Mineralogy and geochemistry of pitchblende in the Changjiang U ore field, Guangdong Province, South China: Implications for its mineralization

Abstract

The Changjiang U ore field developed typical granite-related U mineralization in the Zhuguangshan complex, China. Pitchblende is the most important ore mineral in these mineralizations. In this study, the mineralogy and geochemistry of pitchblende were investigated by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to identify the genesis of the Changjiang U ore field. Pitchblende exhibits colloidal, fragmented, spherulitic and fine-grained crystals in U ores. Its geochemical compositions are similar to those of other granite-related U deposits in South China, which have elevated contents of U, Sr, As and W; low contents of Pb, Th, Zr, Nb, Ta, Hf, Co, Ni and rare earth elements (REEs); and variable amounts of Ca, Si, Bi, Y, V and Zn. These geochemical signatures suggest that mineralization occurred through hydrothermal genesis and that the hosting Youdong and Changjiang granites acted as the dominant U sources. The uraninite in these granites might be the major U source mineral. Uranium mineralization occurred under the following conditions: low temperature (<250°C), low oxygen fugacity (log f O2 = -29.5 --25.5), weakly acidic (pH = 5.3-5.9), high CO 3 2and Fcontents and a silicon-saturated solution. Rapid changes in the physicochemical conditions of the ore-forming fluid are responsible for the precipitation of pitchblende. Combined with previous studies, we propose that U-rich granites, Cretaceous-Tertiary crustal extensions, regional faults and hydrothermal alterations were the critical factors for U formation in the Changjiang ore field.

Uranium in Fluorite, a Case Study: The La Azul Fluorspar Deposit, Taxco, Guerrero, Mexico

“…Considering the textural and compositional characteristics and the hydrothermal origin of the uranium-rich inclusions studied in the fluorite samples from the La Azul mine, these can be defined as pitchblende. The results obtained are chemically very similar to the pitchblende reported by the authors of [63] in a hydrothermal system. Figure 10 compares the chemical results obtained for uraninite from the La Azul mine with those of pitchblende obtained by these authors.…”

“…The name uraninite is essentially used for the crystalline (isometric) uranium dioxide (UO 2 ) mineral with low water content, while the name pitchblende refers to the microcrystalline or colloform amorphous variety, with its water content varying from about 2 per cent to 5 per cent. The small grain size may be attributed to rapid crystallization at low temperatures in mesothermal deposits, e.g., [63,64].…”

Insights from Dikes for Multistage Granitic Magmatism in the Huayangchuan Uranium Polymetallic Deposit, Qinling Orogen

“…Furthermore, the whole-rock and mineral geochemistry defined a magmatic-hydrothermal genetic model directly related to the intrusion of early Yanshanian granites in the Nanling belt. Zhong et al (2023) [20] studied the chronology and petrogenesis of the dikes of the Lujing uranium ore field and found that the Mesozoic dikes provided a favorable oxidation reduction interface and secondary structure fractures for a uranium ore-forming space. However, to our knowledge, only a few studies have been conducted on the granitic dikes around the Huayangchuan deposit, with minimal investigations of the genetic relationship between granitic magmatic activity and U-Nb-REE mineralization [21][22][23][24][25][26].…”