磷灰石地球化学特征对花岗岩锡成矿能力的指示——以滇西腾冲-梁河锡矿带小龙河锡矿床为例

The indicative significance of apatite geochemical characteristics on tin metallogenic capacity of granite:A case study of the Xiaolonghe tin deposit in the Tengchong-Lianghe tin belt,western Yunnan

锡矿床全球空间分布高度不均,成矿与花岗岩密切相关,对花岗岩Sn成矿作用的研究受到学界高度重视。准确示踪岩浆源区和精细刻画岩浆演化过程对理解花岗岩与对Sn成矿之间的关系十分关键。磷灰石作为花岗岩类岩石中常见的副矿物,其化学组成在示踪花岗岩岩浆源区和成岩过程方面有独特优势。本文对滇西腾冲-梁河锡矿带具有代表性的小龙河锡矿床,对矿区内的花岗岩展开磷灰石原位化学成分分析。研究结果表明,小龙河锡矿区的花岗岩为一套高分异花岗岩,显示A型花岗岩特征,主要源于地壳物质熔融,花岗岩形成于相对还原的环境,富F且含有一定量的Cl元素。上述岩石地球化学特征有利于花岗岩浆演化过程中Sn的富集和迁移,说明磷灰石的成分特征可以很好地指示花岗岩浆的成因、演化及其物理化学条件,能有效评价花岗岩的Sn成矿能力。

Tin mineralization is extremely uneven distributed in the world,and is closely related to granitic magmatism,which attached considerable attention on the granite tin metallogenic capacity study.It is important to well constrain the magmatic source and accurately trace the magmatic evolution process for understanding the tin metallogenic capacity of granite.Apatite,as a common accessory mineral in granitoids,its chemical composition has a unique advantage in tracing the magmatic sources and diagenetic process of its host granite.In this study,apatite in situ chemical composition analysis of granite from the Xiaolonghe tin deposit in the Tengchong-Lianghe tin belt in western Yunnan Province was carried out.The results show that the granite from the Xiaolonghe tin deposit is of highly differentiated granite,and characteristic of A-type granite.The granite magma is mainly originated from the ancient continental crust.The granite,with rich F and certain Cl content,was formed in a relatively reductive environment.These characteristics of the Xiaolonghe granite indicate that it is conducive to the accumulation and migration of Sn in the granitic magmatic evolution process.Thus,the structure and chemical composition of apatite can well constrain the granite genesis,magmatic evolution,physical and chemical conditions of magma,which can effectively evaluate the tin metallogenic capacity of granite.