Carius Tube Research Articles

A comparison of high accuracy isotope dilution techniques for the measurement of low level sulfur in gas oils

A comparison of high accuracy methods for the analysis of total sulfur in gas oils by three metrology institutes is described. The work contains a comparison of three different aspects of the analysis: sample digestion, instrumental measurement and isotope dilution strategies. Thermal ionisation mass spectrometry (TIMS) in combination with high pressure asher (HPA) or Carius tube digestion has traditionally been used for such high accuracy analysis. However, this paper demonstrates that the faster, less laborious technique of ICP-MS in combination with microwave digestion is equally capable. Results from the comparison experiments show excellent agreement for fuel samples containing sulfur concentrations in the range 11–200 μg g −1. This excellent agreement across the different sample preparation, measurement and isotope dilution techniques has been exploited in the certification of two new diesel fuel reference materials.

Poly[(2,2'-bipyridine)tetrakis(imidazolato)diiron(II)]: structural and spin-state phase transitions and low-temperature magnetic ordering in a unique 2-dimensional material.

Poly[(2,2'-bipyridine)tetrakis(imidazolato)diiron(II)] was synthesized by the reaction of ferrocene with imidazole in an excess of 2,2'- bipyridine in a Carius tube at 130 degrees C. Dc magnetic susceptibility studies at an applied field of 1000 G reveal that on cooling from room temperature, the material undergoes two structural phase transitions designated alpha --> beta and beta --> gamma at 151 and 133 K, respectively. On warming, the gamma --> beta and beta --> alpha transitions are observed at 137 and 151 K, respectively; a 4 K thermal hysteresis clearly detectable in the lower temperature beta <--> gamma transition. These structural phase transitions have also been studied by detailed, variable-temperature, ac susceptibility and Mössbauer spectroscopy techniques. Single-crystal X-ray diffraction studies done at 294, 143, and 113 K reveal 2, 12, and 6 unique iron centers in the alpha-, beta-, and gamma-forms, respectively. All three forms have the same basic structure involving 2D extended double layer sheets (bilayers) of alternating tetrahedral and octahedral irons singly bridged by imidazolate ligands, with the octahedral centers additionally coordinated by 2,2'-bipyridine ligands that occupy positions between the sheets. Magnetic susceptibility and bond length data reveal that in the gamma-phase one in three six-coordinate sites corresponds to spin singlet ground-state iron(II); i.e., the overall alpha --> gamma process involves a spin-crossover transition such that at least 1/6 of the iron sites in the gamma-phase correspond to S = 0. This is supported by the low-temperature Mössbauer spectra of the gamma-phase, which reveal the simultaneous presence of both S = 2 and S = 0 iron(II) centers. The compound magnetically orders, with a resultant small remnant magnetization, at low temperatures. The magnetic phase transition, studied by a combination of dc and ac susceptibility and Mössbauer techniques, occurs at T(c) approximately 6.5 K.

Platinum group element geochemistry of komatiites from the Alexo and Pyke Hill areas, Ontario, Canada

