Apatite and zircon geochemistry for discriminating ore-forming intrusions in the Luming giant porphyry Mo deposit, Northeastern China

Abstract

The Luming giant porphyry Mo deposit in NE China host >0.89Mt Mo, but which intrusion induced the Mo mineralization is still in debated. In this study, apatite and zircon geochemistry from three mentioned ore-forming granites, namely monzogranitic porphyry (MGP), granodiorite (GD) and monzogranite (MG) in Luming ore district are presented in order to constrain the real ore-forming granite. Apatite and zircon U-Pb dating of the MGP, GD and MG yield a crystallization age of ca. 177 Ma, ca. 187 Ma and ca. 186 Ma, respectively. Whole-rock geochemistry, in-situ apatite Sr-Nd and zircon Hf isotopic compositions suggest that these granites formed by partial melting of juvenile lower crust with different depth. Both the MGP and GD have adakitic affinities and the depth of their magma source is > 45 km with garnet as residual phase, whereas the source depths for the MG was < 33 km with plagioclase as residue. Apatite and zircon geochemical features indicated that the magma of MGP and GD have higher oxygen fugacity, water contents and lower Ti-in-zircon temperatures than these of the MG, which make the MGP and GD are more favorable for Mo mineralization, but the less volume of GD limited its metallogenic potential. Decoupled Nd-Hf isotopes of the MGP, GD and MG could be induced by recycled ocean sediment added in their source region, and the addition of recycled sediments could be account for Mo concentrate in the source and regional Mo mineralization.