准噶尔盆地南缘构造抬升剥蚀不均一性对砂岩型铀矿的制约

摘要

准噶尔盆地南缘与伊犁和吐哈典型产铀盆地成矿地质背景相似,然而,至今未发现铀矿床.现存铀矿(化)点主要受控于构造形态和抬升剥蚀程度,本文主要通过恢复准噶尔盆地南缘构造抬升剥蚀量,探讨构造抬升剥蚀不均一性对砂岩型铀成矿的制约,指出有利构造保矿的适宜地段.采用镜质体反射率(R0)反演技术,结合目的层成岩作用研究,估算出四棵树和硫磺沟地区剥蚀量分别为2880～3680 m和2400～3680m,相对较小.分析抬升剥蚀不均一性的形成机制发现,两个地区发育走滑断层主导的传递带致使抬升剥蚀量相对较小,主要表现为地层的逆冲缩量相对较小和发育不同的构造调节方式(盆山耦合方式).四棵树地区主要发育逆掩冲断型盆山耦合方式,对后期铀成矿不利;硫磺沟地区发育冲隆-掀斜型盆山耦合方式,对铀成矿的保存较为有利.地表露头和深部钻孔均显示硫磺沟地区存在层间氧化带及其铀矿体的可能,是寻找剥蚀残留“古矿”的优选地段.%The geological background of the southern margin of the Junggar Basin is similar to those of the Yili Basin and Tuha Basin that are famous for typical sandstone-hosted uranium deposits in China.However,no uranium deposit has been founded in the southern margin of the Jungger Basin yet.Almost all founded sandstone-hosed uranium deposits are located in the first fold belt in the northern part of the Tianshan Orogen,and are dramatically controlled by structural patterns and tectonic uplifting.By restoring the tectonic uplifting-denudation thickness of the southern margin of the Junggar Basin,this paper aims to investigate the favorable tectonic areas for uranium mineralization and preservation.Based on the data of vitrinite reflectance,combined with the study of diagenesis of the target strata (Jurassic),we calculated the denudation thickness.Our results suggest that the Sikeshu and the Liuhuanggou areas,with denudation thicknesses of 2880-3680m and 2400-3680 m,respectively,have less denudation thicknesses than the other areas.Comparative analysis of the formation mechanism of uplift-denudation inhomogeneity in the two areas show that the relatively less denudation thicknesses was due to the development of longitudinal strike-slip fault,which presents less amount of shortening and different basin-range coupling ways.The Sikeshu area is disadvantageous to uranium mineralization due to its over-thrust type of basin-range structure.In contrast,the Liuhuanggou area with thrust-tilt type of basin-range structure is favorable for uranium mineralization and preservation.Furthermore,outcrop and drill holes reveal that the interlayer oxidation zone and uranium formation occur in the Liuhuanggou area,and is likely a favorite area for exploration of sandstone-hosted uranium deposits.