Identification Characteristics, Composition and Genesis of Euclase in Mahuaping Tungsten-Beryllium Polymetallic Deposit in Yunnan Province, Southwest China
JIA Fu-dong1, 2, ZHANG Chang-qing1*, HUA Zhi-xin3, LOU De-bo1, LI Bao-long1, SUN Jia1
1. MNR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China
2. School of Earth and Space Sciences, Peking University, Beijing 100871, China
3. Shangri-la Tiger-leap Xinlei Tungsten Mining Industry, LLC, Diqing 674402, China
Abstract：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 2V=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 3 588，3 577，1 060，907，638，571，393，255 and 174 cm-1.
Key words：Euclase; Identification characteristics; Composition; Raman spectra; Color genesis
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