We present novel data sets of rare earth element (REE) distributions in a hydrothermal vent field at Yonaguni Knoll IV in the Okinawa Trough. Vertical REE profiles in three water columns showed horizontal variation of REE concentrations within 1000–1200 m. Hydrothermal plumes were discovered by anomalous values of methane, manganese and transmissometry at that site. Europium anomalies in the North Pacific deep water (NPDW) (Nozaki et al., 1999) normalized pattern decreased with distance from the hydrothermal vent site, indicating that the dilution of hydrothermal fluid in the plume can be traced using REE. The horizontal variation of negative Ce-anomalies represents the continuous scavenging of REE by suspended matter in the plume. In addition, we measured nine hydrothermal fluid samples. The REE geochemistry of hydrothermal vent systems had been investigated intensively at sediment-starved mid-oceanic ridges, but few studies had examined sediment-hosted hydrothermal systems like those of the Okinawa Trough. The chondrite-normalized REE patterns of the fluids collected at Yonaguni Knoll IV show typical lighter rare earth elements (LREE) and Eu enrichment similar to at the Mid-ocean Ridge sites. A remarkable characteristic of the Yonaguni Knoll IV fluid pattern is its higher concentrations of heavier rare earth elements (HREE) and La composition than the hydrothermal fluids of the sediment-starved East Pacific Rise and Trans-Atlantic Geotraverse. Such a feature is explainable by influences of covering sediments in the back-arc basin Okinawa Trough. At the hydrothermal vent, lighter REE (LREE) in the fluid was reduced systematically during fluid mixing with seawater within the chimney. Light REE elimination resembles fractionation caused by particle scavenging within the water column. However, the lack of Ce depletion, which is a typical REE feature in the water column, along with distinctive Eu reduction, were unique in the Yonaguni Knoll IV fluid, suggesting that fluid REE fractionation at the vent site was induced predominantly by coprecipitation with hydrothermally originated minerals (e.g. sulfate and carbonate), not by adhesive removal by Fe and/or Mn oxide particles. Previous studies had shown that REE removal and fractionation of the hydrothermal system were observed only in deposit samples. Results of this study elucidated REE fractionation in fluid samples using previous analytical data. We were also able to distinguish REE removal mechanisms occurring at the vent site and water column using REE pattern characteristics.

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In this study, we investigated the natural attenuation of antimony (Sb) in the drainage water of an abandoned mine. Drainage water, waste rocks, and ocherous precipitates collected from the mine were investigated in terms of their mineralogy and chemistry. The chemistry of the drainage water was analyzed by measuring pH, oxidation-reduction potential (ORP), and electric conductivity on site as well as by inductively coupled plasma mass spectrometry and ion chromatography. As the drainage flowed downstream, the pH decreased rapidly from 7.05 to 3.26 and then increased slowly to 3.50. In a section where the pH increased, ocherous precipitates occur on a drainage water channel. We determined Sb levels in the drainage water, and the distribution of Sb in the mineral phases of waste rocks and precipitates was estimated by means of a sequential extraction procedure. The results of these investigations indicated that Sb, which is generated by the dissolution of stibnite (Sb₂S₃) and secondary formed Sb minerals in waste rocks, was attenuated by iron-bearing ocherous precipitates, especially schwertmannite, that form over time in the drainage water. The Sb concentrations in the ocherous precipitates were up to 370 mg/kg, whereas the Sb concentrations in the drainage water downstream were below background levels (0.6 μg/L). Bulk distribution coefficients (K_d) for this Sb adsorption to the precipitates ranges up to at least 10⁵ L/kg.

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The Dabie-Sulu ultrahigh-pressure orogenic belt resulted from the early Mesozoic collision of the North China block and South China block (comprising the Yangtze and the Cathaysia) and subsequent exhumation of the subducted South China continental slabs. This belt consists of tectonically juxtaposed rock units of different metamorphic grade. Provenance of the low-grade metamorphic terranes exposed along the northern part of the belt can offer useful information about the location of the boundary between these two continental blocks. This study reports detrital zircon ages and Nd-Hf isotopic composition of sedimentary rocks of the low-grade Penglai Group, situated north of the Sulu UHP terrane. Results show that detrital zircon grains mostly crystallized during Mesoproterozoic time, clustering at 1.7 Ga to 1.6 Ga and 1.2 Ga. Nd isotopic composition (T_DM value) of the Penglai Group suggests that sedimentary sources are similar to average crustal material of the Yangtze block and mostly formed in Paleo- to Mesoproterozoic. Late Mesoproterozoic detrital zircons probably demonstrate that sedimentary material was derived from the boundary of the Yangtze and Cathaysia blocks, which was formed by the late Mesoproterozoic convergence. Absence of Neoproterozoic detrital zircons from the Penglai sediments probably suggests a late Mesoproterozoic to early Neoproterozoic deposition age (about 1.1 Ga to 0.8 Ga). The age and isotopic evidence implies that the Penglai Group originated from the South China block and probably was thrust onto the basement of the North China block during the early Mesozoic continental collision.

