中国吉林长白山地区地幔捕虏体中硫化物熔体包裹体

Mantle xenoliths are common in the Cenozoic basalts of the Changbaishan District,Jilin Province,China.Sulfide assemblages in mantle minerals can be divided into three types:isolated sulfide grains,sulfide-meh inclusions and filling sulfides in fractures.Sulfide-meh inclusions occur as single-phase sulfides,sulfide-silicate melt,and CO_2-sulfide-silicate melt inclusions. Isolated sulfide grains are mainly composed of pyrrhotite,but cubanite was found occasionally.Sulfide-meh inclusions are mainly composed of pontlandite and MSS,with small amounts of chalcopyrite and talnakhite.The calculated distribution coefficient K_(D3)for lherzolite are similar to that of mean experimental value.The bulk sulfides in lherzolite were in equilibrium with the enclosing minerals, indicating immiscible sulfide melts captured in partial melting of upper mantle.Sulfide in fractures has higher Ni/Fe and(Fe Ni)/S than those of sulfide melt inclusions.They might represent later metasomatizing fluids in the mantle.Ni/Fe and(Fe Ni)/S increase from isolated grains,sulfide inclusions to sulfides in fractures.These changes were not only affected by temperature and pressure,hut by geochemistry of Ni,Fe and Cu,and sulfur fugacity as well.     

Sulfide-oxide minerals in eclogite from Stockdale Kimberlite,Kansas

The opaque minerals in eclogite xenoliths from Stockdale Kimberlite are rutile, ilmenite, and a complex polysulfide assemblage. Rutile shows exsolutions of ilmenite and spinel. Discrete ilmenite contains up to 10 wt % MgO in solid solution and is a primary mineral, but not of kimberlitic origin. Pyrrhotite containing exsolved pentlandite is the major sulfide mineral, and is usually rimmed by chalcopyrite which may display exsolution of cubanite. A veneer of monosulfide solid solution (12 wt % Ni and 5 wt % Cu) forms a rim on the chalcopyrite-pyrrhotite masses. The simple model of sulfide liquid immiscibility within a silicate melt may account for the origin of the pyrrhotite-pentlandite-chalcopyrite assemblage, but it fails to explain the occurrence within one and the same sulfide globule of a monosulfide_ss rim, separated from an exsolved pyrrhotite core by chalcopyrite. The monosulfide_ss is probably a metastable phase produced by the partial melting of a preexisting sulfide assemblage of similar bulk chemical composition to that existing at present. The melting possibly took place instantaneously when the eclogite was incorporated into the rising hot kimberlitic magma. Fast cooling during the explosive ascent of the kimberlite could have led to the quenching of the monosulfide solid solution. Rutile in the eclogite xenolith was unaffected by the heating, but secondary amphibole and biotite may have possibly formed during this event.     

江苏六合新生代玄武岩中地幔捕虏体的硫化物相研究

江苏六合一带碱性玄武岩中的出露有以尖晶石二辉橄榄岩为主的地幔捕虏体,这些地幔矿物中普遍有硫化物相出现：（１）被寄主矿物捕获的早期硫化物颗粒。（２）产于矿物晶粒边界或次生裂隙充填物,（３）硫化物包裹体,包括单相硫的包裹体、硫化物－玻璃两相熔体包裹体和ＣＯ／２－硫化物－玻璃（含硅酸盐子矿物）的多相包裹体,电子探针分析表明,硫化物包裹体比例隙中硫化物具有更高的相对Ｆｅ和Ｓ含量,较低的Ｎｉ含量。硫化物包裹     

