Application of surface‐wave tomography to mineral exploration: a case study from Siilinjärvi, Finland

Abstract

In order to assess the feasibility and validity of surface‐wave tomography as a tool for mineral exploration, we present an active seismic three‐dimensional case study from the Siilinjärvi mine in Eastern Finland. The aim of the survey is to identify the formation carrying the mineralization in an area south of the main pit, which will be mined in the future. Before acquiring the data, we performed an accurate survey design to maximize data coverage and minimize the time for deployment and recollection of the equipment. We extract path‐averaged Rayleigh‐wave phase‐velocity dispersion curves by means of a two‐station method. We invert them using a computationally efficient tomographic code which does not require the computation of phase‐velocity maps and inverts directly for one‐dimensional S‐wave velocity models. The retrieved velocities are in good agreement with the data from a borehole in the vicinity, and the pseudo three–dimensional S‐wave velocity volume allows us to identify the geological contact between the formation hosting most of the mineralization and the surrounding rock. We conclude that the proposed method is a valid tool, given the small amount of equipment used and the acceptable amount of time required to process the data.

Surface-wave tomography for mineral exploration: a successful combination of passive and active data (Siilinjärvi phosphorus mine, Finland)

“…Passive data from all stations were recorded at 500 Hz and stored in 1-minute segy files. The deployment design was chosen to respect site and instrumentation logistical constraints and to optimize subsurface illumination (in terms of wavelength and azimuth coverage) in the areas of interest (Da Col et al, 2020).…”

“…to increase depth and resolution of the shear-wave velocity model retrieved for the southern continuation of the mineralization by active SWT (Da Col et al, 2020).…”

“…The result is a 3D matrix having kx-ky spectra as planes at the different investigated frequencies (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). This frequency band was chosen to lower the frequency content retrieved from active DCs, generally in the range 7-48 Hz (Da Col et al, 2020). The position of the spectral maximum in each kx-ky plane provides wavenumbers and azimuth of the dominant SWs propagating at that frequency during the 2-s window.…”

“…Promising examples, though, have shown its potential to be used as a low-cost and environmentally friendly investigation method, also in hydrocarbon (e.g. Bussat and Kugler, 2009) and mineral (Hollis et al, 2018;Lynch et al, 2019;Da Col et al, 2020) exploration.…”

Integrated Geological and Geophysical Mapping of a Carbonatite-Hosting Outcrop in Siilinjärvi, Finland, Using Unmanned Aerial Systems

“…Our area of investigation is the Siilinjärvi apatite ore mine in Finland [25]. The site is an ideal testing ground due to the wealth of existing evaluation data, including geophysical [26][27][28][29] structural-geological [30][31][32], geochronological, and mineralogical information [33,34]. We used two on-site survey days to acquire high-resolution UAS data and ground validation in an area of about 1 km 2 .…”