Re-Os and U-Pb geochronology of porphyry Mo deposits in central Jilin Province: Mo ore-forming stages in northeast China

摘要

Central Jilin Province lies along the eastern edge of the Xing-Meng orogenic belt of northeast China. At least 10 Mo deposits have been discovered in this area, making it the second-richest concentration of Mo resources in China. To better understand the formation and distribution of porphyry Mo deposits in the area, we investigated the geological characteristics of the deposits and applied zircon U-Pb and molybdenite Re-Os isotope dating to constrain the age of mineralization. Our new geochronological data show the following: the Jidetun Mo deposit yields molybdenite Re-Os model ages of 164.6-167,1 Ma, an isochron age of 168 ± 2.5 Ma, and a weighted mean model age of 165.9 ± 1.2 Ma; the Houdaomu Mo deposit yields molybdenite Re-Os model ages of 167.4-167.7 Ma, an isochron age of 168 ± 13 Ma, and a weighted mean model age of 167.5 ±1.2 Ma; and the Chang'anpu Mo deposit yields a zircon U-Pb age for granodiorite porphyry of 166.9 ± 1.5 Ma (N = 16). These new age data, combined with existing molybdenite Re-Os dates, show that intense porphyry Mo mineralization was coeval with magmatism during the Middle Jurassic (167.8 ± 0.4 Ma, r > 0.999). The geotectonic mechanisms respon sible for Mo mineralization were probably related to subduction of the Palaeo-Pacific plate beneath the Eurasian continent. Combining published molybdenite Re-Os and zircon U-Pb ages for northeast China, the Mo deposits are shown to have been formed during multiple events coinciding with periods of magmatic activity. We identified three phases of mineraliza tion, two of which had several stages: the Caledonian (485-480 Ma); the Indosinian comprising the Early-Middle Triassic (248-236 Ma) and Late Triassic (226-208 Ma) stages; and the Yanshanian phase comprising the Early-Middle Jurassic (202-165 Ma), Late Jurassic-early Early Cretaceous (154-129 Ma), and Early Cretaceous (114-111 Ma) stages. Although Mo deposits formed during each phase/stage, most of the mineralization occurred during the Early-Middle Jurassic.