The Dahutang World – class Porphyry Tungsten Deposits in North Jiangxi: Geological Characteristics and Tectonic Setting

Yangtze Craton and south to the Middle – Lower Yangtze River Valley porphyry – skarn Cu-Au-Mo-Fe ore belt (YRB) have a combined tungsten resource of ca. 3 million tonnes (Mt) and represent one of the most important tungsten regions in the world. The Dahutang porphyry tungsten deposit, with reserves of >1 Mt, is one of the largest of them. The mineralization in the Dahutang tungsten deposit is genetically associated with Cretaceous granitoids, comprising three stages of porphyritic biotite granite, finegrained biotite granite and granite porphyry diykes from early to late, and is mainly hosted within a Neoproterozoic biotite granodiorite batholith. The mineralization in the Dahutang tungsten deposit comprises veinletsdisseminated (~95% of the total reserve), breccia (~4%) and wolframite–scheelite quartz vein (~1%) ore styles. The mineralization is accompanied by zoned hydrothermal alterations that includes greisenization, K-feldspar alteration, silicification, carbonatization, chloritization and fluoritization arranged in time (early to late) and space (bottom to top) surounding the pegmatite shell between the Cretaceous porphyritic biotite granite stocks and Neoproterozoic biotite granodiorite intrusion. The molybdenite Re/Os dating shows Re/Os model ages ranging from 138.4 Ma to 143.8 Ma, with an isochron age of 139.18±0.97 Ma (MSWD=2.9). The quite low Re content in molybdenite falls between 0.5 ppm and 7.8 ppm, indicating the upper crustal source. This is quite different from molybdenites in the Middle – Lower Yangtze River Valley Cu–Au–Mo–Fe porphyry–skarn deposits (YRB) that contain between 53 ppm and 1169 ppm Re, indicating a mantle source. Further researches on the petrogenisis of the ore related Cretaceous granitoids have been performed. The zircon U–Pb analyses yield ages of 147.4±0.58 Ma – 148.3±1.9 Ma for porphyritic biotite granite, 144.7±0.47 Ma 146.1±0.64Ma for fine-grained granite, and 143.0±0.76 Ma 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 granitoids 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 peraluminous granite. The P2O5 contents of the granitoids are 0.13-0.37% and have a positive correlation with SiO2, and are thus believed to be S type. They exhibit initial Sr/Sr of 0.7153 to 0.7365 and εNd (T) of 0.7210 to 0.7251 and -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 moderate negative Eu anomaly, indicating that they were derived from the Proterozoic pelitic and pasmmitic basement strata and experienced strong fractional crystallization of plagioclase. The porphyry – skarn tungsten ore blet comprising the Dahutang tungsten system is sub-parallel with the YRB porphyry–skarn Cu–Au–Mo–Fe system at north. Both are situated in the north margin of the Yangtze Craton and have a close spatial–temporal relationship. This possibly indicates a comparable tectonic setting but different metal sources. Both systems are possibly related to subduction of the Paleo-Pacific plate beneath the Eurasian continent in Early Cretaceous. We propose that the Cretaceous granitoids and ores formed during a tearing up of the subducting Izanagi slab at ca. 150-140 Ma, which caused the upwelling of asthenosphere and resulting mantle-crust interaction. The S-type granitoids and related W-Mo 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. MAO Zhiaho, XIONG Bikang, ZHENG Wei, LIU Jiajun, XIANG Xinkui, LUO Xiaohong, 2014. The Dahutang World – class Porphyry Tungsten Deposits in North Jiangxi: Geological Characteristics and Tectonic Setting. Acta Geologica Sinica (English Edition), 88(supp. 2): 457.