攀西红格钒钛磁铁矿矿田富钴硫化物中钴的地球化学特征及其地质意义

攀西红格钒钛磁铁矿矿田白草矿区发育富钴硫化物矿物,关于其成因和形成环境方面的研究较为薄弱。本文采用矿物学、矿物化学、地球化学等方法对其进行系统研究。矿石中主要富钴硫化物为磁黄铁矿（Po）、黄铁矿（Py）、镍黄铁矿（Pn）、硫钴镍矿（Se）。磁黄铁矿Co、Ni平均质量分数分别为0.21%、0.42%,Co/Ni平均值为1.10;黄铁矿Co、Ni平均质量分数分别为0.18%、0.29%,Co/Ni平均值为0.77;镍黄铁矿Co、Ni平均质量分数分别为2.67%、34.30%,Ni/Fe平均值为1.08、S/Fe平均值为1.91、M/S^#平均值为1.13;硫钴镍矿Co、Ni平均质量分数分别为24.30%、22.90%,Co/Ni平均值为1.06。根据Po-Py矿物温度计,白草矿区富钴硫化物结晶温度在267~490℃之间,表明其形成于中高温的条件。通过与地幔包体镍黄铁矿S/Fe、M/S^#特征值的对比,结合磁黄铁矿具有陨硫铁（Tr）同质多象晶体的特征,认为白草矿区硫化物具有地幔源的特征,说明成矿物质来源于地幔。白草矿区钴地球化学特征研究表明,在硫化物熔体分离过程中,钴迁移至单硫化物固溶体形成Po-Py固溶体,再由Po-Py固溶体中迁移至Pn、Se,形成了Se、Pn、Po-Py、Ccp（黄铜矿）中Co质量分数依次递减的现象。     

Petrogenetic analysis of fluid and melt inclusions in minerals from mantle xenoliths from the Bele pipe basanites (North Minusa depression)

Results of study of different types of inclusions in minerals from mantle xenoliths from the Bele pipe basanites are presented. Two groups of inclusions were recognized in the host minerals according to their genesis. The first group includes single, apparently primary, fluid inclusions. They were discovered only in orthopyroxenes and consist of CO₂ (95 mol.%) and N₂ (5 mol.%). These inclusions had partly leaked. The densities of two least leaked inclusions from different xenoliths are 1.05 and 1.14 g/cm³, and their trapping pressures are estimated at >8.5 and 12 kbar, respectively. The second group includes syngenetic secondary fluid, melt, and crystalline inclusions. In composition the secondary fluid inclusions differ from the primary ones in higher concentrations of N₂ (up to 7 mol.%). Their maximum density is 0.57 g/cm³, which corresponds to 2.4–2.6 kbar and 1100–1200 °C (homogenization temperature of secondary melt inclusions). Comparison of data on melt inclusions in xenolith minerals and host-basanite phenocrysts shows that the secondary inclusions in the xenoliths are, most likely, the result of infiltration and partial reaction of basanitic melt with the xenoliths. On the ascent, the basanitic melt vigorously reacted with mantle xenoliths, which led to the appearance of secondary inclusions in nodule minerals at shallow depths and interstitial mineral assemblages in the xenoliths.     

地幔捕虏体中的流体-熔体包裹体

地幔流体的研究现已成为国内外前沿课题。地幔岩捕虏体中的流体-熔体包裹体是地幔流体的直接证据,通过对它们的研究可以直接获取地授流体的信息。包裹体按相态特征主要有三类：二氧化碳流体包裹体、二氧化碳-硅酸盐熔体包裹体、硫化物-熔体流体包裹体。本总结了地幔岩中流体-熔体包裹体的基本特征、微量元素地球化学、硫化物-熔体包裹体和二氧化碳流体包裹体稳定同位素特征的研究进展状况。讨论认为：地幔流体是由C、H、O、S等元素的挥发份和硅酸盐熔体组成;上地幔流体在化学成分上明显富含CO2、硫化物、LILE和BEE,它引起地幔交代作用和地授部分熔融;上地授流体的分布存在不均匀性,其组成也存在地区性差异。     

The origin of reaction textures in mantle peridotite xenoliths from Sal Island, Cape Verde: the case for “metasomatism” by the host lava

