Geochronology and tectonic setting of Pb-Zn-Mo deposits and related igneous rocks in the Yinshan region, Jinzhai, Anhui province, China

摘要

The Gaijing Pb-Zn-Mo deposit and Shapinggou Mo deposit in the Yinshan region, Jinzhai, Anhui province, China, are hosted in various granitic intrusions with ~(40)Ar/~(39)Ar ages obtained for biotite and hornblende of 136.8±1.6Ma (medium-grained monzogranite), 130.4±1.2 Ma (fine-grained granite), and 125.4±1.0Ma (fine-grained diorite). The modes of occurrence and cross-cutting relationships among the igneous intrusions indicate that alkali quartz-syenite and quartz-syenite porphyry (cryptoexplosive breccia) formed later than the calc-alkali monzogranite, granite, and diorite. Molybdenum mineralization occurs in pipe-like bodies hosted in cryptoexplosive breccia (pipe), quartz-syenite (porphyry), monzogranite, and granite, whereas Pb-Zn mineralization occurs in veins distally from the Mo mineralization. The Re-Os isotopic model ages of molybdenite from the Gaijing Pb-Zn-Mo deposit are 112.6 ±1.3 and 113.5 ±1.3 Ma, consistent with the ages of other molybdenum deposits throughout the East Qinling-Dabie metallogenic belt. The geological characteristics and isotopic ages of the Gaijing Pb-Zn-Mo and Shapinggou Mo deposits indicate a genetic relationship to the emplacement of the quartz-syenite (porphyry) and to shallow-seated porphyry-cryptoex-plosive breccia intrusions. The present results, combined with existing data, suggest that the Pb-Zn-Mo deposits and related igneous rocks were formed in a geodynamic setting of regional lithospheric thinning, de-lamination, and thermal erosion in East China. The deposits are part of the East Qinling-Dabie molybdenum belt, which in turn is part of a large-scale E-W-trending metallogenic belt in East China.