Thirty-three whole-rock drill core samples and thirteen olivine, chromite, and sulfide separates from three differentiated komatiite lava flows at Alexo and Pyke Hill, Canada, were analyzed for PGEs using the Carius tube digestion ID-ICP-MS technique. The emplaced lavas are Al-undepleted komatiites with ∼27% MgO derived by ∼50% partial melting of LILE-depleted Archean mantle. Major and minor element variations during and after emplacement were controlled by 30 to 50% fractionation of olivine Fo93–94. The emplaced lavas are characterized by (Pd/Ir)N = 4.0 to 4.6, (Os/Ir)N = 1.07, and Os abundances of ∼2.3 ppb. Variations in PGE abundances within individual flows indicate that Os and Ir were compatible (bulk DOs,Ir = 2.4–7.1) and that Pt and Pd were incompatible (bulk DPt,Pd < 0.2) during lava differentiation, whereas bulk DRu was close to unity. Analyses of cumulus olivine separates indicate that PGEs were incompatible in olivine (DPGEsOl-Liq = 0.04–0.7). The bulk fractionation trends cannot be accounted for by fractionation of olivine alone, and require an unidentified Os-Ir-rich phase. The composition of the mantle source (Os = 3.9 ppb, Ir = 3.6 ppb, Ru = 5.4 ppb, Pt and Pd = 5.7 ppb) was constrained empirically for Ru, Pt, and Pd; the Os/Ir ratio was taken to be identical to that in the emplaced melt, and the Ru/Ir ratio was taken to be chondritic, so that the absolute IPGE abundances of the source were determined by Ru. This is the first estimate of the PGE composition of a mantle source derived from analyses of erupted lavas. The suprachondritic Pd/Ir and Os/Ir of the inferred Abitibi komatiite mantle source are similar to those in off-craton spinel lherzolites, orogenic massif lherzolites, and enstatite chondrites, and are considered to be an intrinsic mantle feature. Bulk partition coefficients for use in komatiite melting models derived from the source and emplaced melt compositions are: DOs,Ir = 2.3, DRu = 1.0, DPt,Pd = 0.07. Ruthenium abundances are good indicators of absolute IPGE abundances in the mantle sources of komatiite melts with 26 to 29% MgO, as Ru fractionates very little during both high degrees of partial melting and lava differentiation.

A closed system digestion and purification procedure for the accurate assay of chlorine in fossil fuels

This paper describes a robust and quantitative method to separate, purify, and assay the amount of chlorine in fossil fuels using isotope dilution mass spectrometry. The digestion/extraction process uses Carius tubes containing the fossil fuel samples in the presence of HNO3, AgNO3 and a 37Cl spike. The closed system oxidation permits complete equilibration of the sample and spike Cl. The evolved chlorine is trapped as AgCl within the Carius tube, and can then be separated and cleaned. The purified AgCl is also amenable to isotopic analysis by solid or gas source isotope ratio mass spectrometry. For isotope dilution mass spectrometry, the chlorine can be readily measured in a thermal ionization mass spectrometer in a negative ion mode as 37Cl/35Cl ratios with an approximate detection limit (LOD) of 0.3 μg Cl and a precision of 0.2%, relative. This technique may also be used to produce samples suitable for high precision measurements of chlorine isotopic variations in fossil fuels and chlorinated hydrocarbons.

Re–Os systematics of UB-N, a serpentinized peridotite reference material

The reference material (RM) UB-N is a typical representative of earth's upper mantle. It is a serpentinized garnet and spinel-bearing peridotite (a metamorphosed lherzolite) from the Vosges mountains, France, that is well characterized for major and many trace elements. In order to test whether UB-N is a suitable Re–Os reference material, 32 digestions in three different laboratories (CRPG/CNRS, MPI (Mainz) and University of Leoben) with four different digestion techniques (low-temperature acid attack, Carius tube dissolution, high-pressure asher (HPA-S) acid attack and alkali fusion) were performed. The results show that the low-temperature acid attack is unsuitable for the study of the Re–Os systematics of UB-N. Surprisingly, the well-established Carius tube acid digestion technique also fails to completely digest all Os-bearing mineral phases. Only alkali fusion and HPA-S acid attack yield the highest Os concentrations. Though sample inhomogeneity has been recognized (approximately 6% RSD for 2-g sample aliquots), it is possible to determine a well-defined average Os concentration of 3.85±0.13 ng g −1 (95% confidence; 19 digestions, fusion and HPA-S only). Rhenium-bearing minerals are very homogeneously distributed and replicates within each laboratory yield highly reproducible results independent of the digestion technique. A value of 0.2095±0.0040 ng g −1 (95% confidence; n=24) is assigned to the Re concentration. The best estimate for the whole-rock 187Os/ 188Os is 0.1278±0.0002 (95% confidence; n=12). The UB-N reference material now has well-understood Re–Os systematics that are typical of fertile upper mantle rocks. Analysis of this standard is, thus, highly recommended for the validation of Re–Os analytical procedures.