Reaction zones around minerals in mantle xenoliths have been reported from many localities worldwide. Interpretations of the origins of these textures fall into two groups: mantle metasomatic reaction or reaction during transport of the xenoliths to the surface. A suite of harzburgitic mantle xenoliths from Sal, Cape Verde show clear evidence of reaction during transport. The reactions resulted in the formation of olivine–clinopyroxene and Si- and alkali-rich glass reaction zones around orthopyroxene and sieve-textured clinopyroxene and sieve textured spinel, both of which are associated with a Si- and alkali-rich glass similar to that in the orthopyroxene reaction zones. Reaction occurred at pressures less than the mantle equilibration pressure and at temperatures close to the liquidus temperature of the host magma. In addition, there is a clear spatial relation of reaction with the host lava: reaction is most intense near the lava/xenolith contact. The residence time of the xenoliths in the host magma, determined from Fe–Mg interdiffusion profiles in olivine, was approximately 4 years. Our results cannot be reconciled with a recent model for the evolution of the mantle below the Cape Verde Archipelago involving mantle metasomatism by kimberlitic melt. We contend that alkali-rich glasses in the Sal xenoliths are not remnants of a kimberlitic melt, but rather they are the result of reaction between the host lava or a similar magma and xenolith minerals, in particular orthopyroxene. The formation of a Si- and alkali-rich glass by host magma–orthopyroxene reaction appears to be a necessary precursor to formation of sieve textured spinel and clinopyroxene.     

Phlogopite in mantle xenoliths and kimberlite from the Grib pipe,Arkhangelsk province,Russia:Evidence for multi-stage mantle metasomatism and origin of phlogopite in kimberlite

We present petrography and mineral chemistry for both phlogopite,from mantle-derived xenoliths(garnet peridotite,eclogite and clinopyroxene-phlogopite rocks)and for megacryst,macrocryst and groundmass flakes from the Grib kimberlite in the Arkhangelsk diamond province of Russia to provide new insights into multi-stage metasomatism in the subcratonic lithospheric mantle(SCLM)and the origin of phlogopite in kimberlite.Based on the analysed xenoliths,phlogopite is characterized by several generations.The first generation(Phil)occurs as coarse,discrete grains within garnet peridotite and eclogite xenoliths and as a rock-forming mineral within clinopyroxene-phlogopite xenoliths.The second phlogopite generation(Phl2)occurs as rims and outer zones that surround the Phil grains and as fine flakes within kimberlite-related veinlets filled with carbonate,serpentine,chlorite and spinel.In garnet peridotite xenoliths,phlogopite occurs as overgrowths surrounding garnet porphyroblasts,within which phlogopite is associated with Cr-spinel and minor carbonate.In eclogite xenoliths,phlogopite occasionally associates with carbonate bearing veinlet networks.Phlogopite,from the kimberlite,occurs as megacrysts,macrocrysts,microcrysts and fine flakes in the groundmass and matrix of kimberlitic pyroclasts.Most phlogopite grains within the kimberlite are characterised by signs of deformation and form partly fragmented grains,which indicates that they are the disintegrated fragments of previously larger grains.Phil,within the garnet peridotite and clinopyroxene-phlogopite xenoliths,is characterised by low Ti and Cr contents(TiO_21 wt.%,Cr_2 O_31 wt.% and Mg# = 100 × Mg/(Mg+ Fe)92)typical of primary peridotite phlogopite in mantle peridotite xenoliths from global kimberlite occurrences.They formed during SCLM metasomatism that led to a transformation from garnet peridotite to clinopyroxene-phlogopite rocks and the crystallisation of phlogopite and high-Cr clinopyroxene megacrysts before the generation of host-kimberlite magmas.One of the possible processes to generate low-Ti-Cr phlogopite is via the replacement of garnet during its interaction with a metasomatic agent enriched in K and H_2O.Rb-Sr isotopic data indicates that the metasomatic agent had a contribution of more radiogenic source than the host-kimberlite magma.Compared with peridotite xenoliths,eclogite xenoliths feature low-Ti phlogopites that are depleted in Cr_2O_3 despite a wider range of TiO_2 concentrations.The presence of phlogopite in eclogite xenoliths indicates that metasomatic processes affected peridotite as well as eclogite within the SCLM beneath the Grib kimberlite.Phl2 has high Ti and Cr concentrations(TiO_22 wt.%,Cr_2O_31 wt.% and Mg# = 100× Mg/(Mg + Fe)92)and compositionally overlaps with phlogopite from polymict brecc:ia xenoliths that occur in global kimberlite formations.These phlogopites are the product of kimberlitic magma and mantle rock interaction at mantle depths where Phl2 overgrew Phil grains or crystallized directly from stalled batches of kimberlitic magmas.Megacrysts,most macrocrysts and microcrysts are disintegrated phlogopite fragments from metasomatised peridotite and eclogite xenoliths.Fine phlogopite flakes within kimberlite groundmass represent mixing of high-Ti-Cr phlogopite antecrysts and high-Ti and low-Cr kimberlitic phlogopite with high Al and Ba contents that may have formed individual grains or overgrown antecrysts.Based on the results of this study,we propose a schematic model of SCLM metasomatism involving phlogopite crystallization,megacryst formation,and genesis of kimberlite magmas as recorded by the Grib pipe.     

