Study On Gemological And Mineralogical Characteristics And Genesis Of Red Corundum In Yuanjiang,Yunnan

The Yuanjiang red corundum deposit in Yunnan Province is located in the Yangtze plate-western margin orogenic belt and occurs in the marble of the high temperature metamorphic belt in South Yunnan.It belongs to the marble red corundum deposit together with the Mong Hsu deposit in Myanmar and the Yen Bai deposit in Vietnam.This article uses the gemological testing,gem endoscopic and polarizing microscope observation,electron probe,micro X-ray fluorescence spectrometer,infrared and Raman spectrometer,laser ablation-plasma mass spectroscopy,ultraviolet-visible absorption spectra test means such as observation,the Yuanjiang red corundum gemological properties,chemical composition and spectroscopy characteristic has carried on the system research.Most of the crystal morphology of Yuanjiang red corundum is irregular granular,and a few are hexagonal column and hexagonal barrel.Under the ultraviolet fluorescent lamp（LW）shows an extremely strong red fluorescence.The internal cracks and cleavages are densely developed.Through thin section observation and Raman spectroscopy,red corundum is confirmed to contain apatite,calcite and characteristic inclusions containing iron minerals.Al element distribution is uniform,Cr element distribution is not uniform,with the characteristics of rich Cr,poor Fe,high Ga trace elements,the main chromogenic ions are Cr,Fe and Ti.Among them,the content of Cr in the purplish red corundum is between 0.472%and0.806%.In a certain range,the level of red toning saturation is positively correlated with the content of Cr.The impurity ions of Fe and Ti make the red corundum appear purple or bluish purple red.Only La and Ce are common rare earth elements,and the content is very low.There were a few splitting peaks in the IR spectra.In addition to the Al-O vibration absorption peaks of red corundum,some test points showed double absorption peaks of bauxite at 1980cm^-1and 2107cm^-1.The typical characteristic peaks of Raman spectrum were 376cm^-1,415cm^-1and 641cm^-1.The UV-Vis absorption spectra of Yuanjiang red corundum with different saturation levels are similar,with strong absorption bands at 350nm～460nm and 470nm～620nm generally occurring,absorption lines at 679nm,705nm and 712nm.By analyzing the main and trace element test data,the Fe-Cr ratio of Yuanjiang red corundum is coincident with that of marbles red corundum deposits in Myanmar and Vietnam.The analysis of the mass fraction ratio relations of Cr-Ti,Cr-Fe,Ti-Fe,V-Ga,V-Mg and Fe-Ga can identify the red corundum deposits of different genesis,but it is difficult to identify the red corundum from Yuanjiang,Myanmar and Vietnam.