Geochemistry, Zircon U–Pb Age, and Lu–Hf Isotope of the Granite Porphyry in Leimengou Mo Deposit in the East Qinling Molybdenum Ore Belt, China

摘要

The Leimengou Mo deposit is one of the typical porphyry deposits in the East Qinling molybdenum ore belt. The Mo mineralization mainly hosts in the Leimengou intrusion, with minor by the gneiss of Archean Taihua Group. The Leimengou intrusion is composed of granite porphyry and monzonitic granite porphyry. Zircon U–Pb LA-(MC)-ICP-MS dating of the two rocks yield the same age of 131 ± 0.6 Ma (N = 23, MSWD = 1.6), consistent with 132 ± 2 Ma of Mo mineralization age obtained by the Re–Os method. The Leimengou intrusion is peraluminous (A/CNK = 1.06–1.28) and high-K calc-alkaline series (K 2 O + Na 2 O = 7.84%–9.07%). The REE and trace elements are enriched in large ion lithophile elements (LREE, K, Rb, Ba, Sr, Th and U), and depleted in high-field strength elements (HREE, Nb, Ti and P), with moderately negative abnormal of Eu. Both granite porphyry and monzonitic granite porphyry show a large variation in zircon Hf isotopic compositions with ε Hf ( t ) values of ?27.9 to ?16.9 and ?26.0 to ?15.2, and two-stage model ages of 2259 to 2946 Ma and 2149 to 2827 Ma, respectively. Whole rock geochemistry and zircon Lu–Hf isotopic compositions suggest that the Leimengou intrusion was derived mainly from an ancient continental crust (probably Archean Taihua Group), with the addition of mantle-derived components.