The ultra-low-grade Fe ore resource (content of total Fe is lower than 20% ) hosted in mafic-ultramafic complexes in Chengde plays an important role in the iron production of Hebei Province, China. In order to investigate the ore-forming age and ore genesis of the Tiemahabaqin ultra-low Fe deposit, which makes a significant contribution to Chengde's iron production, this study presents electron microprobe and Ar/ Ar isotopic data of the hornblendes from iron-bearing hornblendites. The electron microprobe data shows that major elements of the hornblendes from hornblendites of the Tiemahabaqin complex are Ca-rich, Mg-rich, Na-rich and K-poor with limited aviation range, which were attributed to pargasites or magnesiohastingsites. The genetic mineralogy study indicates that the mantle source derived hornblendes were contaminated with crust materials. The 40Ar/39Ar plateau ages of the hornblende from hornblendites yielded 379 -401 Ma, which indicates that the ore-forming process was formed in the Devonian period. Tectonically, the iron-bearing hornblendites are probably related to post-collisinoal extension after the arc-continental collision between the Bainaimiao arc belt and the northern margin of the North China craton during the latest Silurian period.%河北承德一带基性-超基性岩中的超贫铁矿石(全铁TFe含量＜20％)资源在河北的铁精矿产量中占有重要地位,其中以铁马哈叭沁超贫铁矿床贡献最大.本研究以铁马哈叭沁岩体中的超贫铁矿石即钒钛磁铁矿化的角闪石岩中的角闪石为研究对象,通过电子探针分析和40 Ar/39 Ar测年,结合野外地质特征,探讨了超贫铁矿床的成矿时代及矿床成因.野外和岩相学特征表明,铁马哈叭沁超贫铁矿床为岩浆晚期分异型铁矿床.电子探针分析表明,角闪石岩中角闪石主量元素变化范围较小,具有富Ca、富Mg、富Na、贫K的特征,属于韭闪石和镁绿钙闪石.角闪石成因矿物学研究表明,角闪石岩主要为幔源成因,并受到了地壳物质的混染.角闪石岩中角闪石单矿物的40Ar/39Ar年龄为379～401 Ma,表明成岩成矿时代为泥盆纪,形成于白乃庙岛弧与华北克拉通北缘发生弧-陆碰撞后的伸展阶段.
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