Evidence for aqueous activity on comet 81P/Wild 2 from sulfide mineral assemblages in Stardust samples and CI chondrites

The discovery of nickel-, copper-, and zinc-bearing iron sulfides from comet 81P/Wild 2 (Wild 2) represents the strongest evidence, in the Stardust collection, of grains that formed in an aqueous environment. We investigated three microtomed TEM sections which contain crystalline sulfide assemblages from Wild 2 and twelve thin sections of the hydrothermally altered CI chondrite Orgueil. Detailed structural and compositional characterizations of the sulfide grains from both collections reveal striking similarities. The Stardust samples include a cubanite (CuFe₂S₃) grain, a pyrrhotite [(Fe,Ni)_1−xS]/pentlandite [(Fe,Ni)₉S₈] assemblage, and a pyrrhotite/sphalerite [(Fe,Zn)S] assemblage. Similarly, the CI-chondrite sulfides include individual cubanite and pyrrhotite grains, cubanite/pyrrhotite assemblages, pyrrhotite/pentlandite assemblages, as well as possible sphalerite inclusions within pyrrhotite grains. The cubanite is the low temperature orthorhombic form, which constrains temperature to a maximum of 210 °C. The Stardust and Orgueil pyrrhotites are the 4C monoclinic polytype, which is not stable above ∼250 °C. The combinations of cubanite and pyrrhotite, as well as pyrrhotite and pentlandite signify even lower temperatures. The crystal structures, compositions, and petrographic relationships of these sulfides constrain formation and alteration conditions. Taken together, these constraints attest to low-temperature hydrothermal processing.Our analyses of these minerals provide constraints on large scale issues such as: heat sources in the comet-forming region; aqueous activity on cometary bodies; and the extent and mechanisms of radial mixing of material in the early nebula. The sulfides in the Wild 2 collection are most likely the products of low-temperature aqueous alteration. They provide evidence of radial mixing of material (e.g. cubanite, troilite) from the inner solar system to the comet-forming region and possible secondary aqueous processing on the cometary body.     

辉石巨晶中的硫化物及其成因

我国一些地区玄武岩辉石巨晶中的硫化物球泡(0.02-0.05mm)呈点阵式、散布式、定向带状或微裂隙羽状分布。硫化矿物组合是磁黄铁矿-镍黄铁矿-黄铜矿,其中以磁黄铁矿为主(～90％)。根据硫化物的规则排布以及高温矿物组合推测点阵式、散布式硫化物形成于地幔。是由溶解了～1％S的硅酸盐熔体在减压上升过程中析出过饱和的硫所致。     

Evidence of kimberlite-grospydite reaction

A xenolith from the kimberlite pipe of the Roberts Victor Mine, O.F.S. shows a marginal rim rich in garnet (Py₅₀Alm₃₅Gro₁₅), presumably resulting from reaction between the grospyditic inclusion and kimberlitic host. Similarity between the reaction rim-garnets, and those of the common mafic inclusion of the Roberts Victor pipe, suggests that the rare grospydite inclusions are accidental xenoliths, not directly related in origin to the kimberlites in which they are found.     

