Abstract
The Jiazishan porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. To better understand the link between mineralization and host igneous rocks, we studied samples from underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Seven molybdenite samples yield a Re–Os isochron weighted mean age of 135.4 ± 2.1 Ma, whereas the porphyry granite samples yield crystallization ages of 139 ± 1.5 Ma (Jiazishan deposit) and 133 ± 1 Ma (Taolaituo deposit). The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to Early Cretaceous porphyry emplacement. Re contents of the molybdenite range from 21.74 ppm to 52.08 ppm, with an average of 35.92 ppm, whereas δ34 S values of the sulphide vary from 1.3‰ to 4.2‰. The ores have 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.178–18.385, 15.503–15.613, and 37.979–38.382, respectively. We also obtained a weighted mean U–Pb zircon age of 294.2 ± 2.1 Ma for the oldest granite in Jiazishan area. All granites are A-type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Jiazishan deposit occurred contemporaneously with Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in Northeast China.
Highlights
Economic molybdenum deposits include porphyry, skarn, and hydrothermal vein types (Luo et al 1991)
The Great Hinggan Range is located in the eastern section of the Central Asian Orogenic Belt (CAOB) between the Siberian Craton and North China Craton (NCC) (Zhai et al 2014; Mao et al 2014) (Figure 1)
The Aershan pluton: an A-type affinity The term ‘A-type granite’ was introduced by Loiselle and Wones (1979) to distinguish a group of granitic rocks that occur in extensional tectonic environments but there is no clear consensus on their origin (e.g. Loiselle and Wones 1979; Collins et al 1982; Clemens et al 1986; Whalen et al 1987; Turner et al 1992; Smith et al 1999; Anderson et al 2003; Franco Pirajno et al 2008)
Summary
Economic molybdenum deposits include porphyry-, skarn-, and hydrothermal vein types (Luo et al 1991). Molybdenite Re–Os dating is a powerful tool for precise age determination of ore deposits (cf Jingwen et al 1999; Mathur et al 2000, 2005; Creaser et al 2002; Gilmer et al 2003; Selby and Creaser 2003; Mao et al 2006a, 2008) In this contribution, we present new S and Pb isotopic compositions of the main sulphides along with U–Pb ages of magmatic zircon and the Re–Os isochron age of molybdenite from the Jiazishan deposit to constrain the sources of ores and the relationships between Mo mineralization and regional geodynamic evolution. This work contributes to a better understanding of ore genesis, timing of the ore system, and the Mesozoic geodynamic evolution of the central-southern segment of the Great Hinggan Range in Northeast China
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