鄂尔多斯盆地北东部纳岭沟铀矿床红色蚀变矿石成因及其地质意义

鄂尔多斯盆地北东部纳岭沟铀矿床是近年来发现的大型砂岩型铀矿床。与国内外典型层间氧化带型铀矿床明显不同,纳岭沟铀矿床不仅矿体呈板状、似层状产出,受单层灰绿色古氧化砂体与下伏灰色砂体的交界面控制,且远离顶底板,部分含矿岩石在宏观上表现为红色含炭屑矿石,微观上出现铀石-赤铁矿(针铁矿)-黄铁矿等特殊矿物共生组合。在综合岩矿鉴定、电子探针分析、酸解烃分析等成果认识的基础上,结合前人流体障铀成矿理论的实验和数学模拟结果认为,纳岭沟铀矿床是含氧含铀水与深部还原性流体相互作用的产物,且矿体形成过程中含氧含铀水和深部还原性流体的界面变化是红色蚀变矿石形成的关键原因,而持续强的含氧含铀水和较弱的深部还原性流体作用是形成板状矿体的主要因素。

The genesis of uranium ore with red alterations in the Nalinggou deposit, northeastern Ordos Basin, and its geological implications

The large-sized Nalinggou sandstone type uranium deposit was recently discovered in northeastern Ordos Basin. Distinctly different from the typical uranium deposits of interlayer oxidation zone type in the world, this deposit is characterized not only by the tabular or stratoid orebodies controlled by the interface between monolayer grayish green paleo-oxidized sand body and underling gray sand body but also by being far away from the roof and bottom plate. Part of the ore-hosting rocks appear macroscopically as reddish and charcoal debris-bearing ores and microscopically as special paragenetic mineral assemblages consisting of coffinite, hematite (goethite), pyrite and siderite. Based on the results of rock-mineral identifications, EMPA and acidolysis hydro-carbon decomposition analysis, combined with the results of the experiments and mathematic simulations for fluid barrier theory of uranium metallogenesis by former researcher, the authors hold that the Nalinggou uranium deposit resulted from interaction between oxidizing uraniferous brine and deep-seated reducing fluid and, furthermore, the changing of the oxidizing-reducing inter-face in the ore-forming process was the key factor for reddish alteration of ores, and the interactions between persistent strong oxi-dizing uraniferous fluid and weak deep-seated reducing fluid might have been the primary factor responsible for the formation of the tabular orebodies.