The role of eclogites in the redistribution of water in the subcontinental mantle of the Siberian craton: results of determination of the water content in minerals from the Udachnaya pipe eclogites

A comprehensive study of 26 mafic mantle xenoliths from the Udachnaya kimberlite pipe was carried out. The contents of major and trace elements, equilibrium temperature parameters, and water content in the rock-forming minerals were determined. The temperatures of formation of the studied rocks are estimated at 800–1300 °C. According to IR spectroscopy data, the water content in clinopyroxenes from the studied eclogites varies from values below the detection limit to 99 ppm. The IR spectra of garnets lack bands of water. The water content in clinopyroxene and orthopyroxene from garnet websterite is 72 and 8 ppm, respectively. The water content in the average rock, calculated from the ratio of the rock-forming minerals, varies from a few to 55 ppm. No relationship among the water content, equilibrium temperatures, and rock composition is established. The low water contents in the eclogites are close to the earlier determined water contents in peridotites from the same pipe and are, most likely, due to the re-equilibration of the eclogites with the rocks of the peridotitic lithospheric mantle. The dehydration of the protolith during its subduction and the partial melting of eclogites before their removal by kimberlitic magma to the surface might be an additional cause of the low water contents in the mantle eclogite xenoliths.     

Metasomatic processes in the lithospheric mantle beneath the V. Grib kimberlite pipe (Arkhangelsk diamondiferous province,Russia)

New data on metasomatic processes in the lithospheric mantle in the central part of the Arkhangelsk diamondiferous province (ADP) are presented. We studied the major- and trace-element compositions of minerals of 26 garnet peridotite xenoliths from the V. Grib kimberlite pipe; 17 xenoliths contained phlogopite. Detailed mineralogical, petrographic, and geochemical studies of peridotite minerals (garnet, clinopyroxene, and phlogopite) have revealed two types of modal metasomatic enrichment of the lithospheric-mantle rocks: high temperature (melt) and low-temperature (phlogopite). Both types of modal metasomatism significantly changed the chemical composition of the peridotites. Low-temperature modal metasomatism manifests itself as coarse tabular and shapeless phlogopite grains. Two textural varieties of phlogopite show significant differences in chemical composition, primarily in the contents of TiO₂, Cr₂O₃, FeO, Ba, Rb, and Cs. The rock-forming minerals of phlogopite-bearing peridotites differ in chemical composition from phlogopite-free peridotites, mainly in higher FeO content. Most garnets and clinopyroxenes in peridotites are the products of high-temperature mantle metasomatism, as indicated by the high contents of incompatible elements and REE pattern in these minerals. Fractional-crystallization modeling gives an insight into the nature of melts (metasomatic agents). They are close in composition to picrites of the Izhmozero field, basalts of the Tur’ino field, and carbonatites of the Mela field of the ADP. The REE patterns of the peridotite minerals make it possible to determine the sequence of metasomatic enrichment of the lithospheric mantle beneath the V. Grib kimberlite pipe.     

Sulfide evolution in high-temperature to ultrahigh-temperature metamorphic rocks from Lützow–Holm Complex, East Antarctica

The high-temperature (HT) to ultrahigh-temperature (UHT) metamorphic rocks from Lützow–Holm Complex, East Antarctica show a systematic difference between sulfide assemblages in the rock matrix and those found as inclusions in the silicates stable in high-temperatures. Matrix sulfides are commonly pyrite with or without pentlandite and chalcopyrite. On the other hand, inclusion sulfides are pyrrhotite with or without pentlandite and chalcopyrite lamellae. When recalculated into integrated single-phase sulfide compositions, inclusion sulfides from the UHT region showed a wider range of solid–solution composition than the inclusion sulfides from the HT region. The host minerals of the sulfides with extreme solid–solution compositions are those stable at the peak of metamorphism such as orthopyroxene and garnet. One of the most extreme ones is included in orthopyroxene coexisting with sillimanite ± quartz, which is the diagnostic mineral assemblage of UHT metamorphism. These observations suggest that sulfide inclusions preserve their peak metamorphic compositions. Pyrrhotite did not revert to pyrite because of the closed system behavior of sulfur in inclusion sulfides. On the other hand, in the rock matrix where the open system behavior of sulfur is permitted, original sulfides were partly to completely altered by the later fluid activity.     

