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1.
江苏六合新生代玄武岩中地幔捕虏体的硫化物相研究   总被引：13，自引：3，他引：10  
徐九华  储雪蕾 《岩石学报》2000,16(4):492-498
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  相似文献   

2.
福建牛头山新近纪碱性玄武岩中地幔岩包体内硫化物研究   总被引：3，自引：0，他引：3  
岳可芬  赫英  刘文峰 《地质科学》2005,40(1):114-i004
福建牛头山一带新近纪碱性玄武岩中含有尖晶石二辉橄榄岩包体。这些地幔岩包体内普遍存在有硫化物。硫化物按产状和成因分为两类:1)分布于寄主矿物内部,未与裂隙相连,是地幔岩浆作用的产物;2)分布于颗粒内或颗粒边部,在裂隙上或与裂隙相连,是地幔流体交代作用的产物。电子探针分析表明,15个硫化物测点中,除2个黄铜矿、1个硫铜铁矿外,其余为不同Ni/Fe(mol比)比值的铁镍硫化物:6个测点为富镍镍黄铁矿,其Ni/Fe=0.98～2.79,(Fe+Ni)/S=1.03～1.08;2个为针镍矿,其Ni/Fe=5.5,(Fe+Ni)/S=1.01;4个测点为富镍磁黄铁矿,其Ni/Fe=0.29～0.49,(Fe+Ni)/S=0.79～0.94。4粒单一硫化物矿物的成份是不均一的,多数表现为自中心到边部Ni含量和Ni/Fe值呈增加趋势,而Fe和Cu含量呈减少趋势。本研究还发现单一硫化物中由中心到边部金与镍大致有相同的变化趋势。  相似文献   

3.
http://dx.doi.org/10.1016/j.gsf.2016.06.008   总被引：1，自引：1，他引：0  
The mineral schreibersite, (Fe,Ni)3P, provides a reactive source of phosphorus capable of forming phosphorylated molecules. These molecules may have been an important component of prebiotic chemistry, allowing their build-up and eventual commencement of autopoiesis. Discussed here are potential geochemical routes to providing schreibersite, as a potentially important prebiotic mineral, to the Hadean Earth. Two routes are identified: delivery of phosphides by meteoritic material and the reduction of phosphates to phosphides by high-temperature, low-redox conditions. About 1–10% of all crustal phosphorus is estimated to have been in schreibersite during the Hadean, making the long-term reaction of this mineral with organic-laden water plausible for many years. Ultimately, such conditions would have been conducive to the formation of life as we know it today.  相似文献   

4.
The coarse-grained fraction of C2 chondrites is composed mostly of single crystals and aggregates of crystals of Mg-rich olivine and pyroxene. They do not possess compelling textural evidence of being the solidification products of rapidly-quenched molten droplets. Metal inclusions in the silicates contain 3·82–8·88 mole% Ni, 0·16–0·70 per cent Co, 0·17–1·07 per cent Cr and up to 5·70 per cent P. Thermodynamic calculations show that alloys of these compositions may be condensates from the solar nebula. The implication is that the high-temperature fraction of C2 chondrites consists mostly of high-temperature condensates. Chemical data show that the high-temperature fraction has an Fe/Mg atomic ratio of ? 0·31 compared to 1·3 in the matrix, indicating that much of the iron has been lost from the high-temperature fraction and converted to the troilito and oxidized iron of the low-temperature fraction. The presence of low-Ni metal grains in the aggregates and high Ni/Fe and Co/Fe ratios in the matrix of some C2's indicates preferential loss of early NiCo-rich metal from the high-temperature fraction during condensation.  相似文献   

5.
徐九华  谢玉玲 《岩石学报》2007,23(1):117-124
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.  相似文献   

6.
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.  相似文献   

7.
Bulk chemical compositions of matrix material in Antarctic CM chondrites and other non-Antarctic CM and CI chondrites have been determined using microprobe defocused beam techniques. These are used, along with the results of previously published mineralogical studies, to provide mass balance constraints on the relative proportions of intergrown and intermixed phyllosilicate phases in carbonaceous chondrite matrices. Results of these calculations indicate differing amounts of PCP (a mixture of approximately 25% tochilinite and 75% cronstedtite) and serpentines (Mg-rich and Fe-rich varieties in varying proportions or intermediate compositional varieties). Additional sulfide phases are also probably necessary to account for excess Ni and S. Fe/Si ratios for matrices of individual meteorites range from 1.21 to 2.77, corresponding to PCP/(PCP + SERF) ratios of 0.16 to 0.58. Progressive aqueous alteration of matrix appears to have occurred by formation of tochilinite, then cronstedtite and Mg-rich serpentine, and finally Fe-rich serpentine and sulfides. CM matrix clearly did not behave as an isolated system during alteration. CI chondrite matrices appear to contain little if any PCP; this may be a natural consequence of the absence of chondrule-associated metal, from which PCP forms, in the unaltered precursor material. These data provide a more quantitative picture of low-temperature aqueous alteration processes in carbonaceous chondrite parent bodies than has heretofore been possible from TEM studies alone.  相似文献   

