40Ar/39Ar ages of auriferous quartz veins from the Fengyang and Zhangbaling regions and their geological significance

• Published in: Acta geochimica 2003-07, Vol.22 (3), p.215-221
• Main Authors: Hanlong, Ying, Liqing, Zhao
• Format: Article
• Language: English
• Subjects: Age; Amphibolites; Barite; Carbonates; Cenozoic; Cratons; Cretaceous; Deposits; Fault lines; Fault zones; Geochemistry; Gneiss; Gold; Gold ores; Isotopes; Mesozoic; Metamorphic rocks; Mineral deposits; Mineralogy; Outcrops; Quartz; Radiometric dating; Regions; Sedimentary facies; Sulfides; Sulphides; Veins (geology); Volcanic rocks
• ISSN: 1000-9426; 2096-0956; 1993-0364; 2365-7499
• DOI: 10.1007/BF02842865

Geotectonically the Fengyang and Zhangbaling regions belong to the North China craton and the Dabie-Sulu orogene, respectively. Neo-Archean gneiss and amphibolite and metamorphosed sea-facies sodic volcanic rocks are the main outcrops in the two regions, respectively. The Zhangbaling terrane strike-skipped along the Tancheng-Lujiang fault zone in Mesozoic and Cenozoic eras and got close to the Fengyang terrane. Mesozoic Yanshanian intrusions occur broadly in the two regions. Gold-bearing quartz veins occur in the metamorphic rocks in the Fengyang region and in the granodiorite and metamorphosed sea-facies sodic volcanic rocks in the Zhangbaling region. Generally, the formation of the auriferous quartz veins involved three stages. At the first stage, gold-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 carbonate veins were formed. The^sup 40^Ar/^sup 39^Ar step-heating 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 ages 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 considered as the formation age range of the quartz. It is reasonable and reliable to take the^sup 40^Ar/^sup 39^Ar age range of the quartz as the formation age range of gold-bearing quartz veins on the basis of spatial relationship between gold-bearing quartz veins and their country rocks. The gold deposits in the two regions were formed in Aptian, Cretaceous, when the Tancheng-Lujiang fault zone moved as a normal fault with slightly right-lateral strike-skip, was extensional and experienced very strong magmatic process. It is shown that the magmatic hydrothermal fluid is a very important part of the gold ore-forming hydrothermal fluid in the Fengyang and Zhangbaling regions. The formation of the gold ore deposits in the Fengyang and Zhangbaling regions had genetic relations with the extensional movement of the Tancheng-Lujiang fault zone and 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 processes.[PUBLICATION ABSTRACT]