河南舞阳铁山铁矿床地球化学特征及其地质意义
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Geochemistry of Tieshan iron deposit in Wuyang Aera, Henan province and its geological implications
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    摘要:

    河南省舞阳地区铁山铁矿床为一个新太古代大型鞍山式铁矿床, 本文对铁山矿床进行了岩石学、地球化学方面的研究, 并与国内外该类型矿床进行对比。通过对铁山铁矿床围岩和矿石的地球化学分析,得出本区条带状硅铁建造可能与海相火山沉积物有关,属于前寒武纪火山沉积变质型铁矿床。流体包裹体测温结果表明,含矿围岩中的包裹体均一温度集中在120~360°C之间,矿石中包裹体均一温度峰值为120~320°C,成矿流体具有低盐度 (w(NaCl)为1%~14%)、低密度(0.75 -1.00 g/crn3)特征。成矿溶液是一种低盐度的Na+、Ca2+、SO42-、Cl-型水,并含有较高的CO2和一定量的O2、N2和少量CH4。岩石学研究结果认为其经受了绿片岩相至低角闪岩相变质作用, 磁铁矿部分受到变质重结晶, 但局部仍保存有化学沉积的特征。在 TFe-(CaO+MgO)-SiO2图解中, 其分布与鞍山、五台山条带状铁矿和世界条带状铁矿分布区一致。铁山矿床稀土元素含量较低, 具有太古宙海洋沉积的特征, 在 PAAS(太古宙后平均澳大利亚沉积岩)标准化的稀土配分曲线中显示轻稀土的相对亏损和重稀土的相对富集, 具有明显的 Eu 正异常(Eu/Eu*=0.30~2.21)和明显的 Y正异常(Y/Y*=1.34~3.19), 具有一定的La正异常(La/La*=0.81~1.60)和轻微Ce负异常(Ce/Ce*=0.87~1.01), 这一特征与我国鞍山弓长岭和五台山及世界许多地区的太古宙 BIF 特征一致。微量元素中 Ti、V、Co、Ni、Mn、Sr、Ba 等元素的含量都较低, 在原始地幔标准化的微量元素配分曲线中具 U、Ta、La、Ce、P 正异常, K、Nb、Sr、Hf、Zr 负异常。对铁山条带状铁矿中 Sr/Ba、Ti/V 等元素的比值与其他地区进行了对比。综合研究结果认为铁山条带状铁矿具有与火山热液伴生的铁质,形成于缺氧的海洋化学沉积环境。铁矿床经历了前期含硅铁沉积物的沉积阶段和后期的区域变质作用阶段,变质成矿流体发生了不混溶现象,对成矿元素的富集起到一定的促进作用。

    Abstract:

    Located in Wuyang area of Henan Province and geotectonically on the southern margin of the North China Craton, the Tieshan banded iron formation (BIF) constitute a large iron deposit of Anshan type formed in Neo-Archaean. In this paper, petrology and geochemistry of Tieshan BIF were studied and a comparison was made with other BIF in the world. Systematic chemical analyses of wall rocks and ores indicate that the banded iron formation might have been related to marine volcanic-sedimentary volcanic rocks,and the ore deposit probably belongs to the Precambrian volcanic-sedimentary metamorphic iron deposit. The homogenization temperatures of fluid inclusion show a peak at 120~360°C for the wall rock and 120~320°C for the ore, and the ore-forming fluids have low salinity(1%~14%)and low density (0.75~1.00 g/cm3).Ore-forming fluid is a kind of low salinity water of Na+, Ca2+, SO42-, Cl-, and contains high amount of CO2 and small quantities of O2, N2 and CH4.Petrological studies show that the BIF suffered greenschist facies to low amphibolite facies metamorphism and part of the magnetite was recrystallized whereas the other part of the magnetite preserved the characteristics of chemical sediments. In the diagram of TFe-(CaO+MgO)-SiO2, Tieshan BIF has a consistent distribution area with Anshan BIF and Wutaishan BIF and other BIF in the world. The REE contents of Tieshan BIF are low, showing characteristics of marine sediments in Archean. In the PAAS-normalized REE pattern, LREE are depleted and HREE are enriched relatively, with obvious Eu positive anomaly(Eu/Eu*=0.30~2.21), obvious Y positive anomaly(Y/Y*=1.34~3.19) and visible La positive anomaly(La/La*=0.81~1.60), slightly negative Ce anomaly(Ce/Ce*=0.89~1.01). These characteristics of Tieshan BIF are similar with characteristics of Gongchangling, Wutaishan and many other Archean BIF in the world. As for trace elements, contents of Ti, V, Co, Ni, Mn, Sr and Ba are low. In trace elements distribution diagram normalized by primary mantle, U, Ta, La, Ce and P have positive anomalies, whereas things are just the opposite for K, Nb, Sr, Hf and Zr. The ratios of Sr/Ba, Ti/V and some other elements are also considered in this paper. A comprehensive study of Tieshan BIF shows that its ferruginous material was associated with volcanic hydrothermal solution and was formed in a marine chemical sedimentary environment. It is thus held that the Tieshan iron deposit underwent the ferrosilicon sedimentary deposition stage followed by further enrichment during the late regional metamorphic process.In the late stage,the metamorphic fluids from the original homogeneous metamorphic ore-forming solution resulted in immiscibility and hence the enrichment of ore-forming elements.

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李永峰,谢克家,罗正传,李俊平.2013.河南舞阳铁山铁矿床地球化学特征及其地质意义[J].地质学报,87(9):1377-1398.
Liyongfeng, Xiekejia, Luozhengzhuan, Lijunping.2013. Geochemistry of Tieshan iron deposit in Wuyang Aera, Henan province and its geological implications[J]. Acta Geologica Sinica,87(9):1377-1398.

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  • 收稿日期:2013-05-02
  • 最后修改日期:2013-05-02
  • 录用日期:2013-09-13
  • 在线发布日期: 2013-09-13
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