攀西地区太和镁铁质层状岩体及Fe-Ti-V氧化物矿床成因研究

Magmatic Fe-Ti-(V) oxide deposits are commonly present in the mafic-ultramafic layered intrusions and the massif anorthosites. They are the important metal source of Fe、Ti、V. The Fe-Ti-(V) oxide deposits belong to a part of these complexes and have close relation with the fractional differentiation of the magma. However, the genetic model for the formation of the oxide deposits remains subject to ongoing controversy. Numerous mafic-ultramafic layered intrusions hosting giant Fe-Ti-(V) oxide deposits in the Pan-Xi area are associated with the Emeishan Large Igneous Province. Recent studies on these layered intrusion as well as the Fe-Ti-(V) oxide deposit acheived some new progress and understanding, nevertheless, the enrichment process of Fe, Ti,V and ore-forming model are still debatable. This project focuses on the poor-understood Taihe mafic layered intrusion which hosting giant Fe-Ti-(V) oxide deposit. On the basis of detailed field investigations、observations on the thin sections and previous studies, systematic petrology, mineralogy, PGE geochemistry and Sm-Nd isotope geochemistry will be used to investigate the characteristics and differentiation trend of the parental magma, the process of magma emplacement and the possibility of multiple pulses of magma, magma dynamic process during mineral crystallization as well as the crystallization and enrichment mechanism of the Fe-Ti-(V) oxide deposit.

岩浆成因Fe-Ti-(V)氧化物矿床通常存在于镁铁-超镁铁层状岩体及斜长岩体中，是Fe、Ti、V等金属的重要来源。Fe-Ti-(V)氧化物矿床是这些岩体的一部分且与岩浆的结晶分异过程存在密切联系，然而其成因机制仍存在较大争议。攀西地区分布有数个与峨眉山大火成岩省有关的赋存超大型Fe-Ti-(V)氧化物矿床的镁铁-超镁铁岩体。近来对这些岩体及其氧化物矿床的研究取得了一些新的进展和认识，但是对于矿床的元素富集过程及成因机制仍存在较大争议。本项目拟选取本区研究程度较低、赋存有超大型Fe-Ti-(V)氧化物矿床的太和镁铁质层状岩体为研究对象，在详细的野外地质、室内岩矿研究及前人研究基础上，系统运用岩石学、矿物学、PGE地球化学及Sm-Nd同位素地球化学数据综合研究，探讨层状岩体的母岩浆性质及其演化趋势、岩浆就位及是否有不同期次岩浆注入、矿物结晶的岩浆房动力学过程及Fe-Ti氧化物的沉淀富集机制。

攀西地区分布有数个赋存超大型Fe-Ti氧化物矿床的镁铁-超镁铁层状岩体。主要氧化物矿层分布于这些岩体的中下部，之上的辉长岩通常含有大量的堆晶磷灰石。本研究选择攀西地区太和镁铁-超镁铁岩体及同时代的红格及攀枝花岩体为主要研究对象。我们研究表明，太和岩体是由小体积镁铁质岩浆持续的注入太和岩浆房形成。其母岩浆成分为Fe-Ti氧化物饱和，磷灰石近饱和的演化程度高的岩浆。该母岩浆同时具有较高的氧逸度，导致Fe-Ti氧化物的早期结晶。大量Fe-Ti氧化物的分离使残余岩浆的SiO2快速增加，Ca/Na比值降低，Mg/Fe2+比值不变，从而使磷灰石在岩浆演化过程中提前饱和。通过对比攀西地区红格和攀枝花岩体，我们发现这些赋矿岩体的母岩浆成分存在明显差异。红格岩体母岩浆近似于峨眉山高Ti玄武质岩浆，而攀枝花岩体母岩浆则接近与中Ti玄武质岩浆。因此，母岩浆成分并不是形成超大型Fe-Ti氧化物矿床的关键因素。岩浆的多期侵入，较高的氧逸度，Fe-Ti氧化物的早期结晶与重力分异对矿床的形成起着关键作用。