Early Cretaceous Ningguo-Guangde weakly fractionated I-type granitoids, Jiangnan tungsten belt, China: Implications for petrogenesis and W[sbnd]Mo mineralization

Abstract

Most W mineralization in the world is genetically related with highly fractionated granitoids, but little is known about petrogenesis of weakly fractionated granitoids and its relationship with W mineralization. To reveal the petrogenesis of the weakly fractionated granitic rocks and related mineralization, a combined study of zircon UPb ages, whole-rock major-trace elements and Sr-Nd-Pb isotopes as well as apatite in-situ geochemistry was carried out for the Ningguo-Guangde granitoids in the world-class Jiangnan W belt (total resource of approximately 6.06 Mt WO3), China. Zircon UPb ages indicate that the Ningguo-Guangde granitoids were emplaced in the Early Cretaceous (ca. 138–125 Ma). These samples with moderate silicon (SiO2 = 65.5–68.4 wt%) mainly consist of high-K calc-alkaline granodiorites and monzogranites, which exhibit an affinity for the weakly fractionated I-type granite, with enrichment in light rare earth elements (LREEs), Rb, Th and U, and negative Eu (δEu = 0.64–0.91), Nb, P and Ti anomalies. All samples have Mg# values of 40.3–51.2, Sr contents of 266–411 ppm and Sr/Y ratios of 9.11–29.6, negative whole-rock εNd(t) values (−6.6 to −5.1), high radiogenic Pb isotopic compositions, and high logfO2 values (−21.7 to −12.0). The integrated interpretation of geochemical data show that the Ningguo-Guangde granitoids were likely originated from Neoproterozoic crustal components mixing with metasomatized mantle-derived magmas. A comprehensive discriminant analysis indicates that metal-rich magma source, shallow fractional crystallization and high oxygen fugacity were favorable factors for the weakly fractionated I-type granite-related WMo mineralization in southern region of Anhui Province, eastern China. Furthermore, porphyry or skarn WMo deposits can be regarded as important exploration targets in the Ningguo-Guangde region.