High Precision Ru, Pd, Ir, Pt, Re and REE Determinations in the Stevns Klint Cretaceous‐Tertiary Boundary Reference Material (FC‐1) by Isotope Dilution Multiple Collector Inductively Coupled Plasma‐Mass Spectrometry

We present high precision Ir, Ru, Pt, Pd, Re and rare earth element (REE) determinations by isotope dilution multiple collector‐ICP‐MS on the Cretaceous‐Tertiary boundary sedimentary reference material FC‐1. Samples for platinum‐group element measurements were digested in Carius tubes followed by acid digestion. The platinum‐group elements were subsequently separated by anion exchange chemistry and determined by multiple collector‐ICP‐MS. The accuracy of the platinum‐group element analyses have been verified by comparative analyses of the reference materials WITS‐1 and GP13 (sample size 0.5‐1 g). Replicate analyses of FC‐1 (sample size 0.2 g) exhibit good reproducibility (RSD &lt; 5%) for all the analysed platinum‐group elements. REE data also exhibit excellent reproducibility (RSD &lt; 0.5%), which indicates that this sample is homogeneous for the determination of the platinum‐group elements and REE at the 0.2 g level.

Direct determination of trace levels of Os, Ir, Ru, Pt and Re in kimberlite and other geological materials using HR-ICP-MS

A fast and simple method for the direct determination of low concentrations of Os, Ir, Ru, Pt and Re from the same sample aliquot has been developed. It exploits the superior mass resolution capabilities of a double focussing sector field mass spectrometer (Finnigan MAT Element), in combination with a highly sensitive, high TDS tolerant teflon® Microflow nebulizer. Samples are spiked with an Os isotopic tracer, and digested in inverse aqua regia in sealed Carius tubes for 24 hours at 240 °C. Osmium is subsequently separated from the matrix (which contains the other PGEs) in a previously developed solvent extraction step, and measured in low resolution mode. The remaining sample solution is dried, redissolved in 2% HCl and analyzed directly for Ir, Ru, Pt and Re using the method of standard addition, in high resolution mode. Procedural blanks are <0.009 ppb for all PGEs except Pt (∼0.046 ppb) and Rh (∼0.0143 ppb). Instrumental detection limits based on the 3σ criterion for background are 0.0009 ppb for Re, 0.0048 ppb for Os, 0.002 ppb for Ru, and 0.003 and 0.01 ppb for Ir and Pt, respectively. The accuracy of the analytical method has been verified by comparing the results obtained in this study for three PGE reference materials (komatiite WITS1, komatiite KAL1, and peridotite GP13) with those reported in the literature.

Determination of Cr in certified reference material HISS-1, marine sediment, by cold plasma isotope dilution ICP-MS and INAA: comparison of microwave versus closed (Carius) tube digestion

The recovery of Cr from National Research Council Canada (NRCC) certified reference material HISS-1 sediment was investigated by non-destructive instrumental neutron activation analysis (INAA) and isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) after two different chemical treatments: (1) microwave dissolution using HNO3, HF, and HClO4, followed by reflux with concentrated HClO4, and (2) a closed system method using sealed Carius tube digestion with HNO3 and HCl at high temperature (240 °C) and high pressure (1 × 107 Pa, ∼100 atm). The first chemical treatment gave recoveries of only ∼50% in agreement with observations of Yang et al. of NRCC. Samples digested in Carius tubes gave recoveries that ranged from 79 to 110% which may reflect heterogeneity in the samples rather than differing recoveries. This is supported by the excellent agreement of the mean value determined by INAA of 31.4 ± 4.5 µg g−1, and the mean value of 28.1 ± 3.9 µg g−1 by Carius tube digestion and the observation that these standard deviations are essentially equal and much larger than the measurement precisions. The results from this study are also in excellent agreement with the certified value of 30.0 ± 6.8 µg g−1. This preliminary study demonstrates that chemical treatment of this sediment with HNO3 and HCl acids in closed system Carius tubes is an efficient and capable preparation method for the determination of Cr in silicate materials which typically contain refractory Cr-bearing minerals. This study also demonstrates the unique advantage of using two independent methods for the determination of Cr in a complex matrix which has a high potential for low chemical recovery.

