Geological And Geochemical Characteristics Of The Magmatic Rocks And The Genetic Connection With Ore Deposits,Nanling-Xuancheng Area,Anhui Province

The Nanling-Xuancheng area of Anhui Province,a Meso-Cenozoic volcanicsedimentary basin,is located in the southeastern limb of the northeastern part of the Middle-Lower Yangtze River Valley Tectonic-Magmatic-Metallogenic Belt.The previous geological surveys,ore exploration and scientific research are relatively weak,and the published research results of regional geology,magmatic rocks and deposits are rare.Ever since the twenty-first century,with the advancement of deep prospecting,various work has made continuous progress,especially in recent years,the prospecting results show that the area has great prospecting potential and prospects,and the mineralization is closely related to magmatism.Based on this,this paper focuses on LA-ICP-MS Zircon U-Pb dating,major elements,trace elements,rare earth elements and Sr-Nd-Pb-Hf isotope of the magmatic rocks from the area,and compared with those of the magmatic rocks in other areas of the Middle-Lower Yangtze River Valley Tectonic-Magmatic-Metallogenic Belt,for determing the ages and discussing the petrogenesis of the magmatic rocks and the relationship between the magmatism and mineralization.In the Nanling-Xuancheng area,a part of the magmatic rocks intruded into the basement of the basin or erupped as the cover rocks of the basin,and the other part of the magmatic rocks occured in the nappe above the basin.The intrusive rocks are mainly granodiorite,granodiorite porphyry,quartz diorite,quartz diorite porphyrite,diorite porphyrite and pyroxene diorite,and the volcanic rocks are dacitic pyroclastic rocks and lavas.Our results indicate that the LA-ICP-MS zircon U-Pb ages of the intrusive rocks are between 138~135Ma,and the ages of the volcanic rocks are all less than 134 Ma,suggesting that the magmatism occurred in Early Cretaceous of the late Yanshanian stage.The characteristics of major elements show that the magmatic rocks are high for Si,K and Na,belonging to sub-alkaline and high-K calc-alkaline series.The magmatic rocks have the similar characteristics of trace elements and rare earth elements.The characteristics of trace elements show that the magmatic rocks are rich in Rb,Th,U and K,and poor in Ti,Nb and Ta.The volcanic rocks are more deficient from intrusive rocks in Sr and P contents.The REE distribution pattern shows that the magmatic rocks are rich in LREE and weak negative Eu anomalies.The characteristics of Sr-Nd-Pb isotope and Zircon Hf isotope indicate that the isotopic composition of the magmatic rocks is between the enriched mantle and the lower crust,the magmatic rocks were generated by the mixing of crust-derived and mantle-derived magma.The magmatic rocks originated from the enriched lithospheric mantle,affected by the crustal mixing.The magmatism is restricted by the geodynamic background of the Middle-Lower Yangtze River Valley TectonicMagmatic-Metallogenic Belt,which occurred in a tectonic setting changed from compression to extension.Above all indicates that the late Mesozoic magmatism in the Nanling-Xuancheng area has the dual characteristics of the those in upwelling area and depression area in the Middle-Lower Yangtze River Valley Tectonic-Magmatic-Metallogenic Belt,that is,the study area not only developed intrusive rocks the isotopic geological ages and geological and geochemical characteristics are same as those in the upwelling area(such as the Tongling district),but also developed volcanic rocks the isotopic geological ages and geological and geochemical characteristics in the depression area(such as the Luzong and Ningwu basins).The duality of magmatism may imply the mineralization duality,that is,the study area may develop hydrothermal porphyry-type,skarn-type and vein-type polymetallic copper-gold deposits related to intrusive magmatism of the upwelling area,also porphyry iron(sulfur)deposits associated with volcanic-subvolcanic rocks of the depression area.