites, consistent with a high-temperature condensation origin for the inclusions. Os, Ir and Ru were probably incorporated by the inclusions as tiny nuggets of an alloy in which they were dissolved in cosmic proportion to one another. Sc and Hf entered the inclusions in a separate phase, also in cosmic proportion, accompanied by a fraction of the REE. Bulk REE abundances are independent of the major minerals in the inclusions; yet, data from mineral separates suggest that the REE were partitioned between coexisting melilite and pyroxene according to crystal structure controls. A two-stage model is proposed in which the REE first entered the inclusions as trace, refractory condensate phases and then re-distributed themselves between the crystallizing major phases after the inclusions were melted in the nebula. 相似文献
4.
通过能谱和电子探针分析了西藏罗布莎豆荚状铬铁矿石刚玉中的含钛合金和含钛氧化物包裹体特征,分析发现刚玉中含Ti合金矿物包裹体主要有Ti-N、Ti-B、Ti-C、Ti-Si-P和Ti-Si-Fe以及Ti-Al-Zr氧化物.Ti-N合金呈磨圆状、梅花状,粒度约17 μm×35 μm;Ti-B合金呈长柱状,10 μm×58 μm;Ti-C合金呈自形、他形,粒度约40 μm×50 μm;Ti-Si-P和Ti-Si-Fe合金成分不均一,呈一个熔融体包裹在刚玉中;Ti-Al-Zr氧化物成分纯净.结合铬铁矿石中发现大量的微粒金刚石和碳硅石等超高压异常地幔矿物,提出罗布莎铬铁矿石中的刚玉及其中的特殊矿物包裹体组合形成于高压环境的深部地幔. 相似文献
5.
Summary ?Platinum nuggets recovered from a placer located about 6.5 km NNW of Kompiam (Enga Province, New Guinea Highlands) show characteristics
typical of PGE mineralization from Alaskan-type intrusions. They are composed of (Pt, Fe) alloys with average (Fe+Cu) concentrations
varying from 14 to 17 at.%, that are significantly lower than required for isoferroplatinum indicating a disordered structure.
Rare nuggets contain exsolutions of native osmium. Platinum crystallized after chromite and some silicates (diopsidic clinopyroxene
and amphibole). Chromite included in nuggets shows a high Fe3+/M3+ ratio and high TiO2 content. The TiO2 concentration in chromite can be used as a discriminating factor to distinguish between PGM originating from ophiolitic complexes
and those related to Alaskan-type complexes. The chemical composition of the alloys indicates a source strongly depleted in
Ru and Pd while enriched in Pt with respect to chondrites. However, this PGE fractionation cannot be attributed to immiscibility
or sulphuration processes. Two types of silicate inclusions were observed in the Pt nuggets: (1) monomineral inclusions of
a Na-, Ca-, Mg-, Al-silicate (amphibole?), plagioclase of the composition An20–50, and rare diopside representing cumulate mineral phases caught by the ore-forming liquid; (2) hydromagmatic inclusions of
ore-forming silicate liquid manifested by skeletal clinopyroxene crystals, pargasitic amphibole and albite. The chemical composition
of clinopyroxene crystallized from the hydromagmatic liquid indicates that the PGE transporting system had an alkaline nature.
It is therefore affirmed that the platinum nuggets from the Kompiam area originated from an Alaskan-type complex, probably
represented by the Maramuni diorite associated with andesitic lavas and pyroclastics. Platinum-bearing placers in Papua New
Guinea are thus derived from two magmatic sources: ophiolitic complexes and Alaskan-type intrusions.
