Yoshimasu Kuroda

Mineralogy and hydrogen isotope geochemistry of clay minerals in the Ohnuma geothermal area, Northeastern Japan

Abstract Mineralogical and hydrogen isotopic studies have been made on clay minerals occurring in the Ohnuma geothermal area, northeastern Japan. Here, clay minerals such as smectite, kaolinite, dickite, sericite, and chlorite were formed by hydrothermal alteration of Miocene rocks. A chemical equilibrium can be assumed to be attained from the fact that the amount of expandable layer in the interstratified chlorite/smectite decreases and the polytype of sericite changes from 1M to 2M 1 with increasing depth and temperature. The hydrogen isotopic composition (D/H) of the clay minerals is lighter than that of the geothermal and local meteoric waters by about 20–40‰. The hydrogen isotopic fractionation factors α mineral-water are as follows: 0.972–0.985 for kaolinite and dickite, 0.973–0.977 for sericite, and 0.954–0.987 for chlorite. In the temperature range from 100 to 250°C, the hydrogen isotopic fractionation factors between these minerals and water are not sensitive to the temperature. α chlorite-water depends on the kind of octahedrally coordinated cations which lie close to the hydroxyl groups; it becomes large with an increase of Mg content of chlorite.

Hydrogen isotope composition of deep-seated water

D/H ratios of phlogopites and amphiboles from rocks of possible mantle origin and also those of water from (glass?) inclusions in olivines of the olivine nodule and peridotites have been determined. The mantle water seems to have aδD value of —85±10‰ on the basis of results of inclusions in the nodule-olivine.

D/H ratios of the coexisting phlogopite and richterite from mica nodules and a peridotite in South African kimberlites

The water content and D/H ratio of pairs of phlogopite and richterite in kimberlite samples were measured. The water contents of both minerals were lower than the formula content. On the basis of D/H ratios of the pair, phlogopite and richterite can not be regarded as a simple equilibrium product with respect to hydrogen isotope exchange. It seems impossible to estimate D/H ratio of the mantle water through D/H ratios of the hydrous silicate pairs.

A preliminary study of D/H ratios of chlorites

Chemistry dependence of δD of chlorites is inferred from data for natural chlorites. δD of water equilibrated with those chlorites is estimated to be −2∼−8‰.

D/H study of the magnetite-series granitic plutons from the Kitakami district, Northeast Japan

Abstract δD- and X Fe -values of coexisting biotite and hornblende in the magnetite-series granitic plutons from the Kitakami district were investigated. The slopes of tie-lines of coexisting biotite and hornblende in the δD- X Fe diagram are parallel to those obtained from Suzuoki and Epsteins experimental work of D/H fractionation among biotite- and hornblende-water systems. The δD- and X Fe -values of biotite and hornblende become lower during crystallization, i.e. δD-values vary from −65 to −85% for biotite and −60 to −80% for hornblende, and X Fe from 0.5 to 0.4 for biotite and 0.4 to 0.3 for hornblende. These δD- X Fe relationships are different from those of the ilmenite-series granitic rocks, and are explained by an open-system shallow magma reservoir of comparatively high oxygen fugacity. The estimated δD-values of the magmatic waters are in the range from −60 to −40%.

The tin-tungsten ore system of Pilok, Thailand

Abstract The tin-tungsten mineralization in the Pilok mining area is centered on apical parts of probably Late Cretaceous alkali feldspar aplite stocks (aplogranite) which intrude earlier K-feldspar megacrystic biotite granite. The aplogranites are of transitional magmatic-hydrothermal origin and have the typical mineral assemblage of quartz-microcline-albite-muscovite-tourmaline-spessartine-fluorite-beryl. Quartz-muscovite-tourmaline alteration is dominant in and along mineralized fractures, followed locally by chloritization. Mineralization is fracture-controlled and consists of stockworks, veins and veinlets with an ore association composed mainly of the metal group As-Fe-Zn-Cu-Sn-W-Bi-. The gangue assemblage is quartz-muscovite-tourmaline-fluorite ± K-feldspar ± beryl ± apatite. Major and trace element trends in the granitic rocks suggest a magmatic evolution controlled by fractional crystallization. The distribution pattern of Ti vs Ta defines a degree of fractionation of less than, or equal to, 0.1 and follows very closely the Erzgebirge tin-granite suite. Hydrothermal metal redistribution is widespread in the Pilok ore system. Large-scale tin depletion and local tin ore enrichment are complementary features of the same process. Stable isotope data suggest a strong magmatic input into the early fluid system, whereas the disturbed Sr isotope pattern of the Pilok aplogranites indicates external fluid overprint.

Deuterium/Hydrogen Ratios and Water Content of Some Silicate Melts at High Pressure

Various approaches have been made by different workers to determine the role of water in the mantle or the lower crust. For example, Kuroda et al. [1] determined the water content of some hydrosilicate minerals under high pressure and high temperature conditions. The stability field of some hydro-silicate minerals was studied by Kushiro [2], Kushiro et al. [3], Lambert and Wyllie [4], Hariya et al. [5,6] and others. The investigations of the role of water on the magma genesis (Allen et al. [7], Kushiro [8], and Burnham and Davis [9]) and the hydrogen and oxygen isotope frac-tionation of hydrous minerals (Kokubo et al. [10], Sheppard and Epstein [11], and Kuroda et al. [12]) also provide valuable information as to the concentration of water in the upper mantle or the lower crust.