An Acetic Acid‐Based Extraction Protocol for the Recovery of U,Th and Pb from Calcium Carbonates for U‐(Th)‐Pb Geochronology

A new method for the simultaneous recovery of U, Th and Pb from ca. 0.5 g calcium carbonate samples for the purpose of U‐(Th)‐Pb geochronometry is presented. The protocol employs ion‐exchange chromatography. Standard anion exchange resin (AG 1‐X8 100–200 mesh) was used as the static phase, and 90% acetic acid was used as the mobile phase to elute the unwanted matrix components; dilute nitric acid was used to elute the U, Th and Pb. Blanks of 1.8 pg Th, 6.4 pg Pb and 8.4 pg U were obtained. The protocol was evaluated by determining the isotopic composition of U‐Th‐Pb separates obtained from an in‐house reference material (prepared from a natural speleothem) by MC‐ICP‐MS. An independently dated speleothem was also reanalysed. Based on these tests, the extraction protocol had an acceptable blank and produced a Pb separate sufficiently free of matrix‐induced instrumental biases to be appropriate for U‐Th‐Pb chronology.     

Provisional Elemental Values for IAEA‐Sewage Sludge by Instrumental Neutron Activation Analysis

The International Atomic Energy Agency (IAEA) organised a proficiency test (PT), IAEA‐CU‐2010‐02, for the determination of elements in sewage sludge. The PT sample was analysed by semi‐absolute standardless k₀‐instrumental neutron activation analysis (k₀‐INAA). Results for seven elements (As, Co, Cr, Fe, Hg, Se, Zn) were submitted to the IAEA by our laboratory. All of our results were scored ‘acceptable’ by the ‘result evaluation criteria’ adopted by the IAEA. The same analytical methodology produced quantitative results for twenty‐six additional elements. In total, thirty‐six elements were determined with uncertainty varying from 4 to 11%. This paper presents the provisional mass fractions of twenty‐six additional elements (Ag, Al, Br, Ca, Ce, Cl, Dy, Eu, Ga, Hf, I, K, La, Mg, Mn, Na, Rb, Sb, Sc, Sm, Ta, Tb, Th, V, U, W) not reported by the IAEA. The analytical methodology was discussed with important sources of spectral, nuclear and fission‐product interferences. It was shown that the important components of uncertainties were the k₀ factor, Q₀ factor, detector efficiency, mass and counting statistics. The methodology was validated by analysing the IAEA‐S7 reference material.     

An Optimised 1,10‐Phenanthroline Method for the Determination of Ferrous and Ferric Oxides in Silicate Rocks,Soils and Minerals

A precise, accurate and rapid method for the sequential determination of FeO and Fe₂O₃ in rocks, soils and some non‐refractory minerals by 1,10‐phenanthroline spectrophotometry is described. Fe(II) and Fe(III) were leached from the sample (?200 mesh) using a mixture of NH₄HF₂ and H₂SO₄ at 40–80 °C for 10 min on a hot plate. Both Fe(II) and Fe(III) could be conveniently estimated sequentially from the same reaction mixture at the μg g^?1 to percentage level. The method is better than the existing wet chemical methods, including the commonly used Pratt9;s titrimetric redox method, for Fe(II) and Fe(III) determinations in rock and soil samples in terms of precision, accuracy and rapidity. The throughput of the method was very high; at least forty to fifty samples could be estimated easily in a day. The results obtained compare favourably with those obtained by Pratt9;s method, as well as for certified/recommended values of a set of eleven certified reference materials having FeO and Fe₂O₃ contents in the range 0.21–14.63% and 0.58–8.48%, respectively. The optimised 1,10 phenanthroline method was found to be accurate to within 0.21% m/m FeO and 0.30% m/m Fe₂O₃ compared with the literature values of the certified reference materials studied.     

