Geochronology and geochemical features of Longwogou granite in Xiaoshan Mountain, western Henan Province, and their geological implications

Abstract：In order to study petrogenesis, geodynamics and mineralization potential of small intermediate-acid igneous bodies in north Xiaoshan Mountain, the authors determined the age and geochemical compositions of Longwogou granite body, which is one of these igneous bodies. Longwogou body is composed of porphyritic biotite monzonitic granite with extensively distributed K-feldspar megacrysts. 206Pb/238U ages of 30 zircons by LA-ICP-MS method are from 125 Ma to 132 Ma, and the weighted average age is (128±1) Ma. Longwogou granite is characterized by higher SiO2 and alkali, enrichment of K2O, and lower MgO and CaO. Compositional spots of Longwogou granite fall into high-K calc-alkaline series in the SiO2?K2O diagram. A/CNK ratios of Longwogou granite are from 1.00 to 1.11. According to the petrologic and geochemical features of Longwogou granite, it belongs to K-rich calc-alkaline granite (KCG). In chondrite-normalized REE patterns, Longwogou granite samples have shown the characteristics of LREE-enrichment and HREE depletion without obvious Eu anomaly. The (La/Yb)N ratios of Longwogou granite are from 18.55 to 26.92. In spider diagram, the enrichment of Rb, Th, and trough of Nb and Ta are displayed. Samples of Longwogou granite have higher Sr and lower Y, and the Sr/Y ratios are in the range of 30.8-60.8, suggesting that Longwogou granite is adakitic granite. Longwogou granite originated from partial melting of the thickened lower crust, and its residual phases of partial melting source included garnet, rutile and hornblende. North Xiaoshan Mountain area underwent lithosphere delamination in early Cretaceous, and it was one of geological responses to huge lithosphere thinning of eastern China in Mesozoic. The formation age of Longwogou body falls into the time interval of extensive and intensive endogenetic mineralization in east Qinling orogen belt. Samples from Longwogou body display obvious enrichment of Au, Ag, Mo and W. It is considered that Longwogou granite and its concealed part have large mineralization potential.