Geology and molybdenite Re-Os age of the Dahutang granite-related veinlets-disseminated tungsten ore field in the Jiangxin Province, China

摘要

This is a brief research report about the recently-discovered and currently being explored Dahutang tungsten de posit (or ore field) in northwestern Jiangxi, south-central China. The deposit is located south of the Middle-Lower Yangtze River valley Cu-Au-Mo-Fe porphyry-skarn belt (YRB). The mineralization is genetically associated with Cretaceous porphyritic biotite granite and fine-grained biotite granite and is mainly hosted within a Neoproterozoic biotite granodiorite batholith. The Dahutang ore field comprises veinlets-disseminated (～95% of the total reserve), breccia (-4%) and wolframite-scheelite quartz vein (～1%) ore styles. The mineralization and alteration are close to the pegmatite shell between the Cretaceous porphyritic biotite granite and Neoproterozoic biotite granodiorite and the three styles of ore bodies mentioned above are related to zoned hydrothermal alteration that includes greisenization, K-feldspar alteration, silirifkation, carbonatization, chloritization and fluoritization arranged in time (early to late) and space (bottom to top). Five samples of molybdenite from the three types of ores have been collected for Re/Os dating. The results show 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 that is indicative of the upper crustal source. This is quite different from molybdenites in the YRB Cu-Au-Mo-Fe porphyry-skarn deposits that contain between 53 ppm and 1169 ppm Re, indicating a mantle source. The Dahutang tungsten system is sub-parallel with the YRB porphyry-skarn Cu-Au-Mo-Fe system. 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 related to subduc-tion of the Paleo-Pacifk plate beneath the Eurasian continent in Early Cretaceous. The Cu-Au-Mo-Fe porphyry-skarn ores are believed genetically related to granitoids derived from the subducting slab, whereas the porphyry W deposits are associated with S-type granitoids produced by remelting of the upper crust by heat from upwelling asthenoshere.