Hydrogen isotopic composition of MnO(OH) minerals from manganese oxide and massive sulfide (Kuroko) deposits in Japan

The hydrogen isotopic composition of structural water in MnO(OH) minerals from manganese oxide and massive sulfide deposits (Kuroko) in Tertiary formations fall within a narrow range from -261 to -275 permil relative to standard mean ocean water (SMOW). The δD of two manganites from manganese deposits in Paleozoic formations were -236 and -298 permil, indicating a wider range than in those of Tertiary manganese deposits. The MnO(OH) minerals are more deuterium-depleted. than any other hydrothermal minerals reported to date. Hydrogen isotopic fractionation factors between manganite and water were experimentally determined to be 0.7894, 0.7958, and 0.8078 at 150°, 200°, and 250° C, respectively, under hydrothermal conditions at 500 bars. The present experimental results indicate that if manganites were formed at temperatures below 250° C under isotopic equilibrium conditions, then most manganite mineralization in the ore deposits must have precipitated from meteoric hydrothermal solutions.