滇西梁河盆地南林组沉积学特征及其对砂岩型铀矿的控制

Sedimentary facies and their controls over mineralization of sandstone type uranium deposits in Nanlin Formation in Lianghe Basin, Western Yunnan, China

关键词:  梁河盆地  南林组  沉积相  岩相古地理  砂岩型铀矿

Key words:  Lianghe Basin  Nanlin Formation  sedimentary facies  paleogeography  sandstone type uranium deposits

摘要:

本文以滇西梁河盆地朗蒲寨地区铀矿勘查工程第一手钻探资料为素材，分析上新世梁河盆地性质与演化过程，厘定含矿层系南林组的沉积体系、沉积相类型及其有利赋矿微相组合。在此基础上，分析沉积演化序列对赋矿层纵向空间分布的控制规律，并通过重建赋矿古冲积扇体的岩相古地理格局，预测有利赋矿部位，尝试为该地区和同类型盆地砂岩型铀矿勘查提供科学依据。研究表明，梁河盆地南林组主要发育山间断陷盆地冲积扇沉积体系，包括3种亚相、5种微相。对钻孔岩心的精细沉积学分析显示，砂岩型铀矿的赋矿层主要发育于扇中亚相，尤以砾质辫状河道微相最为常见，赋矿岩相主要为含砾长石砂岩和含砾岩屑长石砂岩。赋矿层及底板沉积期岩相古地理格局显示，在扇根—扇中沉积转换期，相对水位上升，研究区整体呈现退积型演化，扇中相区面积扩大，砾质辫状河道微相更为发育，为形成良好铀储层提供更为有利的条件，并据此认为上蔺家寨—朗蒲寨一线以东的扇中亚相分布区为砂岩型铀矿的有利勘查区。

Abstract:

Based on the first hand drilling data of uranium exploration project in Langpuzhai area, Lianghe Basin, western Yunnan, the characteristics and evolution process of Pliocene in Lianghe Basin are analyzed, and the sedimentary system, sedimentary facies type and favorable ore-bearing microfacies combination of Nanlin Formation are determined. On this basis, the ore-controlling regularity of sedimentary evolution sequence on the vertical spatial distribution of ore-bearing layers is analyzed, and the favorable ore-bearing locations are predicted by reconstructing the lithofacies and paleogeography pattern of ore-bearing ancient alluvial fan body, trying to provide scientific basis for the exploration of sandstone type uranium deposits in the area. The study shows that the alluvial fan system of mountain discontinuous basin is mainly developed in Nanlin Formation of Lianghe Basin, including three subfacies and five microfacies. Fine sedimentological analysis of borehole cores shows that the host beds of sandstone-type uranium deposit are mainly developed in the fan sub-facies, especially in the Gravelly braided river microfacies. The host lithofacies are mainly containing gravel feldspathic sandstone and containing gravel lithic feldspathic sandstone. The lithofacies palaeogeographic pattern before and during the ore-bearing sedimentary period shows that the relative water level rises during the sedimentary transition period from fan root to middle fan, and the study area presents a regressive evolution as a whole, the area of middle fan facies enlarges, and the gravelly braided channel microfacies becomes more developed, which provides more favorable conditions for the formation of good uranium reservoir. It is considered that the central sub facies distribution area of the fan east of the Jiazhai-Langpuzhai line is a favorable exploration area for sandstone type uranium deposits.