Received October 15, 1998;/revised version accepted April 9, 1999 相似文献
Résumé ?Pépites de platine de la région de Kompiam, Province d’Enga, Papouasie Nouvelle Guinée: mise en évidence d’un complexe alaskéen Des pépites de platine trouvées dans un placer situé au sein de New Guinea Highlands, à 6,5 km environ NNO de Kompiam (Province d’Enga) présentent des caractéristiques d’une minéralisation liée à un complexe alaskéen. Elles sont constituées d’alliages (Pt, Fe) avec des teneurs moyennes en (Fe+Cu) allant de 14 à 17% at., nettement plus basses que celles d’isoferroplatine. Ceci fait entrevoir leur structure désordonnée. Les pépites contiennent rarement des exsolutions d’osmium natif. La cristallisation du platine est postérieure à la chromite et certains silicates (diopside et amphibole). La chromite incluse dans les pépites se distingue par un rapport Fe3+/M3+élevé et par une forte teneur en TiO2. Ces caractéristiques sont typiques des chromites provenant des intrusions de type alaskéen. La concentration en TiO2 de la chromite peut être utilisée comme un facteur discriminant, permettant de préciser si les platino?des proviennent des complexes ophiolitiques ou des intrusions alaskéennes. La composition des alliages indique une source fortement appauvrie en Ru et Pd et enrichie en Pt par rapport aux chondrites. Ce fractionnement ne peut pas être attribuéà des processus d’immiscibilité ou de sulphuration. Deux types d’inclusions silicatées ont été observées dans les alliages (Pt,Fe): (1) inclusions correspondant à un liquide hydromagmatique du système minéralisant, constituées de: clinopyroxène en cristaux squelettiques, amphibole pargasitique et albite; (2) inclusions monominérales de diopside, d’un silicate à Al, Mg, Ca et Na (amphibole?) et de plagioclase An20–50, représentant des minéraux de cumulats piégés par le système minéralisant. Le chimisme du clinopyroxène cristalliséà partir du liquide hydromagmatique, met en évidence une composition alcaline du système transportant les PGE. Les pépites de platine du placer de la région de Kompiam proviennent d’un complexe alaskéen, probablement de la diorite de Maramuni associée à des laves et pyroclastites andésitiques. Il appara?t par conséquent que les placers, porteurs de platino?des en Papouasie Nouvelle Guinée sont issus de deux sources magmatiques bien distinctes: complexes ophiolitiques et intrusions alaskéennes.
Received October 15, 1998;/revised version accepted April 9, 1999 相似文献
6.
Dr. E. Slansky Dr. L. M. Barron Mr. D. Suppel Dr. Z. Johan Dr. M. Ohnenstetter 《Mineralogy and Petrology》1991,43(3):161-180
Summary The Fiîeld Platinum Province, New South Wales, Australia, contains Alaskan-type mafic-ultramafic complexes with notable PGE mineralization. This mineralization has evolved in several stages ranging from high- to low-temperature hydromagmatic, with weathering and latertic concentration followed by erosion and placer accumulation in alluvial channels. This last stage has furnished the largest quantity of platinum from the area. PGM nuggets were collected in a corridor, south and southeast of Fifield, joining the leads exploited in the past and continuing northwards.The following PGM association was observed in the nuggets: isoferroplatinum, native osmium, osmiridium, iridosmine, laurite and bowieite. Isoferroplatinum is the matrix mineral in the nuggets, while (It, Os, Pt) alloys occur as exsolutions. The nuggets sometimes carry inclusions of euhedral chromite. Two sulphidic phases-laurite and bowieite-are rare and occur embedded as trapped early formed crystals in isoferroplatinum.This PGM association is entirely different, when compared to the PGM in pegmatoid clinopyroxenites (P-units) described previously (Johan et al., 1989), both as to the nature of the mineral species and to the chemistry of isoferroplatinum common to both occurrences. This proves conclusively that the source for the alluvial nuggets must be of a different nature from the presently established hard rock mineralization.The co-existence of iridosmine and osmiridium exsolutions in isoferroplatinum proves a high temperature origin for the nuggets, and excludes a low temperature origin through in situ overgrowth from aqueous solutions in either the laterite or the erosive profile. The presence of chromite inclusions of a certain diagnostic composition indicates that the original host rock for the nuggets was a chromitite within dunite. The chemistry of the coexisting alloy phases provides a temperature estimate of about 800 °C, which is compatible with Alaskan complexes in Alaska and the Urals. The textural study of the nuggets shows different rates of cooling from nugget to nugget, with many textures relating to heterogeneous nucleation in metallurgical processes.
