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 Shanvolcanic cycle together with the hauyne-trachyte porphyry of NiangniangShan cycle are all the comagmatic products formed. at various stages ofmagma event. All these rocks display light REE enriched patterns which plotparallel to each other. As a consequence of evolution of magma, the HREEare fractionated and concentrated in the minerals crystallized in the earlystage, while the LREE are remained in the residue and concentrated in thelatter formed rocks with increasing in negative Eu anomaly. It indicates thatthe magmatic differentiation is dominated by the fractional crystallization ofthe mafic minerals, while that of the plogioclase is quite mild in this area. Inaccordance with the rock assemblages, the data of stable isotopes as well asthe features of the REE patterns, it may be suggested that this rock seriesmay have been derived from upper mantle with some portions of partiallymelted oceanic cxust and contaminated by spore continental cxustal materials. The REE are mobile during hydrothermal alteration. Although there isno significant variation in their total concentration in the process of So-calleddark-colored alteration, they are migrated away in large amounts during thelight-colored alteration, enlarging the (La/Yb)N ratio and negative Euanomaly.