The linkage between the Jiawula-Chaganbulagen Ag-Pb-Zn and adjacent porphyry Mo-Cu mineralization, Inner Mongolia, northeast China

Abstract The Jiawula-Chaganbulagen (Jia-Cha) super-large, magmatic-hydrothermal Ag-Pb-Zn ore field in the southern Erguna Block, northeast China, is characterized by a large and well-developed alteration and metallic zonation (∼56 km2) that is centered on porphyry Mo-Cu mineralization. The ore field includes two intermediate-sulfidation epithermal Ag-Pb-Zn deposits, which are located at Jiawula and Chaganbulagen. A weighted-mean molybdenite Re-Os age of 135.1 ± 2.1 Ma (MSWD = 0.16) and a molybdenite 187Re-187Os isochron age of 135.4 ± 2.3 Ma (MSWD = 0.44) were obtained for the Mo-Cu mineralization, and the host quartz monzonite porphyry yielded a weighted-mean zircon U-Pb age of 141.9 ± 2.4 Ma (MSWD = 0.044). Geochronological data suggest that the epithermal mineralization occurred at 135 to 133 Ma, and the porphyry age is little older than the porphyry-epithermal mineralization. The porphyry Mo-Cu mineralization is interpreted as the hydrothermal center of the ore field, based on the metal zonation:Mo-Cu → Zn-Cu → Zn-Cu-Pb-(Ag) → Zn-Pb-Ag-(Cu) → Ag (Au)-Pb-Zn → Ag, with vertical ore minerals zonation from deeper molybdenite-chalcopyrite to shallower sphalerite-galena-chalcopyrite through molybdenite-chalcopyrite-sphalerite. Trace element analyses by LA-ICP-MS of pyrite and pyrrhotite show that micro-inclusions exhibit similar “ore field-scale” trace element zonation: Bi-Ag → Bi-Sb-Ag → Sb-Ag. Geological and geochronological evidence indicates that the Jia-Cha epithermal system is genetically related to the adjacent porphyry Mo-Cu mineralization. XRF element mappings of the replaced ores revealed that late ore stage oxidizing fluids dissolved the early chalcopyrite at depth, and then replaced the sulfides in the main ore stage. Porphyry-epithermal mineralization system in the Jia-Cha ore field is significant for further exploration for porphyry Mo-Cu and epithermal Ag-Pb-Zn deposits in northeast China.