Study On Mineralogical Characteristics And Genesis Of Gemstones "Sprinkled Gold Black Cyan Nephrite" In Xinjiang

In recent years,a kind of black cyan nephrite associated with pyrite has appeared in the domestic market,commonly known as"Sprinkled Gold Black Cyan Nephrite".It is mainly produced in hetian and kashi regions of Xinjiang,and is dark green black as a whole and a large amount of pyrite can be seen on the surface.In this paper,the Xinjiang"Sprinkled Gold Black Cyan Nephrite"is taken as the research object,the mineral composition and microstructure characteristics were obtained by polarized light microscope observation and phase analysis of xray diffraction（XRD）,its spectral identification characteristics are obtained by infrared spectroscopy and Raman spectroscopy,and its geochemical characteristics of major,trace and rare earth elements are obtained by X-ray fluorescence spectroscopy（XRF）,electron probe analysis（EPMA）and laser inductively coupled plasma mass spectrometry（LA-ICP-MS）,discussion its mineralogical origin and deposit genesis are characterized by isotopes of hydrogen,oxygen,and sulfur,and the main research results are as follows:The main mineral composition of"Sprinkled Gold Black Cyan Nephrite"in Xinjiang is tremolite,which has a typical fiber interwoven structure.The mineral particles are small and these are closely intertwined in a plaque crystal,needle or fibrous manner;The secondary mineral is mainly pyrite,which is widely distributed in the tremolite matrix as idiomorphic semi idiomorphic particles.In addition,it also contains graphite,phlogopite,chlorite,epidote,sphene,zircon and other mineral components.The results of electron probe analysis show that the main mineral components are consistent with the standard theoretical values of tremolite,with Mg/（Mg+Fe）values ranging from 0.80 to 0.95,and some tremolite has been converted to actinolite.The results of infrared and Raman spectroscopy analysis show that the spectral peaks of the main minerals tend to be consistent with the standard spectral peaks of tremolite.The infrared spectra focus on the fingerprint area of 400～1200cm^-1,and the main characteristic peaks are 1140cm^-1,1040cm^-1,996cm^-1,747cm^-1,677cm^-1,650cm^-1,540cm^-1 and 462cm^-1.Some spectra have missing or peak position shift;The main characteristic peaks of Raman spectrum in the low frequency range of 100～1500 cm^-1 are 1060 cm^-1,930 cm^-1,675 cm^-1,391 cm^-1,225 cm^-1,and the characteristic peaks in the high frequency range of 3000～4000cm^-1 are 3674 cm^-1 and 3663 cm^-1.The peaks of pyrite spectrum are 380cm^-1,346cm^-1 and438cm^-1,which are consistent with the standard Raman spectrum peak of pyrite.The mineral composition of"Sprinkled Gold Black Cyan Nephrite"in Xinjiang is complex.The results of X-ray fluorescence spectroscopy combined with electron probe testing show that the main components of tremolite are Si O₂,Ca O,Mg O,containing Cr,Co,Ni,Fe,Mn,Ti,Zn and other trace elements,of which Mn,Ti,Zn are relatively high;The total content of rare earth elements is less,and it is different from the rare earth distribution pattern of nephrite in other regions.Pyrite is mainly composed of S and Fe,containing a small amount of Co,Ni,Se,Au and other elements.According toδFe-δS of the theoretical value migration and Co/Ni value indicate that the pyrite in the sample belongs to hydrothermal origin,and the source of hydrothermal solution is not single.It is speculated that it is a mixture of magmatic hydrothermal solution and metamorphic hydrothermal solution;Based on the characteristics of hydrogen and oxygen isotopes,it is speculated that the"Sprinkled Gold Black Cyan Nephrite"in Xinjiang is of contact metasomatic metamorphic origin.Besides the magmatic water and atmospheric water,the metamorphic water may also participate in the ore-forming hydrothermal solution;The results of sulfur isotope characteristics show that the source of pyrite is the mixture of sea water sulfur,mantle sulfur and stratum sulfur.