Study on the Mineralogical Properties of an Unknown Ti-Zr-U Oxide Using EPMA, SEM, Raman Spectroscopy and EBSD Techniques
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摘要:
本文应用电子微探针(EPMA)、扫描电镜(SEM)在阿尔金地区的榴闪岩中发现了一种微米级含铀氧化物矿物, 结合光学显微镜、拉曼光谱和电子背散射衍射(EBSD)技术对该矿物的化学成分、赋存状态、物理及光学性质、晶体结构等矿物学特征进行了研究。结果表明, 该矿物在空间上与钛铁矿关系密切且主要产于其边部, 为一种不透明矿物; 主要化学组成为TiO2、ZrO2和UO2, 实验化学式为(Zr, U)Ti2O6, 其中U与Zr互为类质同象替代; 具独特的拉曼光谱特征, 初步确定为斜方晶系且具有序的铌钙矿结构。通过电子微探针U-Th-Pb定年获得等时线年龄为451±49 Ma, 可能代表了寄主岩石的退变质年龄。将该矿物与化学成分类似的晶体进行对比, 发现与斯里兰卡石等已知天然矿物存在差异, 而与一种人工合成晶体Zr5Ti7O24在化学成分和晶体结构上较为相似, 可以初步推断Ti-Zr-U氧化物为一种未被人们发现的新矿物。
Abstract:Asub-micron uranium-bearing mineral in pomegranate amphibolite in the Altyn area was identified by Electron Microprobe(EPMA) and Scanning Electron Microscopy(SEM).Optical Microscope, Raman Spectroscopy and Electron Back Scattering Diffraction(EBSD) were used to study the chemical composition, occurrence state, physical and optical properties and crystal structure.Results show that this mineral is an opaque mineral closely associated with ilmenite and occurs at the edge of ilmenite.The mineral is composed of TiO2, ZrO2 and UO2 and the crystallochemical formula is(Zr, U)Ti2O6 with isomorphous substitution of U and Zr.It has a unique Raman spectrum characteristic and possibly belongs to orthorhombic system with a fersmite structure.EPMA Th-U-Pb dating of Ti-Zr-U oxide mineral yields an isochron age of 451±49 Ma, which represents the retrograde age of the host rock.Compared to the crystals which have a similar chemical composition to Ti-Zr-U oxide, the crystal structure of Ti-Zr-U oxide was found to be different from that of Srilankite, but similar to a synthetic crystal(Zr5Ti7O24) in chemical composition and crystal structure.Therefore, it is inferred that the Ti-Zr-U oxide is previously undiscovered mineral.
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表 1 Ti-Zr-U氧化物电子微探针分析结果
Table 1. Compositions of Ti-Zr-U oxide analyzed by EPMA
项目 元素 样品1 样品2 样品3 样品4 样品5 样品6 样品7 样品8 样品9 样品10 Ti-Zr-U氧化物的电子微探针成分(%) TiO2 55.18 52.22 53.26 53.96 55.47 55.26 53.81 49.98 52.72 52.89 ZrO2 38.81 34.06 34.81 36.67 39.00 38.35 36.72 26.90 34.43 33.26 UO2 3.55 9.05 7.34 5.16 2.08 5.61 7.45 19.07 9.31 9.67 Al2O3 0.23 0.13 0.16 0.15 0.07 0.07 0.18 0.17 0.05 0.14 SiO2 0.00 0.20 0.06 0.08 0.06 0.00 0.07 0.00 0.01 0.00 CaO 0.10 0.12 0.14 0.12 0.06 0.04 0.03 0.10 0.00 0.01 FeO 0.18 1.08 1.32 1.22 1.18 0.21 0.22 0.33 0.28 2.04 Ce2O3 0.16 0.29 0.32 0.25 0.34 0.05 0.26 0.17 0.24 0.22 ThO2 0.21 0.37 0.22 0.26 0.08 0.23 0.16 0.58 0.24 0.30 PbO2 0.20 0.58 0.42 0.48 0.04 0.40 0.41 1.20 0.72 0.60 总计 98.61 98.10 98.05 98.35 98.38 100.22 99.31 98.49 98.01 99.13 氧原子数为6时电子微探针计算的阳离子数 Ti 2.018 1.996 2.012 2.007 2.020 2.016 2.004 2.021 2.016 2.008 Zr 0.920 0.844 0.852 0.884 0.921 0.907 0.886 0.705 0.854 0.819 U 0.038 0.102 0.082 0.057 0.022 0.061 0.082 0.228 0.105 0.109 Al 0.006 0.004 0.005 0.004 0.002 0.002 0.005 0.005 0.002 0.004 Si 0.000 0.010 0.003 0.004 0.003 0.000 0.003 0.000 0.001 0.000 Ca 0.005 0.007 0.008 0.006 0.003 0.002 0.002 0.006 0.000 0.001 Fe 0.007 0.046 0.055 0.050 0.048 0.009 0.009 0.015 0.012 0.086 Ce 0.001 0.003 0.003 0.002 0.003 0.000 0.002 0.002 0.002 0.002 Th 0.002 0.004 0.003 0.003 0.001 0.003 0.002 0.007 0.003 0.003 Pb 0.003 0.008 0.006 0.006 0.001 0.005 0.005 0.017 0.010 0.008 总计 3.002 3.023 3.028 3.025 3.023 3.004 3.001 3.007 3.004 3.040 注：8、9点成分为具环带结构的同一颗粒，其中8为核部，9为边部。 
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