8.
捕虏体麻粒岩是了解下地壳形成和演化的重要样品。汉诺坝新生代玄武岩中的二辉麻粒岩捕虏体样品中富含各种硫化物相,主要类型有:①孤立产出的球状出溶硫化物;②矿物颗粒之间或颗粒内的粗晶硫化物;③次生硫化物包裹体群;④裂隙充填硫化物。电子探针分析表明,硫化物的矿物成分均为贫镍磁黄铁矿,(Ni+Co+Cu)/Fe(原子比)远小于0.2;(Fe+Cu+Co+Ni)/S(原子比)比地幔岩的磁黄铁矿小,多小于0.875,反映了一种S过饱和环境。各种产状的磁黄铁矿中Au、Ag都有一定的含量,其平均值分别为0.19%～0.22%(Au)、0.01%～0.02%(Ag),反映下地壳的麻粒岩化与金矿化的成因联系。磁黄铁矿的Ni、Co、Cu含量与S正相关,说明微量重金属元素与S具有同源的关系,由于地幔去气伴随S而进入下地壳。  相似文献   

9.
Typical magmatic sulfides are dominated by pyrrhotite and pentlandite with minor chalcopyrite, and the bulk atomic Cu/Fe ratio of these sulfides is typically less than unity. However, there are rare magmatic sulfide occurrences that are dominated by Cu-rich sulfides (e.g., bornite, digenite, and chalcopyrite, sometimes coexisting with metallic Cu) with atomic Cu/Fe as high as 5. Typically, these types of sulfide assemblages occur in the upper parts of moderately to highly fractionated layered mafic–ultramafic intrusions, a well-known example being the Pd/Au reef in the Upper Middle Zone of the Skaergaard intrusion. Processes proposed to explain why these sulfides are so unusually rich in Cu include fractional crystallization of Fe/(Ni) monosulfide and infiltration of postmagmatic Cu-rich fluids. In this contribution, we explore and experimentally evaluate a third possibility: that Cu-rich magmatic sulfides may be the result of magmatic oxidation. FeS-dominated Ni/Cu-bearing sulfides were equilibrated at variable oxygen fugacities in both open and closed system. Our results show that the Cu/Fe ratio of the sulfide melt increases as a function of oxygen fugacity due to the preferential conversion of FeS into FeO and FeO1.5, and the resistance of Cu2S to being converted into an oxide component even at oxygen fugacities characteristic of the sulfide/sulfate transition (above FMQ?+?1). This phenomenon will lead to an increase in the metal/S ratio of a sulfide liquid and will also depress its liquidus temperature. As such, any modeling of the sulfide liquid line of descent in magmatic sulfide complexes needs to address this issue.  相似文献   

10.
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   

11.
A chrysotile-like phase, cronstedtite, polygonal serpentine, pentlandite, and finely intergrown tochilinite comprise the fine-grained rim (FGR) mineralogy of the Cold Bokkeveld CM chondrite. Transmission electron microscope images combined with compositional data indicate reaction among cronstedtite, the chrysotile-like phase, and polygonal serpentine. The Mg/(Mg+Fe) ratios of the cronstedtite are higher than those reported for the less altered Murchison CM chondrite. Cronstedtite grains exhibit layer separations, particularly at their boundaries.The FGRs surround different chondrule types but have similar bulk compositions and mineralogy. Ca is depleted in the FGRs relative to the bulk CM chondrite. The FGRs display non-uniform thicknesses, especially where they coat embayed chondrule areas, and they exhibit grain-size coarsening outward from the chondrules they enclose. FGR formation in Cold Bokkeveld is most plausibly explained by multiple accretionary episodes during which progressively coarser dust was deposited onto chondrules, presumably in the solar nebula. The compositional and mineralogic data are consistent with aqueous alteration on the parent body.  相似文献   

