Geochemistry and origin of hydrothermal apatite in Carlin-type Au deposits, southwestern China (Gaolong deposit)

Apatite can record the evolution of magmatic-hydrothermal ore systems, but it is unclear whether it is suitable for investigating low-temperature, sediment-hosted hydrothermal ore systems. To fill the knowledge gap. we investigated the Gaolong Carlin-type Au deposit in the Guangxi Zhuang Autonomous Region, southwestern China (Youjiang Basin). Results show that the hydrothermal apatite occurs in quartz-sulfide ores, has an intact crystal form and homogeneous texture, and is F-rich (2.77-3.67 wt%) and Cl-poor (<0.01 wt%). The apatite is enriched in rare earth elements (REEs; Sigma REE = 739-2481 ppm) and has middle-REE-enriched chondrite-normalized REE patterns with positive Eu anomalies (delta Eu = 1.35-2.00). These REE features were inherited from a reducing hydrothermal system in which anion complexation was dominant. The apatite has high Sr contents (up to 0. 9 wt %) and relatively uniform initial Sr-87/Sr-86 ratios (0.709055-0.709208), suggesting that Sr was leached or derived from the deep continental crust. In situ U-Pb dating of 156.8 +/- 8.3 Ma for apatite shows that the Late Jurassic-Early Cretaceous was an important time for the formation of Carlin-type Au deposits in the Youjiang Basin. The Au mineralization was associated with far-field tectonism and deeply sourced hydrothermal oreforming fluids. Hydrothermal apatite can be used to fingerprint low-temperature, sediment-hosted hydrothermal ore systems.