鄂尔多斯盆地西南缘彭阳铀矿区矿物学研究及其对区域成矿的指示

绝大多数砂岩型铀矿均赋存于河湖相或滨浅海相等沉积地层中。彭阳铀矿床是近期在鄂尔多斯盆地西南部新发现的一个大型铀矿床,也是中国首个产出于风成砂岩中的砂岩型铀矿床。矿体主要赋存于洛河组砂岩中,岩性主要为中细粒长石砂岩和岩屑长石砂岩。洛河组以沙漠沉积相为主,靠近盆地边缘地区发育冲积扇及河流相沉积。本文在详细的野外调研和矿相学研究基础上,围绕富铀地层洛河组开展详细的矿物学研究,利用扫描电镜、背散射、电子探针等方法,发现洛河组中的铀矿物主要为沥青铀矿,其次为含钛铀矿物,以及少量铀石,基本查明了铀矿物的矿物学特征、化学成分及共生矿物组合。铀矿物大多呈星点状与锐钛矿、磷灰石(胶磷矿)、黄铁矿等密切共生,或者呈条带状分布于石英等碎屑颗粒边缘。与伊犁盆地和鄂尔多斯盆地典型矿床的团块状铀矿物相比,彭阳铀矿床的铀矿物以多呈星点浸染状为特征。洛河组风成砂岩中还原剂十分缺乏,推测有油气等还原物质参与了砂岩型铀矿的氧化还原作用并导致铀矿的沉淀富集。

Mineralogical Study of Pengyang Uranium Deposit and its Significance of Regional Mineral Exploration in Southwestern Ordos Basin

Sandstone-type uranium deposits commonly occur in sedimentary strata of fluvio-lacustrine facies and littoral-neritic facies.The newly discovered Pengyang deposit is a large-scale uranium deposit in the southwestern margin of the Ordos Basin,and is the first sandstone-type uranium deposit found in eolian sandstone in China.The ore body mainly exists in the Luohe Formation medium-fine arkose and lithic feldspar sandstone.The sedimentary facies of the Luohe Formation are dominated by the desert facies,and some alluvial fans and fluvial facies are deposited near the edge of the basin.Based on detailed field investigation and mineralogy research,the mineralogical characteristics,chemical composition and paragenetic assemblage of uranium minerals are identified by scanning electron microscopy,electron probe and backscattering.The results show that the uranium minerals are mainly pitchblende,followed by titanium-bearing uranium minerals and a small amount of coffinite.Most of the uranium minerals are closely associated with anatase,apatite(collophane)and pyrite,or distributed in strips on the edge of quartz fragments.The Luohe Formation aeolian sandstone lacks reducing agent,we,therefore,infer that allochthonous reducing materials such as oil and gas might have participated in the precipitation and enrichment of uranium.