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1.
Abstract. The supergiant Xikuangshan Sb deposit is located in the Middle to Upper Devonian limestone of central Hunan, China. Primary ores are composed of early-stage stibnite and calcite with rare pyrite, early main-stage stibnite and quartz, and late main-stage stibnite and calcite. New sulfur isotope data reveal the clustering of δ34S values (+5 ∼ +8 %) for both early and late main-stage stibnite; a single early-stage stibnite exhibits δ34S value (+7.5 %) identical to its main ore-stage counterparts and the coexisting calcite has almost unmodified carbon isotope composition (-4.4 %). The data suggest a probable common source of sulfur for stibnite that was deposited at different paragenetic stages. A much wider variation in δ34S values for early main-stage stibnite (+3.5 to +16.3 %, av. +7.5 %) compared to that for late main-stage stibnite (+5.3 to +8.1 %, av. +6.2 %) can be interpreted to be due to local interaction of earlier ore fluid with Devonian host rocks. The previous studies show that the Precambrian basement contains elevated Sb concentrations, and two distinctive sulfur reservoirs with δ34Spyrite values at ca. +11 ∼ +24 % and -7.0 ∼-11 %. The homogenizing effect for sulfur hydrothermally leached from the two reservoirs might have provided ore constituents for the Xikuangshan fluids.  相似文献   

2.
Quartz-hosted melt inclusions from latite dykes of the Eocene El Salvador copper porphyry system in northern Chile display wide ranges in both boron concentration (15–155 p.p.m. B) and isotope composition (δ11B −7 to +12‰; n  = 10), likely reflecting slab-derived fluid input from seawater-altered oceanic crust. In contrast, the major Miocene tin-silver and tin porphyry systems in the Bolivian back-arc region (Cerro Rico de Potosi, Chorolque, Llallagua) have distinctly different melt inclusion compositions with δ11B of −11.4 ± 2.7‰ ( n  = 10), and magmatic boron enrichment up to several hundred p.p.m. B. The `seawater' signature in the El Salvador melt inclusions explains the oxidized mineral assemblage of the copper porphyry system, as opposed to the more reduced nature of the Bolivian tin porphyry systems, which reflect intracrustal melting of pelitic rocks.  相似文献   

3.
The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution.  相似文献   

4.
We present data on the concentration, the isotope composition and the homogeneity of boron in NIST silicate glass reference materials SRM 610 and SRM 612, and in powders and glasses of geological reference materials JB-2 (basalt) and JR-2 (rhyolite). Our data are intended to serve as references for both microanalytical and wet-chemical techniques. The δ11 B compositions determined by N-TIMS and P-TIMS agree within 0.5% and compare with SIMS data within 2.5%. SIMS profiles demonstrate boron isotope homogeneity to better than δ11 B = 2% for both NIST glasses, however a slight boron depletion was detected towards the outermost 200 μm of the rim of each sample wafer. The boron isotope compositions of SRM 610 and SRM 612 were indistinguishable. Glasses produced in this study by fusing JB-2 and JR-2 powder also showed good boron isotope homogeneity, both within and between different glass fragments. Their major element abundance as well as boron isotope compositions and concentrations were identical to those of the starting composition. Hence, reference materials (glasses) for the in situ measurement of boron isotopes can be produced from already well-studied volcanic samples without significant isotope fractionation. Oxygen isotope ratios, both within and between wafers, of NIST reference glasses SRM 610 and SRM 612 are uniform. In contrast to boron, significant differences in oxygen isotope compositions were found between the two glasses, which may be due to the different amounts of trace element oxides added at ten-fold different concentration levels to the silicate matrix.  相似文献   

