Molybdenite Re-Os Age of the Yaochong Molybdenum Deposit in the Northern Margin of the Dabie Mountain and Its Geological Significance

Yaochong Mo deposit,located in Xinxian County,Henan Province,is a newly discovered porphyry Mo deposit in the northern foot of Dabie Mountains.The orebody occur mainly in the Proterozoic Dabie complex at the outer contact of the granite porphyry and controlled by underlying porphyry and structures.The mineralization can be divided into 4stages:(Ⅰ)quartz-K-feldspar stage;(Ⅱ)molybdenite-K-feldsparquartz stage;(Ⅲ)molybdenite-quartz stage;(Ⅳ)Calcite stage.The molybdenite-K-feldspar-quartz stage and molybdenite-quartz stage are the main mineralization stages.In this study we useD the inductively coupled plasma mass spectrometry(TJA X-series ICP-MS)and six molybdenite samples in the Yaochong deposit have been selected for precise Re-Os dating.We got their Re-Os isochron age of 136.9±1.20Ma and weighted average age of 137.19±0.79Ma,which indicates the mineralization age is Early Cretaceous.Based on the research of the isotopic composition of Re and S in the molybdenite of the Yaochong deposit,we suppose that the materials of the deposit mainly came from lower crust,with a minor contribution of mantle.With the references of former researches in the northern foot of Dabie Mountains,we also suppose that there were two pulses of the Mo mineralization(~140Ma and 127~110Ma)in this area,which was consistent with the second and third pulses of Mo mineralization in the East Qinling molybdenum belt.The Mo deposits in the northern foot of Dabie Mountains can be ascribed to the response of the tectonic regime transformed from extrusion to extension and to regional large-scale lithospheric thinning in the Dabie orogenic belt after Indosinian.