二连盆地土壤微细粒铀地球化学分布特征及找矿方向

Regional Geochemical Distribution of Uranium in Fine-Grained Soil and Prediction of Prospecting in Erlian Basin

二连盆地是我国砂岩型铀矿的重要产地之一,已相继发现了多个砂岩型铀矿床.盆地中部赛汉高毕-苏尼特左旗地区南北缘发育大量古-中生代的花岗岩体,铀源丰富;且该区发育北东向展布的巴彦乌拉、赛汉高毕等古河道,为铀矿体的形成和保存提供了有利的构造条件,具有较好的找矿前景.目前针对该地区砂岩型铀矿的勘查主要是通过地球物理勘探(电法、地震、重力、航磁)和钻探,常规的地球化学勘查方法在该区效果不理想.为了满足大范围找矿勘查的需求,基于土壤微细粒分离测量技术在赛汉高毕-苏尼特左旗地区开展1∶25万区域化探扫面工作. 2 821件土壤样品中Hg、As、Mo、F、Zr、Sr、Sb、Li、Th、U等元素既有相对较高的富集系数,又有相对较大的变异系数.通过元素相关分析和R型聚类分析将其分为Zr-Th-U-Mo组合和As-Sb-F-Li-Sr-Hg组合,优选U-Mo为铀矿的成矿指示元素.依据U-Mo衬值地球化学综合异常圈定了3个铀矿找矿有利地段,其中地段I和II位于盆地次级坳陷内部,异常与古河道砂体有关,寻找砂岩型铀矿的潜力较大.

Erlian Basin is one of the most important uranium ore producers in China, in which a series of sandstone-type uranium deposits have been continuously discovered including the Nuheting giant uranium deposit and Saihangaobi medium-sized deposit. A number of Paleozoic to Mesozoic granite intrusions emplaced in the northern and southern margin of Saihangaobi-Sunitezuoqi area,which provided abundant uranium source. In addition, NE-trending Bayanwula and Saihangaobi paleo-channel sand body in this region provided favorable tectonic conditions for the formation and preservation of uranium orebodies. At present, geophysical exploration(electric, seismic, gravity, aeromagnetic) and drilling are the main exploration methods for sandstone-type uranium deposits in this area, while conventional geochemical exploration is seldom carried out in this area, or the effect is not satisfied.Given the development of deep penetrating geochemistry theory, fine-grained soil prospecting method has raised attention in the exploration practice of uranium deposit in sedimentary basins of northern China. To meet the needs of large-scale prospecting, the regional 1: 250 000 geochemical scanning is carried out in the Sihangaobi-Sunitezuoqi area of middle Erlian basin based on finegrained soil prospecting method in this study. A total of 2 821 samples were collected and analyzed, the results show that Hg, As,Mo, F, Zr, Sr, Sb, Li, Th and U not only have relatively high enrichment coefficients, but also show relatively high variable coefficients. These elements could be divided into two groups including Zr-Th-U-Mo and As-Sb-F-Li-Sr-Hg, and U-Mo are selected as mineralized indicators of uranium deposit based on the element correlation analysis and R-type clustering analysis. The high abundance of U ad Mo is closely associated with widely-distributed granitic plutons and paleo-channel sand body. Three favorable prospecting places are delineated based on the U-Mo comprehensive abnormal development area. The No. I and No. II favorable prospecting places are located in the depression of Erlian basin, and the uranium anomalies in this place are caused by the distribution of paleo-channel sand body, indicating that No. I and No. II have great potentials to explore sandstone-type uranium deposit.