5.
Abstract: Interstitial water expelled from gas hydrate-bearing and -free sediments in the Nankai Trough are analyzed in terms of Cl-, SO42-, δ18O and δD. The baselines for the Cl- concentration and δ18O value are close to seawater values (530 mM and 0%), indicating that the interstitial water is of seawater origin. The δD values decrease with depth, implying isotopic exchange of hydrogen between upwelling biogenic methane depleted in D and interstitial water. The Cl- concentrations in gas hydrate-bearing sediments are anomalously low, while the δ18O and δD values are both high, suggesting that the water forming these gas hydrates was poor in Cl- and enriched in 18O and D during gas hydrate formation. Calculation of the gas hydrate saturations using Cl "and δ18O anomalies gives results of up to 80 % in sand, and shows that the δ18O baseline is not consistent with the Cl" baseline. The δ18O baseline increases by +1% in gas hydrate-free clay and silt. This is considered to be caused by clustering of water molecules after gas hydrate dissociation in response to the upward migration of the base of gas hydrate stability, as indicated by the presence of a double bottom-simulating reflector at this site. The water clusters enriched in 18O are responsible for the increase in the δ18O baseline with normal Cl". The abrupt shallowing of the base of gas hydrate stability may induce the dissociation of gas hydrates and the accumulation of gases in the new stability zone, representing a geological process that increases gas hydrate saturation.  相似文献   

6.
The carbon (δ13 C) and oxygen (δ18O) isotopic composistion in mollusc shells in mainly determined by the isotopic composition of water and dissolved bicarbonate. The δ18O values of water show a good correlation with the salinity of the Baltic. This correlation served as a basis for reconstructing palaeosalinity and for stratifying the marine sediments according to the δ18O values of the carbonate skeletons of subfossil shells. The δ13C values in shells are mainly determined by the isotopic composition of land-originating bicarbonate, especially in the carbonate skeleton of Lymnaea balthica , which inhabits the immediate coastal zone. According to the δ18O data, salinity in the investigated area (the coastal area of W and NW Estonia) was highest (about 9–11%) during the Littorina stage. The Limnae a stage had, in general, a salinity similar to the contemporary one, but during some phases possibly exceeding it by 2–3%.  相似文献   

7.
We report a new approach to conduct fast and accurate lithium isotope ratio measurements by MC-ICP mass spectrometry after wet chemical sample preparation. In contrast to most previously published methods our MC-ICP-MS set-up did not use a desolvating system to achieve appropriate ion beam intensities and, therefore, was less affected by matrix-induced shifts of the instrumental mass bias. As the total lithium background and build-up in the sample introduction system was low, previous sample residues could be washed out by an extended uptake of the new sample. Elimination of a nitric acid rinse step increased the sample throughput by a factor of two and allowed the instrumental mass bias drift to be tracked more precisely. δ7Li values of powdered silicate rock reference materials and seawater obtained in this study revealed good accuracy and an overall analytical uncertainty of typically 0.5‰ (2s). On the basis of a comparison between our lithium isotope data and compiled literature data, we recommend preliminary average δ7Li values for seawater (+30.8‰) and several silicate rock reference materials (BHVO-1: +5.0‰; JA-1: +5.6‰; JB-2: +4.8‰). The compilation of published δ7Li values for seawater suggests that the observed large lithium isotope differences are due to inter-method and/or interlaboratory bias. Most recently published δ7Li values for seawater show little variation and confirm a constant lithium isotope composition (at the sub ‰ level) of seawater in well mixed ocean basins.  相似文献   

