Uraninite is the main contributor to the bulk-rock uranium concentration in many U-rich granites and is the most important uranium source for granite-related uranium deposits. However, detailed textural and compositional evolution of magmatic uraninite in granites during alteration and associated uranium mobilization have not been well documented. In this study, textures and geochemistry of uraninites from the Zhuguangshan batholith (South China) were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The geochemical data indicate that the Longhuashan and Youdong plutons are peraluminous leucogranite, the Changjiang pluton is highly fractionated high-K calc-alkaline granite, and the Jiufeng pluton belongs to a high-K calc-alkaline association. Uraninites from the Longhuashan and Youdong granites have lower concentrations of ThO₂ (0.9–4.0 wt %) and rare earth elements (REE)₂O₃ (0.1–1.0 wt %) than those from the Changjiang and Jiufeng granites (ThO₂ = 4.4–7.6 wt %, REE₂O₃ = 0.7–5.1 wt %). Uraninites observed in the Longhuashan, Youdong, Changjiang, and Jiufeng granites yielded chemical ages of 223 ± 3, 222 ± 2, 157 ± 1, and 161 ± 2 Ma, respectively. The samples (including altered and unaltered) collected from the Longhuashan, Youdong, and Changjiang granites are characterized by highly variable whole-rock U concentrations of 6.9 to 44.7 ppm and Th/U ratios of 0.9 to 7.0, consistent with crystallization of uraninite in these granites being followed by uranium leaching during alteration. Alteration of uraninite, indicated by altered domains developing microcracks and appearing darker in backscattered electron (BSE) images compared to unaltered domains, results in the incorporation of Si and Ca and mobilization of U. In contrast, the least altered samples of the unmineralized Jiufeng granite have low U concentrations (5.3–16.4 ppm) and high ΣREE/U (13.6–49.4) and Th/U ratios (2.1–5.6), which inhibit crystallization of uraninite, as its crystallization occurs when the U concentration is high enough to exceed the substitution capacity of other U-bearing minerals. These results indicate that the Longhuashan, Youdong, and Changjiang granites were favorable uranium sources for the formation of uranium deposits in this area. This study highlights the potential of uraninite alteration and geochemistry to assist in deciphering uranium sources and enrichment processes of granite-related uranium deposits.

The Jiajika rare-metal deposit located in western Sichuan Province (China) is renowned as the largest lithium deposit in Asia, and the No. 134 pegmatite dike is the largest lithium pegmatite under mining conditions in the area. On the basis of a detailed characterization of textures and minerals in the Jiajika No. 134 pegmatite, two zones (the barren Zone I and the spodumene Zone II) and three subzones (Zone II was subdivided into microcrystalline, medium-fine grained and coarse-grained spodumene zones) have been identified. The detailed mineralogical characteristics of lithium minerals and other indicator minerals from each zone were evaluated by EPMA for illustrating the magmatic–hydrothermal evolution and the cooling path of the Jiajika No. 134 pegmatite. From the outer zone inwards, grain size gradually increased, the typical graphic pegmatite zone was absent, and spodumene randomly crystallized throughout nearly the whole pegmatite body. This evidence indicated a Li-saturated melt prior to pegmatite crystallization, which could be the main cause of the super-large-scale Li mineralization of the Jiajika No. 134 pegmatite. A comparison of the Cs content between primary beryl in the Jiajika No. 134 pegmatite and other important Li-Cs-Ta pegmatites in the world indicates that No. 134 pegmatite shows a high degree of fractional crystallization. The evolution of mica species from muscovite to Li-micas from Zone I to Zone II marks the transition from the magmatic to the hydrothermal stage in pegmatite evolution. The absence of individual lepidolite and the relatively limited scale of alteration of spodumene (<10 vol%) suggest that the activity of the hydrothermal fluids in the system is limited, which contributes to the preservation of the easily altered Li ores and is also an important controlling factor of the super-large-scale Li mineralization of the pegmatite. Spodumene–quartz intergrowth (SQI) usually occurs partly along the rims of the spodumene grains in the Jiajika No. 134 pegmatite. Combined with the pegmatite mineral equilibria, the results of fluid inclusion studies of the pegmatite and the metamorphic conditions in the area, a constrained P-T path of the magmatic–hydrothermal crystallization of the Jiajika No. 134 pegmatite is proposed. The unusual steeply sloped cooling path of the No. 134 pegmatite could be attributed to the fast pressure drop triggered by the intrusion of a pegmatitic melt along the fractures surrounding the Majingzi granite, which could also be the dominant evolution process for other spodumene pegmatites with similar SQI features in the world. The feature of limited internal geochemical fractionation suggested by mineral-scale geochemical analyses of spodumene and micas, combined with the clear textural zoning of the No. 134 pegmatite, can best be ascribed to the effect of undercooling during pegmatite formation. This effect might be one of the non-negligible rules of pegmatite petrogenesis, and would significantly upgrade the potential of Li mineralization by minimizing diffusional Li transfer to the country rocks.

锂-铍-铌-钽是重要的关键金属矿产资源，其矿石矿物“稀”、“伴”和“细”的特征决定了一些锂、铍、铌、钽矿床在开采利用上有较大难度，需要加强工艺矿物学研究。除了品位和储量，还要考虑矿石的可选性指标，才能对矿床工业价值进行准确评价。本文在基于锂铍铌钽矿床成矿规律及典型矿床研究的基础上，尝试从工艺矿物学角度提出一套综合性评价锂-铍-铌-钽矿产资源的指标体系。具体内容包括矿床类型、矿石品位、主要工业矿物、主要矿物组成、主要目的组分的平衡配分、矿石结构构造，目的矿物工艺粒度、目的矿物嵌布特征、可综合利用矿物或伴生/共生组分、杂质元素/有害元素。通过矿床实例对不同类型锂-铍-铌-钽矿床的评价指标进行了简要评述，影响伟晶岩型、花岗岩锂矿和铍矿价值的主要矿物学指标是“主要工业矿物”和“主要目的组分的平衡配分”及“目的矿物工艺粒度”，影响黏土型/沉积岩型锂矿价值的主要因素是锂的赋存状态，影响火山岩型铍矿价值的主要矿物学指标有“主要工业矿物”、“目的矿物的工艺粒度”和“目的矿物嵌布特征”，影响碱性岩型和矽卡岩型铍矿价值的主要矿物学因素是“主要工业矿物”、“主要目的组分的平衡配分”和“目的矿物嵌布特征”，影响伟晶岩型和花岗岩型铌钽矿的主要因素是“目的矿物工艺粒度”，影响碳酸岩型和碱性岩型铌钽矿的主要因素是“主要工业矿物”和“目的矿物工艺粒度”。应用矿物学评价指标体系时应注意，对于不同类型的矿床，不同矿物学指标的权重有所不同，需要具体矿床具体分析。