Toshio Mizuta

Mobilization and enrichment of high-field strength elements during late- and post-magmatic processes in the Shuiquangou syenitic complex, Northern China

Abstract The Shuiquangou syenitic complex consists of melasyenite and leucosyenite. In the northeastern part, there is a small area where the leucosyenite was affected by alteration. The altered leucosyenite contains much higher concentrations of high-field strength elements (HFSE), especially Nb, Zr, REE and Y compared to fresh leucosyenite. REE patterns of the altered leucosyenite show moderate negative Eu anomaly, in contrast to the slightly positive to non-anomalous Eu signature of the fresh syenitic rocks. Allanite from the hydrothermal mineral assemblage in the altered leucosyenite also contains much higher concentrations of REE and Ti than the euhedral magmatic allanites in unaltered leucosyenite. The enrichment of HFSE in altered leucosyenite was interpreted to be caused by the hydrothermal fluids based on mineral chemistry and whole-rock data. Within the fresh leucosyenite, allanite occurs in two habits, euhedral ones indicating a primary magmatic origin and anhedral ones suggesting a late-magmatic origin. The latter has higher concentrations of REE and Ti than the former. The anhedral allanite was presumed to be formed coeval with the alteration of the euhedral allanite as a result of residual magmatic fluid derived directly from the syenitic magma. The alteration of magmatic euhedral allanite and the enrichment of REE and Ti in the anhedral late-magmatic allanite suggest that these elements were mobilized by the residual magmatic fluid. Both residual late-magmatic and hydrothermal fluids have an inferred composition characterized by high alkalic and F contents, suggesting that F may be the most ligand that complexed the high-valence cations.

Characteristic Features of Ra‐Pb‐Sr‐Rare Metal‐bearing Tamagawa Acidic Thermal Water Derived from a Deep‐seated Magmatic System in Akita Prefecture, Japan

Ohbuki hot spring in the Tamagawa hot spring area, which is associated with volcanic activity, is a famous hot spring characterized by strong acidity and presence of radium. Many studies on the thermal water of Ohbuki hot spring have been carried out. Iwasaki et al. (1963) reported that the anions in thermal water of Ohbuki hot spring are transported by volcanic gas derived from active magma, while Yoshiike (1996) proposed that the cations in the thermal water are derived from volcanic rocks in the shallow underground part around Tamagawa. We examined the chemical characteristics of thermal water on the basis of concentrations of major and trace elements and Sr, Nd and Pb isotopic ratios of the thermal water and estimated the source of elements in the thermal water.

Instrumental Neutron Activation Analysis of Tungsten Content in Mineralized and Non-mineralized Granite.

Tungsten content in granitic rocks is precisely determined by an instrumental neutron activation analysis method (INAA) using several standard samples. Natural geostandard rocks are GSJ geostandard of JG-1, JG-1a, JG-2, JR-2 and JR-3, and artificial standard materials of JR-2 with added scheelite powder and tungsten-doped quartz sand were employed for the analysis. Each sample (100mg) was irradiated for short time (1min, 2min and 3min) at thermal neutron flux 2.8×1013n/cm2/s and for long time (60min) at thermal neutron flux 2.3×1013n/cm2/s. Gamma-ray spectrum of 187W at 685.72keV was used for the tungsten analysis in geostandards. The 187W gamma-ray spectrum was not recognized for Na-rich JG-1 (W concentration=1.5ppm), while the gamma spectrum of that was recognized for JR-2 (1.8ppm). S/N ratios of 187W for geostandards that irradiated for 3min and after cooling for 6 day were higher than those of another irradiation conditions. The analytical error of tungsten in geostandards with the confidential limit of 95% was ± 4.7ppm. This INAA with 3min irradiation is the most suitable method for the tungsten-bearing samples was successfully applied to wide range of tungsten (i. e. low W concentration of non-mineralized granites to high W concentration of mineralized granite and scheelite-bearing ore).