NSG2020 3rd Conference on Geophysics for Mineral Exploration and Mining

Achieving a sustainable ecosystem is important in trying to reduce soil contamination along with other aspects. Investigating the fate of pollutants in soil that causes soil and groundwater contamination, soil erosion, reduced plant growth and irreversible environmental changes are some of the most important issues. Resistance-based geophysical methods and induced polarization parameter suitable to estimate soil contamination development. This study aimed to evaluate the plant’s root system able to remove contamination from mining drainage subsurface. Soil contamination was studied by resistivity and induced polarization in a lead and zinc drainage irrigation under subsurface around the olive and grape bushes. 2D apparent resistivity and partial induced polarization were obtained by inverse modeling. Therefore, contamination propagation is spread vertically and laterally. Overtime after 2 weeks of irrigation, the contaminated area decreases, due to the uptake of contamination by plant roots and soil microorganisms. Plants are highly efficient in absorbing soil pollutants from the soil due to their extensive root system. Also, because the olive tree has broad roots and grape shrubs have short, compact roots that make a different condition in absorbing pollutants from the soil and also reduce the risk of leaching and movement of heavy metal pollutants into groundwater resources.

To improve safety in coal mine, particularly around roadway, non-destructive and cost-effective seismic methods need to be developed. We focus our research on dispersive waves which propagate inside the coal seam in the vicinity of the roadway. We call it tunnel-channel waves (TC-waves). We demonstrate how the group velocity and frequency of the dominant energy of TC-waves behave based on finite-difference 3D numerical modelling and confront it with a dataset recorded in the Rydułtowy coal mine in Poland. We observe connection between investigated parameters and velocity anomaly in the numerical model as well as rock mass deformation due to past exploitation in the mine.

The growing demand for affordable exploration techniques initated the launch of the research project “SIT4ME” to improve current small- and large-scale mineral exploration in deep basement environments. In course of this research project (Seismic Imaging Techniques for Mineral exploration) we would like to introduce a hybrid method combining underground reflection seismic ( Orlowsky et al. 2018 ), tunnel VSP ( Brückl et al. 2001 ) and 3D borehole radar ( Orlowsky et al. 2016 ). Both, a 3D borehole radar measurement and a reflection seismic acquisition were performed within a gallery of a former underground salt mine used as a deep geological repository for radioactive waste. After preparing, editing, processing and evaluating both datasets we noticed that both techniques helped to identify several structures of the local salt dome. The seismic measurement resulted in mainly 2D resolution of several layer boundaries within the salt dome and detected the limits of the salt dome. The borehole radar measurement provided a good 3D insight of internal stratigraphic layering, faults, layer boundaries and the in-mine workings.

Seismic methods are an affordable and effective way of studying the subsurface for mineral exploration, particularly when target depths are beyond what other geophysical methods can resolve (e.g., > 500 m). With the goal of testing new technologies for exploration in highly challenging mining areas, a seismic survey was conducted at the Neves-Corvo mine, south Portugal. The seismic data acquired consisted of two perpendicular 2D surface profiles positioned above the known Lombador deposit. Due to active mining operations, the data show a highly noisy nature. To supress the noise, carefully designed processing algorithms were applied enhancing reflections present in the data, interpreted to originate from lithological contacts and the Lombador deposit. These interpretations were validated using 3D exploding reflector modelling taking advantage of the known deposit geometry. Additionally, source points activated in an exploration tunnels located approximately 650m below the surface were synchronized and simultaneously recorded on the surface via a newly-developed GPS-time system. Providing a unique opportunity for estimating seismic velocities between the tunnel and surface profiles, using them as a guide for time-to-depth conversion and helping identify a low-velocity zone in the southern portion of the surface profile that may be related to lithological contacts or observed faulting.

We develop and compare two methods of jointly inverting airborne gravity gradiometry (AGG) and total magnetic intensity (TMI) data in the presence of remanent magnetization. One is based on Gramian structural constraints, and the other uses a joint focusing stabilizer. Enhancing structural similarity between multiple geophysical models can help isolate mineralized targets. In the areas with remanent magnetization, one should invert not only for magnetic susceptibility, but for a 3D distribution of magnetization vector as well. The Gramian structural constraints enforce the correlation of the model gradients. The joint focusing stabilizer is implemented using minimum support approach, which forces a similarity of the shapes of the targets. We apply these novel joint inversion methods to interpretation of the airborne data collected over the Thunderbird V-Ti-Fe deposit in Ontario, Canada. By combining the complementary AGG and TMI data, we generate the jointly inverted models which provide a more consistent image of the geologic structure of the area.

