Identification and significance of methane-rich fluid inclusions in Changba Pb-Zn deposit, Gansu province

Changba Pb-Zn deposit, Gansu Province, China, is considered as SEDEX deposit. But researches about ore-forming fluid, especially fluid inclusions on it still lacked. This study made a systematic research works on fluid inclusions in Changba Pb-Zn deposit and for the first time identified the mono-phase methane-rich fluid inclusions, with homogenization temperatures between -114 similar to -80 degrees C; These methane-rich inclusions have two types of lower temperature phase behaviors on freezing and heating run. Laser-Raman microprobe analysis show that the volatile is dominantly CH4 with some H2S and minor amount of N-2, CO2. Methane-rich fluid in Changba deposit might originate from the reduction of seawater by the organics on the seafloor. The identification of methane-rich fluid further verified the submarine hydrothermal exhalative genesis of Changba Ph-Zn deposit.