Through a study of the petrology ot nost rocks which contain anorthite mega-crysts of occurrence of anorthite and chemical composition of anorthite and related minerals, the authors consider that anorthite megacrysts are authigenic.Anorthite occurs along the bedding in structural zones of weakness and is not restricted within the synsedimentary slumping structure. These features of distribu-tion and the relationship of some elements between anorthite and other minerals indicate that anorthite is the product of reaction of circulating alkaline solutions rich in Al and Si with carbonates during the period of the Indosinian orogeny.The results of this work suggest that the association of authigenic anorthite with bedded orebodies in the Dachang ore district may serve as the evidence that the mineralization is related to the circulation underground hot water.