12.
LORAND  J P. 《Journal of Petrology》1989,30(4):987-1015
Pyroxenite layers in the orogenic spinel lherzolite massifsof Ari?ge are porphyroclastic textured and range in compositionfrom spinel websterite to garnet clinopyroxenite. Each pyroxenitetype forms individual layers or occurs as part of compositelayers in which the Opx/Cpx and Sp/Gt ratios decrease from marginsto core. They are interpreted as crystalline segregations separatedby flow crystallization from continental tholeiites en routeto the surface. The primary magmatic phases consist of Al-richpyroxenes, together with a minor amount of spinel, which startedto crystallize at 1400?C and 20–22 kb pressure; the pyroxeneshave locally survived plastic strains and subsolidus rccrystallizationsand now occur in the form of clinopyroxene and orthopyroxenemegacrysts displaying unmixing features. Although the differentiated silicate liquid was fully expelledduring the flow crystallization process, the layered pyroxeniteshave concentrated the highly incompatible elements S and Cuand locally display significant chalcophile platinum-group elementenrichment (Pd, Pt). Cu and S behave coherently over the wholerange of pyroxenite composition; their highest concentrationsare found in the thinnest websterite layers or at the marginof composite layers. Microscopic investigation of 214 polishedthin sections shows these elements to be present as accessoryCu-Fe-Ni sulfides interstitial among the silicate phase or formingdiscrete bodies included in the relic pyroxene megacrysts. Allthese features indicate the presence of a sulfide liquid, immisciblewith the silicate magma, during the crystallization of the layeredpyroxenites. Sulfide liquid immiscibility probably occurredin response to thermal contrast between the pyroxenites andthe cooler surrounding peridotites. It is proposed that the megacryst-hosted sulfide inclusionswere trapped as linear arrays arranged on host megacryst growthplanes. Due to the slow cooling and complex unmixing historyof the megacrysts, these arrays have been transformed into coarse,isolated sulfide inclusions by subsolidus migration and spheroidizationprocesses. They started to crystallize at T = 1200?C as monosulfidesolid solution (MSS), probably coexisting with a minor amountof Ni- and Cu-rich sulfide liquid down to r=900?C. The reconstructionof the bulk chemistry of each individual inclusion reveals significantbetween-inclusion variations of Cu/Ni+ Fe and Ni/Fe ratios,which would result from strain-induced immobilization of theseliquids. On cooling, the high-temperature MSS has decomposedbelow 230?C into Ni-rich pyrrhotite, nickeliferous pentlandite,chalcopyrite and minor pyrite. The post-magmatic history ofthe interstitial sulfide grains was not unlike that of the inclusions,except at near-surface temperatures where the primary sulfidesresulting from unmixing of MSS have been partly altered intosecondary sulfides by serpentinizing aqueous fluids. In spite of these post-magmatic alterations, the inclusionsand the interstitial sulfide phases are remarkably homogeneousas regards their bulk Ni/Cu ratio, which is close to 3. Thisvalue is characteristic of sulfide separated from primary ratherthan partially differentiated tholeiitic melts. It is thus concludedthat the continental tholeiite parent to the layered pyroxeniteswas saturated with sulfides when it left its mantle source regioaIn this aspect, it would not be different from MORBs which containsimilar sulfide compositions. In both cases, sulfide fractionationcannot be ignored in models for chalcophile trace element fractionationduring initial evolution of these magmas.  相似文献   

13.
This work describes the application of microfocus X-ray absorption spectroscopy (XAS) and X-ray photo-emission electron microscopy (XPEEM) to the study of the complex mineralogical intergrowths within the Santa Catharina meteorite. The Santa Catharina meteorite of this study (BM52283 from the meteorite collection of the Natural History Museum, London, UK) primarily comprises a taenite bulk host phase (Fe:Ni ratio = 70.9 ± 0.8%:29.1 ± 0.8%) with a set of oxide-bearing cloudy zone textured regions (Fe:Ni:O ratio = 40.4 ± 0.3%:49.0 ± 0.7%:10.6 ± 0.8% at the core and Fe:Ni:O ratio = 34.4 ± 1.5%:42.7 ± 0.6%:22.9 ± 1.8% towards the rims) and numerous schreibersite (Fe:Ni:P ratio = 38.6 ± 1.6%:38.4 ± 0.9%:23.0 ± 0.5%) inclusions. Between the schreibersite and the taenite are rims up to 50 μm across of Ni-rich kamacite (Fe:Ni ratio = 93.4 ± 0.4%:6.6 ± 0.5%). No chemical zoning or spatial variations in the Fe and Ni speciation was observed within either the schreibersite or the kamacite phases. The oxide-bearing cloudy zone textured regions mostly comprise metallic Fe–Ni alloy, predominantly tetrataenite. Within the oxide phases, the Fe is predominantly, but not entirely, tetrahedrally co-ordinated Fe3+ and the Ni is octahedrally co-ordinated Ni2+. Structural analysis supports the suggestion that non-stoichiometric Fe2NiO4 trevorite is the oxide phase. The trevorite:tetrataenite ratio increases at the edges of the oxide-bearing cloudy zone textured regions indicating increased oxidation at the edges of these zones. The spatial resolution of the XPEEM achieved was between 110 and 150 nm, which precluded the study of either the previously reported ∼ 10 nm precipitates of tetrataenite within the bulk taenite or any antitaenite.  相似文献   

