Geochronology and significance of granites associated with gold deposits in the Jidong Area, China

The Jidong area is located on the north margin of the North China craton. I t is a nucleus composed of the oldest rocks in China. Precambrian metamorph ic rocks with various Phanerozoic granitoids invaded are widespread. Gold d eposits here have close spatial relations to granitoids. Some deposits occu r within them and others in the outer zone of the contact belt of the intru sion, extending thousands of metres. There have been controversial views in regard to the relations of the deposits to the intrusions although traditi onal techniques have been used to date the intrusions. In order to solve su ch a problem, the SHRIMP technique was adopted to date the U-Pb ages of zir con collected from the Yuerya intrusion which hosts the large-sized Yuerya Au deposit and Qingshankou intrusion 2 km away from the Jinchangyu (larger- sized) Au deposit. Analysis shows that the ages of 175+/-1 Ma and 174+/-3 M a for Yuerya intrusion and the age of 199+/-2 Ma for Qingshankou granite in dicate the Early Yanshanian stage of the Mesozoic. The Yuerya intrusion als o contains inherited zircon aged at about 2500 Ma, indicating that part of its source materials are Archaean metamorphic rocks. In addition to the SHR IMP data of this study, a great deal of data related to the alteration of A u deposits indicate the formation of the deposits at the Yanshanian stage o f the Mesozoic, so the ore formation of Au deposits is inferred to relate t o granitic intrusion.