Genesis of the Xihuashan Au Deposit in Haiyuan, Ningxia Hui Autonomous Region, <scp>NW</scp> China: Evidence From Trace Elements and Stable Isotopes

ABSTRACT The Xihuashan Au‐Cu deposit is among the important polymetallic metallogenic prospects discovered in recent years in Haiyuan, Ningxia Hui Autonomous Region. There is strong tectonic activity and mineralisation of Au, Cu, Pb and Ag in the study area, so this deposit is a typical polymetallic mineralised concentration zone. To investigate the nature and origin of the ore‐forming fluids and the genesis of the deposit in the Xihuashan Au deposit, a comprehensive study was conducted on the rare earth elements (REE) and trace elements, and HOS isotopes of the ore‐bearing lamprophyres and ores in the study area. The results show that the ore‐bearing lamprophyres have the total rare earth element (ΣREE) contents ranging from 84.77 × 10 −6 to 461.01 × 10 −6 , the light rare earth element (LREE) contents ranging from 64.50 × 10 −6 to 424.81 × 10 −6 , the heavy rare earth element (HREE) contents ranging from 20.27 × 10 −6 to 36.20 × 10 −6 , the δEu values range from 0.62 to 0.98, and the δCe values range from 0.86 to 1.00. These suggest a multi‐source origin for these lamprophyres. The δD V‐SMOW values of hydrothermal quartz range from −72‰ to −92‰, and the δ 18 O fluid values range from 6.7‰ to 12.0‰, indicating that the ore‐forming fluids are multi‐sourced. Furthermore, the S isotope results imply that the ore‐forming materials are largely derived from magmatic sources, with a minor contribution from the wall rocks. Based on the geological evolution of the North Qilian orogenic belt, the intense tectonic‐magmatic activity during the late Caledonian period—closely associated with gold mineralisation—provided a crucial heat source and energy. This activity triggered the mobilisation, migration and subsequent enrichment of siliceous and mineralised components from the Haiyuan Group. These components were ultimately concentrated within NE‐ and nearly E–W‐trending transtensional fault zones. After the formation of the earliest mineralised quartz veins, decreasing temperature and pressure, along with ongoing mineralisation, alteration and tectonic activities, led to the fragmentation of the initially formed quartz veins. Subsequent magma differentiation resulted in late‐stage mineralisation, accompanied by the emplacement of lamprophyre veins and the formation of new mineralised quartz veins. The gold‐mineralizing elements underwent multistage enrichment from different sources to form different types of gold mineralisation. Compared with a typical orogenic gold deposit, the Xihuashan Au deposit is a product of orogenic movement in the North Qilian orogenic belt and is an orogenic‐type Au deposit.