The Characteristics and Species Identification of Garnets Hosted in the Kimberlites from Wafangdian, Liaoning Province
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摘要: 辽宁瓦房店金刚石矿区金伯利岩中的石榴石一直被当作镁铝榴石。为了确定矿区颜色复杂的石榴石种类，本文对矿区的石榴石进行了系统的采样分析，测定了112件石榴石样品的晶胞参数、50件样品的微区化学成分和40件样品的红外光谱。利用石榴石晶胞参数、红外光谱、化学成分和化学分子式方法对矿区石榴石进行分类，结果显示：晶胞参数分类法误差大，容易得出错误结论；红外图谱分类法准确度不高，只能作为参考方法；化学成分分类法太过笼统，达不到详细划分石榴石种类的目的；化学分子式分类法可把矿区的石榴石详细划分6个矿种：镁钙铁-铝铬铁榴石、镁铁钙-铝铬铁榴石、镁钙铁-铝铬榴石、镁钙-铝铬铁镁榴石、镁铁钙-铝铬榴石、镁铁钙-铝铁铬榴石，每种石榴石都充分反映了A、B离子的种类及占位特征，是4种分类方法中最为科学的方法。研究认为瓦房店金刚石矿区金伯利岩中石榴石A端元成分以Mg2+离子占位为主；B端元成分以Al3+离子占位为主。由于阳离子替代普遍，A、B端元成分复杂，瓦房店金伯利岩中不存在单纯意义上的镁铝榴石。Abstract: The garnets in the kimberlites of the Wafangdian diamond mining area from Liaoning province have previously been identified as pyrope. In order to define the types of the complicated color garnets in Wafangdian, a systematic sampling and analysis of the garnets in the mining area was taken, including the definition of 112 single mineral crystal cell parameters, the analysis of 50 micro area chemical composition and 40 infrared spectra. The garnets were classified through the following methods: crystal cell parameters, infrared spectrum, chemical composition and chemical formula. The results show that the deviations of the crystal cell parameter classification were large, which may incorrect classification. The results of the infrared spectrum classification were inaccurate, but were only used as a reference method. The chemical composition classification provided general results, which could not classify the garnets in detail. The chemical formula classification classified the garnets into six mineral types: magnesium calcium iron-aluminum chromium iron garnet, magnesium iron calcium-aluminum chromium iron garnet, magnesium calcium iron-aluminum chrome garnet, magnesium calcium-aluminum chromium iron magnesium garnet, magnesium iron calcium-aluminum chromium garnet, magnesium iron calcium-aluminum iron chromium garnet. Each type of garnet reflected A and B ion species and occupation characteristics, which was the most scientific classification method. The results of this research indicate that the A end member ingredient was Mg2+ ion primarily and B was Al3+ ion for the garnets in the kimberlites of the Wafangdian diamond mining area. Due to the common cationic replacement and complex compositions of A and B end members, it was concluded that there is no pyrope in the Wafangdian kimberlites.
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Key words:
