成矿作用过程中赤铁矿-磁铁矿之间非氧化还原转变

Nonredox Transformations of Hematite—Magnetite in Mineralization Process

自然界中铁氧化物的主要存在形式为赤铁矿和磁铁矿,两者之间的相互转变一直是人们关注和研究的热点。磁铁矿和赤铁矿之间的相互转变一直被认为是一个氧化还原反应的结果,反应的发生与一定的氧化剂或还原剂密切相关。然而,近年来一个铁氧化物之间的非氧化还原反应机制被提出,这种非氧化还原反应机制对于认识和了解复杂的成矿作用具有重要的意义。本文阐述了自然界中铁氧化物之间的相互交代结构,对BIF研究和实验学两方面的证据进行了综述,认为这种非氧化还原反应可能存在于很多不同类型的成矿作用过程之中。这种赤铁矿和磁铁矿之间的非氧化还原反应机制具有重要的理论和实际意义:一方面,仅靠地质作用过程中出现磁铁矿或赤铁矿现象不一定就能判别其形成流体的氧化还原状态;另一方面,它可以为勘探含后生赤铁矿的铁矿床提供新的找矿思路,进一步指导深埋在古风化面以下铁矿体的寻找。

The transformations of magnetite and hematite, which are main existing forms of iron oxides in nature, have been debated for many years. The transformation of magnetite and hematite in nature has generally been considered as a result of a redox reaction and linked to a specific oxidant or reductant. However, a nonredox reaction mechanism was proposed in recent years and it might be helpful in better understanding the complicated mineralization process. Ore textures caused by replacement of hematite and magnetite in natural environment was summarized in this paper. The nonredox reactions might exist in many different mineralization processes on the basis of evidences from studying on BIF and experimental ways. Mechanisms for the transformations of magnetite and hematite provide important significances both in theoretical and practical aspects： one hand, it indicates that the presence of magnetite and hematite in geologic formations may not provide meaningful information on the redox state of fluid~ the other hand, it will provide new exploration strategies for hematite rich secondary ores, extending the target for orebodies to deep zones below the paleosurface.