Determination of mercury in coal by isotope dilution cold-vapor generation inductively coupled plasma mass spectrometry.

A method based on isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICPMS) has been developed for high-accuracy determinations of mercury in bituminous and sub-bituminous coals. A closed-system digestion process employing a Carius tube is used to completely oxidize the coal matrix and chemically equilibrate the mercury in the sample with a 201Hg isotopic spike. The digestates are diluted with high-purity quartz-distilled water, and the mercury is released as a vapor by reduction with tin(II) chloride. Measurements of 201Hg/202Hg isotope ratios are made using a quadrupole ICPMS system in time-resolved analysis mode. The new method has some significant advantages over existing methods. The instrument detection limit is less than 1 pg/mL. The average blank (n = 17) is 30 pg, which is roughly 1 order of magnitude lower than the equivalent microwave digestion procedure. The detection limit in coal is blank limited and is approximately 40 pg/g. Memory effects are very low. The relative reproducibility of the analytical measurements is approximately 0.5% for mercury concentrations in the range 10-150 ng/g. The method has been used to measure mercury concentrations in six coal reference materials, SRM 1632b (77.4 ng/g), SRM 1632c (94.3 ng/g), BCR 40 (433.2 ng/g), BCR 180 (125.0 ng/g), BCR 181 (135.8 ng/g), and SARM 20 (252.6 ng/g), as well as a coal fly ash, SRM 1633b (143.1 ng/g). The method is equally applicable to other types of fossil fuels including both crude and refined oils.

In Situ Generation of the Fulvalene Ligand via C–H Activation by Gray Antimony and Its Incorporation into the Tetrahedral Cluster [(μ,η 5 :η 5 -C 10 H 8 ) (η 5 -C 5 H 5 )M 3 (CO) 6 (μ 3 -Sb)] (M=Mo or W) 1

The first tetrahedral clusters containing a single “naked” antimony atom have been prepared by the thermolysis of [CpM(CO)3]2 (M=Mo or W) in the presence of gray antimony at 180°C in toluene in a sealed Carius tube. X-ray structural characterization revealed that, in addition to the incorporation of Sb in the cluster, it has also affected coupling of two Cp rings to form [(μ,η 5:η 5-C10H8)(η 5-C5H5)-M3(CO)6(μ 3-Sb)]. It is only the second example of in situ formation of the fulvalene ligand for group-6 metal. Simultaneous with the C–C coupling reaction, a mirror of Sb forms on the reaction tube; this indicates that SbH3 is formed in the hydrogen abstraction step, which then subsequently decomposes at the tube wall.

High-Precision, Simultaneous Analysis of Pt, Pd, and Rh in Catalytic Converter Samples by Carius Tube Dissolution and Inductively Coupled Plasma Atomic Emission Spectroscopy with Charge-Injection Device Detection

A robust method of analysis that uses multichannel array detector technology is presented for high-precision, accurate measurement of Pt, Pd and Rh in catalytic converters. Catalytic converter samples, National Institute of Standards and Technology (NIST) reference standards, and a fresh converter sample are dissolved and analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Complete dissolution of sample sizes up to 2 g of NIST reference standards is achieved with the use of high-pressure, high-temperature carius tubes. Carius tube dissolution of a modern catalytic converter sample is found to be incomplete because of the presence of higher concentrations of Ce, Ni, and Zr. For this sample, the addition of FeCl3 increases the dissolving power of the carius tube for base metals and noble metals, particularly Rh. Although interference problems are encountered in samples bearing high concentrations of Fe, use of a high-resolution ICP-AES system alleviated these problems. Precise quantitation of Pt, Pd, and Rh is accomplished by using the method of standard additions, with high accuracy and a precision of 1–2% RSD (relative standard deviation). This analysis also confirmed the values determined by NIST by using isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) for standard reference materials (SRMs) 2556 and 2557.

