试谈可地浸层间渗入砂岩型铀矿选区的几个问题

Some problems on target-area selection for searching interstratified infiltration sandstone-type uranium deposits suitable to in-situ leaching

世界上砂岩型铀矿床分布很广,但达到铀矿省级规模、又适合地浸法开采的,目前只发现3处,它们均属层间氧化带型,发育于晚近造山带与地台(台坪)呈“分支倾伏”的结合部位,在地貌上构成从高山区、经低山丘陵到盆地边缘斜坡带这样3个大的“阶梯”,具备良好的水动力条件; 特别在成矿期所处的干旱条件下,年蒸发量大于年降雨量,高山区高位能的冰雪融水就成为低山丘陵和盆地边缘弱构造运动区惟一长期稳定的地下水补给。然而在造山带内有众多的规模较大的山间盆地,至少构成了2个“阶梯”,对寻找含铀煤系砂岩中的层间氧化带型矿床前景看好。许多中外铀矿地质学家都曾注意到,横贯欧洲中部有一条近东西向的海西期铀成矿带,其东段与乌拉尔-天山-蒙古活动带重叠,并与后者一起在中新生代共同受到阿尔卑斯-喜马拉雅期构造运动的影响,造成该带拥有成矿时代不一、矿床类型繁多、空问分布相对集中的复杂景象。此外,贯穿亚洲东部近南北向的“维比尔斯带”被认为是中央亚洲活动带与西太平洋活动带的结合部位,反映出东西部分地壳结构的不均一性。这是两条控制铀成矿作用的全球性构造带,对它们在铀成矿作用中的特点、作用和影响范围在进行战略选区时应予以充分注意。

The sandstone-type uranium deposits are widely distributed in the world, but only 3 regions where deposits reach uranium province size and are suitable for in-situ leaching have been found. Deposits are all of the interstratified-oxidation type, and developed at the combination sites of the most recent orogenic belt with young or old platforms in form of “branching, inclining and disappearing” of the former. Geomorphologically, these regions consist of 3 big “steps” from high mountain regions through lower mountains or hills to the margins of the basin, which are in form of declining slope and form a good hydrodynamic conditions. Climatically, an arid climate was always required for the period of sandstone-type uranium ore formation, while annual evaporation is higher than the annual precipitation, the high mountain regions with high potential energy of water melted from glacier and snow which is thought to be a long-term and steady underground water supplier for lower mountains or hill regions and the margins of the basin. However, in orogenic belt there is a good number of inter-mountain basins with at least two big “steps” indicating a good potential to discover interstratifled-oxidation sandstone-type uranium deposits in coal-bearing basins. Many Chinese and foreign uranium geologists have noticed that there is an east-west oriented Hercynian uranium mineralization belt lying across the middle of Europe, the eastern section is superimposed on the Ural-Tianshan-Mongolian mobile belt and together with the latter it was infected by the Alpine-Hymalayan movement in Meso-Sinozoic. This resulted in a complicated metallogenic scene with different ore-forming times, multiple types of deposits, and spatial concentration. In addition, a sub-meridional-oriented “Vebris belt” running through the eastern part of Asia is considered as combination part of the Central Asian mobile belt with the Western Pacific mobile belt which reflects inhomogeneity in crustal construction of its eastern and western parts. These two structure belts are of global significance and have a control to the uranium ore formation. So, it should be paid more attention to their characteristics, processes and the scope of their influences in strategic prospection area selection.