Alteration, mineralization, and genesis of the Lietinggang–Leqingla Pb–Zn–Fe–Cu–Mo skarn deposit, Tibet, China

Abstract The northeastern Gangdese polymetallic belt is one of the most important metallogenic belts in the Tibetan collisional orogen. In this belt, three types of mineralization including skarn type Fe, skarn and breccia type Pb–Zn–Ag, porphyry and skarn type Mo–Cu–W have been recognized. Some deposits are polymetallic deposits with complex metal paragenetic assemblage which needs to be explained. The Lietinggang–Leqingla skarn deposit is the most typical one which have developed Pb–Zn–Fe–Cu–Mo five kinds of metals in the same deposit. Geological field mapping indicates that the ore district is characterized by a regular spatial zoned alteration and mineralization. Garnet skarns with Fe–Cu–Mo mineralization are developed near the intrusion, while the garnet–hedenbergite skarns and the more distal hedenbergite–ferroactinolite skarns with Pb–Zn–Cu mineralization are developed in the carbonate strata. According to the dating date, the Fe–Cu–Mo and Pb–Zn–Cu mineralization formed in the same metallogenic system. Mineralogical studies suggest that from the prograde skarn alteration stage, during the retrograde alteration stage to the oxide stage, and to the quartz–sulfide stage, the fluid conditions for skarns near the intrusion were moderately acidic and weakly oxidizing, relatively oxygenated and alkaline, and weakly oxidizing and alkaline, respectively. However, for the skarns in the carbonate strata, they were lower acidities and weakly reducing, relatively low acidities and reducing, and reducing with a low pH, respectively. Geochemical analyses give information about the elements for the skarnization and mineralization. About the element sources, the host carbonate rocks were mainly responsible for Ca and the magmatic fluids were responsible for Si, Fe and Mg. About the element migration, during the hydrothermal alteration the grossularite skarns and garnet–epidote skarns gained Fe, Mg, Mn, Ca and Sr, but lost Si and K; the andradite skarns, garnet–hedenbergite skarns and hedenbergite–ferroactinolite skarns gained Si, Fe, Mn and Mg, but lost in Ca, K and Sr; and all the skarns gained Co, V, Y, Pb, Zn and Cu, but lost Rb and Ba. The REE migrated mainly in magmatic fluids and enriched in the skarns during the prograde skarn alteration stage. However, they reacted by the ore-forming fluids and migrated out of the system, which process led to the decreasing of these elements in skarns at last. By summarizing studies here and previously published data, a genetic description for the Lietinggang–Leqingla Pb–Zn–Fe–Cu–Mo skarn deposit can be given as follows. The Fe–Cu–Mo mineralization within the garnet-rich zone formed by the interaction between fluids derived from the Jubuzhari composite intrusion and the neighboring carbonate units under a condition of oxidizing and higher temperature. The Pb–Zn–Cu mineralization within the hedenbergite and ferroactinolite-rich zone formed by the interaction between fluids also derived from the Jubuzhari composite intrusion but migrated relative long distance and distal carbonate units under a condition of reducing and lower temperature.