Abstract
Initial data on the hydrogen-isotopic compositions in hydrous Mn minerals from various occurrences fall in a wide range from −298 to −84‰, relative to SMOW. δ D-values of todorokite and cryptomelane from Tertiary deposits show −89 and −150‰. 10å-manganite and δ-MnO 2 from deep-sea nodules have relatively restricted δ D-values ranging from −96 to −84‰. The δ D-values for manganese bog ores from recent hot springs show almost −105‰. It is recognized that the isotopic values obtained for the deep-sea nodules and recent bog ores are slightly different ranged. Manganite and groutite are unique in their hydrogen-isotopic compositions, having the most depleted δ D-values ranging from −298 to −236‰. MnO(OH) minerals are more deuterium-depleted hydrous minerals than any other hydrothermal minerals from various ore deposits. Hydrogen-isotope 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. the present experimental results indicate that if manganites were formed at temperatures below 250°C, under isotopic equilibrium conditions, most of the manganite mineralization in the Tertiary manganese deposits must have precipitated from meteoric hydrothermal solutions.
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