Behavior of volatile components and mechanism of ore formation in the magmatic-hydrothermal system

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During the solidification of hydrous granitic magma, water of very high salinity separates from the magma. The magmatic water contains volatile components such as CO_2 and H_2S. Since concentration of dissolved metallic ions in magmatic water is rather high, it behaves as an ore-forming solution. In this study, ore deposits that have genetical relation with magmatic water are studied.The skarn-type magnetite deposit at the Beni Bou Ifrour mine, northeastem Morocco, is the one of the major iron deposits in northern Africa. The skarn ore develops between limestone and microgranodioritic intrusions. The genetical relationship between skarn and granodiorite has been argued. The result of K-Ar dating shows that age of skarn mineral is approximately same as that of granodiorite; this agreement suggests ore-forming solution of this deposit was magmatic water that derived from granodiorite. Data obtained from fluid inclusions show very high temperature, 〜500℃, and very high salinity, 〜75 wt% equivalent NaCl. Oxygen isotope values of skarn minerals suggest that water of magmatic origin precipitated skarn minerals. Therefore, magmatic water of high temperature and high salinity was responsible for the transport of large amount of iron during the formation of magnetite deposit.Oxygen isotope values of manganese silicate minerals from the metamorphosed bedded type manganese deposit at the Noda-Tamagawa mine, northeastern Japan, were analyzed. Since this manganese deposit is hosted in the roofpendant just above the granitic body, evidence of magmatic water probably recorded in manganese minerals. However, oxygen isotopic equilibrium has not been attained among manganese minerals of closely associated. This suggests that amount of metamorphic fluid during contact metamorphism has been very small.