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

在含水花岗岩浆的凝固过程中，岩浆中会分离出极高盐度的水。岩浆水中含有CO_2、H_2S等挥发性成分。岩浆水中溶解的金属离子浓度较高，表现为成矿溶液。本文研究了与岩浆水有成因联系的矿床。摩洛哥东北部贝尼布伊弗劳尔矿的矽卡岩型磁铁矿是北非主要的铁矿之一。矽卡岩矿产于石灰岩和微细花岗闪长岩侵入岩之间。夕卡岩和花岗闪长岩之间的成因关系一直存在争议。K-Ar定年结果表明，夕卡岩矿物的年龄与花岗闪长岩的年龄基本一致，这表明该矿床的成矿溶液为花岗闪长岩的岩浆水。流体包裹体数据显示温度很高，约500NaC l，盐度很高，约75wt%当量℃。夕卡岩矿物的氧同位素值表明，岩浆成因的水沉淀了夕卡岩矿物。因此，高温高盐度的岩浆水是磁铁矿形成过程中大量铁迁移的主要原因。对日本东北部野田-玉马川变质层状锰矿的硅酸锰矿物氧同位素进行了分析。由于这个锰矿床赋存于花岗岩岩体上方的屋顶悬垂中，因此岩浆水的证据可能记录在锰矿中。然而，密切伴生的锰矿之间还没有达到氧同位素平衡。这表明接触变质过程中的变质流体数量很少。

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.