云南麻花坪钨铍矿床蓝柱石的鉴定特征及成分与成因分析  

Identification Characteristics, Composition and Genesis of Euclase in Mahuaping Tungsten-Beryllium Polymetallic Deposit in Yunnan Province, Southwest China

作　　者：贾福东[1,2] 张长青 化志新[3] 娄德波 李宝龙[1] 孙嘉[1] JIA Fu-dong;ZHANG Chang-qing;HUA Zhi-xin;LOU De-bo;LI Bao-long;SUN Jia(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Shangri-la Tiger-leap Xinlei Tungsten Mining Industry,LLC,Diqing 674402,China)

机构地区：[1]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037 [2]北京大学地球与空间科学学院,北京100871 [3]香格里拉市虎跳峡鑫磊钨业有限责任公司,云南迪庆674402

出　　处：《光谱学与光谱分析》2020年第10期3185-3192,共8页Spectroscopy and Spectral Analysis

基　　金：深地资源项目(2016YFC0600305);国家自然科学基金项目(41672093,41602103)资助。

摘　　要：通过薄片鉴定、能谱分析、激光拉曼光谱、电子探针和激光剥蚀电感耦合等离子体质谱分析(LA-ICP-MS),研究了云南麻花坪钨铍矿的蓝柱石矿物成分、镜下鉴定特征和拉曼光谱特征,探讨了不同产出环境的蓝柱石成因以及蓝柱石呈现出不同颜色的原因。结果表明,蓝柱石的化学成分简单,除主量元素外,所含微量元素种类少且含量低,可能是由蓝柱石相对简单的晶体结构所致。不同于一般蓝柱石中的低F含量特征,结晶于高度富氟环境中的麻花坪蓝柱石F含量相对较高,表明F可以替代晶体结构中的—OH位进入蓝柱石。通过对比产于大理岩中的蓝色蓝柱石和产于变质碎屑岩中的无色蓝柱石的分析结果,发现除铁元素之外,其他致色元素含量较低,且蓝色蓝柱石中Fe含量明显高于无色或白色蓝柱石,表明Fe是蓝柱石的致蓝色元素,但致蓝色的Fe在蓝柱石中的存在状态仍不清楚,需进一步研究。镜下观察显示,两种不同产出状态的蓝柱石均保留绿柱石的假象,推测可能均由绿柱石蚀变产生,其中产于变质碎屑岩一侧的蓝柱石可能由绿柱石在温度降低时直接蚀变而来;产于大理岩中的蓝柱石形成温度则相对更低,在成矿晚期,伴随着富钾流体的加入,产生了蓝柱石和白云母的共生矿物组合。镜下观察和拉曼光谱均能简单有效地识别蓝柱石。显微镜下,蓝柱石呈无色-浅蓝-浅橙黄色,多色性明显,Ng-浅蓝绿或浅紫红,Nm-浅粉蓝或浅橙黄,Np-无色,晶体多呈半自形-自形的板柱状,具一组完全解理,正中-正高突起,斜消光,消光角Ng∧c=41°~44°,Np∧a=10°~13°,正延性,最高干涉色一级紫红-二级蓝绿,双折射率0.020,二轴晶正光性,光轴角48°。蓝柱石的拉曼特征峰有3588,3577,1060,907,638,571,393,255和174 cm^-1,可作为识别蓝柱石的依据。Identification characteristics,composition and genesis of natural blue and colorless euclases from Mahuaping W-Be deposit,Yunnan,China are investigated by the polarizing microscope,scanning electron microscopy and energy spectrum analysis,Raman spectroscopy,electron microprobe analysis and laser ablation-inductively coupled plasma-mass spectrometry(LA-ICPMS).The results indicate that the chemical composition of euclase is simple,and this can be attributed to its simple crystal structure.Crystallized in the fluorine-rich environment,the fluorine concentration in euclase from Mahuaping is higher than that of other regions.Total iron content in the blue sample is much higher than the colorless one suggesting that the high Fe may explain the blue color of euclase.Both of the euclases from metamorphic clastic rocks and marbles are preserved pseudomorphs of beryl which imply that theyare the alteration products of beryl.Euclase intergrowth with quartz from metamorphic clastic rocks may attribute to the direct alteration of beryl as the temperature went down.While the euclase coexisted with muscovite from marble is formed due to the addition of K-rich fluid at lower temperatures.It is simple and effective to identify euclase by optical microscopic observation and Raman spectrum analyses.Euclase is colorless and displays distinctive light blue to light orange pleochroic color under the microscope and has perfect cleavage.It is a biaxial positive mineral with positive elongation and positive middle to the high protuberance,and with the birefringence value of 0.020 and the axial angle amounted to 2 V=48°.The extinction angle of euclase are of Ng∧c=41°~44°,Np∧a=10°~13°and the highest interference color is first-order purplish red to second-order blue to green.The characteristic Raman peaks of euclase include 3588,3577,1060,907,638,571,393,255 and 174 cm^-1.

关 键 词：蓝柱石 鉴定特征 成分 拉曼光谱 颜色成因 

分 类 号：P575.4[天文地球—矿物学]