陕南凤凰岭南缘变质镁铁质—超镁铁质侵入岩矿物学特征——对Fe-Ti成矿作用的指示

Mineralogical characteristics of the meta-mafic-ultramafic intrusive rocks on the southern margin of Fenghuangling, southern Shaanxi: An indicator of Fe-Ti metallogenesis

陕南凤凰岭南缘变质镁铁质—超镁铁质侵入岩为富含Fe、Ti等有用元素的含矿岩体。利用岩石地球化学方法、偏光显微镜和电子探针技术对该区镁铁质—超镁铁质侵入岩的岩石学、地球化学和矿物学特征进行了研究,并对Fe-Ti氧化物的形成、富集进行了初步探讨,对成岩、成矿作用具有一定的参考意义。结果表明,成矿镁铁质—超镁铁质侵入岩与非成矿镁铁质—超镁铁质侵入岩为不同岩浆源区、同期岩浆作用的产物,镁铁质—超镁铁质侵入岩类的Fe-Ti矿化作用与初始岩浆的源岩之间具有密切关系。Fe-Ti氧化物主要以钛铁矿和榍石的形式存在,局部见少量金红石。化学成分上,钛铁矿具富锰贫镁特征,本区Fe-Ti氧化物的形成和富集过程经历了岩浆结晶分异阶段和热液蚀变阶段。

The meta-mafic-ultramafic intrusive rocks in southern Fenghuangling are ore-bearing rocks with abundant useful ele-ments such as Fe and Ti. In this study, geochemical method, polarizing light microscope and electron probe micro analysis （EPMA） were conducted to investigate the petrologic, geochemical and mineralogical characteristics of the meta-maficultramafic intrusive rocks. The Fe-Ti oxide formation and enrichment were also studied so as to probe into diagenesis and mineralization. The results show that, in this area, ore-bearing meta-mafic-ultramafic intrusive rocks and barren meta-mafic-ultramafic intrusive rocks resulted from simultaneous magmatism of different magma source areas, and the Fe-Ti mineralization of meta-mafic-ultramafic intrusive rocks had a close relationship with the initial magma source rocks. Fe-Ti oxides mostly exist in sphene and ilmenite but sometimes it also exists in a small amount of rutile. Ilmenite is rich in MnO but poor in MgO. The formation and enrichment process of Fe-Ti ox-ide experienced the stages of magma crystallization differentiation and hydrothermal alteration.