Imaging the shallow crustal velocity structure of the Qingchengzi ore field on the Liaodong Peninsula, China, with a short-period dense array using ambient noise tomography

The Qingchengzi ore field, which is located in the middle of the Liaodong Peninsula, has a large number of Au, Ag, and Pb-Zn deposits owing to Mesozoic tectonic and magmatic-hydrothermal activities. To reveal the relationship between shallow crustal velocity and gold mineralization and provide constraints on deep ore prospecting (> 1.5 km), ambient noise tomography consisting of an experimental short-period dense array with 334 seismographs surrounding the study region, is adopted. Shallow crustal velocities at depths less than 5.0 km are obtained by a direct inversion method of Rayleigh wave phase velocity dispersion at a period of 0.5–3.0 s. We obtain the following results. (1) The Jianshanzi fault (JSZF) is well imaged at a depth of 5.0 km. Because ore-forming fluids and materials originated from adjacent concealed granite intrusions characterized by low-velocity anomalies, we infer that the JSZF contributed to mineralization. (2) The Baiyun gold alteration belt in the northern ore field has a high velocity and cuts through the surrounding low-velocity area, extending downward to approximately 0.9 km. This high-velocity belt may be a superposition of the marble of the Dashiqiao Formation and mineralization-alteration, which suggests that the depth of the belt may be of favorable prospecting potential. (3) Based on the obvious low-velocity intrusive anomalies beneath the southern Xiaotongjiapuzi gold belt, we deduce that the mineralization of the Xiaotongjiapuzi gold belt is controlled by unexposed granite intrusions and thus has high mineralization potential at great depths. (4) A geologically reasonable model of the distribution of possible concealed granite intrusions related to deep mineralization and two prospective mineralization areas is presented.