GEOCHEMISTRY AND MINERALOGY OF A MODERN BUSERITE DEPOSIT FROM A HOT-SPRING IN HOKKAIDO, JAPAN

The hot spring water discharging from a flank of an active volcano is precipitating unique monomineralic manganese deposits over volcanic te rrain. The major and trace element chemistry, XRD mineralogy, DTA, and SEM observations indicate that the deposits consist of 10 Angstrom ph yllomanganate (buserite) accommodating inter-layer Ca and Mg with negl igible amounts of detrital minerals. Other metallic elements can be ac commodated by buserite, but concentrations are negligible ranging less than 10 ppm to 500 ppm. Abundance and pattern of REE (less than 100 p pm in total) are similar to those from hydrothermal manganese deposits . The buserite is enriched in Ca and Mg but depleted in Na in comparis on with those in the spring water. The distribution coefficients for C a, Mg and Na between the buserite and the host water were calculated a ssuming an ion-exchange equilibrium in the Yuno-Taki Falls, which prov ed applicable to other manganese deposits from surficial environments on land and oceans.