Innovative seismic imaging of volcanogenic massive sulfide deposits, Neves-Corvo, Portugal — Part 1: In-mine array

Abstract

To evaluate and upscale the feasibility of utilizing exploration tunnels in an operating mine for active-source seismic imaging, a seismic experiment was conducted at the Neves-Corvo mine, in southern Portugal. Four seismic profiles were deployed in exploration drifts ca. 650 m beneath the ground surface, above the world-class Lombador volcanogenic massive sulfide (VMS) deposit. In addition to the tunnel profiles, two perpendicular surface seismic profiles were deployed above the exploration tunnels. The survey was possible due to a newly developed prototype GPS-time transmitter enabling accurate GPS synchronization of cabled and nodal seismic recorders, both below and on the surface. Another innovative acquisition aspect was a 1.65 t broadband, linear synchronous motor (LSM) driven - electric seismic vibrator (e-vib) used as the seismic source along two of the exploration tunnels. Challenges and innovations necessary for active-source tunnel seismic acquisition, characterized by high levels of vibrational noise from the mining activities, are discussed. Additionally, the LSM vibrator’s signal and overall seismic data quality in this hard rock mining environment are evaluated. Processing results from the tunnel data and 3D reflection imaging of the Lombador deposit below the exploration tunnels are shown and the results checked for consistency through constant-velocity 3D ray-tracing traveltime forward modeling. For imaging purposes, 3D Kirchhoff pre-stack depth and post-stack time migration algorithms were used, with both successfully imaging the targeted deposit. The results obtained show that active-source seismic imaging using subsurface mining infrastructure of operational mines is possible. However, it requires innovative exploration strategies, a broadband seismic source, an accurate GPS-time system capable of transmitting GPS-time hundreds of meters below the surface and careful processing. The results obtained open up possibilities for similar studies in different mining or tunneling projects.

Broadband seismic source data acquisition and processing to delineate iron oxide deposits in the Blötberget mine‐central Sweden

“…2b). When an electrical current is induced in the coil, linear forces are generated, acting along a line over the full stroke, which results in lower harmonic distortion, thus allowing a wider range of low frequencies to be produced (Li et al ., 2019; Noorlandt et al ., 2015; Brodic et al ., 2021a, 2021b). The forces generated are transferred into the subsurface via a ground‐coupled base plate while the suppression mechanism reduces the resonance produced by the mass of the carrier vehicle and improves ground coupling.…”

“…To evaluate the electromagnetic vibrator (E‐Vib) in a hardrock setting, a field campaign took place in September 2019. One of the advantages of the E‐Vib is its design and dimensions enabling versatility (Malehmir et al ., 2019; Brodic et al ., 2021a, 2021b) and allowing it to be attached to locally available vehicles such as skid‐steers or telehandlers, and the latter was used in this test (Fig. 3a).…”

3D high-resolution seismic imaging of the iron oxide deposits in Ludvika (Sweden) using full-waveform inversion and reverse time migration

“…Unfortunately, this approach can fail to address all of the imaging challenges. Unlike the oil and gas exploration, where prestack depth migration (PreSDM) is often the standard imaging method, it has been only recently applied to characterise the geologically complex hardrock environment in a mineral exploration context (Schmelzbach et al, 2008;Hloušek et al, 2015;Heinonen et al, 2019;Singh et al, 2019;Bräunig et al, 2020;Brodic et al, 2021).…”

Cost‐effective in‐mine seismic experiments to image platinum deposits and associated geological structures at Maseve platinum mine, South Africa

“…As an alternative solution, and despite suffering from noise produced by mine operations such as blasting, ventilation and drilling, in‐mine seismics has proven useful in improving the imaging resolution of the mineral deposits and geological structures (Brodic et al ., 2017, 2021; Donoso et al ., 2021). The application of in‐mine seismic techniques has grown worldwide; however, the techniques are not yet well established in deep South African mines.…”