Abstract
Stratigraphy and facies analysis in a mining waste domain such as in tailings storage facilities (TSFs) is still a complex task due to sparsely distributed field data. Geophysical techniques and the interpretation of geophysical data in terms of stratigraphy and facies get relevance for integrating geophysics with other models investigating mining waste domains (e.g., hydrogeological-geochemical).In this paper, we introduce a conventional application of differential operators for interpreting geophysical data in terms of stratigraphy and facies analysis in TSFs. The geophysical data is acquired in a tailings area in the Pyhäsalmi mine, Finland, using seismic refraction (SR) and electric resistivity imaging (ERI) techniques. The SR inversion model constrained by a geological model approximated the ground and bedrock layers by delineating P-wave velocities (Vp). The SR layered model served as a constraint for the electrical resistivity (ρ) model in the ERI method. ERI inversion model data was used for facies analysis and interpretation in terms of other subsurface variables (e.g., water saturation, salinity). For this, a first-order derivative (gradient approach) and a second-order derivative combined with a Gaussian filter (Laplacian approach) were applied to highlight facies and transition zones. The approach embeds the data as scalar functions within a space domain defined by the model local structure. When applied to the ERI data, the gradient and the Laplacian functions captured the local extrema and the minimum threshold crossings respectively enhancing local geoelectric zones and layered contacts in line with field observations. This paper demonstrated that such image analysis can be proposed for interpretation of geophysical data in terms of segmentation and analysis of local facies, relevant in model conceptualization and parameterization of hydrogeological models.
Highlights
Reclaimed land in mine sites includes areas previously disturbed by mining activities or areas that hosted mining waste such as tailings or waste rocks
A transition zone is depicted by the curve bend on each travel time curve which is suggested to be the interface between the saturated tailings and the underlying ground
Travel time curves can anticipate a shallower depth of tailings in line K1K7 as it approaches the center of the tailings domain where an early increase of Vp values suggest a transition to a faster velocity propagating stratigraphy
Summary
Reclaimed land in mine sites includes areas previously disturbed by mining activities or areas that hosted mining waste such as tailings or waste rocks These environments are classified as landfill areas for hazardous waste, monitoring the changes and conditions in the subsurface is critical to make decisions such as ensuring their long-term stability and performance. Identifying facies is of importance because they define the constraints and narrow the range of parameters to assign (Pyrcz and Deutsch, 2014) enabling a better description of the depositional domains. Domain properties such as porosity, permeability, clay content, hydrochemistry can be adequately assigned having a clear definition of stratigraphy and facies that are agreeable to field conditions
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