地幔流体与铀成矿作用

MANTLE-DERIVED FLUIDS AND URANIUM MINERALIZATION

文中探讨了地幔流体铀成矿作用的可能性 ,并以相山世界级铀矿田为例 ,阐明了地幔流体铀成矿作用的主要特征。岩石圈之下存在一个富含放射性生热元素的富集圈 ,在造山带崩塌阶段 (岩石圈拆沉或减薄 )以及弧后拉张环境下 ,富集圈中的U、Th将随地幔流体一起上升迁移至地壳中直接成矿。相山铀矿床就是在弧后拉张环境下由当地富集地幔流体上升迁移至早先火山杂岩裂隙带中沉淀成矿而形成的。弧后拉张环境有利于地幔流体上升 ,早先的火山通道和火山杂岩中非常发育的裂隙为成矿流体提供了迁移和赋矿空间 ,成矿与幔源岩浆活动 (煌斑岩 )相伴随 ,成矿流体和成矿物质具有幔源特征 ,地幔中放射性生热元素富集圈为其提供了强大的物质基础 ,从而形成了相山超大型铀矿田。

Taking the world-class Xiangshan uranium deposit field as an example, we have discussed in this paper the possibility of uranium mineralization of mantle-derived fluid and demonstrated their main characteristics. There exists an enrichment zone of U and Th beneath the lithosphere. Such U and Th components may have a direct contribution to the formation of uranium ores under convenient conditions such as extension setting and existence of deep-faults. At Xiangshan the uranium reservoir in the local enriched mantle associated with paleo-Pacific oceanic plate subduction may provide uranium mineralization with significant amounts of metallogenetic materials; Early Cretaceous back-arc extension setting and boundary deep-faults of Gan-Hang extension basin facilitated the upward migration of the local enriched mantle-derived fluid; a great deal of fracture zones occurred in the Xiangshan volcanic complexes may provide space for filling of ore-forming fluid; the shallow meteoric water in fractures of volcanic rocks may result in temperature decreasing and dilution of deep-seated ore-forming fluid and thus the precipitation of uranium ores. All together, the world-class Xiangshan uranium deposit field was thus formed.