Origin and rock-forming environment of the granitoids in the periphery of the Shilu iron deposit

Abstract：The Indosinian granites in the periphery of the Shilu iron deposit belong to the Changjiang granitic body. These granites are mainly monzonitic granites. They lie between metaluminous field and weakly peraluminous field, and belong to high-K calc-alkaline series and shoshonitic series. The granites have ∑REE values of 134.96-241.05 ppm and show relatively strong enrichment of light rare earth elements (LREE/HREE=4.44-9.67), with higher (La/Yb)N ratios of 3.95-10.69 and negative Eu anomalies (δEu=0.28-0.57). Mantle-normalized trace element spidergrams of all samples show obvious negative anomalies of Ba, Nb, Ta, Ce, Sr, P and Ti. The obvious negative Ba, Sr and Eu anomalies indicate that plagioclase existed in the source region or the granites experienced plagioclase crystallization and fractionation. The granites have a range of (87Sr/86Sr)i from 0.710852 to 0.715492 except for one sample (SL10-136) whose (87Sr/86Sr)i value is 0.706364 , a narrow εNd(t) value range of -7.3 to -9.1 and TDM2 model ages of 1.5–1.9 Ga, indicating a homogeneous source and partial melting of the Mid-Proterozoic Baoban Group. The granites were formed in a post-orogenic environment. Based on previous investigation of granite in Hainan Ireland, this paper deals with ireland-arc, syn-orogenic and post-orogenic granitoids in Hainan Ireland. The Hercynian to Indosinian granitoids can be compared with granitoids in northern Vietnam.