Simplified method for the determination of Ru, Pd, Re, Os, Ir and Pt in chromitites and other geological materials by isotope dilution ICP-MS and acid digestion.

A method for the determination of low Ru, Pd, Re, Os, Ir and Pt abundances in geological reference materials by isotope dilution inductively coupled plasma mass spectrometry (ICP-MS) after acid digestion in a high pressure asher (HPA-S) is presented. The digestion technique is similar to that using Carius tubes but easier to handle and reaches higher temperatures. Osmium can be determined as OsO4 with ICP-MS directly after digestion through a sparging technique. The remaining elements are preconcentrated by means of anion column chromatography. The resin is digested directly without elution leading to high yields but this causes problems if Zr is present at higher levels in the silicate rich materials. The analytical results for international platinum group element (PGE) reference materials, chromitite CHR-Bkg, basalt TDB-1 and gabbro WGB-1, are presented and compared with literature data, demonstrating the validity of the described method. Although higher in concentration, PGEs determined for reference material WGB-1 were worse than for TDB-1 indicating a more inhomogeneous distribution of the platinum group mineral phases. The low PGE abundance chromitite standard, CHR-Bkg, is likely to be homogeneous for Ru, Re, Os and Ir and is recommended as a reference material for the study of chromitites. Detection limits (3s x total procedure blank) range from 0.012 ng (Re and Os) to 0.77 ng (Pt), which could be further improved by applying higher quality acids.

A novel sample decomposition technique at atmospheric pressure for the determination of Os abundances in iron meteorites using isotope dilution inductively coupled plasma-mass spectrometry.

A safe and reliable analytical technique for the determination of Os abundances in ten iron meteorites of various chemical groups was developed using isotope dilution inductively coupled plasma-mass spectrometry coupled with a sample decomposition technique. A major advantage of the sample decomposition technique developed here is that the pressure inside the reaction flask is not increased through the decomposition reaction because the flask is a fully opened system, obviating the risk of explosion of the glass apparatus. Another advantage is that there is no restriction in the sample size being decomposed. In this study, about 2 g of metallic sample were decomposed safely, and this sample size, > 10 times larger than that typically used for the Carius tube technique, allows one to obtain more reliable Os data for heterogeneous samples. The metallic samples were decomposed in a glass flask purged with Ar. Since the O2 was purged from the reaction flask, Os was not oxidised to volatile OsO4, thereby preventing significant evaporation loss of Os. The typical recovery of Os throughout the sample decomposition and separation processes was > 80%, and the total Os blank through the decomposition of a 1 g amount of sample was less than 20 pg. Os abundances were determined by means of stable isotope dilution mass spectrometry using a 190Os-enriched isotopic tracer. Except for Sikhote-Alin, the measured Os abundances in almost all the iron meteorites exhibited a good agreement with the previously published Os abundance data, within the analytical uncertainty achieved in this study (2-5%). For the Sikhote-Alin meteorite, on the basis of a better correlation between Os and Ir abundances, we believe that our Os abundance data should be more reliable. The Os abundance data obtained in this work clearly demonstrated the suitability of the newly developed sample decomposition procedure for low level Os determinations.

