Genetic link between the Late Mesozoic granitic magmatism and W mineralization in NE China: Constraints from in-situ U-Pb geochronology and geochemistry of wolframite, and whole-rocks geochemistry analyses of W-bearing granites from the Sansheng W-Mo deposit

Abstract

The Sansheng quartz-vein type W-Mo deposit is located on the southern margin of NE China. Tungsten mineralization occurs mainly in veins and veinlets within the Early Cretaceous granitic pluton. In-situ U-Pb dating of hydrothermal wolframite yields a W mineralization age of 137.3 ± 2.0 Ma (1σ, MSWD = 4.4), which provides evidence for an Early Cretaceous W mineralization event in the Sansheng area. W-bearing granites show petrological, mineralogical, and geochemical characteristics of highly fractionated A-type granites. The rocks belong to the high-K calc-alkaline series and are characterized by the enrichment in large ion lithophile elements (e.g., Rb, Th, U, and K) and significant negative Eu, Ba, Sr, P, and Ti anomalies. They also have higher W concentrations, Rb/Sr and U/Th ratios, and lower (La/Yb)N, LREE/HREE, Eu/Eu*, K/Rb, Zr/Hf, Nb/Ta, and Y/Ho ratios than the contemporary W-barren granitoids in NE China. The geochemical signatures of the W-bearing granites indicate that the primary magmas were derived from partial melting of the lower crust and subsequently underwent extensive fractional crystallization. The W mineralization in the Sansheng is genetically related to the W-bearing granites, and extreme fractional crystallization was critical for W enrichment in granitic magma. The trace element compositions of the wolframite show similar enrichments in HREEs, Nb, Ta, and U, as well as depletion in LREEs, Rb, Ba, Th, Pb, Sr, and Ti, compared to those of the upper continental crust. We demonstrate that isovalent substitution mechanisms could have played critical roles in the formation of hydrothermal wolframite in the Sansheng deposit, and the chemical composition of wolframite is controlled by both the crystallochemical parameters and composition of the primary hydrothermal fluids. In the context of the regional geology, the new data suggest that the Sansheng W-bearing granites and corresponding mineralization formed in a post-collisional extensional setting controlled by the closure of the Mongol-Okhotsk Ocean and the rollback of the Paleo-Pacific Ocean plate during the Early Cretaceous.