柴北缘超高压变质带鱼卡榴辉岩型金红石矿地质特征及原岩性质探讨

摘要

鱼卡榴辉岩型金红石矿床是柴达木盆地北缘超高压变质带首个发现的大型-超大型金红石矿床,其与超高压变质的榴辉岩密切相关.新鲜的富钛块状榴辉岩是金红石矿床的主要赋矿围岩,金红石在矿石中的4种赋存状态分别代表了4个不同的形成及演化阶段.通过详细的野外地质调查和取样,将鱼卡榴辉岩型金红石矿分为高品位矿石(TiO2>2%)和低品位矿石(TiO2<1%~2%).研究结果表明,高品位矿石相对贫硅,富铁、锰、磷,Al2O3/TiO2值(均小于7)偏低,但全碱含量总体偏高.微量元素特征显示,高品位矿石具有洋岛玄武岩的原岩特点,而低品位矿石的原岩为则为板内环境下产出的E-MORB.鱼卡金红石矿床中两类矿石的原岩性质不同反应了柴北缘超高压变质带构造演化的复杂性.%The Yuqia eclogite-type rutile deposit is the first large-super large rutile deposit discovered in Northern Qaidam ultra-high pressure metamorphic belt, which was related to the UHP eclogite.The flesh massive Ti-rich eclogite serves as the major ore-host rock for this rutile deposit, the rutile with four exiting state can be recognized in this deposit, representing for four different stages of formation and evolution, respectively.After the detailed field geological investigation and sampling, the eclogite-type rutile ore in the Yuqia deposit can be divided into high-grade ore (TiO2>2%) and low-grade ore (TiO2 < 1%~2%).The investigation results have shown that the high-grade ore are relatively depleted in SiO2 while they are enriched in TFeO, MnO and P2O5, with lower Al2O3/TiO2 ratios (<7) and higher content of total alkali (K2O + Na2O).Trace element characteristics indicate that the high-grade ore has the protolith characteristics of oceanic island basalt (OIB), but the protolith of low-grade ore was derived from the enriched type mid-ocean ridge basalts (E-MORB) in the intraplate environment.The different of protolith characteristics between Yuqia rutile ore with two types reflect the complexity of the tectonic evolution in Northern Qaidam ultrahigh pressure metamorphic belt.