With 3 plates and 4 figures 相似文献
Platin-Mineralisation in Intrusiv-Komplexen des Alaska-Types bei Fifield, NSW, Australien. Teil 2. Platingruppen-Minerale in Seifenlagerstätten in Fifield
Zusammenfassung Die Platin-Provinz von Fifeld, New South Wales, Australien, enthält mafischultramafische Komplexe des Alaska-Typs mit beachtlicher PGE Mineralisation. Diese hat sich in verschiedenen Stadien entwickelt, die von hoch- bis tief- temperiert hydromagmatisch reichen, und von Verwitterungsbildungen, lateritischer Konzentration, Erosion und Seifenbildung in alluvialen Rinnen gefolgt wurde. Dieses letzte Stadium hat bisher die größte Menge an Platin produziert. PGM Nuggets wurden in einem Korridor südlich und südöstlich von Fifield gesammelt, und diese setzten sich in den Anreicherungen fort, die in der Vergangenheit ausgebeutet wurden.Die folgende PGM Paragenese wurde in den Nuggets beobachtet: Isoferroplatin, gediegen Osmium, Osmiridium, Iridosmin, Laurit und Bowieit. Isoferroplatin ist das Matrix-Mineral der Nuggets, während (Ir, Os, Pt)—Legierungen als Entmischungen erscheinen. Die Nuggets enthalten gelegentlich Einschlüsse von isomorphem Chromit. Zwei Sulfidphasen—Laurit und Bowieit-sind selten und kommen als früh gebildete Kristalle im Isoferroplatin vor.Diese PGM-Paragenese unterscheidet sich grundsätzlich von der in pegmatoiden Klinopyroxeniten (P-units;Johan et al., 1989). Dies betrifft sowohl die Art der Minerale wie auch die chemische Zusammensetzung von Isoferroplatin. Diese Beobachtungen zeigen in überzeugender Weise, daß die Quelle für die alluvialen Nuggets nicht in der jetzt nachgewiesenen Vererzung in Festgesteinen gesucht werden kann.Die Koexistenz von Iridosmin- und Osmiridium-Entmischungen in Isoferroplatin weist auf die hohe Bildungstemperatur der Nuggets hin und schließt eine Tieftemperatur-Bildung durch in situ Überwachsung aus wässerigen Lösungen entweder im Laterit oder im Erosionsprofil aus. Die Anwesenheit von Chromiteinschlüssen definierter Zusammensetzung zeigt, daß das ursprüngliche Muttergestein der Nuggets ein Chromitit innerhalb von Duniten war. Die chemische Zusammensetzung der koexistierenden Legierungen weist auf Temperaturen von ungefähr 800°C; das ist in guter übereinstimmung mit Daten von den Komplexen in Alaska und im Ural. Texturelle Untersuchungen lassen Abkühlungsraten erkennen, die von Nugget zu Nugget schwanken; viele der beobachteten Texturen lassen sich mit heterogener Nukleation in metallurgischen Prozessen vergleichen.
With 3 plates and 4 figures 相似文献
7.
A rare collection of centimetre-scale proximal gold nuggets has been examined in the context of the Late Pleistocene to Holocene eluvial and colluvial sediments in which they occur, in a range of environments from arid temperate to periglacial. Liberation of supergene nuggets from their basement source in fault zones occurred progressively by physical erosion as the host basement rocks were uplifted between middle Miocene and Holocene. The host sediments are made up of poorly sorted angular greenschist facies schist debris. Some nuggets were recycled through several generations of these colluvial deposits, and additional nuggets were liberated to younger sediments during this time. The nuggets did not migrate laterally more than a few tens of metres during this repeated recycling, and were passively elevated vertically with the rising basement on to the crest and slopes of a 1600 m high mountain range. The most recently liberated nuggets retain almost all the morphological features of their supergene origin, including coarse (cm scale) crystal shapes, delicate crystalline internal structure, and imprints of oxidised pyrite crystals. Minor transport in colluvium has caused some abrasion and rounding of gold crystals. Repeated recycling progressively obscured the crystal shapes, although relict crystals are still recognisable on parts of most nuggets. Differential timing of liberation from basement has resulted in a wide range of rounding effects in groups of closely-coexisting nuggets. Variably crystalline gold overgrowths (micron scale) coat abraded surfaces of all or part of most nuggets, commonly intergrown with authigenic smectite clay minerals. These overgrowths developed from alkaline groundwater (pH 7–9) that had undergone extensive chemical interaction with labile minerals in the host colluvium. Abrasion during recycling removed some of the overgrowths, but this was replaced in the new sedimentary hosts. Physical and chemical processes affecting nuggets in these sediments have similarly affected eluvial and colluvial nuggets in a wide range of settings around the world, including Yukon (Canada), California (USA) and arid parts of Australia. 相似文献
8.