Rapid determination of Os isotopic composition by sparging OsO 4 into a magnetic-sector ICP-MS

We present a method for the rapid determination of Os isotopic compositions and platinum group element (PGE) concentrations using ICP-MS on the same sample split. The method makes use of transfer of volatile OsO 4 by an Ar gas stream into the torch of a magnetic sector ICP-MS for analysis. A variety of partial or complete sample dissolution methods can be used, namely (1) microwave oven digestion of samples in pressurized Teflon vessels under oxidizing acidic conditions, (2) NiS fire assay for complete sample dissolution and PGE preconcentration, (3) acid leaching techniques to extract labile PGE fractions, and (4) Carius tube digestion. Microwave oven sample digestion with HF–HNO 3–HCl in an all-Teflon system as well as Carius tube digestion also allows the determination of Os isotopic composition and Os and Re concentrations on the same sample split. Spike–sample equilibration can be monitored on-line during sparging into the ICP-MS. The elimination of a nebulizer for Os isotope ratio measurements minimizes memory problems that are often associated with the determination of Os isotope ratios in liquid samples by ICP-MS. The external reproducibility of 187 Os/ 188Os measurements of an in-house Os standard solution using a single-collector, magnetic sector ICP-MS (Finnigan ELEMENT) is 0.78% (1 S.D., n=13) for analyte amounts ranging from 81 pg to 1.22 ng total Os. The ion yield for 7-min data acquisitions is ∼5×10 −5. Compared to negative thermal ionization mass spectrometry (N-TIMS), sample throughput is about on an order of magnitude higher. If NiS fire assay is used for PGE preconcentration, complementary PGE can be determined in the liquid residue by ICP-MS using a microconcentric nebulizer after the extraction of OsO 4.

Solvent extraction/anion exchange separation and determination of PGEs (Os, Ir, Pt, Pd, Ru) and Re–Os isotopes in geological samples by isotope dilution ICP-MS

A method is described that allows the separation of Re, Os, Pt, Pd, Ir and Ru for determination by isotope dilution via inductively coupled mass spectrometry (ICP-MS) at pg levels, from the same sample aliquot. Samples are digested in Carius tubes, enabling effective attack of PGEs in a wide range of geological materials, including pure chromite separates. Os is isolated by solvent extraction so that it may be precisely analysed for isotopic ratios by ICP-MS or negative-ion thermal mass spectrometry. When Os is analysed by ICP-MS, sample memory is minimised by using a direct injection nebuliser. Following Os extraction, Re, Pt, Pd, Ir and Ru are separated from their sample matrix by anion exchange chromatography. The method thus enables PGE abundances and Os isotopic ratios to be determined on the same sample dissolution, thereby avoiding problems of sample inhomogeneity when comparing data. Furthermore, analysis of Re for the same sample dissolution makes geochronological studies possible. Total procedural blanks are routinely less than 10 pg/g for all elements except Pt (15 to 25 pg/g). Blanks of less than 1 pg/g can regularly be obtained for Ir and Os. We estimate procedural detection limits (3∗STD deviation) of c. 3 pg/g for Os and Ir, 5 pg/g for Re, Ru and Pd, and 15 pg/g for Pt. Such detection limits permit analysis of most bulk rock geological samples. The method is evaluated by replicate dissolution of a komatiite reference material, WITS-1 [Tredoux, M., McDonald, I., 1996. Komatiite WITS-1, low concentration noble metal standard for the analysis of non-mineralised samples. Geostand. Newsl. 20, 267–276] together with unknowns. For WITS-1, concentrations of Os, Ir and Ru reproduce well, within a factor of 2 of that expected based on sampling theory. Potential heterogeneity for Pt, Pd and Re is identified at the 1 g sampling level used, that may be related to alteration. Replicate analyses of picritic basalts in the 1 to 10 ppb range show average 2 σ reproducibilities of better than 5% for Re, Os, Ir, Pt and Pd, with Ru being better than 10%. This compares very favorably with other analytical techniques. We present data for andesites with Ir and Os at the sub 10 ppt level. As expected, reproducibility decreases as sample concentrations decrease but are sufficient at the 10 ppt level to confidently identify inter-element PGE fractionations. The analytical method works well for a wide variety of rocks types.

