Study on Mineralogical and Spectroscopic Characteristics of Turquoise from the Duancengshan, Qinghai

The Duancengshan turquoise mine in Qinghai is an ancient mining site discovered in the northwestern region. Situated in the central distribution zone of Chinese turquoise resources and adjacent to the Tang—Xizang Ancient Road, this mining area holds significant importance for constructing China’s turquoise resource database, investigating ancient turquoise material provenance, and studying material-cultural exchanges across the Qinghai—Xizang Plateau. This study employed polarized light microscopy, Raman spectroscopy, infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy, automated mineral quantitative analysis systems, and electron probe microanalysis to systematically investigate the spectral characteristics, surface micromorphology, mineral composition, and chemical constituents of turquoise samples. Through a comprehensive analysis of fundamental mineralogical features, this research aimed to identify the provenance characteristics of the Duancengshan turquoise. Results indicate that the Duancengshan turquoise primarily consists of microcrystalline aggregates exhibiting well-crystallized forms including small flakes, short columns, platy sheets, and spherulites. Associated gangue minerals comprise quartz, hematite, anorthite, biotite, muscovite, schorl, apatite, and barite. Major chemical components include Al₂O₃ (21.97%-35.00%), CuO (5.21%-7.67%), and FeO^T (2.70%-9.35%), with a negative correlation between Al₂O₃ and FeO^T concentrations, while CuO shows no significant correlation with FeO^T. This suggests a predominant isomorphic substitution of Fe³⁺ for Al³⁺. Comparative analysis with turquoise from central China’s Henan—Shaanxi—Hubei region, Ma’anshan (Anhui), Xinjiang, as well as international sources including Iran, Sonora (Mexico), and Arizona (USA) reveals that Raman and infrared spectral features of the Duancengshan turquoise lack distinctive markers for provenance identification. However, the characteristic mineral assemblage (turquoise+quartz+hematite+mica+anorthite+schorl), coupled with the absence or scarcity of malachite and kaolinite-group minerals, along with elevated FeO^T content attributed to local iron mineralization, establishes diagnostic criteria. Particularly, the presence of schorl combined with mineralogical associations and geochemical signatures is a key indicator for distinguishing the Duancengshan turquoise provenance.