A Comparative Study of Five Reference Materials and the Lombard Meteorite for the Determination of the Platinum‐Group Elements and Gold by LA‐ICP‐MS

A range of independently characterised reference materials (RMs) for LA‐ICP‐MS, used for the determination of the platinum‐group elements (PGE) and Au in a sulfide matrix, were analysed and compared: 8b, PGE‐A, NiS‐3, Po727‐T1, Po724‐T and the Lombard meteorite. The newly developed RM NiS‐3 was used as the RM for the calibration of all LA‐ICP‐MS analyses and the measured concentrations of the other RMs compared against their published concentrations. This data were also used to assess the consistency of concentrations calibrated against the different RMs. It was found that Po727‐T1 and 8b produced results that were comparable, within uncertainty, for all elements. Po727‐T1 also produced consistent results with NiS‐3 for all elements. All other RMs showed differences for some elements, especially Ru in Po724‐T, and Os, Ir and Au in PGE‐A. The homogeneity of the PGE and Au in each RM was assessed, by comparing the precision of multiple LA‐ICP‐MS spot analyses with the average uncertainty of the signal. Po724‐T, Po727‐T1 and the Lombard meteorite were found to be homogeneous for all elements, but 8b, PGE‐A and NiS‐3 were heterogeneous for some elements. This is the first direct comparison between a range of independently characterised PGE and Au LA‐ICP‐MS RMs.     

Annual dissolved fluxes from Central Nepal rivers: budget of chemical erosion in the Himalayas

Annual dissolved element fluxes of Himalayan rivers from Central Nepal are calculated using published river discharge and a new set chemical data of rivers, including monsoon sampling. These are used to study the control on chemical erosion of carbonate and silicate over the whole basin. Chemical erosion of carbonate is mainly controlled by the river runoff but it can be limited by the availability of carbonate in limestone-free basin. Chemical erosion of silicate is well correlated to the runoff. However differences between High Himalayan and Lesser Himalayan basins suggest that physical erosion may also play an important control on silicate weathering. To cite this article: C. France-Lanord et al., C. R. Geoscience 335 (2003).     

The imprinting of aridity upon a lateritic landscape: an illustration from southwestern Australia

The southwestern region of Australia contains the Yilgarn Craton that has been exposed to subaerial weathering since mid-Proterozoic. The gently undulating landscape experienced lateritic weathering so that today variably dissected, deep in situ isovolumetrically weathered regolith is widespread. Imposition of a more arid climate since the Miocene with the cessation of effective external drainage has resulted in substantial geochemical modification of the highly porous regolith. This vast pore volume acts as a reservoir for complex solutions that may be highly saline, extremely acid to alkaline and reducing. Diverse precipitates have formed in the regolith including widespread occurrence of silcrete, calcrete, dolocrete, ferricrete and gypcrete together with localised occurrences of pyrite, alunite, jarosite, barite, halite and other salts. Clearing of bush land for agriculture in the 20th century increased recharge so that rising chemically active groundwaters are damaging farmland and infrastructure throughout the region. To cite this article: B. Gilkes et al., C. R. Geoscience 335 (2003).     

Ground penetrating radar inversion in 1-D: an approach for the estimation of electrical conductivity, dielectric permittivity and magnetic permeability

This paper presents a method for inverting ground penetrating radargrams in terms of one-dimensional profiles. We resort to a special type of linearization of the damped E-field wave equation to solve the inverse problem. The numerical algorithm for the inversion is iterative and requires the solution of several forward problems, which we evaluate using the matrix propagation approach. Analytical expressions for the derivatives with respect to physical properties are obtained using the self-adjoint Green's function method. We consider three physical properties of materials; namely dielectrical permittivity, magnetic permeability and electrical conductivity. The inverse problem is solved minimizing the quadratic norm of the residuals using quadratic programming optimization. In the iterative process to speed up convergence we use the Levenberg–Mardquardt method. The special type of linearization is based on an integral equation that involves derivatives of the electric field with respect to magnetic permeability, electrical conductivity and dielectric permittivity; this equation is the result of analyzing the implication of the scaling properties of the electromagnetic field. The ground is modeled using thin horizontal layers to approximate general variations of the physical properties. We show that standard synthetic radargrams due to dielectric permittivity contrasts can be matched using electrical conductivity or magnetic permeability variations. The results indicate that it is impossible to differentiate one property from the other using GPR data.     