Z. Johan 《Mineralogy and Petrology》2006,87(1-2):1-30
Summary The study of platinum-group minerals (PGM) concentrates from the Nizhni Tagil placers related to the Soloviev Mountain (Gora
Solovieva) Uralian-Alaskan-type intrusion revealed a predominance of (Pt, Fe) alloys over Ir-, and Os-bearing alloys. (Pt,
Fe) alloys (“isoferroplatinum-type”) are interstitial with respect to chromite and show important variations in their chemical
compositions, which are, however, falling within the experimentally determined stability field of isoferroplatinum. Tetraferroplatinum,
enriched in Cu and Ni and tulameenite represent low-temperature mineral phases replacing (Pt, Fe) alloys. Alloys belonging
to the Os–Ir–Ru ternary system have compositions corresponding to native osmium, iridium and ruthenium, respectively, and
to rutheniridosmine. Osmium exsolutions appear in Ir-, and (Pt, Fe) alloys, and iridium exsolutions in (Pt, Fe) alloys. Laurite
is a high-temperature phase included in native iridium and (Pt, Fe) alloys. Low-temperature PGM association comprises Ir-bearing
sulpharsenides, including a phase (Ir, Os, Fe, Pt, Ru, Ni)3(As, Sb)0.85S, and a palladium antimonide Pd20Sb7. These two phases were previously unknown in nature. Furthermore, native palladium occurs in the studied concentrates. This
low-temperature paragenesis indicates an interaction of Pt-, Os-, Ir- and Ru-bearing alloys with late fluids enriched in volatiles,
As and Sb. The chromite composition is characterized by the predominance of Cr3+ → Fe3+ substitution like in other Uralian-Alaskan-type intrusions; that indicates a fO2 variation during the chromite precipitation.
Monomineralic inclusions of euhedral clinopyroxene and chromite crystals in (Pt, Fe) alloys were observed. Furthermore, (Pt,
Fe) alloys contain polyphase silicate inclusions, which occupy the alloy negative crystals. Two types of silicate inclusions
were recognized: (1) Low-pressure inclusions composed of amphibole, biotite, Jd-poor clinopyroxene, magnetite, apatite and
glass; (2) High-pressure inclusions include: omphacitic clinopyroxene (up to 56 mol.% Jd), tremolite, muscovite, apatite,
titanite and glass. In this case, the clinopyroxene is strongly zoned, revealing a pressure drop from about 25 to 5 kbar.
The chemical composition of glass is corundum-normative and its H2O content varies from about 12 to 15 wt.%. The composition of magmatic melts, from which the silicate inclusions have originated
was estimated using EPMA and image analysis interpreted by stereology. Their compositions are close to those obtained experimentally
by hydrous partial melting of upper mantle rocks. The interpretation of analytical data shows that magmatic melts entrapped
by (Pt, Fe) alloys crystallized from about 1100 to 700 °C. The (Pt, Fe) alloys formed after the crystallization of chromite,
clinopyroxene and albite. Consequently, the precipitation temperature of (Pt, Fe) alloys is estimated at about 900 °C. The
significant pressure drop implies a decrease of volatile concentrations in the magmatic melt and the possible formation of
a fluid phase, which might have generated, the precipitation of chromite and PGM. 相似文献
9.
A. A. Borisov 《Petrology》2016,24(2):117-126
Mutual interaction of redox pairs resulting in the origin or decomposition of a metal phase is analyzed based on the concept of intrinsic oxygen fugacity. Reactions are suggested that may be responsible for the synthesis (or decomposition) of submicrometer-sized metal nuggets when experimental melts are quenched and can explain the possible crystallization of Pt—Fe alloys when basaltic melts cool and elucidate the nature of color of Au-bearing ruby glass. Possible disproportionation reactions of certain lower oxides into a higher oxide and respective metal in cooled silicate melts are discussed. 相似文献
10.