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Sericite phyllite from the Sinian Shisanlitai Formation, Dalian area, Liaodong Peninsula, NE China, contains an assemblage of newly-formed lower-greenschist facies minerals (sericite, chlorite, Fe minerals and Ti minerals) plus aggregates of fine-grained monazite. The texture of the monazite, its mineral inclusions, and its close association with Fe oxide minerals show that it is not detrital or diagenetic, but a product of the low-grade metamorphism. SHRIMP U-Th-Pb dating of the monazite at 217 ± 15 Ma shows that the metamorphism, and associated regional deformation and fluid flow, occurred in the Late Triassic, coeval with the waning stages of the Dabie-Sulu orogeny. The Dabie-Sulu tectonothermal event has produced both deformation and metamorphism in rocks of the eastern North China Block at least up to ∼200 km north of the main continent-continent collision zone.

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Hydrocarbons are the main components in natural gases. Although the molecular distribution has been often used to study the origin of hydrocarbon, the occurrence of pentane and hexane isomers has not been discussed for natural gases. This study first reports controlling factors of pentane and hexane isomer ratios of natural gases from Akita, Niigata and Hokkaido in Japan. For the samples from Akita and Niigata, pentane and hexane isomer ratios such as neopentane/isopentane and 2,2-dimethylbutane/2,3-dimethylbutane show positive correlations with δ¹³C (ethane), suggesting that the ratios are affected by the generation temperature. Relation between kerogen type and isobutane/n-butane ratio is also discussed. By the comparison between Akita and Niigata gases that originated from type II kerogen and Hokkaido gases that originated from type III kerogen, the gases from type III kerogen show a higher isobutane/n-butane ratio compared with those originated from type II kerogen. Although carbon isotopic ratios of ethane and propane are good parameters for the gas generation temperature, this study indicates that combinations among pentane isomer ratios and hexane isomer ratios also provide good parameters for the gas generation temperature.

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The Huize ore field, which is the most famous high-grade Zn-Pb ore field in China, comprises the Kuangshanchang and Qilinchang deposits. The Zn and Pb reserves of these two deposits are more than 5 Mt with ore grades ranging from 25% to 35% in weight. Lead, sulfur, carbon, oxygen, hydrogen and strontium isotope geochemistry is reported to help understand the sources of the ore fluid and metals. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb values of the ores range from 18.251–18.530, 15.663–15.855 and 38.487–39.433, respectively. These values are similar to those of the wall rocks. The pyrites disseminated in the wall rocks have indistinguishable Pb isotope composition with the ores. These data indicate that the wall rocks provided metals to the ore fluid. Most δ³⁴S values of the ores range from 13 to 17 per mil. The sulfur of the ores originated by in situ reduction of sulfate. Three kinds of gangue calcite from the ores have similar isotope compositions, which have δ¹³C values in the range of −2.1 to −3.5 per mil with respect to PDB and δ¹⁸O values in the range of 16.8 to 18.6 per mil with respect to SMOW. The δD_FI values of fluid inclusions in the three kinds of gangue calcites have a narrow range of −50 to −60 per mil and the δ¹⁸O_H2O values calculated from δ¹⁸O values of calcite range from 7.0 to 8.8 per mil at 200°C. These data suggest that the ore fluid was a basinal brine that passed through shale, clastic rocks and mudstone underlying the host rock. Initial ⁸⁷Sr/⁸⁶Sr values of the pyrite, sphalerite and calcite from the ores range from 0.714 to 0.717. The initial ⁸⁷Sr/⁸⁶Sr values of unaltered host rock (0.7083–0.7093) are lower than that of the altered host rock (0.7106). It suggests that the ore fluids have higher initial ⁸⁷Sr/⁸⁶Sr values than the wall rocks. These high initial ⁸⁷Sr/⁸⁶Sr values may be due to the reaction between the ore fluid and the shale, clastic rocks and mudstone underlying the host rock or the fluid might have originated from these rocks.

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