A hydrogeochemical exploration using fluoride in stream waters

Abstract

High anomalies of F, Li and Rb in bedrocks have been reported around the Takatori Sn-W deposit (M.I.T.I., 1987). Among them, F is the most effective pathfinder, because it shows the highest concentrations and the highest geochemical contrast. The purpose of the present study is to test the effectiveness of stream water as a geochemical exploration medium, with special attention to fluoride. Samples of stream water were collected from 116 sites and were subsequently analyzed. In addition, leaching experiments on bedrocks taken from this district were carried out. The result are summarized as follows. (1) From the distribution pattern of Fin stream waters, it is clear that the high anomalies of Fform the halo which surrounds the Takatori Sn-W deposit. (2) The halo formed by the high anomalies of Fin stream water, ranging over 2•~4 km, coincides with the known halo formed by the high anomalies of F in the bed rock, ranging over 1.5 •~ 3.5 km around the Takatori Sn-W deposit. (3) Therefore, it is considered that the anomalies of Fin stream water are the secondary geochemical dispersion due to fluoride which dissolved from the bedrocks with high F content around the Takatori Sn-W deposit. (4) As a result of the 6 days' leaching experiments, the high concentrations of dissolved fluoride, which is close to the fluorite saturation value (8.7mg/•¬F-), was obtained from fluorite-bearing bedrocks. On the other hand, relatively much lower concentrations of Fwere obtained from muscovite-bearing but fluorite-lacking bedrocks. (5) .Major F-bearing minerals around the Takatori Sn-W deposit are fluorite and muscovite. Fluorite exists in the bedrocks of which F content exceeds about 1000 ppm, nevertheless muscovite occurs also in the bedrocks with F content less than 1000 ppm. On the other hand, in the area where F content of bedrocks is higher than 500•`1000 ppm, Fconcentration in stream waters is much higher than in other area. These facts are in good agreement with the result of the leaching experiments. (6) In case of programming the geochmical exploation of mineral deposit types associating the fluorite as alteration minerals, it is recommended that Fin stream waters, as well as F in bedrocks, should be used as a usefull pathfinder.