群馬県伊香保温泉おはぐろの湯の含マンガン温泉沈殿物のXPSによる研究  [in Japanese] XPS study on manganese hot spring deposits from Ohaguro, Ikaho Hot Spring, Gunma, Japan  [in Japanese]

Manganese hot spring deposits from Ohaguro, Ikaho Hot Spring, Gunma, Japan were examined mineralogically and chemically. Their Mn⁴⁺/Mn²⁺ ratios were also determined by X-ray photoelectron spectroscopy (XPS). Two samples were taken from the black deposits on the weathered andesite where hot spring water flows out from the bedrock (A), and from a channel where hot spring water flows down (B). The principal mineral identified for both samples by the X-ray powder diffraction is rancieite-takanelite with minor buserite. Both samples mainly contains manganese, oxygen and calcium by the analysis of wide spectrum of XPS. On the basis of the results of constrained least squares fitting of the Mn2<i>p</i> with Ca2<i>p</i> for narrow spectrum, the mole ratios of Mn²⁺:Ca²⁺:Mn⁴⁺ for A and B are 9.8:13.6:76.6 and 14.7:11.7:73.5, respectively. Considering with analysis of water contents, the chemical formula for A and B are obtained as (Mn²⁺_0.50, Ca²⁺_0.69)Mn⁴⁺_3.90O₉·2.99H₂O and (Mn²⁺_0.76, Ca²⁺_0.61)Mn⁴⁺_3.81O₉·3.03H₂O, respectively. This reveals that A and B are rancieite and takanelite, respectively. Considering the hot spring composition together with the occurrences, takanelite-rancieite from Ohaguro, Ikaho Hot Spring is estimated to have been formed by step-by-step oxidation of the deep anoxic Ca-rich deep hot spring water by the mixing with oxic shallow groundwater.