Fluid inclusion study of the Luoboling porphyry Cu-Mo deposit in the Zijinshan ore field, Fujian Province

The Luoboling porphyry Cu-Mo deposit locates in the northeastern Zijinshan ore field, and is hosted by Sifang granodiorite and Luoboling granodiorite porphyry. Orebodies are saddle-like in shape and contain various hydrothermal veinlets. Ore structures are mainly dissemination, stockwork and veins. According to mineral assemblages and crosscutting relationships, the ore-forming process and veins are divided into early, middle and late stages, i.e. the early stage feldspar-quartz magnetite molybdenite veins in the potassic silicate alteration zone, the middle stage quartz molybdenite chalcopyrite pyrite veins and anhydritechalcopyrite veins in the phyllic alteration zone and the potassic alteration zone overprinted by the phyllic alteration zone, and the late stage quartz gypsum pyrite veins in the phyllic alteration zone and the alunite-dickite-phyllic alteration zone. Fluid inclusions in minerals of the early and middle stages are mainly vapor-rich aqueous and daughter mineral-bearing inclusions, together with minor CO2-rich and liquid-rich aqueous inclusions; whereas the late stage minerals only contain liquid-rich aqueous inclusions. Homogenization temperatures and salinities of fluid inclusions in the early stage range from 420 degrees C to 540 degrees C and 0.4% to 62.9% NaCleqv, respectively; while those of the middle stage range from 340 degrees C to 480 degrees C and 0.5% to 56.0% NaCleqv,, respectively. Volume percentage of CO2 phase and oxygen fugacity of fluid inclusions in middle stage minerals are lower than those in the early stage. The late-stage liquid-rich aqueous inclusions yield homogenization temperatures of 140 degrees C similar to 280 degrees C and salinities of 0.4% 8.4% NaCleqv. It is concluded that boiling occurred in middle stage and caused precipitation of voluminous sulfides as stockworks; and that the fluids evolved into NaCl-H2O system, with an input of meteoric water.