九瑞矿集区志留纪西坑组疑源类化石和碎屑锆石年代学研究及其地层意义

九瑞矿集区是长江中下游成矿带中一个最重要的铜金多金属矿集区,区内发育了城门山铜矿、武山铜矿、洋鸡山金矿等重要的多金属矿床。本文对该区域的城门山和望夫山两个剖面的疑源类化石及碎屑锆石开展了详细研究,在城门山剖面原来被认为是志留纪西坑组的地层中发现了化石面貌为新元古代或早寒武世的化石,结合碎屑锆石U-Pb定年工作,推测其时代为早寒武世,该地层与上覆地层泥盆系五通组之间存在一个明显的角度不整合。望夫山剖面仍旧为正常志留纪西坑组地层,疑源类化石和碎屑锆石U-Pb年代学研究表明九瑞西坑组沉积时代应该晚于特列奇阶。九瑞矿集区“扬子抬升”的开始时间应该晚于特列奇阶,结束时间应该晚于中泥盆世早期。

Acritarch fossil and detrital zircon geochronology study of the Xikeng Formation, Silurian, in Jiurui metallogenic district, Jiangxi Province

Jiurui metallogenic district is one of the most important ore concentration areas in the Middle-Lower Yangtze metallogenic belt of eastern China, where occurred Chengmenshan copper deposit, Wushan copper deposit, Yangjishan gold deposit and many other import Cu-Au polymetallic ore deposits. In this paper, we carried out a systematic study on the Acritarch fossils and detrital zircon U-Pb ages from two sections in this district (Chengmenshan and Wangfushan). At Chengmenshan section, we found that the age of the fossils, which comes from the stratum that used to be considered as Early Silurian, is actually Neoproterozoic or Early Cambrian. Combining with the data of the detrital zircon geochronology, we suggest that this stratum should be Early Cambrian. Field observation also revealed that there exists an angular unconformity between Devonian Wutong Formation and this possible Early Cambrian stratum. However, at Wangfushan, the so-called Silurian Xiken Formation is confirmed, and the age for this stratum in the Jiurui district is suggested to be later than Telychian of Silurian epoch. The beginning time of "Yangtze Uplift" in Jiurui district is thought to be later than Telychian and the ending time should be later than early Middle Devonian.