Azimuthal Anisotropy of Ambient Noise Rayleigh Waves Revealing Ore-Controlling Structures and Ore-Related Rock Bodies in a Mineral District

Surface wave signals between station pairs can be obtained by cross-correlating long-term continuous ambient noise recordings, from which group- and phase-velocity dispersion measurements at different periods are obtained and subsequently inverted for 3-D shear-wave velocity structures from shallow crust to upper mantle. This method does not rely on artificial seismic sources such as explosives, features relatively low exploration costs, and is well suited to complex topographic and environmental conditions. In recent years, it has been widely applied to image 3-D isotropic shear-wave velocity structures of mineral districts at different spatial scales (Hollis et al., 2018; Zheng et al., 2022; Jing et al., 2025). However, due to limitations in imaging resolution and the relatively small density contrast between ore-related rock bodies and surrounding host rocks, isotropic velocity structures alone are often insufficient for the effective identification and detailed characterization of ore-related rock bodies.

To address these limitations, we employed a direct surface wave tomography framework (Fang et al.,2015; Liu et al., 2019) to a selected mineral district using dense array ambient noise data. We first resolved the 3-D isotropic shear-wave velocity structure and subsequently retrieved the azimuthally anisotropic velocity structure in the very shallow crust. The results demonstrate that the isotropic velocity structure clearly delineates the major ore-controlling faults and structural framework of the mineral district, providing insights into its ore-forming tectonic regime. Besides, the azimuthally anisotropic shear-wave velocity structure shows strong spatial consistency with the distribution of known ore-related rock bodies and effectively highlights potential favorable mineralization targets. Overall, our study suggests that the combined interpretation of 3-D isotropic and azimuthally anisotropic velocity structures derived from ambient noise surface wave tomography provides an effective geophysical tool for mineral exploration and evaluation at both shallow and deep levels in mineral districts.

Reference

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