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

岩浆-热液系统挥发成分行为及成矿机制

基本信息

批准号：
12440143
负责人：
HAYASHI Ken-ichiro
金额：
$ 2.11万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2002
项目状态：
已结题

项目摘要

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.

在含水花岗质岩浆的凝固过程中，高盐度的水从岩浆中分离出来。岩浆水含有CO_2、H_2S等挥发性组分。岩浆水中溶解的金属离子浓度较高，具有成矿溶液的性质。摩洛哥东北部的贝尼布伊弗鲁尔矿区的矽卡岩型磁铁矿存款是北方非洲的主要铁矿床之一。矽卡岩型矿石产于灰岩与花岗闪长质侵入体之间。讨论了矽卡岩与花岗闪长岩的成因关系。K-Ar定年结果表明，矽卡岩矿物与花岗闪长岩的年龄基本一致，说明该存款的成矿溶液为花岗闪长岩的岩浆水。流体包裹体的温度高达500℃，盐度高达75wt%NaCl。矽卡岩矿物的氧同位素值表明，岩浆水沉淀矽卡岩矿物。本文对日本东北部野田玉川矿区变质层状锰存款中锰硅酸盐矿物的氧同位素值进行了分析。由于该锰存款是托管在屋顶悬垂花岗岩体之上，岩浆水的证据可能记录在锰矿物。然而，在紧密共生的锰矿物中，氧同位素并没有达到平衡。这表明接触变质作用中变质流体的量很小。