Fluid inclusions and formation mechanisms of the Dongjianian silver deposit in Lingbao City, Henan Province, China

The Dongjianian silver deposit, located on the southern margin of the Xiaoqinling Mountains, is controlled by the secondary structures of the Xiaohe fault and is the first large precious metal deposit discovered in the southern belt of the Xiaoqinling Mountains. This deposit has three hydrothermal metallogenic stages, namely the quartz-pyrite metallogenic stage (Ⅰ), the dominant quartz-polymetallic sulfide metallogenic stage (Ⅱ), and the quartz-carbonate metallogenic stage (Ⅲ). Three types of inclusions have primarily developed in the ore bodies, namely gas-liquid two-phase inclusions (W-type), CO2-bearing inclusions (C-type), and pure CO2 inclusions (PC-type). Stage I primarily witnessed the development of C- and W-type inclusions and a small quantity of PC-type inclusions, and stage II mainly saw the development of W-type inclusions and a small amount of C-type inclusions. The quartz fluid inclusions formed in stages I and II have homogenization temperature ranges of 151~270 ℃ and 126~240 ℃, respectively, which exhibits a downward trend. Their salinity varies slightly in the ranges of 3.8%~22.42% NaCleqv and 4.16%~20.48% NaCleqv, respectively, indicating a low-salinity environment. Their CO2 content transformed from enrichment into deficiency. The metallogenic pressure and depth were estimated to be 22.08~76.6 MPa and 3.77~7.13 km, respectively. Therefore, the Dongjianian silver deposit is a low-salinity medium- to low-temperature meso-epithermal silver deposit.