Mesozoic Magma Evolution And Metallogenesis Of Porphyry Molybdenum Deposit In Aershan Area, Da-Hinggan Mountains

Aershan area is located in the middle of Da-Hinggan Mountains, and its geotectonic location belongs to the south-eastern border of Siberia Plate. It is the strong superimposed domain between the Paleo-Asiatic tectonomagmatic domain and the circum Pacific tectonomagmatic domain. The Mesozoic magmatic activities was very strong in the study area, where large scale volcanic eruption, granitoids intrusion and metallogenesis of porphyry molybdenum deposit occurred.Based on the detailed field geological work, this paper carried out regional and case study, and systematic researched of the Mesozoic magma evolution and metallogenesis of porphyry molybdenum deposit under the guidance of contemporary petrology and porphyry mineralization theory.The zircon U-Pb age of Mesozoic volcanic rocks indicates that the volcanic activity begun in Late Jurassic, and its peak period was Early Cretaceous(130Ma～120Ma). Manketouebo Formation formed in Late Jurassic, Manitu Formation formed from Late Jurassic to Early Cretaceous, and Baiyingaolao Formation formed in Early Cretaceous. The study of Sr, Nd, Pb, O isotope show that the volcanic rocks had a close relationship to the mantle and originated from juvenile crust, perhaps a little part from mantle. Manketouebo Formation formed in the transitional periods from compression setting to extension setting, while Manitu and Baiyingaolao Formation formed in the extension setting. The formation of Mesozoic volcanic rocks were resulted from the delamination of lithosphere from Late Jurassic to Early Cretaceous under the background of long-term compression setting from Late Triassic to Middle Jurassic.The mineralization-related granite-porphyry formed in the extension setting. The REE and trace elements characteristics of the granite-porphyry are very similar to the Mesozoic volcanic rocks, indicating that they may have a similar magma source. The granite-porphyry are spatially and temporally accompanied with the volcanic rocks, and they are formed under a unified regional geological-tectonic evolution process and tectonic-magmatic activity.The study of zircon U-Pb age and molybdenite Re-Os age indicate that the porphyry molybdenum deposit formed in Early Cretaceous(140Ma～130Ma). They were produced by tectono-magmatic activities in late Yanshanian, while the porphyry deposits in Mongolia were produced in early Variscan. The characteristics of S isotope suggest that it was mainly derived from the mantle, the characteristics of lead isotope suggest that it maybe derived from the mix of mantle lead and crust lead.The ore-forming materials of Late Mesozoic porphyry molybdenum deposit in the Aersha area are mainly from porphyry themselves, while that of the polymetallic Pb-Zn-Ag deposit mainly from base. The porphyry molybdenum deposits are controlled by NE structures or NE, NW compound structures, and have typical alteration features composed of K-silicate alteration, quartz-sericite alteration, and propylitic alteration from center to outer. The molybdenum mineralization mainly hosted in quartz-sericite alteration zone. The metallogenic model is established through comprehensive analysis of regional geological setting, petrogenesis, ore deposit genesis, petrogenic and metallogenic age, and origin of petrogenic and metallogentic materials. The prospecting clues are summarized, potential prospects and further ore-prospecting suggestions are proposed.