Mineralogical characteristics and genesis of Bama nephrite
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P578.955;P579

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    Abstract:

    Following the discovery of Luodian nephrite and Dahua nephrite, another nephrite mineral spot was also found in Bama, Guangxi, which also belongs to Qian-Gui area. Analysis methods, such as orthogonal polarization microscope, X-ray powder diffraction, electron probe microanalysis and artificial heavy concentrate, were employed to study petrographic characteristics, mineral composition, color-forming factors and the genesis. These studies show that the main mineral composition of Bama nephrite is microcrystalline tremolite or actinolite, and other minor minerals, such as talc, limonite, kaolinite, etc. Bama nephrite shows felty structure,bundle structure and structure of the pattern of aquatic plant. Spots of Mg/(Mg+Fe2+)-Si of Bama nephrite plot into tremolite or actinolite. The hardness of Bama nephrite is between 5.19~5.32, the denstity is between 2.81~3.00 g/cm3, the refractive index is about 1.61. Talc, auxiliary mineral of Bama nephrite, is the cause of lower hardness. According to the electron probe data, the relevant chemical formulas of Bama jade were calculated and compared and analyzed, we found that the green color of Bama nephrite is related to 0.08~0.67 a.p.f.u of Fe in C site in tremolite, which suggests that the increasing content of Fe in C site in Bama nephrite leads to change of the colors of nephrite from light purple to dark green. The data of X-ray powder diffraction show that goethite was in the structure of the pattern of aquatic plant, implying that the structure of the pattern of aquatic plant of Bama nephrite was formed on the surface of the earth. Through field observation, the comprehensively analysis of major elements, rare elements and rare earth elements, and comparison with related features of other mine point, the authors consider that the genetic type of Bama nephrite deposit is belongs to stratabound and contact metasomatic magmatic hydrothermal deposit, which is result-ed from the magmatic hydrothermal contact metasomatism induced by diabase intruding into carbonate rock. Bama nephrite is the same genetic type with Luodian and Dahua nephrite deposits in Qian-Gui area which have been found in previous study. They are belong to the same ore belt.

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黄倩心,王时麒,梁国科,杨晓东,吴祥珂,2021,广西巴马玉的矿物学特征及其成因探讨[J].岩石矿物学杂志,40(5):977~990. HUANG Qian-xin, WANG Shi-qi, LIANG Guo-ke, YANG Xiao-dong, WU Xiang-ke,2021,Mineralogical characteristics and genesis of Bama nephrite[J]. Acta Petrologica et Mineralogica,40(5):977~990.

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History
  • Received:March 24,2021
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  • Online: September 16,2021
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