- kimberlites /
- garnets /
- crystal cell parameters /
- chemical composition /
- infrared pattern /
- garnet classification
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表 1 瓦房店金伯利岩中石榴石晶胞参数
Table 1. The crystal cell parameters of the garnets in the Wafangdian kimberlites
采样地点 样品件数 晶胞参数/nm 1.1459~1.1526 1.1538~1.1574 1.1575~1.1621 1.1622~1.1851 1号无矿岩管 23 - - 11 12 42号中等含矿岩管 42 1 7 34 - 50号贫矿岩管 20 3 14 3 - 51号富矿岩管 27 - 15 12 - 合计 112 4 36 60 12 
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表 2 石榴石微区分析结果
Table 2. The chemical composition of the garnets by microanalysis
采样地点 样品件数 wB /% MgO SiO2 FeO TiO2 Al2O3 Cr2O3 CaO MnO 总和 1号岩管 12 18.262 41.665 7.812 0.085 16.134 9.810 6.885 0.006 100.70 42号岩管深 16 18.715 41.585 7.876 0.083 16.699 8.366 6.863 0.014 100.36 42号岩管浅 4 18.717 41.779 7.044 0.037 16.578 8.860 7.120 0.027 100.43 50号岩管 9 19.856 42.105 9.068 0.208 20.120 4.067 5.175 0.011 100.71 51号岩管 9 20.061 42.454 8.594 0.192 19.899 4.221 4.781 0.017 100.39 注：石榴石中氧化物含量是瓦房店相同金伯利岩管所测石榴石样品的平均值。
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表 3 石榴石分子式计算
Table 3. Garnet molecular formula calculation sheet
石榴石化学成分 MgO SiO2 FeO TiO2 Al2O3 MnO Cr2O3 CaO 氧化物质量分数wB/% 19.0311 41.2511 10.9326 0.4196 20.0084 0.0113 3.4099 4.9361 氧化物分子质量 40.30 60.08 71.85 79.87 101.96 70.94 151.99 56.08 氧化物摩尔数 0.4722 0.6866 0.1522 0.0053 0.1962 0.0002 0.0224 0.0880 氧化物中氧原子数 0.4722 1.3732 0.1522 0.0105 0.5887 0.0002 0.0673 0.0880 氧化物中阳离子数 0.4722 0.6866 0.1522 0.0053 0.3925 0.0002 0.0449 0.0880 分子式中阳离子数 2.06 2.99 0.66 0.02 1.71 0.00 0.20 0.38 注：石榴石中氧化物含量是瓦房店50号岩管7号样中单晶石榴石电子探针的测试值。
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表 4 瓦房店金伯利岩中石榴石分子式和类型
Table 4. The garnets formula and classification of the Wafangdian kimberlites
采样地点 石榴石名称 样品件数 石榴石分子式 石榴石类型 1号岩管 镁钙铁-铝铬榴石 8 (Mg1.98Ca0.53Fe0.47)2.98(Al1.45Cr0.51)1.96Si3.04O12 Ⅲ 镁钙铁-铝铬铁榴石 3 (Mg1.99Ca0.54Fe0.47)3.00(Al1.38Cr0.58Fe0.02)1.98Si3.02O12 Ⅰ 镁铁钙-铝铬榴石 1 (Mg2.01Fe0.49Ca0.48)2.98(Al1.42Cr0.53)1.95Si3.04O12 Ⅴ 42号岩管 镁钙铁-铝铬铁榴石 8 (Mg2.01Ca0.55Fe0.44)3.00(Al1.37Cr0.61Fe0.03)2.01Si3.00O12 Ⅰ 镁铁钙-铝铬铁榴石 4 (Mg2.11Fe0.47Ca0.42)3.00(Al1.62Cr0.34Fe0.03)1.99Si3.02O12 Ⅱ 镁钙铁-铝铬榴石 7 (Mg1.90Ca0.57Fe0.52)2.99(Al1.33Cr0.62)1.95Si3.04O12 Ⅲ 镁钙-铝铬铁镁榴石 1 (Mg1.97Ca1.03)3.00(Al1.23Cr0.32Fe0.30Mg0.24)2.09Si3.06O12 Ⅳ 50号岩管 镁钙铁-铝铬铁榴石 1 (Mg2.12Ca0.50Fe0.38)2.99(Al1.49Cr0.45Fe0.08)2.02Si3.00O12 Ⅰ 镁铁钙-铝铬铁榴石 5 (Mg2.22Fe0.42Ca0.36)3.00(Al1.69Cr0.24Fe0.04Ti0.01)1.98Si3.03O12 Ⅱ 镁铁钙-铝铬榴石 2 (Mg2.01Fe0.52Ca0.47)3.00(Al1.65Cr0.32)1.97Si3.03O12 Ⅴ 镁铁钙-铝铁铬榴石 1 (Mg2.17Fe0.51Ca0.32)3.00(Al1.81Fe0.10Cr0.08Ti0.02)2.01Si3.01O12 Ⅵ 51号岩管 镁铁钙-铝铬榴石 4 (Mg2.15Fe0.46Ca0.39)3.00(Al1.55Cr0.38)1.93Si3.05O12 Ⅴ 镁铁钙-铝铬铁榴石 2 (Mg2.20Fe0.48Ca0.32)3.00(Al1.81Cr0.12Fe0.01)1.94Si3.04O12 Ⅱ 镁钙铁-铝铬铁榴石 2 (Mg2.15Ca0.45Fe0.40)3.00(Al1.40Cr0.49Fe0.04Ti0.01)1.94Si3.05O12 Ⅰ 镁铁钙-铝铁铬榴石 1 (Mg1.87Fe0.76Ca0.37)3.00(Al1.78Fe0.07Ti0.04Cr0.01)1.90Si3.08O12 Ⅵ
