Seismic Reflection Profiles Reveal the Ore-Controlling Structures of Carlin-Style Gold Deposits in Lannigou Gold Fields, Southwestern Guizhou, China

Abstract

Abstract The Carlin-style Lannigou gold deposit is hosted in Triassic flysch in the Nanpanjiang basin in southwestern Guizhou Province, southern China. This study is the first to use seismic exploration data to elucidate the structural architecture of the Lannigou Carlin-style gold deposit. We use regional seismic reflection data to show that gold orebodies are controlled by faults that link with the regional Lannigou-Weihuai fault, and we use this new insight to determine the relationship between mineralization and inverted basin faults to constrain the structural controls of this gold system. A grid of seven seismic sections covering the Lannigou gold fields is combined with field geologic data to reveal two distinct structural patterns. Seismic data reveals that the inverted, E-dipping Lannigou-Weihuai fault is shallowly penetrating (less than 2 km) in the north and increasingly penetrates the pre-Devonian basement rocks to the south, where the fault can be imaged to depths greater than 5 to 7 km. Basement-penetrating faults link the metamorphic basement and overlying basin successions that include potential source rocks for oil generation, interpreted gas reservoirs, and gold deposits. Therefore, these deep-seated faults are important channels for the migration of ore fluids, especially for the transport of hydrocarbon gas, which may have served as an important chemical trap for gold mineralization. Seismic data also reveals the W-dipping Qiaoluo fault that bounds the inverted Qiaoluo half-graben. Fault crosscutting relationships reveal an extensional episode from the Late Paleozoic to the early Anisian age of the Middle Triassic epoch (i.e., the depositional age of the second member of the Middle Triassic Xuman Formation), which is overprinted by an episode of middle Anisian basin inversion during deposition of the third member of the Xuman Formation. This inversion occurred at ca. 248 to 246 Ma. Based on the ore-controlling constraints and previous geochronological data, we consider that the Lannigou gold deposit was formed in the Late Triassic to Early Jurassic during syndepositional inversion of existing basement-penetrating basinal faults in a foreland basin. The first-order faults in the above structural belts, such as the Lannigou-Weihuai fault and the blind Qiaoluo fault, are most favorable targets for further exploration of undiscovered gold orebodies. This study demonstrates that seismic reflection is a powerful tool to reveal deep structures at varying scales from mineral deposits to sedimentary basins.