新疆阿勒泰市阿巴宫铁矿磷灰石微量和稀土元素特征及矿床成因探讨

Trace element and rare earth element characteristics of apatite from Abagong iron deposit in Altay City,Xinjiang

阿巴宫铁矿床产于阿尔泰南缘晚志留世—早泥盆世的酸性火山岩中。矿体呈透镜状、脉状及似层状,受火山断裂构造控制,与围岩界线清楚;围岩蚀变不很发育,矿石品位较高;磷灰石与磁铁矿共生。其特征可以与瑞典北部Kiruna型铁矿床、宁芜玢岩铁矿床等进行对比。对阿巴宫铁矿床两个不同矿区磷灰石的稀土元素及微量元素组成的分析结果表明,磷灰石中∑REE变化于1352.96×10-6～6986.33×10-6之间,平均值为3717.70×10-6;(La/Yb)N比值变化于1.37～9.77之间,平均值5.22;δEu范围在0.22～0.30之间,平均值0.25;以轻稀土元素富集、轻重稀土元素分馏较弱和Eu的显著负异常为特征,与瑞典北部Kiruna型铁矿床、宁芜玢岩铁矿床相一致,表明阿巴宫铁矿床与上述铁矿床成因相同,均属岩浆分异成因。变质流纹岩稀土元素分布曲线形态与磷灰石的非常相似,微量元素特征也基本一致,表明铁的成矿作用与花岗质岩浆的分异-矿浆侵入有关。

Located in late Silurian-early Devonian felsic volcanic rocks along the southern margin of Altay, the Abagong iron deposit occurs as lens, veins and stratoid bodies controlled by volcanic fault structures, with an obvious boundary between the iron body and the host rocks, unclear alteration in host rocks, high ore grade and coexisting apatite and magnetite in iron ore. These features suggest that the Abagong iron deposit is comparable with the Kiruna type iron deposit in northern Sweden and the porphyrite iron deposits in Ningwu area. Trace element and rare earth element compositions of the apatite from two different places in the Abagong iron deposit were analyzed, and the results show that the apatite from the Abagong iron ore contains about 1352.96 × 10^-6 --6986.33× 10^-6 NEE with an average of 3717.70 × 10^-6. that there exist LNEE enrichment, a weak LNEE/ HREE fractionation with （La/Yb）N being 1.37--9.77 （5.22 on average）, and marked negative Eu anomalies with 8Eu being 0.22--0.30 （averagely 0.25）. These characteristics indicate that the Abagong iron ore deposit, the Kiruna type iron ore deposit in northern Sweden and the porphyrite iron ore deposits in Ningwu area have a common genesis of magmatic differentiation. The apparently similar shape of the NEE curve and the consistency of a variety of trace elements between apatite and metamorphic rhyolite indicate that the iron ore-forming process might have been related to the differentiation of granitic magma or the ore magma intrusion.