Relationship between bitumen and zinc–lead mineralization in the Nanmushu zinc–lead deposit, northern margin of Sichuan Basin, China

The Nanmushu zinc–lead deposit is hosted by the Dengying Formation (Z 2 dn ) and lies on the northern margin of Sichuan Basin, China. The deposit is a Mississippi Valley-type (MVT) lead–zinc deposit associated with bitumen. The bitumen can be divided into early and late bitumen, although the abundant late bitumen is unrelated to the Zn–Pb orebodies. Mineral compositions and fluid inclusion characteristics indicate a genetic relationship between Zn–Pb mineralization and oil reservoirs. The two stages of bitumen were derived from the Guojiaba Formation (Є 1 g ), which provided the materials for the Zn–Pb deposit and was also the source of the oil reservoir. The minerogenic age of the ore deposit coincides with the formation and damage of the first-stage oil reservoir. The hydrocarbons extracted Zn–Pb material during primary migration and secondary migration of organic fluids. With the Nanzheng Uplift movement strong, the hydrocarbons underwent thermal cracking and thermochemical sulfate reduction that produced CH 4 and H 2 S. Sphalerite and galena are formed near the oil-water interface. The minerals tended to sink and form deposits in the Dengying Formation due to their higher density.