Petrogenesis of the Hongshiquan granite in the Longshoushan belt, NW China: geochemical constraints and implications for uranium mineralization

Abstract

The Longshoushan metallogenic belt in NW China hosts granite-related and Na-metasomatite-hosted uranium deposits. The ca. 2.4 Ga Hongshiquan uranium deposit has a genetic link to granitic rocks. Although the geology of this deposit has been extensively investigated, the petrogenesis of the Hongshiquan granite and the uranium enrichment mechanism remain poorly constrained. Resolving these issues is critical for evaluating the uranium metallogenic potential of the Longshoushan tectonic belt and guiding future exploration. Here, we present whole-rock geochemical and Sr–Nd isotopic data for the Hongshiquan granite and adjacent biotite–plagioclase gneisses of the Longshoushan Group. The Hongshiquan granite exhibits high-silica, magnesian, high-K calc-alkaline, and metaluminous to strongly peraluminous affinities. It possesses relatively low total rare earth element (REE) concentrations and flat heavy REE patterns, accompanied by pronounced depletions in Ba, Ti and P, as well as enrichments in Rb, Cs and Pb. The granites display distinctly enriched Nd isotopic compositions, with ε _Nd ( t ) values ranging from −4.67 to −8.78; these values are comparable to those of the adjacent biotite–plagioclase gneiss from the Longshoushan Group ( ε _Nd ( t ) = −7.14). These observations indicate that the Hongshiquan granites originated via partial melting of a K -rich source comparable to the biotite–plagioclase gneiss of the Longshoushan Group. The Hongshiquan granites experienced extensive fractional crystallization of plagioclase, together with minor apatite and Fe–Ti oxides. The ore-forming element U displays a positive correlation with magmatic evolution degree. Both the Hongshiquan granite and biotite–plagioclase gneiss of the Longshoushan Group are characterized by marked U enrichment. Accordingly, U -enriched source materials and subsequent intense magmatic differentiation created favorable conditions for uranium enrichment and eventual mineralization within the magmatic system.