皖南姚村A型花岗岩磷灰石特征及其对成岩成矿的指示

Geochemical characteristics of apatite from the Yaocun granite in the eastern Jiangnan Orogen:insights into magmatic properties

磷灰石作为岩浆岩中的常见副矿物,其地球化学特征常被用来指示火成岩的岩浆过程和岩浆属性。中生代A型花岗岩广泛分布于江南造山带东段,其岩石成因和成矿潜力仍有待进一步研究。文章选择江南造山带东段具代表性的皖南姚村A型花岗岩开展磷灰石的地球化学组成研究,为其岩石成因及成矿潜力研究提供新的信息。姚村花岗岩中的磷灰石普遍发育振荡环带,部分表现为均质结构,成分上具有低氯及高氟、稀土、钇、钍含量的特点,指示其为典型的岩浆成因磷灰石。单颗粒磷灰石的稀土、钇和钍等元素含量从核部到边缘呈连续变化,稀土配分模式显示其具有明显的铕负异常,指示岩浆经历过显著的结晶分异作用。磷灰石-熔体的模拟定量计算表明,姚村花岗质岩浆具有高氟和硫、低H_(2)O-Cl和低氧逸度的特征。综合考虑岩浆的物理化学特征与成矿元素行为之间的联系,认为姚村A型花岗岩具有稀有金属成矿潜力。

Due to the fact that apatite is a common accessory mineral in magmatic rocks,its geochemical composition is often used to indicate the petrogenesis of granites and provide constraints on their magmatic properties.Mesozoic A-type granites are widely distributed in the eastern Jiangnan Orogen.At present,the origin of these A-type granites is still controversial,and their mineralization potential is not clear.Therefore,this study investigates the geochemical composition of apatite in the Yaocun granite,constrains the magmatic properties,and evaluates its metallogenic potential.The results show that the apatite in Yaocun granite generally exhibits oscillatory zoning or homogeneous texture,and has high F,REE,Y,and Th,and low Cl contents,indicating its magmatic origins.In addition,the REE,Y,and Th contents of a single apatite grain show continuous changes from the core to the rim,and the REE pattern displays obvious negative Eu anomalies,which can be attributed to fractional crystallization.Quantitative calculations show that Yaocun granitic magma is characterized by high F,low H_(2)OCl,and low oxygen fugacity.Considering the relation between magmatic properties and the behavior of ore-forming elements,our study suggests that Yaocun granite has rare metal mineralization potential.