Jinchang Au deposit in Mojiang is characterized by long history, complicated periods and deep original source, but the geologic research is lacked in this area. The research reveals that the typomorphic minerals(such as magnesiochromite, chromopicotite, kaemmererite etc.) which indicate that the ultrabasic rock is involved in genesis is occur in Jinchang alteration zone, and a relatively large amount of typomorphic mineralogical composition which is characterized by Cr and indicates that the ultrabasic rock is involved in genesis occurs commonly in the alternative rocks and the ore-bodies. Mg is the second characteristic of typomorphic mineralogical composition of Jinchang Au deposit.