Fault geometry and fluid-rock reaction: Combined controls on mineralization in the Xinli gold deposit, Jiaodong Peninsula, China

Abstract

The structures and fluid-rock reaction in the Xinli gold deposit, Jiaodong Peninsula, were investigated to further understand their combined controls on the development of permeability associated with ore-forming fluid migration. Orebodies in this deposit are hosted by the moderately SE-to S-dipping Sanshandao–Cangshang fault (SCF). Variations in both dip direction and dip angle along the SCF plane produced fault bends, which controlled the fluid accumulation and ore-shoot formation. Gold mineralizations occurred in early gold–quartz–pyrite and late gold–quartz–polymetallic sulphide stages following pervasive sericitization and silicification alterations. Theoretical calculation indicates that sericitization caused 8–57% volume decrease resulting in the development/enlargement of voids, further increase of grain-scale permeability, and resultant precipitation of the early gold–quartz–pyrite pods, which destroyed permeability. The rock softening produced by alterations promoted activities of SCF secondary faults and formation of new fractures, which rebuilt the permeability and controlled the late gold–quartz–polymetallic sulfide veins. Quantitative studies on permeability distributions show that the southwestern and northeastern bend areas with similar alteration and mineralization have persistent and anti-persistent permeability networks, respectively. These were likely caused by different processes of rebuilding permeability due to different stress states resulting from changes in fault geometry.