Geochronology and geochemistry of granitoids related to the giant Dahutang tungsten deposit, middle Yangtze River region, China: Implications for petrogenesis, geodynamic setting, and mineralization

Abstract

Porphyry and skarn deposits in the middle Yangtze Valley within the Northern Yangtze Craton have a combined tungsten resource of ~3milliontonnes (Mt) and represent one of the most important tungsten regions in the world. The Dahutang porphyry tungsten deposit, with reserves of >1Mt, is one of the largest deposits. Uranium–Pb analyses for the ore-related granitoids yield ages of 147.4±0.58Ma–148.3±1.9Ma for porphyritic biotite granite, 144.7±0.47Ma–146.1±0.64Ma for fine-grained granite, and 143.0±0.76Ma–143.1±1.2Ma for granite porphyry, a progressive youngling of ages that is consistent with field observations. Geochemical data show that the three types of granite are characterized by enrichments in Rb, Pb, and U, and depletion in Ba, Nb, P, and Ti, with ASI [molar Al2O3/(CaO+Na2O+K2O)]>1.1 that is characteristic of a peraluminous melt. The P2O5 contents of the granites are 0.13–0.37% and have a positive correlation with SiO2, and they are thus S-type intrusions. They exhibit initial 87Sr/86Sr of 0.721 to 0.731 and εNd(t) of −5.06 to −7.99 for porphyritic biotite granite, 0.7196 to 0.7289 and −6.29 to −6.74 for fine-grained granite, and 0.7153 to 0.7365 and −5.09 to −7.64 for granite porphyry. Chondrite-normalized rare earth element (REE) patterns for the granites are characterized by enrichment in the light REE and a strong negative Eu anomaly, indicating that they were derived from the Proterozoic pelitic and psammitic basement strata and experienced strong fractional crystallization of plagioclase. Our ca. 150–140Ma age for the Dahutang S-type magmatism and W mineralization is identical to that of the I-type magmatism related to Cu–Au–Mo–Fe-bearing porphyry and skarn deposits along the middle to lower Yangtze River Valley. We propose that the latest Jurassic to earliest Cretaceous granitoids and ores formed during a tearing of the subducting Izanagi slab, which caused the upwelling of asthenosphere and resulting mantle–crust interaction. The S-type granitoids and related W ore systems resulted from the re-melting of the Proterozoic crust, whereas the I-type granitic rocks and related ores are attributed to the partial melting of the subducted slab.