Innovative seismic imaging of volcanogenic massive sulfide deposits, Neves-Corvo, Portugal — Part 2: Surface array

Abstract

Seismic methods are an affordable and effective way of studying the subsurface for mineral exploration. With the goal of testing new technologies for mineral exploration in highly challenging mining areas, in early 2019 an innovative seismic survey was conducted at the Neves-Corvo mine, south Portugal. This study focuses on the data and results from the surface array data, while an accompanying article deals with the underground seismic data. The surface seismic survey consisted of two perpendicular 2D profiles positioned above the known world-class tier-1 Lombador deposit. Simultaneously a survey inside the active underground mine took place, being unique as it included the testing of a prototype system that enabled accurate GPS-time (micro-second accuracy) synchronization inside the mine tunnels, approximately 650 m below the surface profiles. Due to the active mining operations the surface data are noisy. To handle this a carefully tailored processing algorithm was developed and applied to enhance reflections in the data, interpreted to originate from lithological contacts and the Lombador deposit. The results and interpretations from 2D processing were validated taking advantage of the known deposit geometry using 3D exploding reflector modeling and pseudo-3D cross-dip analysis. These analyses suggest that there is an out-of-plane signature of the Lombador deposit on the surface data. Additionally, source points activated in the exploration tunnels and simultaneously recorded on the surface profiles allowed to create a 2D velocity model that was used for migration and time-to-depth conversion, providing a reliable 2D seismic section of the subsurface under the surface profiles. This study demonstrates that limited surface coverage 2D surveys and a velocity model derived from the tunnel-to-surface seismic recordings, allow for imaging of key subsurface geological structures and to delineate mineral deposits of economic interest.

Integrated Underground Mining Hazard Assessment, Management, Environmental Monitoring, and Policy Control in Pakistan

“…Regardless of whether or not the decision-matrix risk-assessment (DMRA) method is used and based on the assessment of explosion-related activities, the mineral-bearing minerals are broken, and rock excavation products and equipment are destroyed [60]. In mineral exploration, the goal is to find out where the mineral deposits are located underground [61,62]. In mining, the goal is to test the wall for labor movement in the mine, and, in road accessibility, the goal is to transport the excavated minerals to the proper location within the matrix without causing any major harm or recoverable injuries [63,64].…”

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

“…The source provides a flat amplitude response capable of a 2–200‐Hz bandwidth at a peak force of approximately 7 kN. Earlier tests with the source were done at a sedimentary rock setting and inside mining tunnels (Brodic et al ., 2021a, 2021b; Donoso et al ., 2021), while in this study we validated the source on the surface at a hardrock site, more specifically, an iron oxide deposit located near Blötberget in central Sweden (Fig. 1).…”

3D reflection seismic imaging of volcanogenic massive sulphides at Neves‐Corvo, Portugal

“…The northern part of the 3D grid coincides with a 2019 surface and in-mine seismic survey (Figure 1), where two profiles were acquired on the surface above the Lombador deposit, while simultaneously four seismic profiles were deployed and recorded inside mining and exploration tunnels at 650 m depth, arguably the first time a seismic acquisition survey of this size has been carried out inside an active mine (Brodic et al, 2021;Donoso et al, 2021). The 3D data processing job in this article benefited from the experience and velocity models found in the 2019 survey.…”

“…The reprocessing results benefited from a more robust refraction static solution, improved velocity model obtained from previous research done in the mine tunnels (Donoso et al., 2021) as well as a thorough analysis of the common depth‐point binning size, which is deemed essential in obtaining an improved 3D seismic volume of the study area. The study also highlights the importance of 3D seismic methods for accurate targeting and mapping by comparing them with previous 2D seismic processing results (Donoso et al., 2020).…”