Charmockites exposed inMashikou area,northwestern Hebei,intruded into tonalitic gneisses and assume lenticular and elliptical forms.Charnockites have low K2O,CaO,TiO2,high Al2O3,Na2O,rich LREE,depleted HREE,and strongly fractionated patterms.K/Rb ratios range from 500 to1000.These Chemical characteris are similar to those of typical Archean gray gneisses in the world. U-Pb single zircon isotope ages of the charmockites have been obtained.The coarse charmockites with block structure have ages of 2462±1Ma(Z9143B)and 2477+85-77Ma(Z9146),suggesting that charmockites were formed in the period of 2477—2461Ma.The fine-grained charmockite with gneissosity has an age of 2272+68-52.As the sample underwent multi-episodic Pb loss,the age has no clear geological implication.