Re-Os ages for molybdenum mineralization in the Fengning region of northern Hebei Province, China: New constraints on the timing of mineralization and geodynamic setting

A recently recognized molybdenum (Mo) metallogenic belt is present within and adjacent to the northern part of the North China Craton (NCC). More than 20 Mo deposits are present in the belt, including the Sadaigoumen and Dacaoping porphyry deposits located in the Fengning region of the northern part of Hebei Province. The Sadaigoumen deposit has a Re-Os molybdenite weighted mean age of 236.5 ± 2.2 Ma (MSWD = 1.4, n = 6), which is more reliable than existing dates and is interpreted as the precise age for formation of the deposit. The Dacaoping Mo deposit is about 100 million years younger, with a Re-Os molybdenite isochron age of 140.1 ± 3.4 Ma (2σ, MSWD = 0.26, n = 5), which is within error of the weighted mean age of 139.4 ± 0.9 Ma. The ages of the two deposits show that there are at least two episodes of Mo porphyry formation in the Fengning region. In combination with the regional geological evolution of this part of the craton margin, we propose that the Triassic Mo event at Sadaigoumen is associated with a collisional event during the closure of the ancient Asian Ocean, whereas the Early Cretaceous Mo event at Dacaoping is associated with lithospheric thinning of the NCC.