Contrasting tectonic regimes between late Jurassic and Early Cretaceous porphyry-epithermal Cu-Mo-Au mineralization in NE China: A perspective from the petrogenesis of the adakitic rocks in the Sishanlinchang porphyry Cu-Mo deposit

Abstract

The Mongol–Okhotsk and Paleo-Pacific tectonic regimes both have an influence in NE China during the late Mesozoic. The Sishanlinchang and several newly reported late Mesozoic porphyry Cu–Mo deposits in NE China are typical products of this interaction. A systematic study of these deposits provides new insights into the genesis of porphyry Cu–Mo systems in the region. Here we present petrological, geochronological, whole–rock geochemical and isotopic data from the ore-forming rocks in the Sishanlinchang deposit, together with a compilation of data from late Mesozoic porphyry Cu–Mo deposits in NE China, to reveal their magma source, and corresponding geodynamic settings. Zircon U–Pb dating shows that the studied granites were emplaced at 111 Ma, which contrasts with previously reported occurrences of late Jurassic porphyry Cu–Mo deposits in the northern NE China, indicating at least two episodes of porphyry Cu–Mo mineralization during the late Mesozoic. Whole-rock geochemical data show that all of the late Mesozoic ore-forming granites have low Y and Yb, high Sr contents, and high Sr/Y ratios (35.70–71.59), which exhibit an adakitic affinity. High Na2O, Cr, and Ni contents, and Mg# (47–58) values, a low proportion of garnet in the source, positive whole-rock εNd(t) values (1.21–2.27) and pronounced positive zircon εHf(t) values (6.85–9.37) indicate that the adakitic rocks were derived from partial melting of oceanic crust with assimilation of enriched mantle materials. Combined with our studies and previous studies, we conclude that the Early Cretaceous porphyry–epithermal Cu–Mo–Au deposits in the eastern NE China were controlled by the Paleo-Pacific tectonic regime, which is different from the Late Jurassic Cu–Mo deposits in the northern NE China controlled by the Mongol–Okhotsk tectonic regime.