河南省铁山河铁矿床地球化学特征及成因探讨

Geochemical characteristics and genesis of Tieshanhe iron deposit in Henan Province

铁山河铁矿床赋存于古元古界银鱼沟群地层中,是华北陆块南缘一个重要的富铁矿床。文章对铁山河铁矿床进行了系统的野外地质调查和矿床地球化学研究,并与国内外典型的沉积变质型铁矿床进行了对比。结果显示:铁山河铁矿床保存有明显的化学沉积的特征,化学成分主要由Fe_2O_3、FeO和SiO_2组成,Al_2O_3和TiO_2含量较低;稀土元素总量较低,稀土元素配分模式呈轻稀土元素亏损、重稀土元素富集的特征,具有明显的Eu、Y、La正异常,弱的Ce异常,Y/Ho比值与海水的分布范围相近,Sr/Ba和Ni/Co比值分别与鞍山弓长岭铁矿和山西五台山、冀东迁安地区铁矿相似,但与基性岩浆活动相关的Co、Ni、Cr、V、Ti元素含量相对偏高。这些特征表明:该矿床的形成可能与海相火山沉积物有关,属于火山沉积变质型铁矿的范围,区内基性岩脉广泛发育,矿床可能遭受了后期热液的叠加改造作用;成矿物质来源于热液和海水的混合作用,矿床形成于相对缺氧的环境。

The Tieshanhe iron deposit occurs in the Paleoproterozoic Yinyugou Group and is an important iron-rich deposit on the southern margin of the North China block. In this paper, field geology and geochemistry of the Tieshanhe iron deposit were studied systematically, and a comparison was made with other sedimentary metamorphic type iron deposits in the world. The results show that the Tieshanhe iron deposit has obvious characteristics of chemical deposition, and the average bulk compositions of ores are characterized by rich Fe2O3, FeO and SiO2, and very low Al2O3 and TiO2. REE concentrations in ores are very low, the shale-normalized REE patterns display LREE depletion and HREE enrichment with obvious Eu, Y, La positive anomalies and weak Ce anomaly, and the Y/Ho ratios of ores are in the same range as those of seawater. The ratios of Sr/Ba and Ni/Co are similar to things of the Gongchangling iron deposit in Anshan City, the iron deposits in Wutai Mountain area in Shanxi Province and Qian＇an area in eastern Hebei Province respectively; nevertheless, its association with mafic magma activity of Co, Ni,Cr, V, Ti content is relatively high. These chemical features show that the deposit might have been related to marine volcanic sediments, thus belonging to the volcanic sedimentary metamorphic iron deposit, but it was probably superimposed and reformed by hydrothermal fluid later, as evidenced by the extensive development of mafic dikes in the region. In addition, ore-forming materials in the deposit formed in the hypoxic environment might have been derived from mixing of hydrothermal fluid and seawater.