Gemmological And Mineralogical Studies Of The Tatelekesu Nephrite Deposit,Xinjiang

The Tatelekesu nephrite deposit in Qiemo,Xinjiang Province is one of the largest primary nephrite deposit in China at present.In this paper,12 typical specimens from Tatelekesu nephrite deposit were collected and studied in combination with some experiments such as traditional gemological test,Scanning Electron Microscope(SEM),Fourier Transform Infrared Spectroscopy(FTIR),Electron Probe Micro-Analysis(EPMA),SHRIMP U-Pb zircon dating,and so on.After learning references,gemology,mineralogy,geochronology,geological structure and other aspects of the 12 specimens have been conducted.Conclusions are as follows:The main products of the Tatelekesu Nephrite deposit are light green nephrite and light greenish white nephrite,rarely light yellowish white nephrite and brown nephrite can also be found.Major constituent mineral of nephrite from Tatelekesu is tremolite,the content of tremolite can reach more than 98%.The gemological properties and infrared absorption peaks of typical samples from Tatelekesu nephrite deposit are consistent with the typical characteristics of nephrite.The typical structure of the Tatelekesu Nephrite is fibrous crystalloblastic.The tremolite aggregations are formed with micro-fibrous-columnar tremolite grains appearing as fasciculate,felt-like,areatus,etc.The particle size in the nephrite usually smaller than grains in the contact zones and wall rocks which could achieve a micro cryptocrystalline texture.According to the micro deformation structure of nephrite from Tatelekesu,the formation of nephrite could be divided into three stages: automorphic and semi-automorphic bulky tremolite grains ? fibrous and columnar tremolite grains ?micro cryptocryptic tremolite grains.In addition to tremolite,other minerals of Tateleksu Nephrite include apatite,epidote,diopside,titanite,zircon,biotite,quartz,feldspar,magnetite,chlorite,talc,dolomite,etc.Minerals such as titanite and biotite in the wall rocks and contact zones could indicate the temperature,pressure and other environmental changes during the formation of Tatelekesu nephrite deposit.SHRIMP U-Pb zircon dating experiment of granite wall rocks and granite mixed metamorphic rocks from the Tateleksu nephrite deposite,yield three age groups of 924 ± 11 Ma,938 ± 8Ma,and 928 ± 12 Ma,which constitutes a small-range age gradient which could represent the continuous crystallization process of magma intruding into marble veins in the Tatelekesu nephrite deposit.It is speculated that the formation of the Tatelekesu Nephrite is related to the magmatic hydrothermal activity of the Qinbaikou formation in the Neoproterozoic.Combined with previous studies,this stage of magmatic intrusion may be related to the magmatism of the Altyn group at 900~950 Ma.The formation of the Tatelekesu nephrite deposit can be divided into three stages: the formation of the Mesoproterozoic carbonate formation ? the Neoproterozoic magma intruded into the marble to produce contact alternations-hydrothermal alteration to form nephrite ? the nephrite was compressed Superficial effects such as extrusion and crushing,disseminated erosion and other weathering effect.