Uraninite from the Guangshigou Pegmatite-Type Uranium Deposit in the North Qinling Orogen, Central China: Its Occurrence, Alteration and Implications for Post-Caledonian Uranium Circulation

The Guangshigou deposit is the largest pegmatite-type uranium in Shangdan domain of North Qinling Orogenic Belt, which characterized by enrichment uraninite hosted biotite granitic pegmatites. At Guangshigou, commonly occurs as mineral inclusions quartz, K-feldspar and or interstices these rock-forming minerals with magmatic characteristics (e.g., U/Th < 100, high ThO2, Y2O3 REE2O3 contents low concentrations CaO, FeO SiO2). It crystallized at 407.6 ± 2.9 Ma from fractionated calc-alkaline high-K pegmatitic melts under conditions 470–700 °C 2.4–3.4 kbar deduced compositions coexisting peritectic biotite. primary mineralization took place during Late Caledonian post-collisional extension Orogen. After this event, has experienced multiple episodes fluid-assisted metasomatism, generated an alteration halo assemblages. (or radiohalo) was result combined effects metamictization metasomatism assemblage goethite, coffinite unidentified aluminosilicate (probably clay minerals) around altered uraninite. This concomitant albitization subsequently followed coffinitization major period 84.9–143.6 Ma, determined U-Th-Pb chemical ages. Further investigations revealed that metasomatic overprinting on initially preferentially along microcracks cavities induced promoted their amorphization, release U Pb structure incorporation K, Ca Si fluids, finally resulting various degrees coffinitization. released were transported alkali-rich, relatively oxidizing fluids then re-precipitated locally amorphous U-Pb-rich silicate to moderate temperature (85–174 °C). compositional changes uraninite, its amorphization together paragenetic sequence secondary phases, therefore, corroborate a intense influx alkali–metasomatic Mesozoic Yanshanian event region. Hence, remobilization circulation Orogen most likely driven post-Caledonian magmatism hydrothermal activities related large-scale tectonic events. In regards, Paleozoic may represent significant source for identified Belt.