Chaihulanzi gold deposit is an alteration-type mesothermal gold deposit, situated in the northern margin of North China Plate. Its metallogenesis is related to the early Mesozoic augite diorite, in which anumerous xenoliths were occurred, at the northern part of the ore deposit. The xenoliths at the Chaihalanzi gold deposit maybe grouped as mafic and amphibolite xenoliths. The mafic xenoliths usually have fine blastic texture and cribriform blastic texture, mainly consist of clinopyroxene, hypersthene and mafic plagioclase, and various amount of amphibolite and phlogopite which was formed in late retrograde metamorphism. Amphibolite xenoliths has granoblastic texture and replacement texture, mainly consists of amphibolite, plagioclase and less amount of pyroxene and quartz. Geochemistry, P-T conditions and isotopes of the mafic xenoliths indicates that it has experienced granulite metamorphism, was from continental lower crust and resulted from the magmatic underplating during early Mesozoic. The amphibolite xenoliths were from the upper part of lower crust and the lower part of middle crust, bring up to the shallow area of crust . The occurrence of mafic granulite xenoliths and regional geotectonic data indicate that the lithosphere of studied area was in extensional state, which has provided favorable tectonic background for basalt underplating. The similarity in geochemistry and isotopic composition between host rock and mafic granulite xenoliths indicate that they were the product evolved from the same magma sources. The cumulates deposited from early underplated basalt magma were heated by later arrived basalt magma, experienced granulite facies metamorphism, then entrained and were transported into shallow crust as mafic granulite xenoliths by the evolved diorite magma resulted from underplated basaltic magma. The closely relationship between mafic granulite xenoliths, host augite diorite and gold deposit suggests that the underplating during early Mesoic had been played an important role to the ore source, the formation and migration of ore-forming fluids and the precipitation and enrichment of in Chaihulanzi gold deposit, H2O and CO2 constitutes is key factors to control the formation and evolution of ore-forming fluids. The occurrence of the mafic xenoliths vigorously supports the point of view that the metallogenetic material of Chaihulanzi gold deposit was from the deep area.