辽宁歪头山铁矿床两类矿石地球化学特征及其对成矿作用的制约

Geochemical Characteristics of Two Iron Ores from the Waitoushan Iron Deposit,Liaoning Province:Constraints on Ore-Forming Mechinisam

歪头山铁矿床是鞍山—本溪地区条带状铁建造(BIFs)的典型代表,并且有一定规模的富铁矿分布。本文开展了矿区内较贫铁矿石和较富铁矿石的地球化学特征对比研究,结果表明两类矿石既有一致性又存在差异性。一致性表现在:所有矿石主要由TFe2O3和SiO2组成,其他氧化物含量很少,结合微量元素和稀土元素特征,指示其属阿尔戈马型BIFs,但受到了火山热液作用的影响;矿石的稀土元素总量很低,经太古界后平均澳大利亚页岩(PAAS)标准化后,呈现重稀土相对富集,轻稀土相对亏损的配分模式,都具有明显的Eu正异常和比较高的Y/Ho比值,与热液相关的Cr、Co和Ni含量也相对较高,暗示其成矿物质来源于海底热液,同时具有海水的特征。差异性表现在:较富铁矿石具有明显的热液特征,并且K2O含量大于Na2O含量,某些微量元素组成也与混合花岗岩具有相似性,结合野外地质特征,暗示较富铁矿石可能是在较贫铁矿石的基础上受混合岩化热液作用形成的。

The Waitoushan iron deposit is a typical deposit of banded iron formations （BIPs） in the Ansnan- Benxi area because of its large scale and widely-distributed orebodies. We carried out a comparison research over the geochemical characteristics of iron-poor and iron-rich ores. The results reveal that both similarities and differences exist in two iron ores. The similarities of two ores show the the ores predominantly consist of TFez03 and SiO2, with minor other oxidates. Combined with the characteristics of trace and rare elements, it is suggested that the iron ores of the Waitoushan iron deposit belong to Algoma BIFs, but influenced by volcanic hydrothermal activity. But the total REE concentrations of iron ores is very low, but the PAAS-normalized REE and Y diagram display depletion of LREE relative to HREE, distinct Eu positive anomalies and high Y/Ho ratios, and higher concentrations of ferromagnesian trace elements relatively, such as Cr, Co and Ni. Trace and REE elements analysis suggests that ore forming material may originate from deep sea hydrothermal fluid with seawater signatures. The differences of two ores show that Fe-rich ores present distinct hydrothermal signatures, with K2 O more than Na20. In addition, trace elements composition is similar to granitization granite. Combined with field investigation, it can be inferred that the higher grade iron ore may be formed by leaner iron ore though activities of migmatization hydrothermal.