Seismic methods are routinely used for hardrock imaging and mineral-exploration purposes. However, hardrock seismic data requires careful processing, where weathering layer - refraction static corrections have shown to be of great importance for successful imaging. In our study, six differently obtained data-driven weathering layer static solutions are analyzed and compared using a seismic dataset from a mining site in Sweden. Three of the six approaches utilize first-breaks and are based on (1) the standard refraction-inversion method (RI), (2) the application of the RI after adding additional first-breaks via supervirtual seismic interferometry (SVSI), and (3) a tomography-based static solution (Tomostatics). The other three approaches employ surface-waves and are based on (4) the direct transformation of SW dispersion curves, (5) joint inversion of dispersion curves as well as first-breaks and (6) surface-wave tomography. All tested methods were successful in enhancing coherency of the main ore body reflection. A crosscutting reflection can also be seen following the first-break based refraction statics, with highest coherency seen after the application of the SVSI-enhanced RI refraction statics. The examples presented suggest that these methods can be complementary and in the absence of notable first-breaks, surface waves can be utilized to estimate weathering layer static corrections.

"Gravity observations have been classically used to improve the geological knowledge of a studied region for purposes related to resources exploration. A classical solution to perform such an operation, usually called gravity interpretation, consists in applying a proper filter to the observed gravitational field followed by a visual matching between the residual observations and the known map of geological units. In the current work, we present an alternative solution, in which the observation filtering is substituted by a proper removal of the gravitational effect of an a-priori model of sediments and mantle, while the visual matching is replaced by a Bayesian algorithm. The result is a fully automatic methodology to improve an a-priori map of geological units on the basis of gravity observations. The algorithm is tested by means of a realistic synthetic example."

Deep mineral resources need to be discovered and accessed to ensure the ever increasing needs of minerals in our society. Seismic methods have proven their capacity to image important targets in deep, crystalline environments, but their use is not yet a standard within conventional mineral exploration activities. The EIT-RawMaterials Programme has funded the “Seismic Imaging for Mineral Exploration - SIT4ME” project, aimed to develop seismic imaging approaches for mineral exploration within crystalline settings, at a reduced cost. The aim of this transnational initiative is to test the efficiency of seismic methods to image target ore structures by comparing control and natural source seismic data-sets in two real case-studies, the Zinkgruvan mine in Sweden and the Sotiel mine in Spain. This work describes the main objectives and activities carried out as part of the project, and outlines the expected outcomes of this initiative.

Dense and regular trace sampling is of great importance when utilizing seismic methods for exploration. An increment in the fold coverage can improve the illumination of the subsurface, resulting in better images of potential deposits and also the structures hosting them. Additionally, different advanced seismic processing and imaging algorithms require dense and regular datasets in order to achieve optimum results. Thus, we propose using data retrieved by seismic interferometry as a data-driven method to provide missing traces for relatively large source or receiver gaps. Together with a data-reconstruction algorithm, we merge these two datasets in an optimal way for further processing as just one dataset. We apply the proposed methodology to an active-source dataset acquired at the Ludvika Mines of Sweden for imaging of its iron-oxide deposit.

A capable and light-weight aeromagnetic surveying system is invariably preferred because of its cost-effectiveness, low personnel risk, and so on. However, developing such a system requires a solid understanding of noise from the platform on which it is built – an unmanned aerial vehicle (UAV). Therefore, we investigate static and dynamic noise from a hybrid UAV. The static noise from the platform is discontinuous leading to the spiky 4th difference due to radio transmission and cultural noise in the vicinity, whereas the dynamic noise is mainly due to the attitude of the aircraft, which can be reduced by proper aeromagnetic compensation. Consequently, the high noise level requires some painstaking effort to improve the current design of the system, such as increasing the distance between the magnetic sensors and sources of interference.