山东省东平—汶上铁矿带铁矿床地球化学特征分析

Geochemical characteristics of iron ore deposits from Dongping-Wenshang iron ore belt in Shangdong province

东平—汶上铁矿带是鲁西重要的鞍山式铁矿带,矿床赋存于新太古界泰山群山草峪组变质岩中,目前已经探明10余处大、中型铁矿床。铁矿体一般呈层状、似层状,长一般800m,厚度6m;矿石主要为磁铁石英岩,发育条带状构造。文章阐述了通过采集典型矿床矿石及围岩样品,测试其常量元素、稀土元素、微量元素,结果显示磁铁石英岩总体表现为高硅,低磷、低铝;矿石和围岩的稀土元素含量都较低(w(ΣREE)=23.74×10^(-6)~141.22×10^(-6)),相对富集轻稀土,亏损重稀土(w(LREE)/w(HREE)=4.10~5.42),Eu负异常(δEu=0.61~0.96,平均0.86),Ce不显异常(δCe=0.93~1.05,平均0.94);富集大离子亲石元素K、Rb、Ba、Th,高场强元素Ta、Nb、Zr、Hf、Ti等相对亏损。研究结果表明,东平—汶上铁矿成矿带的赋矿原岩形成于大陆边缘和火山岛弧构造环境;山草峪组变质岩原岩可能经历了多个完整的火山-沉积旋回,火山活动提供了成矿物质铁和硅;成矿期海水为缺氧的弱还原环境。

Dongping-Wenshang iron ore belt is an important Anshan type iron ore belt in the west of Shandong province with iron deposits occurring in the metamorphic rock of Shancaoyu Formation of the Neoarchean Taishan group.There are more than ten proven large or medium sized iron ore deposits.Generally,ore bodies are layered or layeroid,800 mlong and 6m wide.The banded iron formation（BIF）is the ore.The paper presents analysis of the major elements,rare earth elements and trace elements of samples collected from ore and wall rock of typical deposits showing that results of the banded iron formation are similar to those of BIF in Wutai area and Anshan-Benxi area,high Si,low P and Al,ore and wall rock low rare earth content（ΣREE=23.74~141.22）,LREE enriched,and HREE depleted relatively（LREE/HREE=4.10~5.42）,negative Eu anomaly（δEu=0.61~0.96,average 0.86）,slight negative Ce anomaly of（δCe=0.93~1.05,average0.94）,HFSE（Ta、Nb、Zr、Hf、Ti）relatively depleted,LILE enriched.All this indicate that original rock of the BIF was formed at the continental margin and volcanic island arc tectonic environment and the rock of Shancaoyu formation was exposed to multiple complete volcanic-sedimentary cycles.Volcanism provided the ore materials,Si and Fe precipitated under weak reduction condition.