Mineral Chemistry and Chronology Investigation of Uraninite in the Jinguanchong Uranium Deposit in Eastern Hunan Province and the Implications for Geological Significance.

Abstract

Jinguanchong deposit, a part of the Mingyuefeng ore field in eastern Hunan Province, China, is a typical perigranitic uranium deposit (a subtype of granite-related deposit) discovered recently with considerable uranium mineralization. Herein, uraninite, the primary ore mineral in the deposit, was investigated via scanning electron microscopy and electron probe microanalysis. Additionally, laser ablation-inductively coupled plasma-mass spectrometry was used for the first time to determine the in situ U-Pb age and the rare-earth element characteristics of uraninite. Uraninite mainly comprises UO2, CaO, and PbO with a low ThO2 content. Uraninite exhibits a low total content of rare-earth elements with a distinct fractionation between light and heavy rare-earth elements while displaying a negative Eu anomaly. The presence of major elements and rare-earth elements in uraninite suggests its formation within a hydrothermal environment at moderate to low temperatures below 350 °C, thereby classifying the Jinguanchong deposit as a typical hydrothermal vein-type uranium deposit. The uranium metallogenic age is determined to be 93.8 ± 1.4 Ma, falling within the midlate Cretaceous period. This age corresponds to the Mesozoic lithospheric extension and thinning events (approximately 85-95 Ma) in South China, suggesting that the formation of the Jinguanchong uranium deposit might be associated with the tectonic dynamics of lithospheric extension and thinning.