幔源铀成矿作用的地球化学证据——以下庄小水“交点型”铀矿床为例

文章以小水铀矿床为例,探讨了下庄矿田"交点型"铀矿成矿物质来源。研究表明:(1)小水"交点型"铀矿床矿石主要由沥青铀矿、方解石和萤石等矿物组成,方解石产于矿脉两壁,萤石和沥青铀矿沉淀于矿脉中间部位;(2)沥青铀矿年龄为71.8~75.2 Ma,与围岩基性脉岩(120~100Ma)之间存在较大的矿岩时差;(3)萤石中流体包裹体的δD为-124.44‰~-97.08‰,δ18OSMON为7.40‰~11.02‰,具有幔源同位素组成特征;(4)在微量元素地球化学特征上,矿石与辉绿岩表现出相似性,与下庄花岗岩则具有明显的差异。笔者认为,下庄矿田小水"交点型"铀矿床成矿流体中的矿化剂来自地幔,铀源可能直接来自与辉绿岩具有相似源区性质的富集地幔;推测铀的沉淀成矿与富含CO2、F、H2S、U等组分的超临界态成矿流体在临界点附近发生沸腾作用相关。

Geochemical evidences for mantle-derived uranium metallogenesis:A case study of Xiaoshui intersection-type uranium deposit in Xiazhuang area

Based on a case study of Xiaoshui uranium deposit,the source material for intersection-type uranium metallogenesis in Xiazhuang area is discussed in this paper.The study shows that:(1)Mineral composition of the uranium ores in Xiaoshui deposit is mainly pitchblende、calcite、fluorite and pyrite et al.,the calcite locates on the two walls of ore vein,and pitchblende and fluorite deposit in the middle part of the vein;(2)Pitchblende is with the age of 73.5 Ma(U-Pb isotope),and bears distinct time difference to the age of wallrocks(diabase);(3)The δD values of fluid inclusions in fluorites ranges from -124.44‰ to -97.08‰,and δ~(18)O_(SMON) is between +7.40‰ to +11.02‰,which show isotopic features of mantle-derived fluids;(4)In the characteristics of trace elemental geochemistry,uranium ores is much similar to diabase but different to that of Xiazhuang pluton.It can be concluded that solvent of mineralized fluids in Xiaoshui intersection-type uranium deposit is derived from the mantle,and the uranium source may directly come from the enrichment mantle that is with the similar provenance to diabase;and it can be conferred further that uranium precipitations is related to the boiling of supercritical state mineral fluid which enriched in CO_2,F,H_2S,U component at the critical point.