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摘要: 由于碧玉的样品来源、测试技术单一，有关碧玉的成因及其与大理岩型软玉之间的成因差别都不明确。本文采集了我国青海、俄罗斯、加拿大、新西兰、巴基斯坦等全球代表性碧玉样品，采用显微镜观察、X射线粉晶衍射、电子探针、电感耦合等离子体质谱和稳定同位素质谱等技术进行岩相学、矿物组成、微量和主量元素、氢氧同位素测试，对碧玉的成因进行综合分析，同时和澳大利亚大理岩型软玉进行对比性研究，以明确两种类型的软玉之间的成因差别。碧玉样品测试结果表明：①碧玉的主要组成是透闪石，次要矿物有石英、滑石、黑云母、铬铁矿、石墨、石榴石等；②氢氧同位素组成（δD值-69.763‰~-29.251‰，δ18O值4.7‰~13.4‰）显示由明显的变质水组成；③全岩Fe2+/（Mg+Fe2+）值为0.11~0.32，Cr含量约22.9~3400 μg/g，Ni含量为700~1800 μg/g，表明了明显的幔源物质参与成矿的特征。通过对比发现，碧玉与大理岩型软玉的地球化学性质有明显不同，这种差别与两者的产出环境有关：大理岩型软玉的矿物组成和地球化学特征受控于花岗岩和镁质大理岩，而碧玉的地球化学特征与幔源物质组成和变质流体相关。Abstract:
BACKGROUND In previous studies, due to the limited samples with specific origins and limited methods for measurement, the genesis of serpentinite-related green nephrite and its relationship with dolomite-related nephrite were unclear. OBJECTIVES To understand the genesis of serpentinite-related green nephrite. METHODS Green serpentinite-related nephrite deposits have been collected from Qinghai province in China, Russia, Canada, Australia, New Zealand and Pakistan for systematic analysis. X-ray Diffraction (XRD), Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), Electron Microprobe Analysis (EMPA), X-ray Fluorescence Spectrometry (XRF) and Stable Isotope Mass Spectrometry were employed. RESULTS ① Serpentinite-related green nephrite is mainly composed of tremolite with minor quartz, talc, biotite, chromite, chlorite, and garnet. ② O-H isotopic values of samples (δD=-69.763‰--29.251‰, δ18O=4.7‰-13.4‰) indicate that the ore-forming fluids are mainly metamorphic water. ③ whole-rock major elements of Fe2+/(Mg+Fe2+)values range from 0.11 to 0.32. The contents of Cr range from 22.9 to 3400 μg/g, whereas Ni ranges from 700 to 1800 μg/g. All of these geochemical characteristics indicate the input of the mantle material in the formation of serpentinite-related nephrite. CONCLUSIONS Geochemical characteristics of serpentinite-related and dolomite-related nephrite are different, which are related to the geological environment. For example, the composition of dolomite-related nephrite is controlled by the granite and dolomite marble, whereas the composition of serpentinite-related green nephrite is related to the mantle material and metamorphic fluids. -
Key words:
- serpentinite-related green nephrite /
- geochemistry /
- nephrite /
- genesis
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表 1 世界各地碧玉全岩主量和微量元素分析数据
Table 1. Major and trace elements composition of nephrites in the world deposits
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表 2 世界各地透闪石的氢氧同位素数据
Table 2. Hydrogen and oxygen isotope data of tremolite in the world deposits
样品编号 矿床产地 δD
(‰)δ18O
(‰)δDH2O(‰) 350~650℃ 330℃ QH-1 青海 -56.167 8.6 -34.467 9.09 QH-2 青海 -59.678 8.1 -37.978 8.59 RUS-1 俄罗斯 -52.623 8.3 -30.923 8.79 RUS-2 俄罗斯 -50.828 8.2 -29.128 8.69 RUS-3 俄罗斯 -51.376 8.5 -29.676 8.99 CAN-1 加拿大 -45.247 12.3 -23.547 12.79 CAN-2 加拿大 -60.491 9.5 -38.791 9.99 CAN-3 加拿大 -47.670 9.4 -25.970 9.89 NZ-1 新西兰 -29.251 8.0 -7.551 8.49 NZ-2 新西兰 -69.763 4.7 -48.063 5.19 BL-1 巴基斯坦 -43.337 13.0 -21.637 13.49 BL-2 巴基斯坦 -55.723 13.2 -34.023 13.69 BL-3 巴基斯坦 -53.764 13.4 -32.064 13.89 AUS-2 澳大利亚 -46.075 1.3 -24.375 1.79 AUS-3 澳大利亚 -42.199 1.6 -20.499 2.09
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表 3 蛇纹石型和大理岩型软玉的元素特征对比
Table 3. Comparison of element characteristics in serpentinite-related nephrites and dolomite-related nephrites
样品 元素 与蛇纹石相关的软玉 与大理岩相关的软玉 透闪石 Cr2O3(%) 0.08~0.36[7]，0.07~0.43[4]，0.020~0.127[3]，
0.08~1.65(本文)0.39~1.14[15]，0.00~0.07[4]，0.03~1.18[5]，
<0.05~0.09[23]NiO(%) 0.08~0.25[7]，0.08~0.36[4]，0.14~0.22(本文) 0.00~0.08[4]， < 0.05~0.06[23] δ18O(‰) 4.5~5.3[10]，6.9~9.6[2]，4.7~13.4(本文) -9.9~-8.2[2]，0.5~3.4[3]，1.1~5.6[4]，
3.2~6.2[5]，1.3~1.6(本文)δD(‰) -67~-33[10]，-54~-39[2]，
-69.763~-29.251(本文)-114~-105[2]，-124~-56[2]，-72.4~
-55.7[4]，-94.7~-83.0[5]，-113± 4.8[11]透辉石 Cr2O3(%) 0.018~0.640[3] 0.00~0.03[5] 全岩 Cr(μg/g) 1220~1890[7]，900~1113[8]，1505.3~2812.1[9] 8.95~178.7[5]，1.9~67.9[9] Ni(μg/g) 1199~1484[7]，1887~1898[8]，958.7~1304.4[9] 0.05~3.95[5]，22.2~470.7[9] Co(μg/g) 204~207[8]，42.0~53.0[9] 0.5~9.8[9] Fe2+/(Mg+Fe2+) >0.060[9]，0.11~0.32(本文) < 0.060[9]
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