8.
Abstract. The Onsen site is an active submarine hydrothermal system hosted by the Desmos caldera in the Eastern Manus Basin, Papua New Guinea. The hydrothermal fluid is very acidic (pH=1.5) and abundant native sulfur is deposited around the vent. The δ34S values of native sulfur range from -6.5 to -9.3 %o. δ34S values of H2S and SO4 in the hydrothermal fluid are -4.3 to -9.9 %o and +18.6 to +20.0 %o, respectively. These δ34S values are significantly lower than those of the other hydrothermal systems so far reported. These low δ34S values and the acidic nature of the vent fluids suggest that volcanic SO2 gas plays an important role on the sulfur isotope systematic of the Onsen hydrothermal system. Relationship among the δ34S values of S-bearing species can be successively explained by the model based on the disproportionation reaction starting from the volcanic SO2 gas. The predicted δ34S values of SO2 agree with the measured whole rock δ34S values. δD and δ18O values of clay minerals separated from the altered rock samples also suggest the contribution of the magmatic fluid to the hydrothermal system. Present stable isotopic study strongly suggests that the Onsen hydrothermal site in the Desmos caldera is a magmatic submarine hydrothermal system.  相似文献   

9.
Refinements have been made to achieve over 99% yield in the conversion of CO to CO2 in order to improve the reproducibility and accuracy of δ18 O measurements in sulfates. BaSO4 (10-15 mg) was mixed with an identical amount of spectrographic-grade graphite and loaded into a Pt boat. The mixture was gradually heated to 1100 °C to reduce sulfate to CO and CO2; the former gas was simultaneously converted to CO2 by a glow discharge between Pt electrodes immersed in a magnetic field (produced by a pair of external neodymium magnets). A small memory effect was noticed during the analysis (less than 0.3‰ per 10‰ difference in δ18 O between two subsequently analysed samples). The memory effect, however, was suppressed by repetitive preparation of the same specimen. CO2 produced in this way from sulfate reference samples was analysed on a dual inlet and triple collector mass spectrometer along with CO2 equilibrated with VSMOW, GISP and SLAP water reference samples. To avoid large departures of measured isotope ratios from 18O/16O of the working calibrator we used CO2 gas prepared from ocean water sulfate for this purpose. The calibrated δ18 O values (in ‰) obtained in this way for NBS-127, IAEA SO-5 and IAEA SO-6 reference materials were 8.73 ± 0.05, 12.20 ± 0.07 and -10.43 ± 0.12, respectively.  相似文献   

10.
ABSTRACT
The mineralogy and isotope geochemistry of carbonate minerals in the Coorong area are determined by the water chemistry of different depositional environments ranging from seawater to evaporitically modified continental water. The different isotopic compositions of coexisting calcite and dolomite suggest that each of the above two minerals was formed from water of composition and origin unique to that specific mineral. In addition, the dolomite was not formed by simple solid state cation exchange.
The occurrence of two types of dolomite was shown by isotope analysis and SEM observations. The dolomite, which is isotopically light (δ13C = -1 to -2% 0 ; δ18O=+3 to +5%0) and of fine grain size (˜ 0·5 μm) probably precipitated under the influence of evaporitically modified continental water. Coarser grained dolomite (up to 4 μm) is isotopically heavier (δ13C=+3 to +4%0; δ18O=+5 to + 6%0) contains Mg in excess of Ca and was formed in or close to equilibrium with atmospheric CO2 probably by the dolomitization of aragonite.  相似文献   

11.
Carbon isotope measurements carried out on 201 carbonate samples from the early Proterozoic of the Kola Peninsula, N. Karelia and Norway yield δ13C (PDB) spanning - 20.5% to + 11%. A general δ13C secular trend shows that prior to 2.33 Ga values are typically 'normal' marine, averaging around - 3%0. Between 2.33 and 2.06 Ga, in Jatulian time, there follows a rapid excursion to positive δ13C of around + 6%. Post-Jatulian time is characterized by δ13C of sedimentary carbonates fluctuating between - 5% and +3%; also it is remarkable for the first pronounced development of diagenetic carbonates, which have δ13C between - 14 % and - 6% . The c. 6% positive δ13C shift with a duration of about 270 Myr coincides with a maximum in the diversity and abundance of stromatolites, and with widespread development of 'red beds', but does not coincide with the maximum of buried Corg mass. The Fennoscandian Shield represents the largest isotoically anomalous carbonate province yet reported, and the positive δ13C excursion together with a series of major global palaeoenviromental changes seems to be more intense than the Precambrian/Cambrian transition events. However, it is still not clear what kind of mechanism this phenomenon could be attributed to. An increase of the 'Ronov ratio', and/or 'Broecker ratio' and other possible models are discussed as the target for future investigations.  相似文献   

