凤-太盆地硅质岩系地球化学特征及热水成矿效应
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中国地质调查局综合研究项目(1212010511807);长江大学科研发展基金项目


School of Geosciences, Yangtze University, Jingzhou 434023, China
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    摘要:

    陕西凤(县)-太(白县)泥盆纪沉积盆地内硅质岩系分布广泛,硅质岩系的岩石组合主要为硅质铁白云岩、铁白云石硅质岩和硅质岩。其产状稳定,延伸较远,与区域矿产关系密切。通过野外观测、显微镜研究、等离子质谱及电子探针等分析,对盆地内八卦庙金矿和八方山铅锌矿成岩[CD*2]成矿硅质岩系的硅质岩系常量、微量及稀土元素的地球化学特征进行了详细研究。结果表明,硅质岩系富含Fe、Mn,而贫K、Na和Ti,Fe2O3/FeO值小于1,为还原环境沉积形成;Fe、Ti、Mn和Al元素含量比值反映了其沉积位置为大陆边缘;硅质岩系中Pb、Zn和Cu富集明显,稀土元素具有总量低(12.10×10-6~40.46×10-6),轻重稀土元素分异较明显(2.34~8.68),球粒陨石标准化配分曲线呈右倾趋势,铈和铕均为中等负[CD*2]弱正异常。硅质岩、铁白云石硅质岩和硅质铁白云岩中的铈异常变化规律反映了沉积环境由还原向氧化条件的系统变化特征。

    Abstract:

    Siliceous rocks are widely distributed in FengxianTaibai basin and composed mainly of siliceous ankeriteankeritic siliceous rockssiliceous rocks, characterized by stable and long extension and a close relationship with regional mineralization. Therefore, the survey and study of the genesis of these siliceous rocks help conduct regional prospecting. Based on field observation, microscopic examination, LRM and electron microprobe analysis, the author investigated geochemical characteristics of siliceous rocks in such aspects as major elements, trace elements and rare earth elements. It is shown that concentrations of Fe and Mn in siliceous rocks are high whereas concentrations of K, Na and Ti are low in these rocks. The Fe2O3/FeO ratios are lower than 1, suggesting that they were formed in a relatively reduction condition. The Fe, Ti, Mn and Al concentrations also imply that the depositional environment of siliceous rocks belongs to a continental margin. Pb, Zn and Cu in siliceous rocks are obviously concentrated. The ∑REE values are low (12.10×10-6~40.46×10-6) and the differentiation between LREE and HREE is evident (2.34~8.68). The chondritenormalized REE patterns of siliceous rocks are inclined to the right, and Ce and Eu assume intermediately negativepositive anomalies. The variation of Ce anomalies from siliceous rocks to siliceous ankerite also indicates that the depositional environment changed from reduction to oxidation.

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李 强,2009,凤-太盆地硅质岩系地球化学特征及热水成矿效应[J].岩石矿物学杂志,28(3):243~250.

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