K. N. Malitch T. Auge I. Yu. Badanina M. M. Goncharov S. A. Junk E. Pernicka 《Mineralogy and Petrology》2002,76(1-2):121-148
Summary ?Geological, mineralogical and Os isotopic data for detrital PGE-mineralization derived from the Guli and Bor-Uryah ultramafic
massifs, within the Maimecha-Kotui Province (the northern part of the Siberian Platform, Russia), are presented for the first
time. The detrital platinum-group minerals (PGM) are dominated by Os–Ir–(Ru) species, which is typical for ophiolites or Alpine-type
complexes. However, the PGM assemblage in the placers investigated is similar to that derived from zoned platiniferous clinopyroxenite–dunite
massifs (also known as Uralian-, Alaskan-type and Aldan-type massifs). The unique features of the Au-PGE placers at Guli are
(1) the dominance of Os-rich alloys over other PGM and Au, and (2) the considerable predicted resources of noble metals, particularly
osmium.
Dominant chromite, olivine and clinopyroxene inclusions recorded in Os–Ir–(Ru) alloys imply that they were derived from ultramafic
sources (e.g., chromitite, dunite and clinopyroxenite). The first in situ osmium-isotope measurements by laser ablation -
multiple collector - inductively coupled plasma mass spectrometry of different, intimately intergrown, PGM (e.g., laurite
and Os-rich alloys) in various nuggets from Guli have revealed low 187Os/188Os and γOs values. They yield a very narrow range of 187Os/188Os (0.12432 to 0.12472) and γOs (− 2.39 to − 2.07). These values are indicative of a common chondritic or subchondritic mantle
source of PGE. 187Os/188Os and γOs values of Os-rich alloys, derived from the Bor-Uryah massif, are different (i.e., γOs ranges from − 2.67 to − 1.30).
The mineral-isotopic data obtained are consistent with the conclusion that the PGM were derived from parent ultramafic source
rocks. Os-isotope model ages in the range of 495 to 240 Ma constrain the age of ultramafic protoliths in the northern part
of the Siberian Craton. The variation in 187Os/188Os values for detrital PGM, where the provenance source is unknown, is considered to be a useful technique for distinguishing
parent bedrock sources.
Received July 12, 2001; revised version accepted December 27, 2001 相似文献
11.
Platinum-group minerals (PGM) have been identified as inclusions in chromite from the Bird River Sill, Manitoba. The inclusions are small (<20 microns) and are commonly euhedral. The PGM inclusions are (Ru, Os, Ir) S2, laurite, and (Os, Ir, Ru alloy), rutheniridosmine: Laurites contain up to 2.99 wt. % palladium. Arsenic content is negligible and no platinum or rhodium has been detected. One platinum-group element alloy contains 0.96 wt. % rhodium but neither platinum nor palladium has been detected. Laurite inclusions in chromite from the ultramafic zone record two compositional trends; first increasing and then decreasing Ru/(Ru+Os+Ir) up section. PGM inclusions and other solid inclusions occur as discrete phases in chromite and are part of the chromite precipitation event. Increasing oxygen fugacity by wall rock assimilation or new magma injection initiates chromite precipitation, locally increasing the sulphur content of the magma to convert PGE alloys to sulphides. 相似文献
12.
西藏康金拉铬铁矿床刚玉中的包裹体研究 总被引：1，自引：1，他引：0
西藏康金拉铬铁矿石的矿物学研究中,发现大量的微粒金刚石和碳硅石等超高压异常地幔矿物,表明它们产在一个强还原的高压环境.本研究在铬铁矿石中还发现了刚玉及其中大量的矿物包裹体.电子探针等方法研究表明,包裹体的种类包括简单氧化物,如金红石;自然钛;Ti-N、Ti-Si、Ti-C、Ti-Si-P、Ti-B等合金类;含稀土元素的硅酸盐矿物,以及一些未知矿物.结合对铬铁矿石中其他矿物的研究成果,认为康金拉铬铁矿石中的刚玉及其中的强还原环境形成的矿物组合形成于深部地幔.因此,康金拉铬铁矿石中的刚玉可以认为是一种新的带有高压环境信息的标志性矿物. 相似文献
13.
Gold grains were studied in 102 till and gravel samples from an area with Au anomalies in the fine fraction of till. The form and size of gold nuggets were studied under the microscope, and the composition of selected grains was determined on a microprobe. The number of visible nuggets per sample was less than 10 per 81. In size, the nuggets were between 0.07 and 1 mm. Most of them were indefinite but flat in form, although idiomorphic gains were also observed. In composition, the gold grains in bedrock differed somewhat from those in till and gravel. Some of the nuggets found in gravel and in till were probably secondary in origin. The possibility that all the grains are not primary is emphasized in the interpretation of geochemical results. 相似文献
14.
