Tracing the formation and modification of the Keketale VMS-type Pb-Zn deposit, Altai Mountains: Insights from ore deposit geology, geochronology, and magnetite geochemistry
Chao Sun, Xiaoyong Yang, Huishan Zhang, Wenhua Ji, Bo Chen, Zengchan Dong, Mohamed Faisal, Dehua Xi
Abstract
The Keketale Pb-Zn deposit (KKTL deposit) is one of the largest VMS-type Pb-Zn deposits in the Altai Mountains, Central Asian Orogenic Belt. Field investigations and microscopic observations suggest that the evolution of the deposit can be divided into two major stages: syngenetic massive sulfide mineralization related to coeval volcanism and epigenetic polymetallic vein mineralization linked to metamorphism and deformation. Supported by the U-Pb dating of zircon and garnet of immediate host rocks (i.e. garnet biotite schist), the former occurred in ∼400 Ma during the Early Devonian, and the latter developed in ∼265 Ma during the Middle Permian. The original VMS hydrothermal system is varying in the physicochemical conditions (e.g., temperature, oxygen fugacity, and sulfur fugacity) in space, together with fluid-rock interactions, causing two types of magnetites with different compositions and textures in different sites. Furthermore, it is revealed that the spatial variations of temperature-sensitive elements (e.g., Ti and Sn) of magnetite can be used to find the location of the hydrothermal vent, which can serve to guide the regional prospecting. Modifications of the KKTL deposit are indicated by deformed sulfides, annealed sulfides, remobilized sulfides, and epigenetic polymetallic veins. We draw a conclusion that the KKTL deposit witnessed the evolution of the Chinese Altai and the Paleo-Asian Ocean, the syngenetic volcanic-associated VMS mineralization was linked with arc/arc-back tectonic setting caused by the subduction of the Paleo-Asian Ocean toward the Chinese Altai, and the modification of the KKTL deposit was related to the collision between the Chinese Altai and the Junggar Block, along with the closing of the back-arc basin.