Age and genesis of the ji’an Pb-Zn deposit in the east of Jiao-Liao-Ji Belt, NE China

• The Ji’ an deposit is a skarn Pb–Zn deposit formed in Early Cretaceous. • The ore-forming fluids and materials originated from the dimetasomatism between the parent magma of quartz porphyry and the limestone of Zhangxia Formation. • Fluid immiscibility and mixing play an important role in the metal precipitation. The Jiao-Liao-Ji Belt (JLJB) is located in the northeast of the North China Craton, which is a gathering place for polymetallic deposits dominated by magmatism. The Ji’an Pb-Zn deposit is situated in the eastern region of the JLJB, where ore bodies were hosted in the Cambrian brecciated limestone. Four mineralization stages have been identified here: the retrograde skarn (Pre-ore), early quartz-sulfide (I), late quartz-sulfide (II) and quartz-carbonate (III) stages. Fluid inclusions (FIs) include three types which are gas-dominated (W 1 -type), liquid- dominated (W 2 -type) and pure-liquid (PL-type) FIs. During the Pre-ore and I Stages, the hydrothermal fluids are characterized by a H 2 O–NaCl ± CO 2 composition, with temperature variations spanning 271–474°C and salinity levels ranging from 4.32–13.30 wt% NaCl eqv. The latter stages, however, are characterized by a simpler H 2 O–NaCl system, with temperatures and salinity levels measured at 131–283 °C and 2.39–9.6 wt% NaCl eqv, respectively. Isotopic analysis of hydrogen and oxygen suggests that these hydrothermal fluids predominantly originate from magmatic source, with subsequent admixture with meteoric waters. Furthermore, in-situ sulfur isotope studies indicate the magmatic genesis of the Pb-Zn sulfides in the Stage II, whereas the Stage III sulfides are deduced to derive from both magmatic and sedimentary sources. in-situ lead isotopic data further infer that the origins of the Pb-Zn minerals are linked to the crust and orogenic belts. Hydrothermal apatite has a U-Pb age of 119 ± 3.4 Ma, which constrain the formation of the deposit to the Early Cretaceous. According to comparative assessments with typical deposits, the Ji’an Pb-Zn deposit is a skarn type formed by metasomatic interactions between subsurface granitic magmas and the limestone of the Zhangxia Formation during the Early Cretaceous. Immiscibility and mixing of hydrothermal fluids play an important role in metal deposition.