12.
Oxygen isotope exchange and closure temperatures in cooling rocks   总被引：3，自引：0，他引：3  
Retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ18O within grains, and the bulk δ18O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ18O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values ('slow cooling'), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures ( T c) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes 'slow' cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two-phase system. In some systems oxygen isotope reversals can be developed. If cooling is not 'slow', then the mineral δ18O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ18O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems.  相似文献   

13.
This paper presents an adapted anion exchange column chemistry protocol which allowed separation of high-purity fractions of Cu and Zn from geological materials. Isobaric and non-spectral interferences were virtually eliminated for consequent multiple-collector ICP-MS analysis of the isotopic composition of these metals. The procedure achieved ∼ 100% recoveries, thus ensuring the absence of column-induced isotopic fractionation. By employing these techniques, we report isotopic analyses for Cu and Zn from five geological reference materials: BCR-027 blende ore (BCR), δ65Cu = 0.52 ± 0.15‰ (n = 10) and δ66Zn = 0.33 ± 0.07‰ (n = 8); BCR-030 calcined calamine ore (BCR), δ66Zn = -0.06 ± 0.09‰ (n = 8); BCR-1 basalt (USGS), δ66Zn = 0.29 ± 0.12‰ (n = 8); NOD-P-1 manganese nodule (USGS), δ65Cu = 0.46 ± 0.08‰ (n = 10) and δ66Zn = 0.78 ± 0.09‰ (n = 9); SU-1 Cu-Co ore (CCRMP), δ65Cu = -0.018 ± 0.08‰ (n = 10) and δ66Zn = 0.13 ± 0.17‰ (n = 6). All uncertainties are ± 2s; copper isotope ratios are reported relative to NIST SRM-976, and zinc isotope ratios relative to the Lyon-group Johnson Matthey metal (batch 3-0749 L) solution, JMC Zn. These values agree well with the limited data previously published, and with results reported for similar natural sample types. Samples were measured using a GVi IsoProbe MC-ICP-MS, based at the Natural History Museum, London. Long-term measurement reproducibility has been assessed by repeat analyses of both single element and complex matrix samples, and was commonly better than ± 0.07‰ for both δ66Zn and δ65Cu.  相似文献   

14.
Calcium Isotopic Composition of Various Reference Materials and Seawater   总被引：1，自引：0，他引：1  
A compilation of δ44/40Ca (δ44/40Ca) data sets of different calcium reference materials is presented, based on measurements in three different laboratories (Institute of Geological Sciences, Bern; Centre de Géochimie de la Surface, Strasbourg; GEOMAR, Kiel) to support the establishment of a calcium isotope reference standard. Samples include a series of international and internal Ca reference materials, including NIST SRM 915a, seawater, two calcium carbonates and a CaF2 reference sample. The deviations in δ44/40Ca for selected pairs of reference samples have been defined and are consistent within statistical uncertainties in all three laboratories. Emphasis has been placed on characterising both NIST SRM 915a as an internationally available high purity Ca reference sample and seawater as representative of an important and widely available geological reservoir. The difference between δ44/40Ca of NIST SRM 915a and seawater is defined as -1.88 O.O4%o (δ44/42CaNISTSRM915a/Sw= -0.94 0.07%o). The conversion of values referenced to NIST SRM 915a to seawater can be described by the simplified equation δ44/40CaSa/Sw=δ44/40CaSa/NIST SRM 915a - 1.88 (δ44/42CaSa/Sw=δ44/42CaSa/NIST SRM 915a - 0.94). We propose the use of NIST SRM 915a as general Ca isotope reference standard, with seawater being defined as the major reservoir with respect to oceanographic studies.  相似文献   

