Abstract

The duration of hydrothermal mineralization processes is one of the most important genetic parameters. The modern appearance of deposits is determined not only by the ore deposition processes, but also by the subsequent alteration of ores. A particular place in the geological history of deposits is occupied by the processes involved in the preliminary concentration of ore components. An isotope–geochronological study of the hydrothermal minerals of the Vostok field—the largest of the molybdenum–uranium deposits in Central Asia and Kazakhstan—using the U–Pb (ID-TIMS) method revealed that the U–Pb isotope systems of its uranium ores clearly captured an event that took place 267 ± 7 Ma ago. The obtained dating is consistent with the results of isotope dating of pitchblende, near-ore metasomatites, and postore quartz–carbonate veins obtained by the Xe_n–Xe_s, K–Ar, and Rb–Sr methods. This event is associated with the formation of postore quartz–carbonate veins, the extraction of radiogenic lead from primary uranium ores (accumulations), and its redeposition in sulphides of different ages. As a result of this event, the primary uranium ores of the Vostok deposit have lost their U–Pb geochronometric markers. Information on the age of primary ores has been preserved in the form of “frozen” isotope ratios, ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb, in redeposited galena. The data from studying the isotope composition of lead from redeposited galena show that the formation of primary uranium ores that served as the source of this lead (or the initial stage of uranium ore formation) occured 413 ± 7 Ma. The estimate of the formation time of primary ores of the Vostok deposit is quite consistent with the lower age limit of this process, which follows from the recently obtained (Golubev et al., 2020) U–Pb and Rb–Sr datings of ore-hosting volcanic rocks and granite porphyries (434–424 Ma) in the Balkashino ore field.

中文翻译：

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根据 U-Pb (ID-TIMS)、Pb-Pb、Xen-Xes、K-Ar 和 Rb-Sr 方法，Vostok 热液铀矿床（北哈萨克斯坦矿区）的年龄

摘要

热液矿化过程的持续时间是最重要的成因参数之一。矿床的现代外观不仅取决于矿石的沉积过程，还取决于随后的矿石蚀变。矿床地质历史中的一个特定位置是矿石成分的初步浓缩过程。使用 U-Pb (ID-TIMS) 方法对 Vostok 油田（中亚和哈萨克斯坦最大的钼铀矿床）的热液矿物进行同位素-地质年代学研究表明，其铀的 U-Pb 同位素系统矿石清楚地捕捉到了发生在 267 ± 7 Ma 前的事件。得到的测年结果与Xe获得的沥青闪石、近矿交代岩和矿后石英-碳酸盐脉的同位素测年结果一致。_n –Xe _s、K–Ar 和 Rb–Sr 方法。这一事件与矿后石英碳酸盐脉的形成、从原生铀矿石（堆积）中提取放射性铅及其在不同年龄的硫化物中的再沉积有关。由于这一事件，Vostok 矿床的原生铀矿石失去了 U-Pb 地质年代标记。有关原生矿石年龄的信息以“冻结”同位素比²⁰⁶ Pb/ ²⁰⁴ Pb 和²⁰⁷ Pb/ ^{204的形式保存}铅，在重新沉积的方铅矿中。研究重新沉积方铅矿中铅的同位素组成的数据表明，作为这种铅来源的原生铀矿石（或铀矿石形成的初始阶段）的形成发生在 413 ± 7 Ma。Vostok 矿床原生矿石形成时间的估计与该过程的年龄下限非常一致，这是根据最近获得的（Golubev 等，2020）矿石的 U-Pb 和 Rb-Sr 测年得出的。在 Balkashino 矿田中拥有火山岩和花岗斑岩（434-424 Ma）。