中国最古老铀矿床成矿年龄及铅同位素示踪铀成矿省

Uranium Ore-forming Ages of the Oldest Uranium Deposits in China and the Tracing of Uranium Metallogenic Provinces with Lead Isotopes

中国发现的最古老铀矿床(点)集中分布在华北地台东部的鞍本地区及辽东地区其他铀矿化点、华北地台中部的中条山地区和华北地台西部的龙首山地区。通过多年来对这些地区所积累的47件晶质铀矿U-Pb同位素数据的整理处理,指出中国最古老铀矿床(矿点)尽管其成矿地域、成矿类型、成矿地质背景不同,但成矿年龄基本相同,在(1800±100)Ma左右成矿,铀成矿作用发生在早前寒武纪末吕梁造山期,而矿床可能主要在燕山运动期受到叠加改造。对华北地台东部诸省200多件方铅矿的铅同位素数据进行铅同位素数据处理:利用H-H模式分别计算了这些矿石铅源区的μ值及Th/U值,并统计了各省区μ值及Th/U值的均方差S和变异系数X;利用Pb构造模式获取不同地区铅的物质来源。文中还报道了特高放射性成因矿石铅的存在地域。矿石铅同位素示踪表明,我国辽东地区应该是很好的潜在铀成矿省。

The oldest uranium deposits discovered in China are situated in eastern North China Platform like Anshan - Benxi area of eastern Liaoning Province, central North China Platform like Zhongtiaoshan area, and western North China Platform like Longshoushan area. Researches on 47 ore-forming ages of uranium deposits and more than 200 ore lead isotopic samples in the North China Platform suggest that the oldest uranium deposits in China were all formed about （ 1800 ± 100） Ma ago in spite of their different ore-forming environments, regional conditions and geological backgrounds. Uranium mineralization occurred in the Luliang orogenic period at the end of Early Precambrian, and the uranium deposits underwent reformation and superimposition during the Yanshanian tectonic movement. Through the calculation of μ and Th/U of original lead ore by the H-H model and a statistical analysis of average squared differences （S） and alteration coefficients （X） of and Th/U in different provinces, the authors obtained both lead isotope composition by the single stage model and that of the region where obvious high anomalous lead isotopes exist. Ore lead isotope tracing suggests that eastern Liaoning area is one of the best potential uranium mineralization provinces.