14.
《Applied Geochemistry》1998,13(2):213-233
Porewater concentration profiles were determined for Fe, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn), sulfide, SO4 and pH in two Canadian Shield lakes (Chevreuil and Clearwater). Profiles of pyrite, sedimentary trace elements associated with pyrite and AVS were also obtained at the same sites. Thermodynamic calculations are used, for the anoxic porewaters where sulfide was measured, to characterize diagenetic processes involving sulfide and trace elements and to illustrate the importance of sulfide, and possibly polysulfides and thiols, in binding trace elements. The ion activity products (IAP) of Fe sulfide agree with the solubility products (Ks) of greigite or mackinawite. For Co, Ni and Zn, IAP values are close to the KS values of their sulfide precipitates; for Cu and Pb, IAP/Ks indicate large oversaturations, which can be explained by the presence of other ligands (not measured) such as polysulfides (Cu) and thiols (Pb). Cobalt, Cu, Ni and Zn porewater profiles generally display a decrease in concentration with increasing ΣH2S, as expected for transition metals, whereas Cd, Pb and Zn show an increase (mobilisation). The results suggest that removal of trace elements from anoxic porewaters occurs by coprecipitation (As and Mn) with FeS(s) and/or adsorption (As and Mn) on FeS(s), and by formation of discrete solid sulfides (Cd, Cu, Ni, Pb, Zn and Co). Reactive Fe is extensively sulfidized (51–65%) in both lakes, mostly as pyrite, but also as AVS. Similarities between As, Co, Cu and Ni to Fe ratios in pyrite and their corresponding mean diffusive flux ratios suggest that pyrite is an important sink at depth for these trace elements. High molar ratios of trace elements to Fe in pyrite from Clearwater Lake correspond chronologically to the onset of smelting activities. AVS can be an important reservoir of reactive As, Cd and Ni and, to a lesser extent, of Co, Cu and Pb. Overall, the trace elements most extensively sulfidized were Ni, Cd and As (maximum of 100%, 81% and 49% of the reactive fraction, respectively), whereas Co, Cu, Mn, Pb and Zn were only moderately sulfidized (11–16%).  相似文献   

15.
In many river basins, floodplain soils have accumulated a variety of metal contaminants, which might be released during periods of flooding. We investigated the dynamics of copper, cadmium, lead, zinc, and nickel in a contaminated freshwater floodplain soil under a realistic sulfate-limited flooding regime in microcosm experiments. We found that most contaminants were initially mobilized by processes driven by the reductive dissolution of Fe(III) and Mn(IV, III) (hydr)oxides. Subsequently, bacterial sulfate respiration resulted in the transformation of the entire available sulfate (2.3 mmol/kg) into chromous reducible sulfur (CRS). Cu K-edge X-ray absorption fine structure (XAFS) spectroscopy revealed that the soil Cu speciation changed from predominantly Cu(II) bound to soil organic matter (SOM) intermittently to 14% metallic Cu(0) and subsequently to 66% copper sulfide (CuxS). These CuxS precipitates accounted for most of the formed CRS, suggesting that CuxS was the dominant sulfide phase formed in the flooded soil. Sequential metal extractions, in agreement with CRS results, suggested that easily mobilizable Cd was completely and Pb partially sequestered in sulfide precipitates, controlling their dissolved concentrations to below detection limits. In contrast, Zn and Ni (as well as Fe) were hardly sequestered into sulfide phases, so that micromolar levels of dissolved Zn and Ni (and millimolar dissolved Fe(II)) persisted in the reduced soil. The finding that Cu, Cd, and Pb were sequestered (but hardly any Zn, Ni, and Fe) is consistent with the thermodynamically predicted sulfide ladder following the increasing solubility products of the respective metal sulfides. The observation that Cd and Pb were sequestered in sulfides despite the presence of remaining SOM-bound Cu(II) suggested that the kinetics of Cu(II) desorption, diffusion, and/or CuxS precipitation interfered with the sulfide ladder. We conclude that the dynamics of multiple metal contaminants are intimately coupled under sulfate limitation by the relative thermodynamic stabilities and formation kinetics of the respective metal sulfides.  相似文献   

