^(40)/Ar^(39)Ar Ages of Auriferous Quartz Veins from the Fengyang and Zhangbaling Regions and Their Geological Significance

Geotectonically the Fengyang and Zhangbaling regions bel ong to the North China craton and the Dabie-Sulu orogene, respectively. Neo-A rchean gneiss and amphibolite and metamorphosed sea-facies sodic volcanic rocks are the main outcrops in the two regions, respectively. The Zhangbaling terran e strike-skipped along the Tancheng-Lujiang fault zone in Mesozoic and Cenozoi c eras and got close to the Fengyang terrane. Mesozoic Yanshanian intrusions oc cur broadly in the two regions. Gold-bearing quartz veins occur in the metamor phic rocks in the Fengyang region and in the granodiorite and metamorphosed sea\ |facies sodic volcanic rocks in the Zhangbaling region. Generally, the formatio n of the auriferous quartz veins involved three stages. At the first stage, go ld-poor sulfide quartz veins were formed; at the second stage gold-rich quartz sulfide veins were formed; and at the third stage gold-poor barite and/or carb onate veins were formed. The \{\{\}\+\{40\}Ar\}/\{\{\}\+\{39\}Ar\} step-heatin g plateau ages of the first-stage and the second-stage quartz aggregates from the Zhuding, Maoshan and Shangcheng gold deposits range between \{116.1\}±\{0.6 \} Ma and \{118.3\}±\{0.5\} Ma and are pretty close to their least apparent age s and isochronal ages, respectively. All plateau, least apparent and isochronal ages range between \{113.4\}±\{0.4\} Ma and \{118.3\}±\{0.5\} Ma, which are c onsidered as the formation age range of the quartz. It is reasonable and reliab le to take the \{\{\}\+\{40\}Ar\}/\{\{\}\+\{39\}Ar\} age range of the quartz as the formation age range of gold-bearing quartz veins on the basis of spatial re lationship between gold-bearing quartz veins and their country rocks. The gold deposits in the two regions were formed in Aptian, Cretaceous, when the Tanchen g-Lujiang fault zone moved as a normal fault with slightly right-lateral strik e-skip, was extensional and experienced very strong magmatic process. It is sh own that the magmatic hydrothermal fluid is a very important part of the gold or e-forming hydrothermal fluid in the Fengyang and Zhangbaling regions. The form ation of the gold ore deposits in the Fengyang and Zhangbaling regions had genet ic relations with the extensional movement of the Tancheng-Lujiang fault zone a nd magmatic activities and took place under the extensional dynamic condition in Late Cretaceous. Therefore, the extensional movement of the Tancheng-Lujiang fault zone presented the energy and space for magmatic and gold ore-forming pro cesses.