CH4-containing fluid inclusion study of the Taipingchuan porphyry Cu-Mo deposit, Inner Mongolia

The Taipingchuan porphyry Cu-Mo deposit is located in northwest of Derbugan fault, Inner Mongolia. The age of host porphyry is about 200Ma. The mineralization of processes can be divided into early, middle and late three stages, which are characterized by assemblages of molybdenite-pyrite-quartz, chalcopyrite-pyrite-(molybdenite)-quartz, and carbonate-pyrite-quartz, respectively. Four types of fluid inclusions in quartz can be observed, i.e., three-phase daughter crystal-containing, two-phase daughter crystal-containing, CH4-H2O, and NaCl-H2O. The former three types were developed in early stage, the latter type is major inclusions in middle and late stages. Fluid inclusions in minerals formed in early, middle and late stages yield homogeneous temperatures of 340 similar to 500 degrees C, 160 similar to 361 degrees C and 148 similar to 220 degrees C, respectively, with salinities of 10. 1% similar to 55. 8% NaCleqv, 0. 7% similar to 10.9% NaCleqv and 2. 1% similar to 11.9% NaCleqv. Laser Raman spectroscopy shows that the early and middle stage inclusions contain H2O and CH4, whereas late-stage inclusions only trap H2O. Some fluid inclusions with similar temperatures are homogenized to different ways, and different types inclusions coexist in same minerals, which strongly suggest that fluid-boiling had occurred in the early stages. Authors believe that the mineralization of early stage may be mainly related to high temperature, high salinity and boiling fluid inclusion with CH4, the middle-late stage mineralization mainly be resulted by the mixing of fluids from different sources. Tectonic environment maybe the continental margin arc formed by the southward subduction of Mongolia- Okhotsk Ocean.