宁芜北段某些次火山岩和蚀变岩中的稀土元素

宁芜北段铁、铜、金的矿化大都与区内广泛发育的次火山岩有关。前人曾做过大量工作。在此基础上,本文试图从次火山岩及其在蚀变过程中稀土元素的地球化学恃征方面进行分析,进一步了解它的成因、蚀变及其与矿化的关系,借以提供一些地质找矿的信息。

The Rare Earth Elements in some Sub-Volcanic and Altered rocks in North Nanjing-Wuhu area

In North Nanjing-Wuhu area, the gabbrodiorite porphyrite, augite-trachy- andesite porphyrite and the quartz-monzonite porphyry of Dawaqg Shan volcanic cycle together with the hauyne-trachyte porphyry of Niangniang Shan cycle are all the comagmatic products formed. at various stages of magma event. All these rocks display light REE enriched patterns which plot parallel to each other. As a consequence of evolution of magma, the HREE are fractionated and concentrated in the minerals crystallized in the early stage, while the LREE are remained in the residue and concentrated in the latter formed rocks with increasing in negative Eu anomaly. It indicates that the magmatic differentiation is dominated by the fractional crystallization of the mafic minerals, while that of the plogioclase is quite mild in this area. In accordance with the rock assemblages, the data of stable isotopes as well as the features of the REE patterns, it may be suggested that this rock series may have been derived from upper mantle with some portions of partially melted oceanic cxust and contaminated by spore continental cxustal materials. The REE are mobile during hydrothermal alteration. Although there is no significant variation in their total concentration in the process of So-called dark-colored alteration, they are migrated away in large amounts during the light-colored alteration, enlarging the (La/Yb)N ratio and negative Eu anomaly.