Geology, Geochemistry And Genesis Of The Qian’echong And Tangjiaping Porphyry Mo Deposits, Dabie Orogen

In recent years, the breakthroughs of prospecting have been achieved in the East Qinling-Dabie area. Especially in the Dabie area, the eastern part of the East Qinling-Dabie area, a number of large-scale porphyry Mo deposits have been discovered. The additional resources of molybdenum are more than3,000,000t, which fully demonstrated the potential of mineralization in the Dabie area. The giant Qian’echong and the large Tangjiaping Mo deposits are important achievements of prospecting and exploration in Dabie area in recent years. In this paper, we chose the Qian’echong and the Tangjiaping Mo deposits as the typical deposits to dissect. Combined with previous studies, we preliminary describe the Mesozoic Mo mineralization discipline and the relationship between the Mesozoic magmatism and the Mo mineralization. Major conclusions can be summarized as following:1. Detailed field geological survey has been carried out in the Qian’echong and the Tangjiaping Mo deposits. We identified the characteristic of the ore bodies, mineral species, ore texture and structure, wall rock alteration types and zones, and also detailed divided the mineralization stages. The sulfur in the both two deposits is mainly from magma. The sulfur isotopic compositions in these two deposits are similar to other porphyry Mo deposits in the East Qinling-Dabie Mo belt.2. SHRIMP zircon U-Pb analyses of Monzogranite and granite porphyry in the concealed stock were done in this study by first time. This analyses yielded ages of130±2Ma for Monzogranite and129±2Ma for granite porphyry. Furthermore, we report the more precise Mo mineralization age, with the molybdenite Re-Os result of129.4±1.5Ma. The above results propose that magmatism and mineralization in the Qian’echong deposit took place during a relatively short interval from130to128Ma. We determined the age of the Tangjiaping granite again, and got the age of115±1Ma. This result is more precise than the previous study (121.6±4.6Ma) and is close to the age of mineralization, and could represent the formation age of the Tangjiaping granite.3. The Qian’echong granites are belong I-type granites. The Qian’echong granites are most likely to derive by partial melting of ultrahigh pressure eclogites at lower crustal levels, and that some Paleoproterozoic-Archean YC crust, such as Kongling complex, has been incorporated into the Qian’echong granites. The granite porphyry, which is more likely related to Mo mineralization, have lower Ce4+/Ce3+than the monzogranite, suggesting oxygen fugacity is not the unconditional factor that control the Mo mineralization.4. Detailed determination of genetic type of the ore-forming granite in the Tangjiaping deposit has been undergone. We studied the fresh and unaltered granites, which sampled from drill cores distributed in the edge of the ore-forming stock. The Tangjiaping granites are belong metaluminous A-type granites, with some transitional characteristics (to I-type granites). The Tangjiaping granites and nearby Shangcheng-Daquandian granites have different source rocks and origin. The Tangjiaping granites derived by partial melting of diorite at the pressure of0.4-0.8GPa, with the corresponding depth of14-28km. The source rocks of the Tangjiaping granites are most likely to be the NDC gneiss, with some enriched mantle. The Shangcheng-Daquandian granites have the same source rocks and origin with other high Sr/Y granites in the Dabie orogen, which might derived from partial melting of thickened eclogitic lower crust. 5. At ca.130Ma, the thickened eclogitic lower crust still exist beneath the Qian’echong deposit. Underplating of hot asthenosphere material triggered partial melting of the source rocks of the Qian’echong granites at lower crustal levels. After130Ma, delamination or foundering of eclogitic lower crust caused the rapid upwelling of asthenosphere material. In the setting of large-scale crustal extension, the Tangjiaping metaluminous A-type magma formed under the conditions of low-pressure, relative poor-water, and high-temperature. Then the Thangjiaping granite and porphyry Mo deposit formed at115-113Ma.6. The mineralization ages of the Mo deposits in the Dabie orogen are almost Cretaceous. In terms of spatial distribution, the Mo deposits occurred as a NWW-trending belt along the regional faults in the northern Dabie. The Mo mineralization closely related to the Cretaceous granitic magmatism. The porphyry-type is the main type of the Mo deposits in the Dabie orogen. The formation of the Mo deposits obviously controlled by faults, and intersection sites of faults in favor of the formation of the Mo deposits. The delamination of lower crust, asthenosphere upwelling, and large-scale crustal extension are main dynamic mechanism, which controlled the mineralization and magmatism in the Qian’echong and Tangjiaping Mo deposits.