16.
The bulk composition, mineralogy and mineral chemistry of base-metal sulfides have been investigated in the Fe-Ni-(Cu) ore deposits of the Ivrea-Verbano basic complex.The sulfide ores mostly display textural evidence of having been primarily deposited as an immiscible melt. Bulk compositions of the ores indicate that considerably low Ni/Fe and Ni/Co ratios are found in deposits developed close to metasedimentary country rocks, possibly as a result of mixing with sedimentary sulfur.Phase relations of primary sulfides indicate that early crystallization of the ore was dominated by a monosulfide solid solution (Mss) with a pyrrhotite composition, from which pentlandite and chalcopyrite were formed through subsolidus exsolution. Pentlandite from contaminated ores is typically enriched in Co. Troilite and hexagonal intermediate pyrrhotite intergrowths frequently occur due to low-temperature equilibration of metal-rich pyrrhotites, suggesting a low S fugacity of the original sulfide melt.The sulfides may be locally mobilized and redeposited along shear zones within the same host rock, giving rise to fairly massive ores having a typical cemented-breccia texture. Bulk composition and assemblages suggest that mobilization occurred at various temperatures during the cooling history of the ore, when sulfides were still in the molten state or at a lower temperature under the influence of abundant deuteric fluids. In this last case, growth of pyrite is seen as being possibly due to sulfurization and/or oxidation.  相似文献   

17.
《Geochimica et cosmochimica acta》1999,63(19-20):3373-3378
Interactions of trace metals with sulfide in anoxic environments are important in determining their chemical form and potential toxicity to organisms. In recent years, a considerable body of observational data has accumulated that indicates very different behavior for various trace metals in sulfidic sediments. These differences in behavior cannot be entirely attributed to thermodynamic relationships, but also reflect differences in ligand exchange reaction kinetics, and redox reaction pathways.Pb, Zn, and Cd, which are generally pyritized to only a few percent of the “reactive” fraction, have faster water exchange reaction kinetics than Fe2+, resulting in MeS phases precipitating prior to FeS formation and subsequent pyrite formation, whereas, Co and Ni, which have slower H2O exchange kinetics than Fe2+, are incorporated into pyrite. Although Hg and Cu have faster reaction kinetics than Fe2+, both are incorporated into pyrite or leached from the pyrite fraction with nitric acid. Hg undergoes significant chloride complexation, which can retard reaction with sulfide, but can also replace Fe in FeS to form HgS, which can only be dissolved in the pyrite fraction. Cu2+ is reduced by sulfide and forms a variety of sulfides with and without Fe that can only be dissolved with nitric acid. Mn2+ does not form a MnS phase easily and is incorporated into pyrite at high iron degrees of pyritization (DOP).Oxyanions of Mo and As are first reduced by sulfide. These reduced forms may then react with sulfides resulting in incorporation into pyrite. However, the oxyanion of Cr is reduced to Cr3+, which is kinetically inert to reaction with sulfide and, therefore, not incorporated into pyrite.  相似文献   

