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Abstract: The paper describes the high-precision U-isotope analysis of rocks. The analysis is based on multicollector inductively coupled plasma mass spectrometry (MC−ICP−MS) and includes, as an essential part, the three-step ion-exchange chromatography separation of uranium from chemically complex solutions. In the analysis, the 235U and 238U mass-bias of the MC−ICP−MS is corrected against the reference ratio of 233U and 236U in a double-spike added. The doublespiking precedes sample chemical digestion. This approach is useful as it corrects isotope data for a possible U-isotope fractionation that could have occurred in the chemical preparation of samples. The double-spike 236U/233U is 1.03183 ± 0.00005. The extraction procedure ensures uranium yield of more than 80%. The accuracy of the analysis was estimated by the study of 238U/235U in an international standard sample IRMM-3184 as well as in monitor samples. The uncertainty was estimated at ±0.008% (2SD), which is comparable with the accuracy of the results previously published by foreign researches. The analysis was elaborated for studying natural 238U/235U ratio variations. It was used by the authors for the high-precision determination of the U-isotope composition in rocks (granites, shales, volcanic rocks) and U-bearing minerals. [ABSTRACT FROM AUTHOR]

This paper reports the results of a detailed isotopic (Sm-Nd, Pb-Pb, and δ34S) and geochemical studies of Neoproterozoic metasedimentary rocks from the Patom and Bodaibo domains of the Baikal-Patom belt (northern Transbaikalia). It was shown that the metasedimentary rocks of these domains are strongly variable in their geochemical and isotope geochemical characteristics. Regular variations in these characteristics were observed, and their correlation with the main stages of the evolution of the sedimentary paleobasin in the Neoproterozoic was established. [ABSTRACT FROM AUTHOR]

The paper describes a new high-precision method for the simultaneous precise determination of Sr/Sr and Sr/Sr ratios in a single portion of a geological sample by multicollector inductively coupled mass spectrometry (MC-ICP-MS). The isotope analysis is carried out with mass bias effect correction by a combination of internal normalization to the standard Zr-isotope ratio and bracketing standard method (external normalization). Our results for geochemical IAPSO and BCR-1 standard samples are in a good agreement with the published data. The reproducibility of the Sr/Sr ratio varies from ±0.015 to ±0.05‰ (depending on the sample features) and, together with the analysis accuracy, is superior to the previously reported methods of MC-ICP-MS analysis. Still ahead is only double spike thermal ionization mass spectrometry with its ±0.02‰ reproducibility. However, the new method allows the simultaneous determination of Sr/Sr and Sr/Sr ratios and its productivity is higher by 5 to 6 times. On the other hand, in sample preparation, it is necessary to strive for at least 95% Sr yield from the chromatographic column; otherwise the sorption-desorption process may lead to a 0.6‰ Sr/Sr ratio bias relative to the true value. [ABSTRACT FROM AUTHOR]

The article focuses on the study on which aims to determine the Riphean age of zircons from alkaline syenites of the Karsakpai massif of South Ulutau in Central Kazakhstan with the uranium-lead (U-Pb) method. It mentions that the granitoids varying in chemical composition associated with Precambrian metamorphic strata were considered as coarse-grained gneissic granites (Zhaunkarskii complex), porphyroblastic granite-gneisses, and sub-alkaline potassic granites (Aktas complex). It states that the characteristics features of syenites of the Karsakpai granites and massif of the Aktas complex are massive structures and an absence of metamorphic transformations. Furthermore, it says that the age of intrusion of the massif allows to consider more ancient metamorphic complexes as Pre-Riphean.

The article offers information on the structural position and age substantiation of Middle Riphean gneiss granites of the Kokchetav Precambrian sialic massif in northern Kazakhstan. It says that the gneiss granites studied in the central areas of Kokchetav Massif such as Kokchetav, Chaikino Settlement, and Lake Chelkar have the development of small blocks and boundinized amphibolite, eclogite, and garnet amphibolite. It states that gneiss granites had structural-metamorphic alterations which transformed into blastomilonites with augen structure and well-developed linearity. Moreover, the age estimate of gneiss granites using uranium-lead (U-Pb) geochronological measurements corresponds to the age value of 1148 ± 8 Ma as deterrmined by discordia for zircon isotope composition.

The development of the MC-ICP-MS method, which was launched about one decade ago and was largely stimulated by the need to solve geological problems, has opened a new avenue in isotope mass spectrometry. One of the advantages of this method is the possibility of applying a newly developed approach to the correction of analytical results for the effect of mass discrimination by normalizing the measured isotope ratios of an element to a reference (standard) isotope ratio of another element. This makes it possible to overcome the main disadvantage of conventional thermal ionization mass spectrometry (TIMS), in which the effect of mass discrimination cannot be fully taken into account during isotope analysis, and thus to implement a highly accurate method for the analysis of Pb-isotope composition. In application to the capability of the NEPTUNE MC-ICP mass spectrometer, we optimized and calibrated a method for high-accuracy Pb isotope analysis in solutions spiked with Tl, with all currently measured Pb-isotope ratios normalized to the standard 205Tl/203Tl ratio (TLN-MC-ICP-MS). The factors affecting the random and systematic analytical errors were examined, and the optimal operating regime and analytical conditions were determined. Much attention was paid to the correlation of the measurement results and the mass discrimination effect determined from the 205Tl/203Tl ratio. The value of the 205Tl/203Tl normalizing ratio was analytically determined through isotope analyses of the NIST SRM 981, and SRM 982 standard samples of Pb-isotope composition. The data obtained for two mixtures Tl + Pb (SRM 982) and Tl + Pb (SRM 981) in ten replicate analyses were 2.38898 ± 12 and 2.38883 ± 20, respectively. These results are in good mutual agreement, and their general mean 205Tl/203Tl = 2.3889 ± 1 coincides (within the error) with the recently published values of 2.3887 ± 7 [Collerson et al., 2002] and 2.3889 ± 1 [Thirlwall, 2002]. The precision of the method (±2SD), which was assayed by the long-term reproducibility of the results of replicate analyses of SRM 981 and seven galena samples (90 analyses) was 0.016–0.018% for the 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios and 0.005 and 0.009% for the 207Pb/206Pb and 208Pb/206Pb ratios, respectively. The precision of the isotope analysis of common Pb was significantly improved (by factors of 6–10 for various isotope ratios) compared with the precision of TIMS techniques acceptable in isotope studies during three decades. The described method was applied to examine the Pb-isotope composition of approximately 250 samples of galena, scheelite, and pyrite from a number of well known (including large) gold, sulfied, and base-metal deposits. The precision of the method (0.01–0.02%) makes it possible to study small inter-and intra-phase differences in Pb-isotope ratios in hydrothermal and magmatic rocks, to assay the scale of regional and variations in the isotope composition of ore Pb, and to correlate the Pb-isotope composition of rocks and ores and reveal its evolutionary trends. [ABSTRACT FROM AUTHOR]