Composition and evolution of lithosphere beneath the Carpathian–Pannonian Region: a review

Our knowledge of the lithosphere beneath the Carpathian–Pannonian Region (CPR) has been greatly improved through petrologic, geochemical and isotopic studies of upper mantle xenoliths hosted by Neogene–Quaternary alkali basalts. These basalts occur at the edge of the Intra-Carpathian Basin System (Styrian Basin, Nógrád-Gömör and Eastern Transylvanian Basin) and its central portion (Little Hungarian Plain, Bakony-Balaton Highland).The xenoliths are mostly spinel lherzolites, accompanied by subordinate pyroxenites, websterites, wehrlites, harzburgites and dunites. The peridotites represent residual mantle material showing textural and geochemical evidence for a complex history of melting and recrystallization, irrespective of location within the region. The lithospheric mantle is more deformed in the center of the studied area than towards the edges. The deformation may be attributed to a combination of extension and asthenospheric upwelling in the late Tertiary, which strongly affected the central part of CPR subcontinental lithosphere.The peridotite xenoliths studied show bulk compositions in the following range: 35–48 wt.% MgO, 0.5–4.0 wt.% CaO and 0.2–4.5 wt.% Al₂O₃ with no significant differences in regard to their geographical location. On the other hand, mineral compositions, particularly of clinopyroxene, vary according to xenolith texture. Clinopyroxenes from less deformed xenoliths show higher contents of ‘basaltic’ major elements compared to the more deformed xenoliths. However, clinopyroxenes in more deformed xenoliths are relatively enriched in strongly incompatible trace elements such as light rare earth elements (LREE).Modal metasomatic products occur as both hydrous phases, including pargasitic and kearsutitic amphiboles and minor phlogopitic micas, and anhydrous phases — mostly clinopyroxene and orthopyroxene. Vein material is dominated by the two latter phases but may also include amphibole. Amphibole mostly occurs as interstitial phases, however, and is more common than phlogopite. Most metasomatized peridotites show chemical and (sometimes) textural evidence for re-equilibration between metasomatic and non-metasomatic phases. However, amphiboles in pyroxenites are sometimes enriched in K, Fe and LREE. The presence of partially crystallized melt pockets (related to amphiboles and clinopyroxenes) in both peridotites and pyroxenites is an indication of decompression melting and, rarely, incipient partial melting triggered by migrating hydrous melts or fluids. Metasomatic contaminants may be ascribed to contemporaneous subduction beneath the Carpathian–Pannonian Region between the Eocene and Miocene.Sulfide inclusions are more abundant in protogranular and porphyroclastic xenoliths relative to equigranular types. In mantle lithologies, sulfide bleb compositions vary between pentlandite and pyrrhotite correlating with the chemistry and texture of the host xenoliths. While sulfides in peridotites are relatively rich in Ni, those in clinopyroxene-rich xenoliths are notably Fe-rich.     

The distribution of platinum group elements (PGE) and other chalcophile elements among sulfides from the Creighton Ni–Cu–PGE sulfide deposit, Sudbury, Canada, and the origin of palladium in pentlandite

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).     

A laser ablation ICP-MS study of platinum-group and chalcophile elements in base metal sulfide minerals of the Jinchuan Ni–Cu sulfide deposit,NW China

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.     

Significance of ancient sulfide PGE and Re–Os signatures in the mantle beneath Calatrava,Central Spain