《Russian Geology and Geophysics》2014,55(8):945-958
This study is concerned with the typochemical features of heavy-concentrate platinum from diamond placers of the Mayat-Vodorazdel’nyi site in the Anabar River basin. Platinum occurs there as Fe-Pt solid solutions (ferroan platinum of Ru-Rh specialization, ~ 90%), as well as minor Pd- and Ir-ferroplatinum. Among PGE minerals, Os-Ir-Ru alloys and chengdeite are revealed. Inclusions of PGE minerals are thoroughly studied, and the scales of their spread, the composition of mineral phases, and the relations between them are determined. Ruthenium-containing high-Rh ferroplatinum bears a lot of inclusions of Rh-S composition: Rh-containing PGE thiospinels and sulfides and arsenides of Rh, Ru, and Pt. In low-Rh platinum, mineral inclusions are much scarcer and usually form other parageneses. The mineral compositions in the system Rh-S-Ru indicate to the existence of a long isomorphous series Rh3S4-Ru3S4, with the content of Ru3S4 reaching 15 at.%. 相似文献
15.
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
16.
This contribution firstly presents particularities of mineral chemistry of platinum-group elements (PGE) mineralization from
placer deposits linked to the Bor-Uryakh massif of the Maimecha-Kotui Province, northern part of the Siberian Craton. The
chemical composition of PGE mineralization has been studied by electron microprobe analysis. At Bor-Uryakh, main platinum-group
minerals (PGM) comprise Os-Ir and Pt-Fe alloys represented by individual crystals, and polyphase PGM assemblages. The majority
(e.g., 12 out of 19) of the Os-rich nuggets are iridian osmium, with subordinate amounts of native osmium (Os) and chengdeite
(Ir3Fe). Pt-Fe alloys have a stoichiometric composition close to Pt2Fe. According to the nomen-clature by L. Cabri and C. Feather [1975] these minerals correspond to ferroan platinum. Based
on geological position and geochemical features of investigated PGE mineralization the particular rock sources have been established.
This study has demonstrated the similarity of chemical characteristics of Os-Ir and Pt-Fe alloys of the Bor-Uryakh massif
to those of PGM from the Guli massif (Maimecha-Kotui Province), platiniferous zoned-type ultramafic massifs (e.g., Kondyor,
Inagli and Chad) of the Aldan Province and Platinum belt of the Urals (Nizhny Tagil, Kytlym, etc.). 相似文献
17.
Vanavan Ekambaram Iwao Kawabe Tsuyoshi Tanaka Andrew M. Davis Lawrence Grossman 《Geochimica et cosmochimica acta》1984,48(10):2089-2105
Samples from ten refractory inclusions in Murchison, some of which are splits of inclusions whose mineralogical and petrographic characteristics are known, have been analysed for thirty-six elements by neutron activation. Six inclusions have group II or group III patterns or variants of such patterns. Two inclusions, BB-5 and MUCH-1, have large negative Yb anomalies unaccompanied by correspondingly large negative Eu anomalies. It is possible that the latter condensed originally with group III patterns and preferentially took up Eu in later exchange processes under reducing conditions. One inclusion, SH-2, has heavy REE enrichment factors that increase with the refractoriness of the REE, indicating the presence of an extremely high-temperature, or ultrarefractory, REE condensate, but it also has a heavy REE/light REE ratio that indicates mixing of that component with a lower-temperature REE condensate. The frequency of highly fractionated REE patterns and absence of group I patterns suggest that refractory inclusions in Murchison stopped equilibrating with the nebular gas at higher temperatures than most Allende coarse-grained inclusions. The lower Ir/Os and Ru/Re ratios of some Murchison inclusions compared to those of Allende coarse-grained inclusions indicate that condensate alloys that contributed noble metals to the former also stopped equilibrating with the nebular gas at higher temperatures than those that contributed noble metals to the latter. Murchison inclusions tend to be lower in non-refractory elements than Allende coarse-grained inclusions, suggesting that, on average, the former underwent less severe secondary alteration than the latter. 相似文献
18.
