Mineralogical-Geochemical Characteristics of Amazonite from Five Localities in Northwest China

Amazonite was a significant gemstone in ancient China, and determining its provenance is crucial for understanding early interregional resource use and cultural exchange patterns. However, previous studies have often been limited to single localities or specific artifacts, lacking systematic multi-regional geological comparisons. This has left the geochemical fingerprint characteristics of amazonite from different sources unclear, hindering the accuracy of artifact provenance studies. This study focuses on five amazonite mining areas in Northwest China: Altay (Xinjiang), Guobaoshan, Baishitouquan (Xingxingxia), Dahongshan (Aksai, Gansu), and Huayangchuan (Shaanxi). Using various analytical techniques, including polarized light microscopy, X-ray powder diffraction (XRD), infrared and Raman spectroscopy, electron probe microanalysis (EPMA), and inductively coupled plasma-mass spectrometry (ICP-MS), the mineralogical, spectroscopic, and elemental composition characteristics of the samples were systematically analyzed, aiming to establish a reliable source identification system. The results show that: (1) Amazonite from all localities consists of microcline with minor albite, though the impurity mineral assemblages allow for preliminary differentiation; (2) Infrared spectral features near 430 cm⁻¹ provide clear provenance indicators: samples from Xingxingxia show a single dominant peak, while those from Altay, Dahongshan, and other localities exhibit split peaks at 427 cm⁻¹ and 448 cm⁻¹; (3) Major and trace element analyses reveal that Rb content, K/Rb ratio, and rare earth element distribution patterns complement each other as effective discriminant indicators. Huayangchuan samples show “low Rb, high K/Rb” and a unique Eu positive anomaly, Xingxingxia samples (from both Guobaoshan and Baishitouquan) exhibit “high Rb, low K/Rb”, and Dahongshan samples show a clear Ce negative anomaly. This study reveals differences in mineralogy, spectroscopy, and elemental composition of amazonite from different localities and establishes a multi-indicator, quantifiable method for source identification. This method can be applied to trace the sources of ancient amazonite artifacts from northwest China, thereby providing scientific support for related studies on cultural exchange.