Abstract:

Mujicun porphyry copper-molybdenum deposit, located in the northern section of Taihang Mountains, is an important ore deposit in the Taihang tectonic-magmatic-metallogenic belt. This article is based on the particular field works and systematic analysis of petrology, geochemical data and Sr-Nd-Pb isotopes. The result shows the ore-bearing diorite-porphyry of Mujicun belonging to the high-K calc-alkaline I-type intrusive rock. Geochemical analysis shows that the diorite-porphyry is rich in SiO₂, Al₂O₃ and Sr, a high ratio of Sr/Y, (La/Yb)N, low in Yb and Y. All the ore-bearing porphyries in the study area have similar distribution of rare earths and trace elements, with right-oblique curve, and unclear postive Eu anomalies. It is characterized by enriched large-ion lithophile elements of Ba, K, U, Sr and depleted high field strength elements such as Nb, Ta, P and Ti with adakite affinity in geochemical characteristic. The diorite porphyry has I_Sr ratios of 0.705 386 to 0.706 838，ε_Nd(t) values of -16.7 to -14.9. The averages of ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb ratios are 36.614, 15.226 and 16.545, respectively, similar to those lead isotope ratios in ore of Mujicun deposit. Sr-Nd-Pb isotopes show that the formations of the magma were probably related to origin of partial melting of lower crust with mantle materials contribution. Combining with the geological background of the study area, the authors considered that the Mujicun ore-bearing diorite porphyry possibly resulted from partial melting in lower crust with the mantle mass exchange.

Key words: porphyry Cu-Mo deposit, geochemistry, Sr-Nd-Pb isotopes, Mujicun, Taihang Mountains