Fluid inclusions study of the Changhanboluo Pb-Zn-Ag deposit, Inner Mongolia

The Changhanboluo Pb-Zn-Ag deposit is located on the northern margin of North China Craton. The concealed orebodies are hosted in quartz porphyry, quartz monzonite, andesite and the contact zone of different lithofacies as lodes and lens. The hydrothermal ore-forming process of the Changhanboluo deposit includes three stages, i.e., the early, middle and late stages: The early stage is disseminated metallogenic stage; the middle stage is lode metallogenic stage which can be divided into quartzpyrite±chalcopyrite±arsenopyrite sub-stage (Ⅰ) and quartz-polymetallic sulfide sub-stage (Ⅱ); the late stage is quartz-carbonate stage. The disseminated metallogenic stage developed NaCl-H2O (W-type) and H2O-CO2 (C-type) fluid inclusions (Fls). The homogeneous temperatures of the W-type and C-type fluids in the disseminated metallogenic stage are mainly 272℃-349℃, with salinities ranging from 1.40% to 7.31% NaCl eqv. The lode metallogenic stage mainly developed W-type fluids. Therefore, fluids of stage 1 mainly have homogenization temperatures between 198 and 348℃, with salinities ranging from 1.40% to 5.86% NaCl eqv.. The stage Ⅱ fluids yield homogenization temperatures of 118℃-199℃ and salinities of 1.40%-4.80% NaCl eqv. In the late stage, the fluids have homogenization temperatures of 106° C-157° C and salinities of 0.88%-2.24% NaCl eqv. The depth of the disseminated mineralization is about 1.8-2.5 km. The mineralization depth of the middle stage (Ⅰ) is possibly at 0.1-1.5 km, while the middle stage (Ⅱ) shows much shallower depth, which is near the surface. The fluid inclusions in the Changhanboluo Pb-Zn-Ag deposit are characterized by low temperatures and low salinities. The mixing of hot magmatic fluids and meteoric water resulted in rapid precipitation of ore-forming materials.