Late Yanshanian Magmatism And W-Mineralization In Yunkai Region,Guangxi Province

Multiple Late Yanshanian granitic magmatism and related W ore deposits were discorved from Yunkai reion in the most southwestern Qinzhou–Hangzhou metallogenic belt.However,these granites and W-deposits haven't been earned much attentions compared to the early Yanshanian W-deposits in South China.In this dissertation,detailed studies have been carried out on the You Mapo,San Chachong,Michang,Songwang and other granites and related W-deposities,including detailed field investigations,U-Pb zircon chronology,petrological geochemistry,isotope geochemistry and fluid geology,to acquire the emplacement ages and genetic types,source nature and tectonic setting of the granitic rocks,mineralization ages,orgin of ore-forming fluids and sources of ore-forming materials,for better understanding the relationships between magmatic activities and W mineralization.The U-Pb dating results of zircons from 8 granites and 1 magic microgranular enclave(MME)from Yuankai region indicate three emplacement episodes of granitic intrusion in 113-110 Ma,105-98 Ma and 88 Ma of the late Yanshanian era,Consistent with those mgmatic episodes and intervals in the Southeast China.The granites dominate I-type granite with minor S-type granite(such as the You Mapo muscovite granite).These I-type granites show high Sr low Y and are characterized by adakitic granite.The I-type and S-type granitic rocks were sourced promiantly from the Mesoproterozoic(TDM2(Hf)=1.5-1.3 Ga)and minor early Paleozoic juvenile crusts at different depth levels.That the coeval emplacement of adakitic I-type granite,S-type granite and together A2-type granite elsewhere in the region suggesting the magmatism occurred in a extensional gectonic background post-collision.Magma mixing occurred to the I-and S-type granites in the region.The W ore deposits in Yunkai region have skarn-type,hydrothermal vein-type and porphyry-type with scheelite ore for the skarn-type and wolframite ore for the high-T hydrothermal vein-type.The You Mapo W deposit,Michang skarn type W deposit,Shan Chachong skarn type W-deposit and Songwang porphyry Mo-W-deposit were formed in Late Cretaceous(80–110 Ma).Ore-forming fluids of these W-deposits show characteristics of middle-high temperature and low salinity.The H-O isotopes indicated that the ore-forming fluids are typical magmatic water origin.The meteoric water added in the ore-forming fluids at the late mineralization stage.The highly-contentrated distribution of d34S values(+2.2‰)of sulfides from these W-deposits implied that sulfur mainly came from the granitic magma.Fe isotopic compositions of pyrites from the ores show narrow variation range and are close to(d56Fe=0.16~0.58 ‰;d57Fe=0.02~0.54‰),indicating ore-forming metals also sourced from the igneous rocks.The W-mineralization occurred a little bit late but within the same magmatic interval of Late Yanshanian in Yunkai region.That thee ore-forming fluids origined from the granitic magmas,the ore-forming materials were sourced from the magmatic rocks and the ore deposits occur closely in space suggest close Temporal and spatial relations and thus extensional tectonic regime post-collision for ore formation at the Late Yanshanian era(110-80 Ma).The late Yanshanian,except early Yanshanian,is also an important time-span for formation of W-mineralization era in South China.The Yunkai area and other neighboring region is the important metallogenic prospect for W.