The Influence of the Ailaoshan‐Red River Shear Zone on the Mineralization of the Beiya Deposit on the Southeastern Margin of the Tibetan Plateau Revealed by a 3‐D Magnetotelluric Survey

Abstract

Abstract The Beiya gold polymetallic ore deposit is one of the largest gold deposit in the world. Previous studies have suggested the formation of the Beiya deposit is closely related to the porphyritic alkaline intrusions. Different tectonic models have been proposed by geologists to explain the alkaline intrusions. However, no consensus has been reached and data for imaging of the deep crustal structure is lacking. In this study, we use magnetotelluric data to image the 3‐D crustal structure beneath the Beiya deposit and adjacent areas. The 3‐D electrical resistivity model is characterized by two conductors and three resistors, which depicts the magmatic system and fluids migration path related to the Beiya deposit. One shallow conductor beneath the Beiya deposit is suggested to represent a cooled magma chamber, which provided essential heat and metal‐rich fluids to the Beiya deposit. The shallow conductor is connected to a deep conductor located beneath the Ailaoshan‐Red River shear zone. Thus, magmas originated from mantle upwelling in an extensional tectonic background is believed to provide the heat that melted the crust and generated intermediate melts, the Ailaoshan‐Red River shear zone is proposed to facilitate ascending of partial melts from the base of the crust. Moreover, two resistors encircles the shallow conductor at upper crustal depths could have acted as an impermeable barrier that helped further subtraction of metal‐rich fluids. The Beiya gold polymetallic deposit is believed to be a typical porphyry‐skarn deposit formed closely related to the Ailaoshan‐Red River shear zone in an extensional tectonic setting.