Sr, Nd, Pb isotopic characteristics of granite in Jinduicheng area and their geological significance

Abstract： A study of petrology and element geochemistry shows that Jinduicheng granite porphyry and Balipo granite porphyry are I–type granites in the Jinduicheng ore concentration area. SiO2 values of Jinduicheng porphyry bodies vary in the range of 72.89%~74.06% (73.48% on average), MgO values are 0.073%~0.30%,∑REE values are 43.29%~93.94%, REE distribution patterns are of “V” type, there exists an evident negative Eu anomaly and a weak negative Ce anomaly, δEu values are 0.43~0.78, and δCe are 0.74~0.86. They are enriched with K, Rb, U, Th and Sr, and strongly depleted in Ba, P and Ti. SiO2 of Balipo granites range from 69.87 to 70.80%, Al2O3 values are 14.93%~15.46%, MgO are 0.28%~0.48%, the total rare earth element concentrations (∑REE) of the rocks are 125.23~139.63×10-6, the ratios of Sr/Y are generally higher than 60, Eu has no anomaly or weak positive anomaly, Ce shows weak negative anomaly, and there exists the enrichment of HFSE (such as Ba, U and K) and the depletion of P, Ta and Sr. Plotting of lead isotopes of granite porphyry on the 207Pb/204Pb diagrams and 208Pb/204Pb versus 206Pb/204Pb evolution curves show that lead of Balipo granite porphyry might have come from crust source area, and lead of Jinduicheng granite porphyry was probably derived from the crust-mantle mixing source area. Jinduicheng has low Nd (ε(Nd,t)= -20.8~-18.3) and high Sr (ε(Sr,t)= 63.0~74.3), Balipo rocks have extremely low ε(Nd, t) of -20.8~-18.3 and relatively high ε(Sr,t) of 63.0~74.3. Sr. Nd and Pb plots show that the Jinduicheng rocks originated from the lower crust, but were contaminated by mantle-derived materials, and the source rock of Balipo is the lower crust, which has considerable ore-forming potential. the values of Sr, Nd and Pb isotopes are similar to the data of the North China plate, suggesting that these intrusives constitute a component part of the North China plate.