| Popis: |
The Jiangnan tungsten belt (JNB), a newly identified in the past decade, has a total resource of more than 6 Mt WO3 and still has a good potential for further prospecting. The JNB, located along the Jiangnan Massif (JM) and its eastern extensional areas, is adjacent to and parallel with the Middle-Lower Yangtze River porphyry-skarn Cu-Mo-Au-Fe belt (MLYRB) at north. Both JNB and MLYRB have the same mineralization periods, i.e., 150–135 and 130–125 Ma. The tungsten mineralization in JNB developed at the proximal contact of granite plutons, whereas the Pb-Zn±Cu veins occurs at the distal areas, exhibiting an obvious zoning in space. Apart from the Dongping quartz vein wolframite deposit, the other W deposits in the JNB belong to porphyry and skarn types. The Zhuxi scheelite skarn deposit with 3.44 Mt of WO3 is the largest one over the world. Meanwhile, the exploration of the Dahutang super-large, and Dongyuan and Yangchuling large porphyry W deposits has proven the porphyry is a new major W type except for both skarn and quartz vein types which were recognized before. Moreover, it is interesting to find unusual scheelite-bearing anorthosite and albitite dikes, which cut through the skarn ores in the Zhuxi deposit area. The scheelite-bearing albitite is proposed to crystallize from Al-, Si-, P-, W-, and F-rich residual magma whereas the scheelite-bearing anorthosite formed when the residual magma was contaminated by pure limestone in a reducing environment. The granitoids associated with W deposits and W-Mo deposits in the JNB are biotite monzonite and granodiorite, respectively. According to the petrology, geochemistry and major accessory minerals, the ore-related granitoids can be recognized as S type (or ilmenite series) with peraluminous nature and I type (or magnetite series) with metaluminous nature. Geochemical and Sr-Nd-Hf isotopic data indicate the W deposits-related granitoids were derived from the remelting of the Neoproterozoic phyllite and slate and the W-Mo deposits-related granitoids were also derived from the same strata but with input of mantle materials. According to the sources of granitoids and the skarn mineral assemblages as well as mineral chemistry it can be recognized as reduced W and the oxidized W-Mo deposits. Usually the reduced W deposit appears as large and super-large scale, such as the Zhuxi and Dahutang whereas the oxidized W-Mo as relatively smaller. A tectonic model is suggested to explain the two periods of mineralization in both JNB and MLYRB, which are corresponding to oblique subduction of Izanagi plate in 150–135 Ma at quite low angle and the extension tectonic regime of post-subduction at 130–125 Ma, respectively. The porphyry-skarn Cu-Mo-Au-Fe system in early period and apatite-magnetite system in late period along MLYRB are related to the granitoids derived from the slab subducted slab and the stagnant slab whereas tow periods of porphyry-skarn as well as quartz vein type W(Sn) deposits are associated with the granitoids which were remelted from the Neoproterozoic phyllite deduced from mantle underplated. Moreover, a deposit model is set up for the relationship among the porphyry-skarn W and W-Mo, and distal Pb-Zn-Ag±Cu veins, which can be referenced for the further prospecting in JNB and the regions with similar tectonic setting. |
