The Study Of Mineralogy And Genesis Of Green Nephrite With Chatoyancy From Ospinsk,Russia

In this study,the research object is the green nephrite with chatoyancy,which is the characteristic of the Ospinsk in Russia.The gemological properties,mineral composition characteristics,trace elements,structural characteristics,spectral characteristics and diagenesis are systematically studied.According to the observation results under the polarizing microscope,the main mineral of the green nephrite with chatoyancy from Ospinsk in Russia is tremolite,which account for about 99%of the green nephrite.The accessory minerals are chlorite,graphite and magnetite;the structure under the microscope is felt-like Interweaving structure,micro-fiber crystal structure,micro blade crystal structure,etc.SEM results showed that the green nephrite with chatoyancy of Ospinsk has a micro-fiber crystal structure,the fiber particles are between 0.3×3?m-5×50?m,and the fibrous tremolite crystals are densely arranged in parallel along the long axis.Infrared Spectroscopy indicated that the main component of the green nephrite with chatoyancy from Ospinsk in Russia was tremolite,and the strong absorption of the OH?MgMgMg?and OH(MgMgFe²⁺)bands in the high-frequency region indicated that Fe²⁺is contained in those samples.In Raman Spectroscopy,the metabolic temperature of graphite that obtained by metamorphism of materials which are carbon-containing is about 474.25?,indicating that during the hydrothermal fluid activity and metamorphism process of the green nephrite,the deposit is likely to be in the medium-high temperature background.Obtained by XRF and Electron Probe,the main chemical components of green nephrite with chatoyancy from Ospinsk in Russia are SiO₂:56.74wt.%,MgO:21.78wt.%,CaO:12.12wt.%;accessory chemical components are:Fe₂O₃,MnO,Al₂O₃,Cr₂O₃.The Trace Element results show that the green hue of the samples are related to Cr and Ni elements.The Rare Earth Element results show that the samples appear to negative anomaly of?Eu which average value is 0.775,indicating that the fluids forming the samples may come from rock bodies that have undergone a relatively high degree of separation and crystallization;and the average value of?REE is 1.973 ppm,indicating the origin of ultrabasic rocks.Comparing the components of ultrabasic rocks,the samples show the characteristics of high Si and Al depletion,indicating that the samples are formed in an environment rich in silicon and poor in aluminum.The calculated Cr,Ni and Co contents of the samples are consistent with serpentine nephrite;the Fe²⁺/(Mg+Fe²⁺)values are all greater than0.060,all of which indicate that it is ultrabasic rock alteration to serpentine nephrite.After researched,it was determined that the green nephrite from Ospinsk in Russia was transformed from ultramafic rock to serpentinite,and then metamorphized by thermal contact metasomatism,forming a nephrite deposit.The serpentine nephrization stage of the mineralization process is accompanied by the unilateral stress brought by the overthrust of the nappe layer.The ore-forming fluid is affected by the regional metamorphism,and the tremolite fiber grows directionally,which ultimately produces chatoyancyt on the macro.