Search

Naturally occurring granular uranium particles are typically fine and are often found as accessory minerals. However, reports of megacrystalline uraninite are rare. The discovery of megacrystalline uraninite is a significant achievement in uranium prospecting and mineralogy in the Kangdian region and China. Our team's research and review of previous studies have led to a systematic summary of the formation age, genetic types, relationship with migmatization, and metallogenic dynamic background of megacrystalline uraninite in the Kangdian region. The key findings are as follows: (1) the formation age of megacrystalline uraninite is Neoproterozoic (790–770 Ma); (2) migmatization preceded uranium mineralization; (3) the formation of megacrystalline uraninite is linked to high-temperature, low-pressure metamorphism caused by partial melting; (4) and the formation of megacrystalline uraninite may be associated with the Rodinia rifting event. This review aims to enhance our understanding of uranium mineralization during the Neoproterozoic in China and worldwide. [ABSTRACT FROM AUTHOR]

Megacrystalline uraninite (up to one centimeter in size) represents one of the most important discoveries in uranium mineralogy in the western margin of the Yangtze Block and even in China in recent years. However, the genesis of megacrystalline uraninite remains controversial. In this study, the megacrystalline uraninite found in the felsic and quartz veins in the Haita area is examined for the first time. The study examined the geochemical characteristics of uraninite in the two veins and resulted in two primary findings. (1) The genesis of the uraninite was likely intrusive and was closely related to partial melting. (2) The quartz vein and feldspar vein are cogenetic and have a simple differentiation evolution relationship. Therefore, the partial melting of felsic materials during migmatization may be the most important mechanism of uranium mineralization in the study area. Furthermore, further simple fractional crystallization may be another important mechanism for the formation of megacrystalline uraninite. This study enriches the REE database of uraninite in uranium deposits worldwide, which is meaningful for studying the genesis of megacrystalline uraninite. [ABSTRACT FROM AUTHOR]

The Datian uranium deposit is a migmatite-hosted, high temperature, hydrothermal deposit in the Kangdian region. Detailed information on the chemical composition and formation age of the uraninite remains lacking, which impedes our understanding of uraninite genesis. Two phases of uraninite have been identified according to their relationships with other minerals and their field relationships. The phase 1 (Ur1) uraninite is characterized by local development of microfractures and pores in the crystal of uraninite, a scattered distribution, and irregular crystal shapes, and it is associated with ilmenite, biotite, and rare earth element (REE) minerals (monazite and xenotime). The phase 2 uraninite (Ur2) has anhedral crystal shapes with well-developed microfractures and pores and is associated with pyrite, albite, pyrrhotite, molybdenite, zircon, and chlorite. X-ray element mapping revealed that the distributions of U, Th, and Pb in the Ur1 uraninite are homogeneous, whereas those in the Ur2 uraninite are heterogeneous. The results of the electron microprobe analysis (EMPA) show that the UO2 and PbO contents of the Ur1 and Ur2 uraninite do not vary significantly. The high ThO2 contents of the Ur1 (1.08–1.68 wt %) and Ur2 uraninite (3.41–4.83 wt %) indicate that they formed at different temperatures. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis results show that the ∑REE of the Ur1 uraninite (3747.5–7032.3 ppm) is lower than that of the Ur2 uraninite (8369.2–11,484.3 ppm), and the REE patterns of the Ur1 and Ur2 uraninite are sickle-shaped with large negative Eu anomalies. The LA-ICP-MS U–Pb dating results revealed that the ages of the Ur1 (841.4 ± 4.0 Ma) and Ur2 (834.5 ± 4.1 Ma–837.2 ± 4.5 Ma) uraninite are in consistent with that of the migmatite. Thus, the Datian uranium deposit underwent at least two hydrothermal events, and the uraninite was formed due to the migmatization. [ABSTRACT FROM AUTHOR]

Taking nickel-based single crystal superalloy DD6 as the research object, different degrees of creep damage were prefabricated by creep interruption tests, and then the creep damage was repaired by the restoration heat treatment system of solid solution heat treatment and two-stage aging heat treatment. The results show that with the creep time increasing, the alloy underwent microstructure evolution including γ′ phase coarsening, N-type rafting and de-rafting. After the restoration heat treatment, the coarse rafted γ′ phase of creep damaged specimens dissolved, precipitated, grew up, and became cubic again. Except for the specimens with creep interruption of 100 h, the γ′ phase can basically achieve the same arrangement as the γ′ phase of the original sample. The comparison of the secondary creep test shows that the steady-state creep stage of the test piece after the restoration heat treatment is relatively increased, and the total creep life can reach the same level as the primary creep life. The high temperature creep properties of the tested alloy are basically recovered, and the restoration heat treatment effect is good. [ABSTRACT FROM AUTHOR]