鄂尔多斯盆地北部直罗组砂岩重矿物分布特征及其指示意义

Distribution characteristics of heavy minerals in the sandstone of Zhiluo Formation of northern Ordos Basin and its implication

近年来,鄂尔多斯盆地砂岩型铀矿资源评价取得了较大进展,关于找矿目的层物源和铀源的问题长期以来备受关注。运用重矿物综合分析方法,探讨鄂尔多斯盆地北部砂岩型铀矿赋矿层直罗组碎屑物质来源和成矿铀源。结果表明,研究区内直罗组的重矿物组合主要为石榴子石+锆石+绿帘石+黑云母+尖晶石,其次包含少量磷灰石、榍石、金红石、角闪石、电气石、钛铁矿等,反映以中高级变质岩和中酸性岩浆岩为主的母岩类型。重矿物特征指数反映了以含石榴子石变质岩为主要源岩类型和近源沉积的特点。综合分析认为,区内直罗组主要的物源为盆地北部大青山和乌拉山地区的中下太古界-元古界的乌拉山岩群、中元古界扎尔泰群以及各时期的中酸性侵入体等。其中,古老基底变质岩与各时期中酸性岩浆岩普遍具有较高的铀含量,沿着NW-SE方向铀迁出明显,为后期铀成矿作用提供了初始铀源。

In recent years,the evaluation of sandstone-type uranium ore in Ordos Basin has made great progress,and the problems about provenance and uranium sources of the target layer have drawn the most attention for a long time.Based on the comprehensive analysis of heavy minerals,this paper discusses the source of detrital materials and ore-forming uranium sources in Zhiluo Formation of sandstone type uranium deposits in the northern Ordos Basin.The results show that the heavy mineral assemblages of Zhiluo Formation in the study area mainly include garnet,zircon,epidote,biotite,spinel,as well as a small amount of apatite,sphene,rutile and hornblende,tourmaline,ilmenite,which reflects the parent rock type of mainly intermediate and high-grade metamorphic rocks and intermediate acid magmatic rocks.The heavy mineral characteristic index reflects the characteristics of the garnet-bearing metamorphic rock as the main source rock type and proximal deposition.The comprehensive analysis shows that the main provenance areas of Zhiluo Formation are the Middle-Lower Archean Proterozoic Wulashan Rock Group,the Middle Proterozoic Zartai Group and intermediate acid intrusive bodies of various periods in Daqingshan and Wulashan regions in the northern part of the basin.Among them,the ancient basement metamorphic rocks and various periods intermediate acid magmatic rocks generally have high uranium content,with an obvious uranium migration along the NW-SE direction,providing the initial uranium source for the later uranium mineralization.