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表 5 瓦房店金伯利岩中石榴石红外光谱特征
Table 5. The infrared spectrum features of the garnets in the Wafangdian kimberlites
样品编号 样品颜色 σ/cm-1 C峰 D峰 C峰－D峰 1-2 玫瑰紫 882.2 863.1 19.1 1-12 玫瑰紫 879.6 861.7 17.9 1-13 玫瑰紫 884.7 861.7 23.0 1-15 玫瑰紫 883.0 865.1 17.9 1-17 玫瑰紫 878.1 867.0 11.1 1-19 玫瑰紫 882.2 865.6 16.6 42-2 紫红 884.7 861.7 23.0 42-11 紫红 888.1 865.8 22.3 42-12 紫红 885.1 861.7 23.4 42-15 紫红 878.1 864.7 13.4 42-21 紫红 881.6 861.7 19.9 42-22 紫红 886.3 865.5 20.8 42-25 紫红 878.1 863.5 14.6 42-26 紫红 884.7 865.8 18.9 42-29 紫红 874.0 863.0 11.0 42-31 紫红 888.7 865.8 22.9 42-32 紫红 887.3 861.7 25.6 42-35 紫红 886.8 861.7 25.1 42-44 紫红 879.1 861.7 17.4 42-54 紫红 884.9 865.8 19.1 42-57 紫红 884.2 865.8 18.4 42-58 紫红 886.8 865.8 21.0 42-60 紫红 887.8 865.8 22.0 50-1 紫青 886.3 867.0 19.3 50-2 深紫红 887.6 861.7 25.9 50-3 浅紫红 889.7 865.7 24.0 50-7 水红 896.9 868.8 28.1 50-9 浅橙红 895.4 869.1 26.3 51-3 淡玫瑰 897.5 871.3 26.2 51-7 淡玫瑰 895.0 869.9 25.1 51-10 玫瑰紫 884.7 865.8 18.9 51-12 玫瑰紫 888.7 865.8 22.9 51-14 褐红色 897.1 872.3 24.8 51-15 褐红色 896.5 874.3 22.2 51-17 褐红色 897.1 871.0 26.1 51-19 淡玫瑰 898.9 872.7 26.2 51-21 淡玫瑰 896.8 873.9 22.9 51-22 玫瑰紫 888.1 869.9 18.2 51-25 褐红色 895.3 865.8 29.5 51-26 淡玫瑰 899.7 872.7 27.0 42-11 紫红 888.1 865.8 22.3 42-12 紫红 885.1 861.7 23.4 42-15 紫红 878.1 864.7 13.4 42-21 紫红 881.6 861.7 19.9 42-22 紫红 886.3 865.5 20.8 42-25 紫红 878.1 863.5 14.6 42-26 紫红 884.7 865.8 18.9 42-29 紫红 874.0 863.0 11.0 42-31 紫红 888.7 865.8 22.9 42-32 紫红 887.3 861.7 25.6 42-35 紫红 886.8 861.7 25.1 42-44 紫红 879.1 861.7 17.4 42-54 紫红 884.9 865.8 19.1 42-57 紫红 884.2 865.8 18.4 42-58 紫红 886.8 865.8 21.0 42-60 紫红 887.8 865.8 22.0 50-1 紫青 886.3 867.0 19.3 50-2 深紫红 887.6 861.7 25.9 50-3 浅紫红 889.7 865.7 24.0 50-7 水红 896.9 868.8 28.1 50-9 浅橙红 895.4 869.1 26.3 51-3 淡玫瑰 897.5 871.3 26.2 51-7 淡玫瑰 895.0 869.9 25.1 51-10 玫瑰紫 884.7 865.8 18.9 51-12 玫瑰紫 888.7 865.8 22.9 51-14 褐红色 897.1 872.3 24.8 51-15 褐红色 896.5 874.3 22.2 51-17 褐红色 897.1 871.0 26.1 51-19 淡玫瑰 898.9 872.7 26.2 51-21 淡玫瑰 896.8 873.9 22.9 51-22 玫瑰紫 888.1 869.9 18.2 51-25 褐红色 895.3 865.8 29.5 51-26 淡玫瑰 899.7 872.7 27.0
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