滇西北斑岩铜矿带中黑云母矿物化学及其成岩成矿指示意义  

Biotite mineral chemistry and their implications for petrogenesis and mineralization in the porphyry copper deposit belt in northwestern Yunnan,China

作　　者：潘彦宁[1] 董国臣[1] 李雪峰[1] 王鹏[1] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地学前缘》2017年第6期194-207,共14页Earth Science Frontiers

基　　金：中央高校基本科研业务费专项(53200859516);国家重点研发计划项目(2016YFC0600502);中国地质调查局项目"云南普朗地区大型-超大型斑岩-夕卡岩型Cu矿床成矿地球动力学背景;过程与定量评价"(1212011220920)

摘　　要：中甸岛弧位于西南三江构造火成岩带义敦岛弧的南端,受甘孜理塘洋俯冲的影响,印支期岩浆活动与带内斑岩型、夕卡岩型铜矿床成矿关系密切。中甸岛弧带内普朗、浪都及松诺岩体的岩石学特征、形成年龄及矿床的地质特征研究较多,在已有研究的基础上,应用电子探针(EPMA)和激光剥蚀-等离子质谱(LA-ICPMS),系统测定普朗、浪都及松诺含矿石英二长斑岩中黑云母矿物的化学成分,并探讨其成岩成矿意义。电子探针主量元素测定结果显示,普朗石英二长斑岩中的黑云母较浪都及松诺富MgO、TiO_2贫FeO、Al_2O_3,但三者在SiO_2、Na_2O、K_2O及CaO值上差别不明显;与三者全岩相比,黑云母中的∑REE不到全岩∑REE的5%(质量分数),同时富集Rb、Ba、K、Ti、Nb、Ta而贫Th、U、Pb、Sr、Zr、Hf、Y等微量元素。此外,成大矿的普朗石英二长斑岩中黑云母的∑REE及Rb、Hf、Cr的值较浪都及松诺高。在成岩方面,普朗大型-超大型斑岩型铜矿较浪都及松诺斑岩型铜矿床(点)形成于相对高温高氧逸度的介质环境中,且其岩浆的分异演化程度略高。同时,在成矿方面,中甸岛弧地区普朗及浪都斑岩型铜矿成矿体中的黑云母Cu含量高于松诺贫矿体中黑云母Cu含量。The Zhongdian island arc is located at the south end of the Yidun island arc within the Sanjiang tectono-magmatic belt. Influenced by subduction of the Ganzi Litang Ocean, Indosinian magmatism is closely related to the Pulang porphyry and Langdu porphyry-skarn type copper deposits and Songnuo porphyry copper spot. Majority of researches thus far have been focused on the petrological, chronological and geological features of Pulang and Langdu mineralized and Songnuo barren quartz monzonite porphyries. In this paper, the major and trace element concentrations of biotites, measured by EPMA and LA-ICP MS techniques, are used to investigate the petrogenesis and mineralization of biotites. The EPMA analyses of major elements demonstrate that biotites from Pulang are distinguished from Langdu or Songnuo biotites by higher MgO, TiO2 and lower FeO, Al2O3 abundances but little differences in SiO2, Na2O, K2O and CaO contents. Analyses of REE suggest that ∑REE of biotites are less than 5 % （mass fraction） of the whole rock in all three regions. Trace elements analyses illustrate that biotite is an important carrier of Rb, Ba, K, Ti, Nb, Ta, but it has less ability in hosting Th, U, Pb, Sr, Zr, Hf and Y in comparison with host rocks; nevertheless, ∑ REE and Rb, Hf and Cr contents in biotites from Pulang are higher than that from Langdu and Songnuo. The mineral chemistry of biotites show that, the quartz monzonite porphyry from Pulang formed under condition of higher temperature and oxygen fugacity, and it has a higher degree of differential evolution compared with porphyry copper deposit from Langdu and Songnuo. Moreover, the results show that Cu concentration is higher in mineralized plutons from Pulang or Langdu than in barren plutons from Songnuo.

关 键 词：中甸岛弧 斑岩铜矿 黑云母 矿物化学 成岩成矿 

分 类 号：P578.95[天文地球—矿物学]