In order to understand uranium migration behavior through geological media, the granitic conglomerate from the Tono uranium mine, Gifu prefecture, central Japan, was studied by grain size division and selective chemical leaching technique. The bulk contents of U and Th in fine-grained samples are larger than those of coarse-grained ones, and have positive correlations with the abundance of detrital biotite grains. The total amount of U eluted by the leaching reagents was more than half in all divided samples. In particular, a large amount of U was leached by sodium acetate/acetic acid (pH 5.0), and hydroxylamine hydrochloride/acetic acid solutions. It is inferred that carbonate and iron oxide minerals play an important role in U ore genesis. The adsorption density of fine-grained samples is larger than that of the coarse-grained one, which suggests that the fine U minerals are abundant in fine-grained sample and/or the U concentration around the complexing site of iron oxyhydroxides may have become high. The bulk ²³⁴U/²³⁸U activity ratio is 0.95 ± 0.05, and the bulk ²³⁰Th/²³⁴U activity ratio is 1.36 ± 0.06. For most of the sieved samples, ²³⁴U/²³⁸U activity ratios are <1, and ²³⁰Th/²³⁴U activity ratios are >1, showing that U is partially removed from the sediments. The uranium nuclides in the matrix of conglomerate are inferred to be not in equilibrium within 300, 000 y. The ion exchangeable U, whose ²³⁴U/²³⁸U activity ratio was >1, is bound weakly and exchangeable with U in the surrounding water such as interstitial water and groundwater with ²³⁴U/²³⁸U activity ratios >1. The ²³⁴U/²³⁸U activity ratios of the residue fraction are less than 1 (finer sample) or more than 1 (coarser sample), indicating that the recoil ejection effect of U is advantageous for the fine-grained samples while injection effect is advantageous for the coarse-grained samples. The ²³⁴U/²³⁸U activity ratios of other fractions are less than 1, which is quite similar to the bulk ratio. The ratio decreases in the order of carbonate > iron oxide > organic/sulfide fractions. The ²³⁰Th/²³⁴U activity ratios is very low in ion exchangeable fraction and >1 in carbonate, iron oxide, and residue fractions. For the residue fraction, ²³⁴U/²³⁸U > 1 and ²³⁰Th/²³⁴U > 1 indicate the elution of U and enrichment of ²³⁴U relative to ²³⁸U by alpha recoil injection. The organic/sulfide complex fraction is depleted in ²³⁰Th compared to ²³⁸U and ²³⁴U. This fact suggests that U was secondarily enriched over Th. As U was enriched at the surface of pyrites, it is inferred that pyrites adsorbed a portion of the eluted U and helped the secondary fixation of U in modern times.

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A program of geochemical surveillance of the volcanic activity at Vulcano island (southern Italy) has allowed to collect a large set of observations, and the main chemical composition of volcanic gases is consequently known for the period from 1978 to 1993. This systematic monitoring with time of fumarolic activity at Vulcano has represented a good opportunity to investigate variations of arsenic concentrations in the condensates of fumarolic gases, and to correlate them both with temperature and chemical composition of the gases. Previous studies on arsenic behaviour in fumarolic gases for a similar long period are not reported in literature so far. Multivariate methodologies are a correct tool in order to investigate the simultaneous relationships between a large number of variables and to evaluate their changes with time. Since the chemical composition of volcanic gases is expressed by closed (or compositional) variables, the log-ratio approach has been adopted to overcome the induced correlations. By considering the results obtained by the application of Principal Component Analysis, the following considerations can be formulated: 1) arsenic behaviour appears to be mainly influenced by the presence of intense hydrothermal circulation as represented by the multivariate association of the element with variables as T, HF/H₂O, NH₃/H₂O and H₂S/H₂O ratios; 2) the hydrothermal circulation, characterised by a continuous increase with time, appears as the main feature of the volcanic system; in this framework, the seismic event occurred in 1984 may have contributed to facilitate the fluid circulation; 3) no obvious relationships appear to link the increase of gas temperature with typical magmatic contributions as expressed by CO₂/H₂O and SO₂/H₂O ratios. The results indicate that the correlations between arsenic and the other physical-chemical parameters characterising the volcanic system are useful to constrain the interpretations on its geochemical evolution with time. This is particularly true if the system is dominated by hydrothermal processes as those of Vulcano island, where arsenic undergoes intensive remobilization.