15.
硼是一种中等挥发性元素,具有11B和10B两个稳定同位素。两个同位素间高达10%的相对质量差使其在地质过程中引起高达-70‰至+75‰的硼同位素变化。硼在自然界主要与氧键合形成三配位(BO3)和四配位(BO4)结构,因而11B和10B间同位素分馏主要受控于三配体(BO3)和四面体(BO4)间配分。本文综述了低温和高温地质过程的硼同位素分馏的理论和实验研究进展。在溶液中B(OH)3和${B(OH)^{-}_{4}}$间硼同位素分馏受pH和热力学p-T条件控制,实验和理论表征获得常温常压条件下的B(OH)3和$B(OH)^{-}_{4}$间同位素分馏系数(α3-4)变化范围为1.019 4至1.033 3。低温条件下矿物(如碳酸盐、黏土矿物(蒙脱石和伊利石)、针铁矿、水锰矿、硼酸盐)与溶液间硼同位素分馏行为除了受p-T-pH影响外,矿物表面吸附引起的分馏效应十分显著。在中高温过程(蒙脱石伊利石化、富硼电气石和白云母矿物与热液流体,以及硅酸盐熔体与流体)中硼同位素分馏行为受到硼配位构型、化学成分以及物理化学条件的控制。随着硼同位素分馏机理研究的深入以及越来越完善的地质储库硼同位素端员特征表征,硼同位素地球化学指标可以灵敏示踪成矿物质来源、探究成矿作用与成因模式和重建成矿过程物理化学条件。目前矿床硼同位素地球化学研究的难点在于实现不同赋存相(如流体、矿物和熔体)中硼配位键合结构和硼同位素组成的精细化表征。  相似文献   

16.
Two sections of the Upper Cenomanian and Lower Turonian in central and south-east Poland were investigated for foraminifers, CaCO3content, carbon content insoluble in HCl (Corg) and in the carbonates (Ccarb), carbon and oxygen isotopic composition of bulk-rock carbonates and elemental abundances. The Cenomanian/Turonian boundary interval is characterized by the appearance of more marly facies, a δ13C and δ18O stable isotope anomaly, a considerable increase in Corg content and decrease in Ccarb content and substantial changes in the foraminiferal assemblages. A major carbon stable isotope excursion with a shift of +2 (PDB) occurs in the lowermost Whiteinella archaeocretacea Zone. The late Cenomanian δ13C anomaly is associated with heavy δ18O values. The peak value of δ13C corresponds to the minima in P/B ratio and in diversity of foraminiferal assemblages. A late Cenomanian anoxic event is thought to be responsible for changes in foraminiferal assemblages. However, elemental abundance analyses do not show changes in the concentrations of trace elements. This may be explained by the long distance between studied area and a source of enrichment which was probably located in the western hemisphere.  相似文献   

17.
A breccia vein sampled from a shear zone in greenschist facies metapelites at Mount Isa, Queensland, Australia, shows a systematic variation in vein geometry that is related to the geometry of folding and faulting within the sample. Calcite vein-fill is coarse grained and equigranular, suggesting precipitation in a fluid-filled space. Partially folded veins suggest that veining occurred during folding and faulting. The breccia vein contains a central zone in which dilation has occurred simultaneously in all directions in the plane of section, implying that this was a zone of high fluid pressure and nearly isostatic differential stress during folding and faulting. From these observations, it can be inferred that the breccia vein was a zone of high permeability and a likely fluid channel during deformation. This hypothesis was tested by stable isotope analysis of veins and host rocks. The calcite veins have δ13C values of -11.1 ± 0.1% and δ18O values of 6-10%o, whereas the host metapelite has δ13C values of -10.62 and -10.11% and δ18O values of 14-15%o. These values are consistent with an igneous-derived, H2O-dominated fluid that exchanged little oxygen with the host rocks, but derived much of its carbon from the wall rock. The isotopic disequilibrium between the veins and the wall rock confirms that the fluid was externally derived, and that the breccia vein acted as a channel for large-volume fluid flow within the shear zone.  相似文献   

