Formation of the Lianhuashan Cu deposit in the southern Great Xing'an Range, NE China: Constraints from fluid inclusions, whole-rock geochemistry, zircon U-Pb geochronology, and H-O-S-Pb isotopes

The medium-sized Lianhuashan Cu sulfide deposit is located in the southern Xing'an Range of Inner Mongolia, NE China. The zoned massive sulfide vein ores are hosted mainly in the Permian Dashizhai Formation, and the ore veins are controlled by NW-NNW-trending structures. The ore-forming process comprises four stages: arsenopyrite-quartz (I); chalcopyrite-pyrite-quartz (II); pyrite-chalcopyrite-sphalerite-galena-quartz (III); and ore-barren sulfide-quartz-carbonate (IV). Three types of fluid inclusions (FIs), namely vapor-rich two-phase (LVtype), liquid-rich two-phase (VL-type), and daughter mineral-bearing three-phase (SL-type), are distinguished. Stage I, II and III contain all types of FIs (LV-, VL-, and SL-type), with homogenization temperatures (Th) of 268-462 degrees C, 230-382 degrees C and 180-340 degrees C and salinities of 3.4-52.3, 3.4-44.5 and 3.7-39.9 wt% NaCl eqv., respectively, whereas stage IV has only VL-type FIs, with Th = 152-232 degrees C and salinity = 3.4-7.9 wt%. Fluid geochemical data show that the Lianhuashan ore fluids were of medium-high temperature (236-382 degrees C), high- salinity (31.5-44.5 wt%), and relatively oxidizing conditions, typical of a NaCl-H2O system. The micro- thermometric and H-O isotope data (delta O-18(H2O) =- 9.0 to 6.1 %o; delta D =- 149.0 to- 99.0 %o) indicate that the ore fluids were initially magmatic with later meteoric water incursion. The sulfide S (delta S-34 =- 2.9-3.8 parts per thousand) and Pb (Pb-206/Pb-204 = 17.954- 18.492, Pb-207/ Pb-204 = 15.427- 15.739, Pb-208/Pb-204 = 37.815- 38.357) isotopes support that the metals were magmatic-derived. Fluid boiling, cooling, and meteoric water mixing were likely the main ore precipitation mechanism at Lianhuashan. We suggest that Cu minerals at Lianhuashan were precipitated with boiling at similar to 1 km depth. For the ore- forming granodiorite porphyry (zircon U-Pb age: 252.8 +/- 1.8 Ma), geochemical data indicate that the primary magma was formed by partial melting of the thickened or delaminated lower crust. Integrating the available age, geological, and geochemical evidence, we suggest that mineralization at Lianhuashan is spatial-temporal and genetically associated with the granodiorite porphyry, and was formed in a volcanic arc setting after the PaleoAsian Ocean closure.