Ir, Ru, Pt, and Pd in basalts and komatiites: new constraints for the geochemical behavior of the platinum-group elements in the mantle

The concentrations of the platinum-group elements (PGE) Ir, Ru, Pt, and Pd were determined in 18 mantle-derived basalts from a variety of tectonic settings and six komatiites from three locations. All analyses were performed using isotope dilution, Carius tube digestion, and the precise technique of multiple collector inductively coupled plasma mass spectrometry. Multiple analyses of two samples indicate external reproducibilities, based upon separate dissolutions, of approximately 2–9% in the ppt to ppb concentration range. Mid-ocean ridge basalts from the Kolbeinsey Ridge, tholeiites from Iceland and alkali basalts from the Cameroon Line define three individual sample suites that are characterized by distinct major, trace, and platinum-group element systematics. All three-sample suites display correlations of the PGE with MgO, Ni, and Cr. The new analytical results are employed to constrain the geochemical behavior of the PGE during the formation and differentiation of mantle–derived melts. The PGE are inferred to be compatible in sulfides during partial melting with sulfide-silicate melt partition coefficients of ∼1 × 10 4. The fractionated PGE patterns of mantle melts are a consequence of the incompatibility of Pd in nonsulfide phases, whereas Ir and Ru must be compatible in at least one other mantle phase. Model calculations indicate that PGE alloys or spinel may be responsible for the higher compatibility of the latter elements during partial melting. It is further demonstrated that the shape of the melting regime has a profound effect on the PGE systematics of mantle magmas. The systematic trends of the three sample suites in plots of PGE against Ni and Cr are the result of magma differentiation processes that involve fractional crystallization of silicate minerals and the concurrent segregation of an immiscible sulfide liquid. The behavior of the PGE during magma fractionation indicates that the segregated sulfides probably equilibrate with >90% of the silicate magma and that PGE scavenging by sulfides is best described by a combination of batch and fractional equilibrium partitioning.

PRELIMINARY RE-OS ISOTOPIC DATA IN PGE RICH CHROMITITE LAYERS OF LUANGA ULTRAMAFIC LAYERED INTRUSION – CARAJAS (PARÀ STATE), BRAZIL

