Early Permian lode gold mineralization in the northern North China Craton: Constraints from S-Pb isotope geochemistry and pyrite Re-Os geochronology of the Chaihulanzi deposit

Abstract

• A newly recognized Early Permian gold deposit in the Chifeng-Chaoyang gold district. • The Chaihulanzi deposit is an atypical orogenic gold deposit. • A metasomatized lithospheric mantle derivation for the ore metals. The Chaihulanzi gold deposit is located in the Chifeng-Chaoyang region in the northern margin of the North China Craton. It contains auriferous quartz veins and disseminated mineralization in hydrothermal alteration zones, controlled by NW-striking faults in mica schist of the Neoarchean-Paleoproterozoic Dayingzi Formation. Pyrite and pyrrhotite are the predominant ore minerals. Gold mineralization is closely associated with pyritic and phyllic alteration. The ore-forming process can be divided into four stages involving stage I quartz-pyrite; stage II quartz-pyrite-pyrrhotite-chalcopyrite; stage III quartz-polymetallic sulfides; and stage IV quartz-calcite. Gold generally occurs in fissures or as inclusions within stage II pyrite and quartz. Stage II pyrite yields a well-defined 187 Re/ 188 Os versus 187 Os/ 188 Os isochron age of 291.8 ± 3.4 Ma (MSWD = 2.1). This is the first record of Early Permian gold mineralization in the Chifeng-Chaoyang district. Sulfur and lead isotope data of stage II pyrite and pyrrhotite show that ore metals are principally derived from metasomatized lithospheric mantle, with few involvements of crustal materials. On the basis of available evidence, we suggest that the Chaihulanzi deposit is an atypical subduction-related orogenic gold deposit. These new findings might have important implications for future gold exploration in the area.