大兴安岭火山岩铁矿中稀土元素地球化学

THE REE GEOCHEMISTRY OF THE VOLCANOGENIC IRON ORE DEPOSITS IN DAXINGANLING DISTRICT

本文以大兴安岭几个上古生代火山岩、蚀变岩和铁矿的稀土元素组成,探讨该区火山沉积铁矿和火山热液的成矿作用和演化规律。

The Upper Palaeozoic volcanic rocks in the Daxinganling district are composed of basalt, undesite, rhyolite and tuff,in which layered volcanic sedimentary iron ore occur.Later metasomatism caused the volcanic country rock forming skams and the layered iron ore bodies forming ore shoods.The REE content of basalt is below the average and wellmatched with that of island arc tholeiite, the distributive pattern of REE is smooth and a slight Eu positive anomaly is shown. The distributive pattern of REE in andesite is similar to that in basalt and a slight Eu negative anomaly is shown, and the layered iron ore bodids are relatively abundant in LREE and with an Eu negative anomaly, indicating that Eu was concentrated in basalt and depleted in andesite and layered iron ore bodies and they all were differential products from the same magma source.The REE distributive pattern of skarns is similar to that of volcanic rocks. The ore shoots formed by metasomatism are ricker in REE that the layered ore bodies. LREE is abundant at tha early alkaline stage and HREE is abundant at the later acid stage, which indicate that REE fractionated in the process of meta-sdomatism.