地学前缘 ›› 2010, Vol. 17 ›› Issue (2): 106-117.

• 论文 • 上一篇    下一篇

斜长岩体中Fe-Ti-P矿床的特征与成因

赵太平, 陈伟, 卢冰   

  1. 1中国科学院 广州地球化学研究所, 广东 广州 510640
    2中国科学院 研究生院, 北京 100049
    3中国科学院 南海海洋研究所, 广东 广州 510301
  • 收稿日期:2010-01-11 修回日期:2010-02-02 出版日期:2010-03-15 发布日期:2010-04-05
  • 作者简介:赵太平(1963—), 男,研究员,博士生导师,岩石学与矿床学专业。Email: tpzhao@gig.ac.cn
  • 基金资助:

    国家自然科学基金项目(40672058,40272041);国家重点基础研究发展计划“973”项目“华北大陆边缘造山过程与成矿”(2006CB403520)

Characteristics and origin of Fe-Ti-P oxide deposits associated with Proterozoic massiftype anorthosite.

 DIAO  Ta-Beng, CHEN  Wei, LEI  Bing   

  1. 1Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
    2Graduate University of Chinese Academy of Sciences, Beijing 100049, China
    3South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
  • Received:2010-01-11 Revised:2010-02-02 Online:2010-03-15 Published:2010-04-05

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摘要：

岩体型斜长岩为由90％以上斜长石组成的岩浆岩,具变压结晶的特点,仅形成于元古宙(2.1~0.9 Ga),常赋存有Fe-Ti-P矿床。Fe-Ti-P矿体既呈整合层状也呈透镜状和席状等不规则形式产出;矿石类型有块状和侵染状，前者矿石矿物含量>70%,后者矿石矿物含量为20%~70%;矿物组成上,不同矿床稍有差别:部分矿床的Fe-Ti氧化物以钛磁铁矿为主、钛铁矿次之,而其他矿床则以赤钛铁矿为主、磁铁矿次之。一些矿床磷灰石含量较高,出现仅由Fe-Ti氧化物和磷灰石组成的铁钛磷灰岩。研究表明,Fe-Ti-P矿床由富Fe、Ti的岩浆演化形成,其母岩浆是在深部岩浆房中大量结晶斜长石后的残余岩浆。部分学者认为不同矿石经正常的结晶分异作用并堆晶形成,但该机制很难解释呈不规则状产出的矿石;其他学者则认为不混熔作用对矿石的富集(尤其是脉状、席状的铁钛磷灰岩)有重要作用,但该机制缺乏岩相学和地球化学方面的证据。河北大庙Fe-Ti-P矿体呈透镜状、席状等不连续地分布于斜长岩中,矿体不发育明显岩浆分层,但仍出现不同矿石的相带。依据详细的岩相学、矿体中矿物含量和成分的变化规律以及全岩地球化学特征,我们判断大庙矿床中不同矿石为堆晶矿物和晶隙流体的混合产物,它们由铁闪长质岩浆经结晶分异和堆晶作用形成,与不混熔作用关系不大。矿体不规则状产出的特点可能与岩浆动力分异作用有关,并伴随有小范围的亚固相迁移。

关键词: 岩体型斜长岩, 铁钛磷灰岩, 变压结晶, 不混熔作用, 大庙Fe-Ti-P矿床

Abstract:

Massiftype anorthosite is referred to igneous rocks consisting of over 90％ plagioclase. The massiftype anorthosite bodies formed in the Proterozoic ranging from 2.1 Ga to 0.9 Ga, and commonly host abundant FeTiP oxide ores. FeTiP ore bodies occurred as conformable layers or irregular shapes as lenses, sheets or veins. The ores usually are of massive and disseminated types; the former type contains more than 70％ ore minerals, and the latter one contains 20% to 70％. Ore minerals from some deposits are mainly titanomagnetite with minor ilmenite, whereas the others are mainly hemoilmenite with minor magnetite. Some of ores contain abundant amounts of apatite, which forms nelsonite containing only FeTi oxides and apatite. These FeTiP ores have been commonly interpreted as forming from a FeTirich magma which usually represents residual magma after extensive crystallization of plagioclase in a deep chamber. However, it is controversial on the oreformation mechanisms. They were assumed to have crystallized from immiscible FeTiP liquids separated from silicate magma or represent cumulate rocks that directly crystallized from silicate magmas. The Damiao FeTiP oxide deposit is the unique deposit hosted in massiftype anorthosite in China. Its ore bodies commonly occur as irregular lenses, veins or pods with sharp contact with anorthosite, and consist of different zones of FeTiP ores upwards instead of obvious igneous layering. Based on detailed petrography, mineral proportions, mineral compositions and wholerock geochemistry, we conclude that various ores at Damiao are mixtures of cumulus mineral and trapped liquids, and that they formed from a ferrodioritic magma by fractional crystallization and accumulation. The discordant occurrence of various ores may be related to the dynamic crystallization process and/or subsolidus remobilization.

Key words:  massiftype anorthosite, nelsonite, polybaric crystallization, immiscibility, Damiao FeTiP deposit

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