法国贝尔纳尔丹铀矿床热液蚀变与成矿特征研究

Study on the hydrothermal alteration and metallogenic characteristics of Bernardan uranium deposit in France

在总结法国贝尔纳尔丹花岗岩型铀矿床蚀变类型、矿物组合、矿物生成顺序等矿化特征基础上,对矿床的蚀变特征和成矿模式进行了探讨。该矿床含矿围岩分别为英云闪长岩-花岗闪长岩(G型)和中-粗粒过铝质二云母浅色花岗岩(L型),其中L型花岗岩为含矿围岩。矿床中与铀矿化密切相关的蚀变类型较多,最典型的当属由富18 O流体进入花岗岩裂隙形成的变正长岩化蚀变,使花岗岩更为碎裂,增加了成矿空间并在之后的流体作用下发生再次蚀变,形成伊利石-蒙脱石并吸附了铀石,伊利石化-蒙脱石化越强烈,铀矿化程度越高。铀矿化是两次蚀变的产物,矿体的形态不仅受变正长岩中形成的裂隙构造所控制,同时矿化还受流经变正长岩的流体和表生作用的控制。

By summarizing the mineralization characteristics such as alteration type,mineral assemblage and mineral formation sequence of the Bernardan granite type uranium deposit in France,this paper discussed the alteration and metallogenic characteristics of the deposit.The ore-hosting surrounding rocks of the deposit are tonalite-granodiorite(G-type)and peraluminous two-mica leucogranites(L-type),in which L-type granite is ore-hosting rock.There are many types of alteration closely related to uranium mineralization in the deposit,the most typical one is episyenitie alteration formed by 18 O-rich fluid entering granite fissures,resulting in more fragmentation of granite,increased ore-forming space and re-alteration under the action of subsequent fluids,forming Illite-montmorillonite and adsorbing uraninite;the stronger the illite-montmorillonite is,the higher the degree of uranium mineralization is.Uranium mineralization is the product of two alterations.The shape of the orebody is controlled not only by the fracture structure formed by episyenitie,but also by the fluid and epigenetic processes flowing through episyenitie.