18.
Petrological, geochemical, and Nd isotopic analyses have been carried out on rock samples from the Rainbow vent field to assess the evolution of the hydrothermal system. The Rainbow vent field is an ultramafic-hosted hydrothermal system located on the Mid-Atlantic Ridge characterized by vigorous high-temperature venting (∼365°C) and unique chemical composition of fluids: high chlorinity, low pH and very high Fe, and rare earth element (REE) contents (Douville et al., Chemical Geology 184:37–48, 2002). Serpentinization has occurred under a low-temperature (<270°C) retrograde regime, later overprinted by a higher temperature sulfide mineralization event. Retrograde serpentinization reactions alone cannot reproduce the reported heat and specific chemical features of Rainbow hydrothermal fluids. The following units were identified within the deposit: (1) nonmineralized serpentinite, (2) mineralized serpentinite—stockwork, (3) steatite, (4) semimassive sulfides, and (5) massive sulfides, which include Cu-rich massive sulfides (up to 28wt% Cu) and Zn-rich massive sulfide chimneys (up to 5wt% Zn). Sulfide mineralization has produced significant changes in the sulfide-bearing rocks including enrichment in transition metals (Cu, Zn, Fe, and Co) and light REE, increase in the Co/Ni ratios comparable to those of mafic Cu-rich volcanic-hosted massive sulfide deposits and different 143Nd/144Nd isotope ratios. Vent fluid chemistry data are indicative of acidic, reducing, and high temperature conditions at the subseafloor reaction zone where fluids undergo phase separation most likely under subcritical conditions (boiling). An explanation for the high chlorinity is not straightforward unless mixing with high salinity brine or direct contribution from a magmatic Cl-rich aqueous fluid is considered. This study adds new data, which, combined with the current knowledge of the Rainbow vent field, brings compelling evidence for the presence, at depth, of a magmatic body, most likely gabbroic, which provides heat and metals to the system. Co/Ni ratios proved to be good tools used to discriminate between rock units, degree of sulfide mineralization, and positioning within the hydrothermal system. Deeper units have Co/Ni <1 and subsurface and surface units have Co/Ni >1.  相似文献   

19.
Djerfisherite, a Cl-bearing potassium sulfide (K6Na(Fe,Ni,Cu)24S26Cl), is a widespread accessory mineral in kimberlite-hosted mantle xenoliths. Nevertheless, the origin of this sulfide in nodules remains disputable. It is usually attributed to the replacement of primary Fe–Ni–Cu sulfides when xenoliths interact with a K-and Cl-enriched hypothetical melt/fluid. The paper is devoted to a detailed study of the composition and morphology of djerfisherite from a representative collection (22 samples) of the deepest mantle xenoliths—sheared garnet peridotite, taken from the Udachnaya-East kimberlite pipe (Yakutia). Four types of djerfisherite were distinguished in the mantle rocks on the basis of morphology, spatial distribution, and relationships with the rock-forming and accessory minerals in the nodules. Type 1 was found in the rims of polysulfide inclusions in the rock-forming minerals of the xenoliths; there, it was younger than the primary sulfide assemblage pyrrhotite + pentlandite ± chalcopyrite. Type 2 formed rims around large polysulfide segregations (pyrrhotite+ pentlandite) in the xenolith interstices. Type 3 formed individual grains in the xenolith interstices together with other sulfides, silicates, oxides, phosphates, and carbonates. Type 4 was present as a daughter phase in the secondary melt inclusions which occurred in healed cracks in the rock-forming minerals of the xenoliths. Along with djerfisherite, the inclusions contained silicates, oxides, phosphates, carbonates, alkaline sulfates, chlorides, and sulfides. The results indicate that djerfisherite from the xenoliths is consanguine with kimberlite. Djerfisherite both in the sheared-peridotite xenoliths from the Udachnaya-East pipe and in different xenoliths from other kimberlite pipes worldwide formed owing to the interaction between the nodules and kimberlitic melts. Djerfisherite forming individual grains in the melt inclusions and xenolith interstices crystallized directly from the infiltrating kimberlitic melt. Djerfisherite bounding the primary Fe–Ni ± Cu sulfides formed by their replacement as a result of a reaction with the kimberlitic melt.  相似文献   

20.
About 435 mineral species have been identified in meteorites including native elements, metals and metallic alloys, carbides, nitrides and oxynitrides, phosphides, silicides, sulfides and hydroxysulfides, tellurides, arsenides and sulfarsenides, halides, oxides, hydroxides, carbonates, sulfates, molybdates, tungstates, phosphates and silico phosphates, oxalates, and silicates from all six structural groups. The minerals in meteorites can be categorized as having formed by a myriad of processes that are not all mutually distinct: (1) condensation in gaseous envelopes around evolved stars (presolar grains), (2) condensation in the solar nebula, (3) crystallization in CAI and AOI melts, (4) crystallization in chondrule melts, (5) exsolution during the cooling of CAIs, (6) exsolution during the cooling of chondrules and opaque assemblages, (7) annealing of amorphous material, (8) thermal metamorphism and exsolution, (9) aqueous alteration, hydrothermal alteration and metasomatism, (10) shock metamorphism, (11) condensation within impact plumes, (12) crystallization from melts in differentiated or partially differentiated bodies, (13) condensation from late-stage vapors in differentiated bodies, (14) exsolution, inversion and subsolidus redox effects within cooling igneous materials, (15) solar heating near perihelion, (16) atmospheric passage, and (17) terrestrial weathering.  相似文献   

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