Petrology, mineralogy, and ore leaching of sandstone-hosted uranium deposits in the Ordos Basin, North China

Highlights

• Injecting H₂SO₄ + H₂O₂ solution will produce calcium sulfate precipitate and block ore bed.

• CO₂ + O₂ leaching technology was successfully used in laboratory and field uranium leaching tests.

• Inhibiting ore bed blockage and increasing the amount of injected O₂ are important routes for leaching.

Abstract

The Nalinggou–Daying uranium metallogenic belt is situated at the northern Ordos Basin, China. Petrographical, mineralogical and geochemical techniques were used to study the ore-bearing sandstones and host rocks in the Nalinggou–Daying uranium metallogenic belt. The present study shows that uranium minerals, i.e., coffinite, pitchblende, and brannerite, are mostly disseminated around pyrite and detrital particles. The ore-bearing sandstones are enriched in organic matter, with which this reductive environment influenced uranium leaching. The carbonate concentration of the uranium ores is markedly higher than that of the host rocks, and intense carbonatization occurs in the ore-bearing sandstones. In this case, the usage of the classical in-situ leach uranium mining technique by injecting H₂SO₄ + H₂O₂ solution produces calcium sulfate precipitate, which can lead to blocking of the ore-bearing strata. For this reason, laboratory and field uranium mining tests were conducted using CO₂ + O₂ in-situ leaching technology and were demonstrated to be successful, illustrating that this approach is technically feasible. Inhibiting ore bed blockage and increasing the amount of injected O₂ are important for uranium leaching in this setting.

Introduction

In the past few years, many large-sized sandstone-hosted uranium deposits in the Yili, Ordos, Erlian, and Kailu basins in North China have been discovered (Feng et al., 2013, Feng et al., 2017b, Shi et al., 2016, Wu et al., 2016a, Wu et al., 2016b, Bonnetti et al., 2017, Hou et al., 2017, Nie et al., 2017, Zhang et al., 2018b, Zhao et al., 2018b). These discoveries have helped China move from 3rd to 1st in reserves of sandstone-hosted uranium deposits (OECD-NEA/IAEA, 2014). Therefore, sandstone-hosted uranium deposits are a major source of uranium prospecting in China (Feng et al., 2017a, He et al., 2017, Jin et al., 2019). Likewise, the economical and environment-friendly in-situ leach uranium mining technique for sandstone-hosted uranium deposits has also been a popular scientific issue (Su et al., 2006, Su and Du, 2012, Xu et al., 2012, Ji et al., 2018).

The Ordos Basin is an important energy basin with abundant gas, oil and coal in China (Feng et al., 2006, Liu et al., 2013, Wang et al., 2018b). The abundance in exploration leads to the discovery of the Huangjingqi and Nalinggou uranium deposits and, importantly, the large-scale Daying uranium deposit (Li and Li, 2011, Chen et al., 2017, Jiao et al., 2018). Both of the Nalinggou and Daying uranium deposits lie in the northeastern Ordos Basin and share many similar features such as in metallogenic setting and ore deposit geology and thus were as a whole for study within this paper, that is, the Nalinggou–Daying uranium metallogenic belt. Mineralization processes and metallogenic models for these two uranium deposits have been extensively studied, with respect to uranium source (Chen et al., 2017b, Feng et al., 2017a), tectonic evolution (Liu et al., 2006, Liu et al., 2007), ore-bearing horizon (Jiao et al., 2005, Chen et al., 2016, Zhao et al., 2018a), ore-forming and hydrocarbon fluids (Peng et al., 2007, Tuo et al., 2010, Xue et al., 2010, Xue et al., 2011) and geochemical behavior of uranium (Hou et al., 2016, Liu et al., 2016, Wu et al., 2016b, Chen et al., 2017b, Tang et al., 2017). However, there are few studies on leaching of uranium from uranium ores according to mineralogical and geochemical aspects. In this study, we analyzed the petrographical and mineralogical characteristics of the ore-bearing sandstones and host rocks in the Nalinggou–Daying uranium metallogenic belt. Based on the results, the application of uranium leaching of the ore is discussed. Furthermore, corresponding leaching tests were designed and performed. Our study provides not only a typical example for in-situ leach mining in the Ordos Basin but also an efficient method for the study of in-situ leach mining in other sandstone-hosted uranium deposits with similar geologic characteristics.