赣南白面石铀矿田成因再认识

赣南白面石铀矿田经上世纪60~80年代勘查,发现和探明了白面石、龙坑、双坑、马荠塘4个铀矿床和黄泥湖铀矿点,成为中国重要的铀资源基地。该矿田产于EW向南岭铀成矿带东段的白面石沉积-火山盆地内。该盆地的基底为印支期白面石花岗岩体;盖层为中侏罗统菖蒲组。盖层的底部为第一层砂岩,其上由基性-酸性双峰式火山岩组合与5层碎屑岩夹层组成。铀矿主要赋存在盖层底部的第一层砂岩中,其次是产在第一层玄武岩与第一层砂岩的接触带,有少量产在基底花岗岩顶部的风化壳中。关于该铀矿田的成因,有砂岩型沉积说、同生沉积后生富集说、成岩成矿热液叠加说、岩浆热液说,等等。为了厘定矿床成因类型,以确立今后的找矿方向,笔者对该矿田的资料进行了重新整理,应用Minesight软件选择典型的白面石铀矿床建立了三维地质模型,并收集了最新的同位素定年和岩石地球化学分析资料。研究表明,白面石铀矿田存在2次成矿（160~156 Ma和99~86 Ma）,其主成矿作用与第一层玄武岩的覆盖,在空间上相伴（铀矿体主要赋存于第一层砂岩及其与玄武岩的接触带）、时间上相近（成矿时间为160~156 Ma,玄武岩成岩时间为173 Ma）、成生上相关（矿化具有明显的中-低温热液蚀变）,为火山热盖成因类型,后期又有大量脉体活动,在岩脉两侧的砂岩层内又有热液型铀矿化叠加,从而形成了火山热盖及热液叠加的复成因矿床。该矿田的成矿条件是：富铀的基底,砂岩的沉积,洼沟的地形,岩浆的热盖,脉岩的入侵。

Genetic recognition of Baimianshi uranium ore field in southern Jiangxi Province

As one of the key uranium resource bases in China shown by 1960s-1980s exploration, the Baimianshi uranium ore field is composed of 4 uranium deposits (Baimianshi, Longkeng, Shuangkeng, Maqitang) and an ore spot (Huangnihu). The Baimianshi uranium ore field is located in a sedimentary-volcanic basin in the eastern segment of the EW-trending Nanling uranium metallogenetic belt. The basement of the sedimentary-volcanic basin is Indosinian Baimianshi granite pluton covered by middle Jurassic Changpu Formation. The Changpu Formation consists of arkosic quartz sandstone at its bottom, covered by basic-acid bi-model volcanic rocks and 5 pyroclastic layers. Uranium occurs in the first sandstone layer and at the bottom of the first basalt layer as well as on the top of basement granite and its weathering crust. There are many controversial theories on its genetic model, such as sandstone theory, syngenetic sedimentation followed by enrichment theory, hydrothermal superimposition upon diagenetic metallogenesis model, and hydrothermal theory. In order to define the genetic mode of the ore field for further exploration, the authors collected the updated isotope geochronologic and lithogeochemical data, built up three-dimensional geological model using Minesight software, and confirmed two-stage metallogenesis(160 Ma and 99 Ma respectively)for the Baimianshi uranium ore field, in which the main metallogenic stage corresponded to the first basalt layer in space and in time as well as in temperature, belonging to volcanic hydrothermal cover type. The uranium ore field then experienced the superimposition of large scale hydrothermal veining. As a result, the Baimianshi uranium ore field belongs to the model of volcanic cover with hydrothermal superimposition, with the metallogenic condition being "uranium-rich basement, sandstone, paleo-tunnel, hydrothermal cover and vein". "Searching volcanic crater, studying basement granite" can serve as a guide for further exploration.