18.
Boron Isotopic Analysis of Proposed Borosilicate Mineral Reference Samples   总被引：2，自引：0，他引：2  
This brief contribution presents new boron isotopic data for a set of proposed borosilicate reference minerals, most of which are described in the companion paper by Dyar et al.2001. The results for a variety of minerals (tourmalines, danburite, prismatine, serendibite, ferroaxinite and a Li mica) show that it is generally possible to reproduce the 11 B/10 B ratio within ± 0.5 per mil with replicate chemistry and mass spectrometry over long time spans. Because the accuracy of boron isotopic analysis is commonly determined by reference to secondary standards, it is suggested that some of the samples used in this study be adopted for interlaboratory comparisons and for quality control on boron isotopic analyses produced by a variety of analytical methods.  相似文献   

19.
Abstract. Carboniferous-Permian limestones of the Akiyoshi Plateau, in the Inner Zone of southwestern Japan, are composed of essentially pure calcium carbonate containing only small amounts of other elements, and they are accompanied by marble and copper skarn deposits near the contact with late Cretaceous granitoids. The δ18O values of the Akiyoshi limestones range widely from 7.6 to 28.3% and are mostly lower than those of other areas of the same age (23–29%), whereas the differences among the δ13C values are small. The δ18O values are negatively correlated with Mn and Fe contents. Samples with high δ18O (>25%) and δ13C (>2%) values do not contain Fe, Zn, or Pb, but those with low δ18O values tend to be rich in these elements, indicating that these elements were introduced by interaction with H2O dominant fluids, possibly of magmatic origin. Potential scores for evaluating the degree of interaction with hydro thermal fluids were calculated for δ18O, δ13C, Fe, Mn, Zn, Pb, and Sr. Higher scores implying much hydrothermal interaction were evident in the Mt. Hananoyama area, where there are many skarn deposits, and along faults oriented mainly NNW-SSE. Therefore, these are promising areas for exploring for blind deposits. It is likely that the hydrothermal fluid traveled through the limestones along fractures at the time of the granitic intrusions. However, the potential scores here are much smaller than those in the Pb-Zn mineralized area of the Kamioka mine, so more detailed petrological and mineralogical investigations are necessary.  相似文献   

20.
Abstract: Carbonate rocks of Cambrian (18 samples) and lower-middle Ordovician (11 samples) ages from South Korea were analyzed for sulfur contents of structurally substituted sulfate (SSS) and sulfides and their δ34S values. The δ34S values of SSS ranging from +25.9 to +45.2 permil, are averaged as +33.6 and +33.5 permil for the Cambrian and Ordovician rocks, respectively, which indicate high δ34S values of the Cambro-Ordovician seawater. The SSS contents in the carbonate rocks are low being 2.9 to 17.3 ppm S (averaged as 7.0 ppm S). Sulfide sulfur, on the contrary, is much abundant containing 3 to 1,880 ppm S and the δ34S values range widely between –17.6 and +31.1 permil. Sulfide sulfur of the studied rocks excluding impure carbonates has an average content of 187 ppm S and δ34S value of +12.8 permil (n=24). The estimated δ34S (sulfate–sulfide) values, which range from 13.8 to 25.4 permil in general with a few exceptions from 36.5 up to 52.3 permil for some impure carbonates, may provide evidence for the persistent oceanic anoxia with its temporary recovery during the Cambro-Ordovician time.
The SSS and sulfide sulfurs have often higher δ34S values than the Mesozoic-Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high δ34S values of the Korean ore deposits might be caused to some extent by 34S enrichment from the host carbonates, resulting in the low SSS contents observed.  相似文献   

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