Characteristics of Uranium Mineralization and Mineralogy in Tianmen Area of Miaoershan Ore Field, Northern Guangxi

Abstract

The research and prospecting of uranium mineralization in South China mainly focus on the Indosinian and Yanshanian granites, and a series of theoretical innovations and prospecting achievements in uranium mineralization were achieved. Miaoershan ore field is an important granitetype uranium ore field in South China, which has strong magmatic activity, the fault depression zone, structure, hydrothermal activity and alteration were widespread, the conditions for uranium mineralization are favorable. Tianmen area is located in the middle of the Miaoershan ore field. In recent years, uranium ore bodies were discovered in the Caledonian granites of this region through geological exploration. The typical samples of black massive uranium mineralization ores were collected in Tianmen area in this paper, and a variety of modern high-precision analysis methods such as optical microscope, scanning electron microscope, electron probe, comprehensive mineral analyzer and high-resolution micro-X-ray fluorescence spectrometer were used to study uranium mineral species, mineral symbiotic association, uranium mineral composition characteristics and uranium occurrence state. The results indicate that uranium minerals are mainly in the form of independent uranium minerals, such as vein and massive pitchblende and a small amount of coffinite. The composition of massive pitchblende is relatively homogeneous, and is rarely affected by significant hydrothermal alteration. Vein pitchblende is closely associated with feldspar, chlorite, calcite and rutile, and the chemical composition of them changes due to the later fluid modification. The average values of UO2, SiO2 and CaO in massive pitchblende are 83.35%, 1.45% and 7.59%, respectively, which have the characteristics of SiO2-poor, UO2-rich and CaO-rich. While the average values of UO2, SiO2 and CaO in vein pitchblende are 79.96%, 5.19% and 5.70%, respectively. In addition, coffinite is closely related to pitchblende, which may be due to the change of pH and Eh and the solubility of SiO2. With the water-rock interaction between the uranium-bearing hydrothermal solution and surrounding rock, under the influence of reducing substances (pyrite or chlorite) and weakly alkaline alteration, the ore-forming hydrothermal solution evolves in the stable physical and chemical field of coffinite and pitchblende, which resulting in the phenomenon of alternating production of coffinite and pitchblende. There are many types of paragenetic association of minerals related to the uranium mineralization, like uranium minerals-chlorite-rutile, uranium minerals-hematite-quartz-feldspar, uranium minerals-pyrite-quartz and uranium minerals-quartz-calcite four types. Comprehensive study shows that there are various mineral associations in the Caledonian granite in the Tianmen area of the Miaoershan ore field. The characteristics of uranium minerals indicate that there may be early and late hydrothermal uranium mineralization.

Keywords

• characteristics of uranium minerals
• pitchblende
• occurrence status
• caledonian granites
• tianmen area