The fluorine content was determined spectrophotometrically for sedimentary rock samples from Tomioka, southern Gunma Prefecture. (1) Twenty six siltstones gave an average fluorine content of 420 ppm, and the value of each sample falls within a rather narrow range compared with that of chlorine. Chlorine in sedimentary rocks is quite labile against the attack of circulating water, whereas fluorine might not so easily be removed as chlorine. As a result, the fluorine content of sedimentary rocks is considered to be controlled mainly by the mineral species which constitute the sediments. (2) Tuffs which contain montmorillonite as a main constituent mineral tend to enrich more fluorine than those composed mainly of chnoptilolite.
Differential thermal analyses were conducted on protodolomite bearing carbonate rocks of the Riukiu limestone in southern Okinawa. The light-colored portion which is composed of protodolomite and calcite shows two endothermic peaks, while the dark-colored portion shows three endothermic peaks at 780∼790°C (medium), 800∼810°C (weak), and 925∼935°C (strong), respectively. These three endothermic peaks indicate the occurrence of ferroan-dolomite, protodolomite and calcite. The occurrence of pyrite was also confirmed by DTA, X-ray and chemical analyses of residues of the dark-colored samples insoluble in dilute hydrochloric acid. It is concluded that the dark-colored portion is composed of calcite, protodolomite, magnesian-calcite, ferroan-dolomite, aragonite and pyrite. The dark color and the amount of K2Cr2O7-consumption of the carbonate rocks are dependent chiefly on the associated pyrite.
Based on the thermochemical data for hydrolysis of a variety of rock-forming minerals (HELGESON, 1969), possible reactions between rocks and seawater at elevated temperatures have been examined. The result reveals that most of natural rock alteration facies can well be explained by the interaction of rocks with seawater at ordinary hydrothermal temperatures. This is consistent with the hypothesis that the hydrothermal ore-forming solution responsible for the Kuroko type mineralization in Japan might have been derived essentially from the coeval seawater (KAJIWARA, 1973a and 1973b). It is suggested that such cyclic seawater would also be essential to the regional metamorphic processes in the earth's crust. Available hydrogen isotope data for hydrated silicate minerals from some igneous and metamorphic rocks may also be interpreted with this view.
The behavior of fluoride during the precipitation of calcium carbonate from calcium bicarbonate solution was studied experimentally. Magnesium ions in parent solutions cause the coprecipitation of fluoride with calcium carbonate. The amount of fluoride coprecipitated with calcite increases with increasing concentration of magnesium ions in parent solutions, whereas the amount of fluoride coprecipitated with aragonite decreases. It may suggest that the mechanism of the coprecipitation of fluoride with calcite is different from that with aragonite. The amount of fluoride coprecipitated with aragonite is larger than that with calcite. The experimental result agrees with the observed fact that the fluoride contents of skeletal aragonite of marine organisms and of natural aragonite formed inorganically in sea water are higher than those of skeletal calcites. Fluoride in parent solutions greatly favors calcite formation.
147Sm-143Nd dating method was applied to a pipe eclogite of Roberts Victor mine. No variation in isotopic abundance of 143Nd was observed in garnet, omphacite and whole rock fractions. An upper limit of the solidification age was set to be 1.3b.y.