Oxygen and sulfur isotopic compositions of sulfate, quartz and sulfide minerals from the veins of the Sambo lead-zinc-barite ore deposits have been measured to study their depositional conditions and evolution of ore fluids. The results are as follows: (1) The δ³⁴S values of sulfides vary from -3.9 to -13.5‰ and those of sulfates from +15.7 to +17.2‰. Isotopic temperatures from barite-sphalerite and barite-galena pairs were 210-290°C, in fairly good agreement with the homogenization temperatures of fluid inclusions in the stage II quartz. At relatively low temperatures (210-290°C), isotopic equilibria were attained between sulfate and sulfide minerals in the Sambo ore deposits. (2) Barites have homogeneous δ³⁴S and δ¹⁸O values of +15.7 to +17.2‰ and +2.4 to +3.9‰, respectively. Calculated δ¹⁸O values of ore fluids in equilibrium with barite and quartz vary from -2.1 to +0.9‰ and -4.2 to -1.3‰, respectively, suggesting a contribution of ¹⁸O depleted meteoric water to ore fluids of the Sambo deposits.

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Atmospheric bulk deposition and aerosol samples were collected simultaneously in the surface air over the west coast of Japan (38°46'N, 139°44'E), and analyzed for ²¹⁰Pb. By coupling data with those previously reported for ²¹⁰Po (Suzuki, 1994), the following results have been obtained. (1) The ²¹⁰Po/²¹⁰Pb activity ratios in aerosols were consistently larger than those in atmospheric depositions, and (2) the activity ratios in April were larger than those in July and October in both aerosol and deposition samples. The results can be variously attributed to the difference of residence time between atmospheric suspending and settling particles, and the difference of contribution from various sources in which ²¹⁰Pb and ²¹⁰Po are in over-, under- or secular-equilibrium.

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In order to study Ne diffusion into glasses, we measured noble gas concentrations in obsidian samples which were degassed in a vacuum at 800°C and subsequently heated in air at various temperatures and heating times. Neon was concentrated in samples which were kept at room temperature, indicating that Ne is easily diffused into obsidians from the atmosphere even at room temperature. We also measured noble gas concentrations in five size-separated fractions of the obsidian (ME1) (>250, 149-250, 74-149, 46-74 and <46 μm fractions) and in three size-separated fractions of tektite (TE6) (>250 and 149-250 μm fractions and powdered fraction) to examine the degassing effect on noble gases by crushing. The Ar and Kr concentrations, and especially the Ne concentration, show a gradual decrease with decreasing grain size of the obsidian samples. For the tektite samples, Ne concentration in the powdered fraction was about half of that in the >250 and 149-250 μm fractions. These results confirm that Ne in glasses mainly resides in vesicles in the glass.

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Carbon/sulfide/iron relationship and sulfate reduction rate were investigated in the East China Sea continental shelf sediments. The area is characterized by median to high sulfate reduction rate, and high concentrations of iron oxide minerals. Organic carbon was found to be the primary limiting factor for the pyrite formation. Sulfate reduction rate increased with increasing organic carbon concentration. C/S ratio displays a typical normal marine sediment ratio. Low DOP values and abundance of highly reactive iron oxide, ferrihydrite and lepidocrocite, indicate that iron is not limited in the East China Sea continental shelf.

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The distribution of two radicals (CO₃^- and SO₂^-) in natural crystalline gypsum in a bore-hole core from the Konya basin in Turkey was imaged using a home-made electron spin resonance (ESR) microscope. The high concentration of SO₂^- at the center of the crystal indicates that the gypsum has grown from the center to the surface. The high concentration of CO₃^- at the surface would be caused by the external β-rays from sediments. The distribution of impurities was also checked by electron probe X-ray microanalysis (EPMA).

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The pressure and temperature conditions were experimentally determined for methane hydrate dissociation in sodium chloride solutions, and an empirical equation of the conditions was obtained in the pressure range up to 18 MPa. The present results indicate that the maximum depth of oceanic sediments where methane hydrate is stable increases as water depth to seafloor increases, and that the maximum depth in saline water is smaller than that in pure water. The difference in the depth between saline and pure waters increases with decreasing the water depth, indicating that salinity of pore water affects significantly the amount of methane hydrate in oceanic sediments, in particular, beneath seafloor at relatively shallow depths.

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A solid-phase extraction technique has been examined for pretreatment of colorimetric determination of soluble reactive phosphorus (SRP) in sediment extracts. The SRP was effectively collected as a molybdophosphoric acid complex by a cartridge column packed with polystyrene divinylbenzen resin. The complex adsorbed on the resin was eluted with a small aliquot (<5 ml) of 0.5 M NaOH solution. The recovered SRP was then determined by the standard molybdenum blue method. Compared with the solvent-extraction technique which has been generally used by previous workers, the present method consists of much easier procedures, and precision and recovery of this method are sufficiently high. The method was then applied for the determination of iron-bound P (Fe-P) in sediment samples from the Tamagawa Estuary. The results suggest that Fe-P in sediments is an important source of P in estuarine and coastal ecosystems through releasing phosphate to estuarine water with increasing salinity.

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