应用扫描电镜-X射线衍射-电子探针研究北山斑岩铜矿区绢英岩中白色云母的特征

Characteristics of Micas from Sericitolite of the Gongpoquan and Baishantang Deposits,Beishan Area by Scanning Electron Microscope,X-ray Diffraction and Electron Microprobe Analyses

绢英岩化蚀变带是近地表寻找斑岩型铜矿的重要矿物学标志之一。公婆泉和白山堂铜矿是甘肃北山成矿带中典型的斑岩型矿床,本文应用偏光显微镜、扫描电镜、X射线衍射仪和电子探针等技术,研究矿区绢英岩化蚀变带中白色云母的结构与化学特征,探讨其成矿指示意义。结果表明,绢英岩中的云母集合体呈边缘不规则的细小花瓣状、扭折板片状和平直板片状等形态;公婆泉矿区云母晶体化学式中四次配位Si原子数为3.04~3.37,白山堂矿区为3.03~3.35,绢英岩中的白色云母结构为1M型普通绢（白）云母与2M1型热液成因的多硅白云母共存。不同多型的云母具有不同的b0值,二者共存的温度和酸度条件,揭示了斑岩铜矿成矿过程中流体从较高温、强酸性快速向低温、弱酸性演化的现象。

The phyllic alteration zone is regarded as one of the most important near-surface markers in mineral exploration of porphyry deposits. The Gongpoquan and Baishantang copper deposits are two typical porphyry deposits in the Beishan metallogenic belt. A comprehensive structural and chemical study for white micas from sericitolites of these two deposits, utilizing polarized microscope, Scanning Electron Microscope （ SEM）, powder X-ray Diffractometer （XRD） and Electron Microprobe Analyzer （EMPA） is reported in this paper. It was discovered that both 1 M polytype common sericites/muscovites and 2M1 polytype phengites co-exist in the samples. The micas occur as irregular petals, kinked platelets or straight platelets during SEM observation. According to XRD analyses, both 1M and 2M1 polytypes co-exist with different bo values in micas, indicating their different forming conditions. The Sirv atoms in micas range from 3.04 to 3.37 and from 3.03 to 3.35 for Gongpoquan and Baishantang deposits, respectively, indicating the co-existence of sericites/muscovites and hydrothermal phengites. The co-existence of two types of white micas in porphyry copper deposits of the Beishan area indicate the rapid changes of ore-forming fluids from higher temperature and acidity to lower temperature and less acidity during mineralization