Mineralogical Characteristic and Geographic Origin Tracing of Turquoise from Tianhudong Site, Xinjiang

Tianhudong site is the earliest turquoise mining site found in northwest China, which provides direct archaeological evidence for the study of the source of ancient turquoise in northwest China. Studying the mineralogical characteristics of turquoise in Tianhudong can provide basic scientific data for judging the origin characteristics and distribution of turquise produced at this site. In this paper, turquoises samples from mining site were tested by polarizing microscope, scanning electron microscope (SEM), X-ray diffractometer (XRD), electron microprob (EMPA) and Raman sepctroscopy to obtain their mineralogical and spectral characteristics.The chemical compositions of turquoise from Tianhudong are characterized by rich Fe. The SEM results show that the turquoise crystals are mainly in columnar, needle and plate shape.And none of which are very different from turquoise from Heishanling, Xinjiang. The polarizing microscope observation shows that the turquoises from Tianhudong mostly show microcrystalline scale and microcrystal fiber structures.The impurity minerals are characterized by quartz and biotite.Compared with turquoise impurities from different origin and producing area, the turquoise impurities show that the turquoise from Tianhudong are of weathering-leaching characteristics.There is no significant difference between the results of Raman spectra and that of turquoise from Heshanling, The only slight differences may be related to the differences in crystallinity, ion displacement, inclusions, impurity minerals and weathering of the two samples.At the same time through Raman spectra, Tianhudong turquoise is also accompanied with apatite minerals rarely seen in other turquoise mines. This characteristic is unique to turquoise from Tianhudong, and is one of the evidences for distinguishing the origin of turquoise in the future.The electron microprobe analysis indicates that the chemical compositions of turquoise from Tianhudong deviate from theoretical value. The contents of Al₂O₃ and P₂O₅in turquoise from Tianhudong are lower than the standard value, while the turquoise from Heishanling is higher, and there are obvious differences between them.