Ambient noise seismic tomography of Tonglushan skarn-type Cu-Fe-Au deposit in Eastern China

Abstract

The Tonglushan (TLS) skarn-type Cu-Fe-Au deposit, located in Hubei Province of China, is facing the challenge of depletion of shallow mineral resources, highlighting the urgent need for deep mineral exploration to sustain future resource development. A range of geophysical methods has been employed to delineate subsurface lithology beneath the TLS deposit, with a particular focus on identifying skarn mineralization, which is commonly occurs along granite-marble boundaries. However, gravity and magnetic methods are less effective for detecting small geological bodies at depths > 1 km, while electromagnetic methods suffer from strong noise interference from ongoing mining activities herein. In this study, we present the first application of ambient noise tomography (ANT) to TLS ore deposit for imaging shear wave velocity structures by using a dense linear seismic array (∼10 km). The velocity images agree well with geological information revealed by drilling holes, accurately delineating the marble formation and fault structures, both of which are characterized by low-velocity anomalies. Notably, the magnetic responses of lithological model inferred from ANT agree well with the observed aeromagnetic data. The inversion results precisely delineate the interfaces between granite and marble, where the largest ore body of the TLS ore deposit is located. The geological model derived from geophysical inversion results provides a more comprehensive understanding of the TLS Cu-Fe-Au mineral system. It reveals that the granite intrusion extends to a depth of ca. 2.5 km, while the captive marble formation may reach depths of up to 2 km beneath the TLS ore deposit. These results provide key clues for finding potential skar-type Cu-Fe-Au ore bodies related to granite-sediment boundaries in the deep space (at ca. 1.0–2.0 km) of the TLS ore deposits.