Original rocks,ages,and its significance for the wall rock of Niutougou gold deposit in northern Helan Mountains

The Niutougou gold deposit is located in the western margin of Ordos block and the northern Helan Mountains. The ore-bearing wall-rocks are a set of medium-deep level metamorphic rocks of the second subgroup of Zongbili Group ( Pt1Z2 ) in Paleo-Proterozoic. Main types of the metamorphic rocks include granulite and biotite-plagioclase-gneiss. Petrochemical study shows that the original rock of the granulite is clastic rock and the original rock of the biotite-plagioclase-gneiss is granodiorite. SIMS zircon U-Pb dating shows that the age of the metasedimentary rock is 2120Ma,biotite-plagioclase-gneiss and diabase are of 1950 ± 8. 9Ma. Authors suggest that the granodiorite should be taken as an intrusive unit apart from metasedimentary system.