Mineralogy and Geochemistry of Turquoise from Tianhu East, Xinjiang, China

China is one of the main producing areas of turquoise in the world, boasting significant deposits mainly located in regions such as Hubei Province, Anhui Province, Shaanxi Province, Henan Province, and Xinjiang. Turquoise deposits in China can be categorized into two types: sedimentary metamorphic rock and magmatic rock^[1]. The turquoises from Hubei Province, Henan Province, and Xinjiang are of the sedimentary metamorphic rock variety, whereas the specimens from Maanshan and Tongling in Anhui Province are extracted from magmatic rock^[1]. The turquoise deposit from Tianhu East is located 180 km southeast of Hami (also known as Kumul) in Xinjiang, China. This deposit had been mined since as early as 1 279-379 BCE^[3]. The turquoise mine from Tianhu East was re-exploited around 2015, and some of the production emerged briefly on the Chinese market. The mining was subsequently prohibited because of the location's protected status as an archaeological site. For a long time, turquoise sourced from sedimentary metamorphic rocks has dominated the Chinese market. Regions such as Zhushan, Yunxi, Yunxian in Hubei, and Baihe in Shaanxi are known for producing this type of turquoise, which is closely associated with black rock series^[4-6]. The metallogenic mechanism of this variety of turquoise has been subject to various interpretations^[6-8]. The geology of turquoise deposit from Tianhu East as well as updated reports and field exploration systematically summarized in this study. The turquoises usually occur as blue and bluish green veins in the fissures and shear zones of quartzite in the Cambrian Pochengshan Formation. It is characterized by high lithium, vanadium, chromium, strontium, and gallium concentrations and low barium contents. Multiple associated minerals (e.g., quartz, apatite, goethite, hematite, jarosite, bonattite, muscovite, atacamite, svanbergite, and gypsum) were identified using Raman spectroscopy and electron probe microanalysis. This study contains the first report of atacamite in Chinese turquoise, a mineral that could serve as a distinctive marker for this specific origin. Petrography, mineralogy, and geochemistry of the bedrock as well as the crystallization sequences of the associated minerals are highlighted. Based on the results, the authors propose a supergene weathering origin and elemental derivation for turquoise from Tianhu East. Black shale is likely the main original source of the aluminum, phosphorus, and copper necessary for formation, while quartzite provides enough space for precipitation.