Geochemistry of the Mesoproterozoic Intrusions, Geochronology and Isotopic Constraints on the Xiaonanshan Cu-Ni Deposit along the Northern Margin of the North China Craton

Mesoproterozoic magma events in the Bayan Obo rift belt have remained poorly constrained and as a result, the Late Paleoproterozoic-Mesoproterozoic tectonic evolution of the rift belt has remained unclear. By a multiple-facetted regional geological investigation of this belt, we have resolved the stratigraphic sequence and geochronology of the Bayan Obo Group and made new discoveries including a three-stage mantle-derived magmatic sequence. Zircon and baddeleyite dating of Xiaonanshan hornblende pyroxenite emplaced into the Bayan Obo Group yields 207Pb/206Pb ages of ca. 1.34 and 1.33 Ga. The geochronological, geochemistry, Hf isotopic analyses place an important constraint on ages of the Late Paleoproterozoic-Mesoproterozoic strata and the evolution of the rift belt. Our field observations and U-Pb dating results suggest that mineralization is genetically related to Mesoproterozoic magmatism in North China Craton, i.e., 1.33-1.34 Ga. The δ34SV-CDT values of sulphide from the ore-bearing ultra-/mafic samples are about 6.2‰, whereas the 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values vary in the ranges of 17.598-18.115, 15.496-15.501, and 37.478-37.952, respectively. The Late Paleozoic mafic gabbro and acidic granite porphyry intrusions are possible to bimodal magmatic event related to the extensional tectonic setting of the Central Asia in this period.