Apatite as a record of ore-forming processes: Magmatic-hydrothermal evolution of the Hutouya Cu-Fe-Pb-Zn ore district in the Qiman Tagh Metallogenic Belt, NW China

Apatite is a common accessory phase in magmatic rocks and associated hydrothermal deposits that holds information about the evolution from magma to ore-forming fluid. In this study, we systematically studied the geochronological and geochemical characteristics of apatites hosted in the Fe skarn ores and associated intrusions of syenogranite and monzogranite in the Hutouya polymetallic Fe-Cu-Pb-Zn ore district, Qiman Tagh Metallogenic Belt (QTMB), NW China, in order to gain insight into the metallogenic processes from magmatic crystallization to hydrothermal fluid exsolution. The apatite U-Pb dating results of skarns and related intrusions are 229-228 Ma, and the monzogranite emplacement is slightly later than the syenogranite emplacement and skarn formation. The REE concentrations of the apatites from the skarn-related intrusions are characterized by LREE-enriched patterns and weak negative Eu anomalies. However, the apatites from the skarn ores have high HREE contents, and are characterized by flat chondrite-normalized patterns and strong negative Eu anomalies. These data, combined with variations of element concentrations and ratios in the apatites (eg., Sr, SO3, F, Cl, REE, (La/Yb)N, (Sm/Nd)N, (La/Sm)N, (Eu/Eu*)N, (Ce/Ce*)N), record the transition of ore-forming processes from the magmatic crystallization to hydrothermal exsolution, and indicate that the skarn-related magmas with moderately reduced signatures may have been derived from partial melting of crustal materials potentially affected by the limited mantle input under an extensional environment.

Automated summary

In this study, the geochronological and geochemical characteristics of apatites in a polymetallic ore district in NW China were systematically studied to understand the metallogenic processes. The results suggest that the apatite U-Pb ages of skarns and intrusions are 229-228 Ma, with the monzogranite emplacement slightly later than the syenogranite emplacement and skarn formation. The apatites in the skarn ores have high HREE contents and strong negative Eu anomalies, indicating the transition from magmatic crystallization to hydrothermal exsolution.