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新疆和田地区大理岩型和田玉的形成及致色因素探讨
Genesis of dolomite-related nephrite from Hetian and color-forming factors of typical nephrite in Hetian, Xinjiang
投稿时间:2017-09-11  修订日期:2018-05-14
中文关键词:和田玉  透闪石  新疆  致色因素  和田地区
英文关键词:nephrite  tremolite  Xinjiang  color-forming factors  Hetian area
基金项目:中国地质调查局中国矿产地质与成矿规律综合集成和服务(矿产地质志)项目(DD20160346);中国地质调查局地质调查项目(1212011020151511-03)
作者单位E-mail
韩冬 自然资源部珠宝玉石首饰管理中心, 北京 100013  
刘喜锋 华南理工大学 广州学院, 广东 广州 510800 liuxf@gcu.edu.cn 
刘琰 中国地质科学院 地质研究所, 北京 100037  
张勇 自然资源部珠宝玉石首饰管理中心, 北京 100013  
郑奋 中国地质大学(北京) 珠宝学院, 北京 100037  
买托乎提·阿不都瓦衣提 新疆维吾尔自治区和田地区质检局, 新疆 和田 848000  
张红清 中国地质大学(北京) 珠宝学院, 北京 100037  
文茈燊 北京大学 地球科学与空间学院, 北京 100871  
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中文摘要:
      采集阿拉玛斯和田玉山料和喀拉喀什河(墨玉河)的和田玉样品,利用显微镜和背散射图像、电子探针等研究手段,结合以往全岩数据对和田玉的形成和致色因素进行了综合分析。研究发现,除透闪石以外,和田玉中还含有大量的绿帘石、透辉石、绿泥石、锆石、磷灰石、尖晶石、石榴石、重晶石、阳起石、闪锌矿、磁黄铁矿、石墨、方解石和氢氧化铁等多种副矿物;Cr、Ni含量(<100×10-6)及Mg/(Mg+Fe2+)-Si投点显示这些样品均属于大理岩型软玉(和田玉)。全岩及其微区成分分析结果显示,从白玉(TFe2O3=0.33%~1.42%)、青白玉(TFe2O3=0.43%~0.96%)至青玉(TFe2O3=0.77%~3.97%),TFe2O3含量逐渐增加,而且所有样品的Cr和Ni含量都分别低于60×10-6和20×10-6,说明从白玉、青白玉至青玉,颜色的加深与透闪石中铁元素含量逐渐增加有关。墨玉的颜色主要与透闪石集合体中的石墨和Fe(OH)3等细脉大量出现有关。为深入研究和田玉的致色因素,同时采集了加拿大的碧玉样品进行对比,发现同样主要为透闪石组成的加拿大碧玉,除Fe外,还含有大量的Cr元素(1 400×10-6~5 100×10-6),碧玉的颜色鲜艳与透闪石C位中含有0.01~0.03 a.p.f.u.的Cr有关,而和田玉中Cr含量较低,在C位中几乎为0。通过野外观察和岩相学分析认为,含和田玉的镁质矽卡岩的形成经历了接触变质、接触交代变质和硫化物阶段,主要通过交代镁质大理岩、透辉石、绿帘石等矿物形成,而和田玉的主要形成机制是多期次的细粒透闪石交代粗粒透闪石。
英文摘要:
      In this study, nephrite samples from Alamas and Karakash Rivers were collected. Also, serpentinite-related green nephrite samples were selected for comparison in colors. Methods such as electronic microprobe analysis and back-scattered electron images were employed to study the genesis and color-forming factors of nephrite. Based on whole-rock chemical analyses of nephrite obtained, the authors studied petrographic characteristics, mineral composition and color-forming factors. In this study, besides tremolite, associated minerals such as diopside, chlorite, actinolite, spinal, zircon, apatite, garnet, barite, pyrrhotine, graphite, calcite, and Fe(OH)3 were found in nephrite. All samples have low concentrations of Cr, Ni (<100×10-6) and spots of Mg/(Mg+Fe2+)-Si, suggesting all these samples are dolomite-related nephrite. According to the whole-rock analysis of nearly all data obtained, the data TFe2O3=0.33%~1.42%,TFe2O3=0.43%~0.96% and TFe2O3=0.77%~3.97% were found in white, white-green and green nephrite, respectively. Also, values of Cr and Ni in these samples have low concentrations below 60×10-6 and 20×10-6 respectively. These chemical compositions suggest that the increasing content of TFe2O3 in crystal structures in tremolite leads to change of the colors in nephrite from white to green. Large amounts of graphite and veinlets of Fe(OH)3 lead to the black color of nephrite. Although both serpentinite-related and dolomite-related nephrite samples have predominated tremolite, serpentinite-related nephrite might have emerald color. In order to further study the coloring factors of Hetian nephrite, the authors collected samples of serpentinite-related nephrite in Canada for comparison. With serpentine-related nephrite in Candia as an example, in addition to the amount of Fe, a large amount of Cr (1 400×10-6~5 100×10-6) was found in them. The emerald color of serpentinite-related nephrite is related to 0.01~0.03 a.p.f.u. of Cr in C site in tremolite. By contrast, there exists nearly no Cr in C site in tremolite in dolomite-related nephrite. Based on the geological field observation and petrographic characteristics, the authors hold that the formation of Mg-skarn has experienced metamorphism, metasomatism and sulfur stages and tremolite formed through the replacement at the expense of the dolomite marble, diopside and other minerals. Multiple replacement of coarse-grained tremolite by fine-grained tremolite leads to the formation of nephrite.
韩冬,刘喜锋,刘琰,张勇,郑奋,买托乎提·阿不都瓦衣提,张红清,文茈燊,2018,新疆和田地区大理岩型和田玉的形成及致色因素探讨[J].岩石矿物学杂志,(6):1011~1026.
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