The stratiform phosphorite deposits of Egypt, which are found in an east-west band between 24° and 27° north latitude, contain from 25 to 100 ppm uranium, a significant portion of which can be shown to have been secondarily adsorbed from groundwater. This fraction is readily leachable in 0.2 N K₂CO₃ and in the Red Sea area has the same ²³⁴U/²³⁸U activity ratio, 1.3, as the U dissolved in the associated groundwater. Both the excess of ²³⁴U and the deficiency of ²³⁰Th relative to ²³⁸U shows that the leachable U was adsorbed within the last 250 ky. Secondary U with the same ²³⁴U/²³⁸U activity ratio also occurs in the Western Desert phosphorite, indicating that it too has been adsorbed relatively recently, even though the groundwater table today is well below the phosphatic strata. On the other hand, the leachable U in the intervening Nile Valley deposits has an activity ratio near 1.0, suggesting that those strata have been above the groundwater table for the last million years. The adsorption of U may not be entirely associated with the principal phosphate mineral, carbonate-fluorapatite (francolite), Ca₅(PO₄, CO₃)(F, OH). Iron, organic and clay phases are also present in the phosphorite ore.

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The diorites-granodiorites emplaced at ca. 175 Ma in southeastern Hunan tectonic-magmatic belt (SHB), South China Block (SCB), are high-K calc-alkaline. They are characterized by LREE-LILE enrichment and HFSE depletion with slight or no Eu anomalies. Age-corrected initial ⁸⁷Sr/⁸⁶Sr ratio spans a narrow range of 0.707962∼0.710396 and ε_Nd(t) of −6.98∼−2.30. These features are significantly different from those of the neighboring other Mesozoic granitic plutons (Eu/Eu* = 0.30–0.70; ⁸⁷Sr/⁸⁶Sr > 0.710; ε_Nd = −12 to −16) in South China, which have been interpreted as the remelting products of Precambrian basement. The crust anatexis cannot account for the geochemical characteristics of these diorites-granodiorites in the SHB. The partial melting of an enriched lithosphere mantle directly produced mafic-intermediate rather than acid magma, and can also not explain the geochemical and isotopic variations exhibited by these diorites-granodiorites. These diorites-granodiorites likely represent partial melting products of mantle-derived basaltic rocks, which were underplated and hybridized with old crust material at lower/middle crust level. Theoretical modeling further suggests that this hybridized source consisted of 15–30% of the lower/middle crust and 70–85% of depleted mantle-derived basaltic rocks. The occurrence of these diorite-granodiorites in southeastern Hunan province therefore marked a major intra-lithospheric extension episode during early Mesozoic.

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Petrographic, petrochemical and Sr-Nd isotopic data are presented for granitoids and microdioritic enclaves from two Cretaceous stocks (Togouchi granodiorite and Tateiwayama granite porphyry) from the Togouchi-Yoshiwa district, northwest Hiroshima prefecture, SW Japan. The data are used to examine the genetic relationships between the microdioritic enclaves and their granitoid hosts. The granodiorite, granite porphyry and the microdioritic enclaves are all calc-alkaline in nature, and belong to the I-type ilmenite series. The Togouchi granodiorite has a Rb-Sr whole rock isochron age of 85.6 ± 4.7 Ma with an initial Sr isotope ratio (SrI) of 0.70634 ± 0.00012 (2σ). The Tateiwayama granite porphyry has a slightly younger Rb-Sr whole isochron age (77.4 ± 3.1 Ma) but similar SrI of 0.70653 ± 0.00015, suggesting that both stocks may have been derived from the same source. Despite diverse whole rock chemistry, the microdioritic enclaves in the respective intrusives have quite similar initial Sr and Nd isotope ratios, suggesting that they formed by fractional crystallization of a single magma, and also that the source of the enclaves in both intrusives had similar geochemical characteristics. In both stocks, however, the enclaves have distinctly lower initial Sr isotope ratios than their respective host rocks, indicating that they were derived from a different source than their hosts. In view of the geochemical and Sr-Nd isotope data, we infer that the enclave magmas were derived from a similar LILE- and LREE-enriched source to that of the Cretaceous basalts and gabbroic-dioritic rocks that are sporadically distributed in SW Japan. Such mafic to intermediate magmas were probably derived from the upper mantle, and transferred both heat and material to the lower crust, thus producing granitic magmas by partial melting. Successive mafic magmas or their differentiates could then have been injected into the granitic magma chamber, trapped and quenched, resulting in the formation of microdioritic enclaves in both granitic stocks.

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The Ryeongnam massif is composed of Precambrian gneisses, Paleozoic and Mesozoic sedimentary rocks and extensive Triassic-Jurassic plutonic rocks of felsic to mafic composition. In the northeast Ryeongnam massif, the oldest rocks belong to the Sobaegsan gneiss complex, which is composed of orthogneisses, paragneisses and mafic plutonic rocks. U-Pb zircon ages for the felsic and mafic intrusive bodies within the Sobaegsan gneiss complex are: the Icheon granite gneiss, 2357 ± 43 and 2342 ± 47 Ma; the Buncheon granite gneiss, 1963 ± 5 Ma; the Pyeonghae granite gneiss, 1936 ± 21 Ma; the Ogbang amphibolite, 1918 ± 10 Ma; the Imwon leucogranite gneiss, 1826 ± 20 Ma. The Hyeondong biotite schist, which is intruded by the Buncheon granite gneiss and the Ogbang amphibolite, yielded an age of 2271 ± 44 Ma. The Nd-Sm-Pb isotopic data indicate that the felsic plutonic rocks are derived from an older Archean crust. The Nd T_DM ages are Archean, and the εNd values are negative for the felsic rocks and positive for the amphibolite. Common Pb isotope compositions also indicate a crustal source for the felsic intrusives. The U-Pb ages of Precambrian rocks of the Ryeongnam massifs are similar to those in the Gyeonggi massif, and may have a similar crustal evolutionary history. The Precambrian rocks of South Korea could be related either to the North China block or to the South China block, as the isotope ages and patterns are not unique to either block. Similarly, a geologic correlation with Japan, although possible, is tenuous at present.

