辽宁齐大山铁矿元素地球化学特征

ELEMENT GEOCHEMISTRY OF QIDASHAN IRON DEPOSIT IN LIAONING PROVINCE

齐大山铁矿大地构造上属于华北地台辽东台背斜的西部.其铁矿层产于鞍山群樱桃园岩组,含矿建造为砂质泥岩-泥岩建造（阿尔戈马型）,变质相为绿片岩相.通过稀土元素地球化学研究,铁矿石表现为轻稀土富集,LREE/HREE比值平均为3.43.围岩表现为重稀土略富集,LREE/HREE比值平均为0.97.铁矿石和围岩稀土元素原始地幔标准化值显示铁矿石稀土元素整体具有弱的正铕异常（δEu为1.03～1.50）,Ce无明显的正负异常（δCe为0.54～1.15）,这与海底喷气沉积产物的特征一致.围岩中无明显Eu异常,平均为1.16.δCe的范围为0.18～1.01,相对比较稳定.这些特征显示属于早前寒武纪海洋化学沉积的产物,表明矿物大地构造背景为大洋岛弧,物源区类型为未切割的岩浆弧.

The Qidashan iron deposit is tectonically located in western Liaodong anteklise of North China Platform, with iron ore layers hosted in the Yingtaoyuan Formation of Anshan Group. The ore-bearing formation is sandy mudstonemudstone（Algoma type）, with metamorphic facies of greenschist. By study on the REE geochemistry of ores and wall rocks,the REE patterns show enrichment of LREE in the ores with LREE/HREE of 3.43, whereas slight depletion of HREE in the wall rocks with LREE/HREE of 0.97. The primitive mantle-normalized REE spiderdiagram shows weak positive anomalies of Eu（δEu = 1.03- 1.50）, without anomalies of Ce（δCe = 0.54- 1.15） in iron ores, which is consistent with the characteristics of submarine exhalative sedimentation. There is no significant anomalies of Eu（average δEu 1.16）and Ce（δCe = 0.18- 1.01）in the wall rocks. The features above suggest that the iron deposit should be the product of marine chemical deposition in Early Precambrian in the tectonic background of oceanic island arc and provenance type of uncut magmatic arc.