Source characteristics of magmatic rocks and zircon U-Pb age in the Mangchang ore field, Danchi metallogenic belt, Guangxi

The Danchi metallogenic belt is an important tin-polymetallic metallogenic belt in Guangxi, China. Previous work focused mainly on the Sn-polymetallic deposits in the Dachang and the Wuxu ore fields, while less work has been carried out on the ages, source features and ore potential fertility of the felsic igneous rocks in the Machang ore field. Magmatic activities are strong in the Mangchang ore field, where concealed small grain granites and porphyritic granites and their related muscovite granite porphyry dykes and porphyry granite dykes were found, respectively. Zircon LA-ICP-MS U-Pb ages of a porphyry granite dyke, and major and trace element compositions of granite porphyry dikes and muscovite porphyry granite dykes are analyzed in order to reveal the ages of their magmatic activities, source features and fertility of the different igneous felsic rocks in the Mangchang ore field. The granite porphyry dyke has a zircon U-Pb age of 89. 1 +/- 0. 9Ma ( MSWD = 0. 9) , which is similar to the zircon ages of felsic igneous rocks and cassiterite U-Pb ages of the ore bodies in the Dachang ore field of the same metallogenic belt. This similar zircon and cassiterite U-Pb ages in the Mangchang and Dachang ore fields suggest that the magmatic activities and related Sn-polymetallic mineralization occurred at about 90Ma in the Danchi metallogenic belt. The muscovite granite porphyry dyke is characterized by high A/CNK (2. 69 similar to 2. 88) , with a mineral assemblage containing muscovite and being distributed along the S-type granite evolution line on the Th vs. Rb diagram, which is the same as those of the Longxiangai biotite granite in the Dachang ore field, indicating that both of them could be classified as S-type granite. The granite porphyry dykes which emplaced later than the muscovite granite dyke have lower SiO2 and higher MgO, Fe2O3T , CaO and TiO2 concentrations than the muscovite granite dyke and the both types of dykes distribute on different domains on the diagrams of SiO2 vs. TiO2, Fe2O3T , Al2O3 and P2O5 without evolution trend, suggesting that they are not derived from the same magma chamber, but from partial melting of different metasedimentary rocks. The muscovite granite porphyry dyke is characterized by high concentrations of Al2O3, K2O , Rb, Cs, Sn, W, Nb, and Ta and is located in the domain of clay rich sedimentary source on the Rb/ Ba vs. Rb/Sr diagram, suggesting that it was sourced from partial melting of clay and rare metal rich sedimentary source formed by strong weathering. Our results indicate that the basement of southwestern China contains clay and rare metal rich metasedimentary rocks, which could provide enough ore forming material for the formation of large and giant Sn( W) and other rare metal deposits in southwestern China and the adjacent area.