On Visualization for Assessing Kriging Outcomes 总被引：7，自引：0，他引：7
James R. Carr 《Mathematical Geology》2002,34(4):421-433
Extant opinion about kriging is that all weights should be positive. Visualizations rendered by converting kriged grids to digital images are presented to show that negative weights may be beneficial to some spatial problems. In particular, variogram models with zero-valued nuggets, already well known to minimize smoothing through kriging, result in a visual resolution substantially superior to that from kriging with a variogram model having a nonzero nugget value in application to satellite acquired data. Negative weights are more likely when using variogram models with zero-valued nuggets, but resultant visualizations often show a smoother transition between extreme data values. This is true even when a variogram model having a nugget value of zero is not optimum with respect to mean square error, as is demonstrated using a nitrate data set. An analogy to digital image processing is used to suggest that the influence of negative weights in kriging is similar to a high-boost kernel. 相似文献
19.
New RNAA determinations of Ba, Sr, Zr, U, Re, Pd, Ag, Zn and Se and INAA measurements of Lu are added to published data for 21 other elements in the same suite of ten samples. On the average, 21 refractory elements are not significantly fractionated from one another. The mean of their enrichment factors relative to Cl chondrites is 17.5 ± 0.4, indicating that the high-temperature condensate inclusions represent 5.7 wt% of the total condensable matter. Os, Ir, Ru, Re and most of the W condensed in one or more refractory siderophile element alloys along with small fractions of the Pd, Co, Au and Ag. The bulk of the Eu and Sr condensed in solid solution in melilite. Sc, Zr, Hf, Ta, U and the remaining REE condensed in a phase whose abundance in the inclusions is negatively correlated with that of melilite, either diopside or one or more minor or trace phases, including perovskite. Ba condensed in a different phase, separately from all these elements. In individual inclusions, fractionations are common between elements which were carried in by different condensate phases. Smaller fractionations are also observed for elements which condensed together. These may be due to variable proportions of them in a common condensate phase in response to different nebular equilibration temperatures or to multiple condensate phases containing different proportions of these elements. Available evidence indicates that some trace elements no longer reside in the phases which carried them into the inclusions, indicating a post-accretion thermal event which redistributed some of them. From the minimal variation of the Zr/Hf ratio in the inclusions, the solar system ratio is estimated to be 29.6 ± 1.8. From the mean U content of the inclusions and estimates of the bulk terrestrial and lunar U abundances, the Earth and Moon are estimated to contain 21% and 22–30% high-temperature condensates, respectively. 相似文献
20.
We present a study of carbonate-bearing polyphase inclusions in garnets from leucocratic granitoids intruding metapelitic granulites of the Southern Marginal Zone (SMZ) of the Neoarchean Limpopo high-grade complex, South Africa, during the post-peak stage (2710–2650 Ma; U-Pb ages for zircons and monazites). Ternary feldspar thermometry suggests that the granitoid magma cooled from temperatures 800–900 °C at a pressure of ca. 6.5 kbar. Abundant CO2 fluid inclusions in quartz and T-XCO2 phase equilibria modeling via PERPLE_X imply action of an essentially carbonic fluid in the granitoids. Cores of almandine-rich garnet grains from the granitoids contain polyphase carbonate-bearing inclusions with a distinct negative crystal shape. The major carbonate in the inclusions is a strongly zoned magnesite-siderite variety, whereas pyrophyllite is the predominant silicate phase. Raman spectra of unexposed inclusions revealed a presence of CO2, as well as CH4 and H2O. The carbonate-bearing inclusions coexist with larger polyphase inclusions composed of biotite, quartz, K-feldspar, plagioclase, sillimanite, which are interpreted as relics of granitic melts. Modeling the mineral assemblage preserved within the carbonate-bearing inclusions shows that their present mineral and chemical compositions are a product of interaction of the trapped aqueous‑carbonic fluid with host garnet during cooling below 400 °C. Despite strong modifications, the inclusions bear evidence for initial saturation of the fluid with Mg‑carbonate. This is taken as an evidence for an origin of the fluids by devolatilization of the Mg-rich carbonate-bearing ultrabasic greenstone rocks of the Kaapvaal Craton that were buried under the SMZ. Being generated at temperatures between 650 and 700 °C, the fluid subsequently participated in anatexis and coexisted with the granite magma during exhumation and interaction of the SMZ granulites with cratonic rocks. 相似文献