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Present study aims at understanding the genetic and tectonic relationship between the enclaves and enclosing granitoids, acidic volcanics and mafic dykes of the Ladakh plutonic complex. Similar rocks from Lhasa Block (Tibet) are also studied and compared. In terms of SiO₂ abundance, the enclaves vary in composition from basic to acidic but are predominantly andesitic-basalt. Mafic dykes intruding the Ladakh plutonic complex are of predominantly andesitic-basalt composition. Granitoids and acidic volcanics from Ladakh and Lhasa blocks are compositionally granodiorite, quartz monzonite and granite. They are predominantly meta-aluminous with slight peraluminous characters. The acidic volcanics, however, have K₂O/Na₂O>1. All these rocks show calc-alkaline characteristics with high Al₂O₃ abundance, their rare earth elements (REE) and multi-element patterns depict enrichment of large ion lithophile elements (LILE)-light REE (LREE) and depletion of high field strength elements (HFSE) including Nb, P and Ti. It is suggested that the enclaves in Ladakh plutonic complex probably represent the initial pulses of magmatism, in response to intra-oceanic northward subduction of Neo-Tethyan ocean beneath an immature arc. Subsequently huge pulses of granitoids were intruded as the arc matured, sutured with southern continental margin of Eurasian plate and the lithosphere thickened. The granitoids in turn were cut by mafic dykes and acidic volcanics probably representing the last significant episode of subduction related magmatism in this region. It is suggested that the youngest, highly siliceous acidic volcanics may represent melts generated by partial melting and/or dehydration of upper part of subducted north Indian continental lithosphere and southern Eurasian active margin wedge, subsequent to the closing of Neo-Tethyan ocean and collision of Indian and Eurasian plates.

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The abundances of rare earth elements (REE) and Y in cherts were precisely determined by ICP-MS: the Archean Marble Bar Chert from the Pilbara Block, Western Australia, Triassic cherts from central Japan, and Cretaceous deep-sea cherts from central Pacific and the Caribbean Sea. Both of W-type and M-type REE patterns are observed for the studied cherts and, in particular, clear W-type tetrad effect is observed for the Archean Marble Bar banded cherts. Appearance of tetrad effect phenomenon is related to their Fe₂O₃^∗ (total iron as Fe₂O₃) and Al₂O₃ concentrations. The cherts relatively enriched in Fe₂O₃^∗ show W-type tetrad effect, while that enriched in Al₂O₃ tends to show M-type tetrad effect. Therefore, impure clastic detritus in the cherts might be responsible for M-type tetrad effect. It is worthwhile noting that, irrespective of their REE patterns of W-type and M-type tetrad and little tetrad effects, the cherts chiefly show non-chondritic Y/Ho ratios between 13 and 27, negative deviations from chondritic value around 28, in contrast with seawaters and limestones characterized by strongly higher Y/Ho ratios ranging from 50 to 80 than the chondritic value. Among the cherts, the lowest Y/Ho ratios between 13 and 18 are observed for the Marble Bar yellowish gray cherts, which suffered disturbance of geochemical features by thermal events at ca. 2.5 Ga. It has been widely recognized that both of Y-Ho fractionation and lanthanide tetrad effect are phenomena observed in the marine environment. However, Y-Ho fractionation is not closely associated with lanthanide tetrad effect. Y-Ho fractionation is suggested to be related to the ligand that dominates the chemical complex in aqueous system, from our results and the observation that silicate-rich part and carbonate-rich part in banded iron formations show lower and higher Y/Ho ratios than the chondritic value, respectively. On the other hand, tetrad effect in the cherts is related to impurity minerals such as Fe-oxides and clastic detritus, with which REE might well by associated. It is interesting that the Archean banded charts, not containing organic nor detrital materials, display clear W-type tetrad effect coupled with slightly lower Y/Ho ratios than chondritic ratio.

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Sulfur isotope composition (δ³⁴S) was measured for soft tissues of Calyptogena soyoae from a cold seep off Hatsushima Islands, Sagami Bay, central Japan. The δ³⁴S values of soft tissues of six specimens collected from one colony greatly but systematically vary from one specimen to another, i.e., gill, -29.1 to -17.2; adductor, -28.0 to -24.5; foot, -17.2 to -15.2; mantle, -10.6 to -7.8‰. The observed isotopic variation between adductor, foot and mantle of a single specimen was interpreted in terms of assimilation of sulfur of different sources; biogenic hydrogen sulfide with lower δ³⁴S (around -20‰) and seawater-sulfate with higher δ³⁴S (+20‰) values.

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