Broadband magnetotelluric (BMT) detecting blind gold deposits with interface-type: A case of deep prospecting in the Getang area, southwestern Guizhou

This paper is the result of mineral exploration engineering.

Objective Accomplished by the gradual depletion of mineral resources of shallow laterite-type gold deposits, e.g., Baozidong in Getang area, it is essential to detect deep alternative resources. Based on the metallogenic prediction factors such as regional metallogeny, geophysical and geochemical anomalies, and typical deposit characteristics, the Si/Ca interface between carbonatite in Permian Maokou Formation (P₂m) and clasolite of Longtan Formation (P₃l) at the footwall of the Haimagu ore controlling fault show an ideal prospect for interface-type gold deposits.

Methods The broadband magnetotelluric (BMT) method was introduced to imagine the electrical structure of 0-2 km depth in the southwest section of the Haimagu fault. The low resistivity zones revealing by the BMT inversion imply the Haimagu fault with multi-stage activity. In the early stage (before the Middle Permian), Haimagu fault is a tensile normal fault dipping to the northeast, and is a compressive reverse fault in the late stage (after the Early Triassic), dipping to the southeast with angel of 70°-80°. According to the gradient zone of high and low resistivity zone, it is inferred that the interface between Maokou Formation and Longtan Formation features paleo-karst landform with relative uplift and depression in the deep.

Results As for the metallogenic model, e.g., prospecting criteria and regional geophysical and geochemical anomalies of the typical deposits in this area, it is considered that the northwest of Haimagu fault with little exploration is worth drilling the deep resource potential.

Conclusions The combination technology of shallow and deep exploration (element geochemical anomaly and broadband magnetotelluric detection technology) can optimize to determine target areas. The relative uplifts of P₂/P₃ and Si/Ca interface adjacent to the Haimagu fault are favorable for drilling verification.