海底可控源电磁测量电路的Linux驱动程序

国外的水合物探测试验证明,可控源电磁法是探测天然气水合物的有效方法之一.开展海底可控源电磁法工作的重点之一在于研制高精度、高可靠、低功耗观测海底可控源电磁信号的设备.为可靠地观测海底可控源电磁场宽频带、大动态范围信号,设计了以Linux与ARM9相结合的测量电路,并开发了Linux2.4内核下的设备驱动程序.本文分别论述了采集硬件原理,Linux字符设备驱动模型,SSC和GPS对钟驱动实例.     

Chemical characteristics of the crater lakes of Popocatetetl, El Chichon, and Nevado de Toluca volcanoes, Mexico

Three crater lakes from Mexican volcanoes were sampled and analyzed at various dates to determine their chemical characteristics. Strong differences were observed in the chemistry among the three lakes: Nevado de Toluca, considered as dormant, El Chichón at a post-eruptive stage, and Popocat9;petl at a pre-eruptive stage. Not surprisingly, no influence of volcanic activity was found at the Nevado de Toluca volcano, while the other volcanoes showed a correlation between the changing level of activity and the evolution of chemical trends. Low pHs (<3.0) were measured in the water from the active volcanoes, while a pH of 5.6 was measured at the Nevado de Toluca Sun lake. Changes with time were observed at Popocat9;petl and El Chichón. Concentrations of volcanic-gas derived species like Cl⁻, SO₄²⁻ and F⁻ decreased irregularly at El Chichón from 1983 until 1997. Major cations concentrations also diminished at El Chichón. A 100% increase in the SO₄²⁻ content was measured at Popocat9;petl between 1985 and 1994. An increase in the Mg/Cl ratio between 1992 (Mg/Cl=0.085) and 1994 (Mg/Cl=0.177) was observed at Popocat9;petl, before the disappearance of the crater lake in 1994. It is concluded that chemical analysis of crater lakes may provide a useful additional tool for active-volcano monitoring.     

Zircon M127 – A Homogeneous Reference Material for SIMS U–Pb Geochronology Combined with Hafnium,Oxygen and,Potentially, Lithium Isotope Analysis

In this article, we document a detailed analytical characterisation of zircon M127, a homogeneous 12.7 carat gemstone from Ratnapura, Sri Lanka. Zircon M127 has TIMS‐determined mean U–Pb radiogenic isotopic ratios of 0.084743 ± 0.000027 for ²⁰⁶Pb/²³⁸U and 0.67676 ± 0.00023 for ²⁰⁷Pb/²³⁵U (weighted means, 2s uncertainties). Its ²⁰⁶Pb/²³⁸U age of 524.36 ± 0.16 Ma (95% confidence uncertainty) is concordant within the uncertainties of decay constants. The δ¹⁸O value (determined by laser fluorination) is 8.26 ± 0.06‰ VSMOW (2s), and the mean ¹⁷⁶Hf/¹⁷⁷Hf ratio (determined by solution ICP‐MS) is 0.282396 ± 0.000004 (2s). The SIMS‐determined δ⁷Li value is ?0.6 ± 0.9‰ (2s), with a mean mass fraction of 1.0 ± 0.1 μg g^?1 Li (2s). Zircon M127 contains ~ 923 μg g^?1 U. The moderate degree of radiation damage corresponds well with the time‐integrated self‐irradiation dose of 1.82 × 10¹⁸ alpha events per gram. This observation, and the (U–Th)/He age of 426 ± 7 Ma (2s), which is typical of unheated Sri Lankan zircon, enable us to exclude any thermal treatment. Zircon M127 is proposed as a reference material for the determination of zircon U–Pb ages by means of SIMS in combination with hafnium and stable isotope (oxygen and potentially also lithium) determination.