Composition and evolution of fluids forming the Baiyinnuo'er Zn-Pb Skarn Deposit, Northeastern China: insights from laser ablation ICP-MS study of fluid inclusions

The Baiyinnuo'er skarn deposit is one of the largest Zn-Pb deposits in northeastern China, with 32.74 million metric tons (Mt) resources averaging 5.44% Zn, 2.02% Pb, and 31.36 g/t Ag. The deposit formed in three stages: the preore stage (prograde skarn minerals with minor magnetite), the synore stage (sulfides and retrograde skarn minerals including calcite and minor quartz), and the postore stage (late veins composed of calcite, quartz, fluorite, and chlorite; cutting the above mineral assemblages). In this study we analyzed the composition of single fluid inclusions using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to (1) determine the composition of the fluids and the evolution through the stages, (2) infer the fluid and metal sources, and (3) explore the metal deposition mechanisms. The preore fluids trapped in pyroxene have higher homogenization temperatures (432°–504°C), higher salinity (36.5–46.1 wt % NaCl equiv), and higher concentrations of Zn (~0.9 wt %), Pb (~1.4 wt %), and other elements (e.g., Na, K, Li, As, Rb, Sr, Cs, Ba, Cl, and Br) than synore mineralizing fluids (<370°C, <10 wt % NaCl equiv, ~450 ppm Zn, and ~290 ppm Pb). The postore fluids show lower temperatures (<250°C) and a rather dilute composition (