高温高盐度流体参与基鲁纳式铁矿床成矿的实验岩石学研究

Kiruna-type iron deposits are among the important sources of high-grade hypogene iron ores. The origin of Kiruna-type iron deposits worldwide remains hotly debated. It has been suggested that the Kiruna-type deposits formed from the volatile-rich, iron oxide magma. Experiments have shown that it is possible to form a Fe rich melt, but such iron-rich melt also contains high concentrations of Si, Ti, and V and therefore forms the Fe-Ti oxides rather than the high-grade iron ore and low-Ti magnetite which have been observed in many Kiruna-type iron deposits such El Laco and Kiruna iron deposit. Current fluid inclusion studies have shown that many IOA deposits in association with hypersaline fluid (up to 90 wt.% NaCl eq) at extremely high temperatures (~800°C). The objectives of this study are twofold. The first is to determine the magnetite solubility in different salinity fluids, especially in the hypersaline fluids (up to 90 wt.% NaCl eq.). In addition, the magnetite-aqueous fluid partition coefficients involving in such fluids can be calculated as well in the same set of experiments. The second objective is to synthesize the Kiruna-type ores, which will explore the role of hypersaline fluid and anhydrite in the formation of Kiruna-type deposits. The elemental composition of the magnetite and fluorapatite from these experiments will then be evaluated and compared with nature samples. This study will yield an improved metallogenic model for the well-known Kiruna-type iron deposits and provide important experimental data useful in magnetite geochemistry.

基鲁纳式铁矿床是最重要的内生富铁矿床之一，对其成因一直存在矿浆成因和热液成因的激烈争论。前人基于熔体体系的实验岩石学研究结果认为此类矿床是由含铁硅酸盐岩浆发生液态不混溶作用形成，但相关的实验结果尚不能很好解释这类矿床中磁铁矿相对贫钛、具有显著的溶解－再平衡现象、矿石具有高品位等特征。近两年新的研究及申请人研究表明，这类矿床可能与高温高盐度流体关系密切，但是这种关系长期以来被忽略。因此，本项目拟开展不同流体条件下磁铁矿的溶解度实验，为基鲁纳式铁矿床的成因和演化提供新的实验岩石学制约。在流体体系开展高温高压实验研究，获取磁铁矿的溶解度及元素在磁铁矿和流体之间的分配系数，为高温高盐度条件下铁的迁移、富集和成矿及利用磁铁矿元素地球化学来认识基鲁纳铁矿床成因提供重要实验岩石学依据。在富亚铁流体条件下，通过添加氧化剂直接合成磁铁矿-磷灰石矿石，建立更符合地质事实及实验观察的基鲁纳式铁矿床成因模式。

基鲁纳式铁矿床是最重要的内生富铁矿床之一，对其成因一直存在矿浆成因和热液成因的激烈争论。前人基于熔体体系的实验岩石学研究结果认为此类矿床是由含铁硅酸盐岩浆发生液态不混溶作用形成，但相关的实验结果尚不能很好解释这类矿床中磁铁矿相对贫钛、具有显著的溶解－再平衡现象、矿石具有高品位等特征。近几年新的研究及申请人研究表明，这类矿床可能与高温高盐度流体关系密切，但是这种关系长期以来被忽略。因此，本项目通过开展不同流体条件下磁铁矿的交代，合成及溶解度实验，为基鲁纳式铁矿床的成因和演化提供新的实验岩石学制约。实验岩石学及天然样品的研究结果显示在高温高盐度条件下流体条件下磁铁矿具有较高的溶解度，能够有效的搬运铁，并能形成热液成因的高钛磁铁矿高钛磁铁矿并不是岩浆磁铁矿特有的特征。在高盐度的流体作用下磁铁矿能发生溶解再沉淀作用，造成钛从磁铁矿中迁出而形成低钛磁铁矿。研究结果还显示IOA矿床可能遭受了不同程度的溶解-再沉淀作用形成了低钛磁铁矿，表明钛元素能在高温高盐度流体迁移，而V元素在这一过程中比较稳定。总之，本项目通过开展不同流体条件下磁铁矿的高温高压实验及天然样品的研究，为基鲁纳式铁矿床的成因和演化提供了新的资料。 ..