白云鄂博磷灰石的矿物化学特征及其成因意义

Chemical Compositions of Apatites from Bayan Obo and Their Petrogenetic Implications

本文对白云鄂博地区广泛分布的磷灰石进行了系统的电子探针分析。结果表明,赋矿粗粒白云石大理岩中磷灰石的矿物化学特征与碳酸岩岩墙中的非常相似,它们均属于富含锶和稀土元素的氟磷灰石,具有典型的火成碳酸岩特征。然而,它们在稀土元素分布模式以及轻稀土元素之间的分馏作用方面却存在着差异。造成这些差异的原因是,磷灰石的寄主岩石受富含氟和稀土元素的流体影响的程度不同:粗粒白云石大理岩受流体的影响比碳酸岩岩墙要大。

Apatites from carbonatite dykes and coarse-grained ore-hosted dolomite marble in Bayan Obo, Inner Mongolia, China, are systematically analyzed with the electron microprobe analyzer, indicating that they are similar in chemical compositions, belong to fluorapatite bearing strontium and rare earth elements (REE), and have characteristics of carbonatitic origin. However, there are differences in REE patterns and light REE fractionation between these apatites, revealing that they underwent different influence by fluids bearing fluorine and REE that might be derived from evolved carbonatite rather than those related to granite or subduction. In other words, the apatite from coarse-grained dolomite marble is affected more heavily by the fluids than that from the carbonatite dykes.