Spinel lherzolite and wehrlite xenoliths from the Cenozoic Calatrava volcanic field carry the geochemical imprint of metasomatic agents that have affected the subcontinental lithospheric mantle beneath Central Iberia. Some xenoliths (mainly wehrlites) were enriched in REE, Sr, P, and CO₂ by silicic-carbonate-rich metasomatic melts/fluids, while others record the effects of subduction-related hydrous silicate fluids that have precipitated amphibole and induced high Ti/Eu in primary clinopyroxene. The petrographic observations and geochemical data suggest that interstitial glass in the xenoliths represent the quenched products of Si-rich melts that infiltrated the mantle peridotite shortly before the entrainment of the xenoliths in the host magmas that erupted ca 2 million years ago. During their infiltration, the metasomatic melts reacted with peridotite, resulting in silica enrichment, while remobilizing grains of iron-rich monosulfide solid solution (Fe-rich Mss) initially enclosed in, or intergranular to, primary olivine and pyroxenes. In situ laser ablation inductively coupled plasma-mass spectrometry analysis of single sulfide grains reveals that the Fe-rich Mss in glass shows platinum-group element (PGE) patterns and ¹⁸⁷Os/¹⁸⁸Os compositions identical to the Fe-rich Mss occurring as inclusions in, or at grain boundaries of primary silicates. Moreover, independent of its microstructural position, Fe-rich Mss exhibits PGE and ¹⁸⁷Os/¹⁸⁸Os signatures typical of Mss either residual after partial melting or crystallized directly from sulfide melts. Our findings reveal that young metasomatic melt(s)/fluid(s) may carry remobilized sulfides with PGE and Os-isotopic signatures identical to those of texturally older sulfides in the peridotite xenolith. These sulfides thus still provide useful information about the timing and nature of older magmatic events in the subcontinental mantle.     

Mineralogy of the upper mantle: A review of the minerals in mantle xenoliths from kimberlite

The importance of ultramafic and eclogitic xenoliths in kimberlite as representing the rocks and minerals of the upper mantle has been widely perceived during the last decade. Studies of the petrology and mineral chemistry of these mantle fragments as well as of inclusions in diamond, have led to significant progress in our understanding of the mineralogy and chemistry of the upper mantle. For example, it is now known that textural differences in the ultramafic xenoliths (lherzolite, harzburgite, pyroxenite and websterite) are partially reflected in chemical differences. Thus xenoliths that display a ‘fluidal’ texture, indicative of intense deformation are less depleted in Ca, Al, Na, Fe and Ti than those xenoliths in which granular textures are predominant. It is believed this relative depletion may indicate the sheared (fluidal texture) xenoliths are representative of primary, undifferentiated mantle. This material on partial melting would produce ‘basaltic-type’ material, and leave a residuum whose chemistry and mineralogy is reflected by the granular xenoliths.Also present in kimberlite are large single phase xenoliths that may be either one single crystal (xenocryst, megacryst) or an aggregate of several crystals of the same mineral (discrete xenolith, or discrete nodule). These large single phase samples consist of similar minerals to those occurring in the ultramafic xenoliths but chemically they are distinct in being generally more Fe-rich. The relation between these xenocrysts to their counterparts in the ultramafic xenoliths is unknown. Also unknown, at the present time, is the exact relation between diamond and kimberlite. Evidence obtained from study of the mineral inclusions in diamond suggests that diamond forms in at least two chemically distinct environments in the mantle; one eclogitic, the other, ultramafic. Interestingly, this suggestion is true for diamonds from worldwide localities.The mineral-chemical results of studies on xenoliths and inclusions in diamond have been convincingly interpreted in the light of experimental studies. It is now possible based on several different geothermometers and barometers to determine relatively reasonable physical conditions for the final genesis of many of these mantle rocks. For the most part the final equilibration temperatures range between 1000 and 1400°C and pressure in the region 100–200 km. These conditions are consistent with an upper mantle origin. Future studies will undoubtedly attempt to more concisely, and accurately, define these conditions, as well as understand better the chemical and spatial relationship of the rock-types in the mantle.     

滇西富碱斑岩中特殊包体岩石的流体包裹体幔源不混溶特征

滇西地区沿金沙江-哀牢山断裂带产出了一套新生代富碱斑岩,其中发现了与镁铁-超镁铁质深源包体岩石共生的含石英的方解石包晶(体)、石英钠长石伟晶岩包体和含玻璃包裹体的纯石英包晶(体)以及富铁熔浆包体.流体包裹体地球化学研究表明,该四类特殊包体的形成与富含CO2流体持续减压而造成的不混溶作用有关;而玻璃包裹体与水溶液包裹体以...