The Luanga layered complex intruded a greenstone belt sequence (Rio Novo Formation) at 2760 Ma (Rb-Sr radiometric dating; Suita and Nilson, 1991). This age is confirmed by relationships with the Lower Proterozoic age of the covering sequence (Salobo and Rio Fresco Units). Lithostratigraphic data based on outcrops and three drillholes confirm the layered nature of the intrusion made up of dunite, peridotite, pyroxenite, norite and gabbro layers from the bottom to the top. Chromitite layers and seams, occur in three well defined horizons located in plagioclase pyroxenites and at the transition zone between dunite and peridotite. The massive chromitite layers show thicknesses between 2 m and a few centimetres. The massive chromitite displays an equigranular texture, with single grains ranging from 0.5 to 2 mm in size. The fresh chromitite layers show: atoll-like texture with olivine and orthopyroxene inside and outside chromite rings, pseudomyrmekitic intergrowth of silicates and chromite. Relationships of the two dominant PGMs (braggite and sperrylite) with the silicates and chromite suggest that PGM crystallization predates the almost contemporaneous precipitation of silicates and chromite. Weathering processes changed only in part the primary composition and mineralogy of the chromitite, for this reason it was possible to select well preserved primary minerals and mineral assemblages for analyses with microprobe, fire assay and neutron activation and mass spectrometry. The chemistry of the chromitite layers is typical of chromites generated by fractionation and cumulus processes, with widely ranging, but generally high Al2O3 and low Cr2O3 contents. PGE chondritic profiles display a PPGE enrichment in all the three horizons (Table 1), (Diella et al., 1995). Preliminary Re–Os isotopic data were obtained on two selected massive chromitite samples from the PGE richer (Lu3) and the relatively PGE poorer (Lu 6) chromitite horizons. These two samples show respectively the highest and the lowest PGE contents of all data collected. Isotopic analyses were performed with the Carius tube isotope dilution procedure, using the PGE standard “WPR- 1” provided by the Canadian Certified Reference Materials Project. Isotopic data (Table 2), in form of 187Os/188Os, were transformed into 187Os/186Os by using a 188Os/186Os ratio of 8,302 (Luck and Allegre, 1983). Initial 187Os/186Os ratios and gOs were determined by considering an age of emplacement of Luanga complex at 2700 Ma. Reliabilty of data is confirmed by very low 2s values for both samples. Isotopic analyses were performed with the Carius tube isotope dilution procedure, using the PGE standard “WPR- 1” provided by the Canadian Certified Reference Materials Project. Isotopic data, in form of 187Os/188Os, were transformed into 187Os/186Os by using a 188Os/186Os ratio of 8,302 (Luck and Allegre, 1983). Initial 187Os/186Os ratios and gOs were determined by considering an age of emplacement of Luanga complex at 2700 Ma. Reliability of data is confirmed by very low 2s values for both samples. Our data were compared with those of other chromitites from layered complexes as Stillwater (A, B, G, I, K chromitites; Marcantonio et al., 1993) and Bushveld (UG1, UG2 chromitites; Hulbert and Gregoire, 1993) and PGE-rich Merensky Reef of Bushveld (Fig. 1). Luanga chromitites show high ratios, similar to those of Merensky Reef, and much higher than CHUR at 2700 Ma. It is possible to state that the mantle-melt system at Luanga underwent some modification and cannot be thought as due to a process of melting of a primary fertile undisturbed mantle. At this stage different processes able to increase (187Os/186Os)i can be envisaged: anomaly in the source due to the presence of a metasomatized mantle, strong differentiation during fractionation or crustal contamination.

Low-blank digestion of geological samples for platinum-group element analysis using a modified Carius Tube design

We have developed a modified Carius Tube design that permits the low-blank digestion of geological samples prior to platinum-group element analysis. The new Carius Tubes incorporate a liner of high-purity quartz glass that retains the sample and acids during the digestion procedure. This dramatically reduces the comparatively high Pt blank associated with dissolutions in conventional Carius Tubes. Using the new Carius Tube design we are able to achieve total procedural blanks for the determination of the PGE in geological samples that are at the 1–15 pg/g level for Ru, Pd, Ir and Pt. This constitutes a reduction of blank values by a factor of ∼10–100 compared to standard NiS fire assay sample preparation techniques.

Carbonyl dibromide: a novel reagent for the synthesis of metal bromides and bromide oxides

M. J. Parkington, T. Anthony Ryan and K. R. Seddon, J. Chem. Soc., Dalton Trans., 1997, 257 DOI: 10.1039/A603977D

Metal‐Assisted Assembly of Chain and Macrocyclic As–S Ligands from Ethylcycloarsathiane (C2H5AsS)n

AbstractTreatment of cyclo‐(EtAsS)n with [RuCl2(Ph3P)3] and [Re‐Br(CO)5] affords the respective complexes [RuCl2{cyclo‐(EtAsS)4}(Ph3P)] (1) and [{Re(CO)3}2{μ‐(Et4As4S5)}] (2). Whereas 1 contains a η3 As coordinated intact cyclotetramer (EtAsS)4, ring cleavage leads to the chain anion Et4As4S52−, stabilised as a bridging hexadentate ligand in 2. Reaction of MCl3 with cyclo‐(EtAsS)n in toluene in a Carius tube enables the metal‐mediated temperature controlled assembly of the novel 16‐ and 14‐membered macrocyclic hexadentate As–S ligands in (M{cyclo‐(Et6As8S10)}] (3: M = Os; 4: M = Ru) and [Ru{cyclo‐(Et4As6S10)}] (5). The structures of the products were established by X‐ray crystallography.