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The waters of modern Lake Baikal circulate well and maintain oxic conditions for the entire lake in spite of its great depth. Past oxic/anoxic conditions in the water column are not known. Because reconstruction of paleo-redox conditions involved with climate changes provides information on dynamics of lake water circulation and biological activity, high-resolution analyses of total organic carbon (TOC), total nitrogen (TN) and total sulfur (TS) concentrations, and gamma ray density (GRD) were carried out using 492 sediment samples over the past 250 kyr (every other 1 cm from the 10 m core Ver98-1 St.5 taken from the Academician Ridge at 325 m water depth). Fifteen events of high TS/TOC ratio (>0.2 atomic) are observed; these are much larger than TS/TOC ratio of typical freshwater sediment (0.001–0.070) and also normal oxic marine sediments (0.13 in average). The sulfur occurs as pyrite by X-ray diffraction (XRD) analysis, probably being produced by sulfate-reducing bacteria (SRB). Such high TS/TOC ratios indicate high SRB activity in the lake and a high input of sulfate to the lake. A high TS/TOC layer often accompanies a decrease of TOC/TN ratio to ca. 5 (atomic). In particular, during a rapid cooling such as the Younger Dryas event, the TOC/TN ratio decreases steeply from 10.4 to 7.8 just prior to the increase of TS/TOC ratio from 0.02 to 0.55. Because the low TOC/TN ratio suggests low terrestrial organic matter contribution to the lake, saline water inflow from rivers could diminish to result in decreased water circulation in the lake. The rapid cooling event may restrict deep-water ventilation and create less oxic conditions in Lake Baikal.

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In order to evaluate the role of sediment subduction in the magma genesis in the Setouchi volcanic belt, SW Japan, bulk rock compositions of both pelagic sediments from the Philippine Sea (GDP 15-12) and trench-filled sediments from the Nankai Trough (DSDP site 582) were determined. The analytical result shows that trace element concentrations, particularly Pb, Ba and Th, of the pelagic sediments are much higher than those of the terrigenous sediments. Mixing calculations using these elements indicate that the terrigenous sediments rather than the pelagic sediments played a major role in producing the Setouchi magmas. To obtain further constraints on the origin of Setouchi magmas, a model of melt-mantle reaction was examined based on the assimilation fractional crystallization formulation (AFC). The result also indicates that the terrigenous sediment is a dominant metasomatic agent. In addition, the model suggests that the fractionation of orthopyroxene with minor hornblende would be essential to produce the Setouchi magmas. Taking the hornblende fractionation into account, Pb/K₂O and Pb/Rb ratios on MgO variation diagrams also indicate similar contributions. Since the breakdown of mica, which is included both in the pelagic and terrigenous sediments, is inferred to induce dehydration melting of the sediments, above geochemical characteristics suggest that both sediments would melt simultaneously beneath the Setouchi area.

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Detailed measurements of temporal variations in the stable isotopic composition of precipitation and lake water were conducted in the permafrost region near Yakutsk, eastern Siberia. The δ¹⁸O ranged from approximately −30 to −5‰ in precipitation and from −25 to −5‰ in lake water were observed from April to August, 2000. Temporal changes in δ¹⁸O of precipitation observed weekly at 12 sites all showed the same trend. The temporal variation of δ¹⁸O in lakes classified into two groups: isotopically steady-state lakes with less than 5‰ variation, and non-steady-state lakes with variation exceeding 10‰. In non-steady-state lakes, the water originated from snowmelt, and the δ¹⁸O of lake water gradually enriched as a result of evaporation during the summer. In steady-state lakes, the water originated predominantly from ¹⁸O-enriched lake water that had evaporated in the previous summer. The temporal volumetric and isotopic variations in alas lakes are accurately depicted by an isotope mass-balance model using Rayleigh fractionation over daily time steps. The inflow of soil water (subsurface flow) was estimated to be constant (200 m³/day) from May to August, based on the difference between observed and simulated lake volumes. Taking the isotopic mass-balance into consideration, the soil water in lower part of the active layer is inferred as a major component of inflow which has a δ¹⁸O of about −23‰.

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All platinum group element (PGE) abundances of a standard rock JP-1 are determined by isotope dilution method (for Ru, Pd, Os, Ir and Pt) and external calibration method (only for Rh) using ICP-MS combined with a fire assay preconcentration technique. The errors range 13–25% (2σ; n = 5), which are comparable with those by the similar methods combined with chemical separation of PGE (Pearson and Woodland, 2000; Meisel et al., 2001). Large deviations between our data and preferable values proposed by the Geological Survey of Japan (GSJ) are observed for Os and Ir. The scattered Os data might be indicative of heterogeneity of Os in JP-1. From various viewpoints, it seems likely that our Ir data are much more reliable than the preferable values proposed by GSJ.

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