Metallogenesis And Metallogenic Prediction Of Lode Gold Deposits In The Western Chifeng-Chaoyang Gold Belt,Northern North China Craton

The study area is located in the western part of the Chifeng-Chaoyang gold metallogenic belt within the northern margin of the North China Craton.There are three lode gold deposits in this area(i.e.,Chaihulanzi,Lianhuashan,and Honghuagou).The orebodies occur as veins in the metamorphic rocks of the Neoarchean Wulashanyan Group.Rocks around the orebodies record intense hydrothermal alteration,with pyritic and phyllic alteration displaying close spatial relationships with gold mineralization.Auriferous quartz veins of the Honghuagou and Lianhuashan deposits are confined to the N-trending faults in the mafic gneiss.Pyrite is the dominant ore mineral,with lesser amounts of chalcopyrite,galena,magnetite,marcasite,and native gold.The ore-forming fluids of Honghuagou and Lianhuashan gold deposits belong to the medium temperature(275?360°C),low salinity(3.4?11.7wt.%Na Cl eqv.)H₂O-Na CL-CO₂±CH₄ system.Gold deposition was likely caused by fluid immiscibility.The Chaihulanzi gold deposit contains quartz-vein type and altered rock type mineralization,controlled by NW-striking faults in the graphite-bearing mica schist.Pyrite is the dominant ore mineral,followed by pyrrhotite and chalcopyrite,with minor galena,sphalerite,and native gold.The Chaihulanzi gold deposit is characterized by unique CH₄–rich fluid,which was most likely resulted from fluid-rock interactions between the graphite-bearing host rocks and initial ore fluids.H-O-C-He-Ar isotopic data reveal that the ore-forming fluids may have originated from mantle fluids.S-Pb isotopic compositios indicate a mixed crustal and mantle source for the ore-forming materials.Pyrite Re-Os dating reveals that gold mineralization at Chaihulanzi occurred at ca.292 Ma and was related to the subduction of the Paleo-Asian Ocean.Taken together,gold deposits in the study area can be classified as orogenic gold deposits.The occurrence of regional gold deposits is controlled by Archean metamorphic strata and fault structures.Notably,geophysical and geochemical anomaly regions are important gold prospecting indicators.Using the weight of evidence model of MRAS,we outlined six metallogenic prospecting areas(I-1,I-2,II-1,II-2,II-3,III-1).