The Guangshigou uranium deposit, northern Qinling Orogen, China: A product of assimilation-fractional crystallization of pegmatitic magma

摘要

Uranium mineralization associated with biotite pegmatites occurs in the Shangdan triangular domain of the northern Qinling Orogen, constituting a significant uraniferous province. The Guangshigou deposit is the most productive uranium deposit in this area. Several Caledonian intrusions were emplaced within the ore district including the Huichizi granite (HG, 441.1 +/- 1.3 Ma), Damaogou granite (DG, 420.9 +/- 1.3 Ma), biotite pegmatite (BP, 415.6 +/- 1.5 Ma), and muscovite-biotite pegmatite (MBP, 412.1 +/- 1.4 Ma). Based on uranium concentration, each BP displays two different zones, i.e., an uranium-bearing zone (UBP hosted at the contact zone) and a non-mineralized zone (NBP hosted in the non-assimilation zone). Two magmatic pulses are distinguished. The Early Silurian HG was derived from a low degree of partial melting of thickened lower basaltic crust interfused mantle-derived materials following the subduction of the Shangdan Ocean. The Late Silurian-Early Devonian intrusions exhibited the same source region but formed during the weakening of convergent action. Fractional crystallization of high-K granitic magma (DG) produced a set of fractionated pegmatites, whereas UBP deviates from a normal magma evolution trend due to country rock contamination in the hybrid zone.