中国大陆科学钻探主孔高钛与低钛榴辉岩地球化学特征对比及其对金红石成矿的指示意义

Geochemical comparison between high-Ti and low-Ti eclogites from the main hole of the Chinese Continental Scientific Drill Project and its implications for rutile mineralization.

榴辉岩型金红石矿床是我国原生金红石矿床的最重要类型。本文以中国大陆科学钻探主孔0～2000m范围内揭露的榴辉岩为对象,通过对榴辉岩中TiO2与其它元素协变关系的全面分析,同时结合我国原生榴辉岩型金红石矿床TiO2的平均品位,将榴辉岩区分为高钛榴辉岩(TiO2>2％)和低钛榴辉岩(TiO2<2％),并据此系统对比了二类榴辉岩地球化学组成的差异。研究结果表明,高钛榴辉岩相对贫硅、贫钾、富铁,Al2O3／TiO2比值和全碱(K2O+Na2O)含量总体偏低,Cs、Rb、Ba等大离子亲石元素和Zr、Hf等高场强元素不同程度亏损,而放射性元素Th、U则相对富集,并总体具有较低的轻重稀土比值。榴辉岩型金红石矿床的形成主要受原岩因素制约,原岩的源区组成、产出环境、起源深度、部分熔融程度和随后的结晶分异过程对Ti的初始富集均具重要影响,富钛基性原岩是榴辉岩型金红石矿床形成的物质基础,高压区域变质作用是这类矿床形成的必要条件。

The eclogite-type rutile deposit is the most important primary rutile deposit in China. Based on a comprehensive analysis of the correlations between the contents of TiO2 and other elements in eclogites from 0 - 2000m of the main hole of the Chinese Continental Scientific Drilling （ CCSD ）, and by taking the mean TiO2 grade of the primary rutile deposit in China into account, this paper grouped the eclogites into a high-Ti （ TiO2 〉 2% ） and a low-Ti （ TiO2 〈 2% ） subgroup, and systematically compared the geochemical differences between the two subgroups of eclogites. The investigation results have shown that the high-Ti eclogites are relatively depleted in SiO2, K2O, enriched in TFeO, and have lower Al2O3/TiO2 ratios and K2O ＋ Na2O values. They also display vary degree depletions of Cs, Rb, Ba, Zr, Hf and enrichments of Th, U, and generally show lower LREE/HREE ratios. Integrated geochemical data indicate that the protolith of ecologite is the main constraint for the formation of the eclogite-typo rutile deposit. The initial Ti enrichment in the protolith rocks is constrained by many factors, such as the source compositions, source depth, tectonic setting, partial melting degree and the crystallization differentiation process, etc. The Ti-rich basic protolith is the material base and the high-pressure regional metamorphism is the essential condition for the generation of the eclogite-typo rutile deposit.