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The advancement of seismic methods is vital for mineral exploration in the ongoing energy transition. In this study, we investigate the application of ambient noise seismic interferometry and surface-wave analysis to characterize the subsurface in a mineral exploration context. We then confirm the results of the passive seismic investigation through an active source experiment. We collected ambient noise data using a 2-D seismic line initially deployed for an active source reflection seismic study. By cross-correlating the signals, we retrieved the surface waves and constructed a 2-D shear-wave velocity profile using conventional surface-wave analysis. We utilized the active source data to establish initial assumptions about the surveyed medium and then validated the passive seismic experiment. The passive seismic results are concordant with the active source results and allow for the interpretation of geological contacts and fault zones. Our work demonstrates the potential of passive seismic methods for investigating local tectonic settings and their role in hardrock mineral exploration.

The undesired drill-bit deviation is a source of drilling risks and requires monitoring. Seismic-while-drilling is one potential method to achieve this and has been tested in a number of previous studies. In August 2020 in Örebro, Sweden, we conducted an experiment to test the feasibility of seismic-while-drilling drill-bit positioning and other applications of the method. We used the hammer drill-bit signal generated while drilling a 200 m deep well in hardrock conditions and implemented vertical stacking of the subsequent impulsive signals from the hammer source, generating enhanced direct arrivals from the drill-bit. Then, we used the relative arrival times to estimate the drill-bit position for selected bit depths, confirming our methodology with two numerical studies. We successfully estimated the position of the drill-bit for the numerical examples and for several of the real data examples, with the accuracy dependent on the receiver array geometry and the quality of the data. We conclude that this drill-bit positioning method shows potential for near-real-time monitoring in drilling operations that could be applicable for both impulsive and noise-retrieved drill-bit signals.

With an increasing demand for critical minerals, the mining industry requires advancements in geophysical exploration methods. A recent seismic experiment in the well investigated Blotberget iron-oxide mining area in central Sweden aims to develop the application of distributed acoustic sensing (DAS) for mineral deposit imaging. We present a comparison between seismic response of different recording arrays, including a synthetic model, broadband MEMS data, and a straight optical fiber, and extract the surface wave dispersion curves. Despite the associated challenges, we believe that distributed acoustic sensing (DAS) is a promising method for surface-wave analysis and reflection seismic applications in hard rock conditions.

Deviation from the desired drilling trajectory may cause operational problems, which may be mitigated with a real-time monitoring of the drill bit position. In this study we examine the feasibility of using the Seismic-While-Drilling (SWD) method for monitoring the deviation of the drill bit based on a case study using the continuous seismic records of a 200 m hammer drilling operation in a hard rock environment in Örebro, Sweden. As a seismic source, we consider the subsequent hammer hits. We propose a processing sequence to retrieve the seismic arrivals from a certain depth. Then, we use the traveltimes to locate the source (drill-bit) position. The results show that the method has the potential to monitor the deviation of the drill bit in near-real-time.

Deviation from the desired drilling trajectory may cause operational problems. Real-time monitoring of the drill bit position helps in mitigating these issues. In this study, we suggest a seismic-while-drilling (SWD) method to detect the (near) real-time drill bit position. We use a homogenous model typical for hard rock environments and conduct 3D finite-difference modeling of elastic wave propagation. We introduce a receiver array at the surface and a drill bit source at different depths deviating from its vertical trajectory. By cross-correlating the records in respect to a virtual source location, we obtain differences of arrival times at a given trace versus arrival times at the virtual source location. The correlation image presents a hyperbola where the apex indicates the horizontal location of the source, i.e. the closes drill-bit receiver path. Considering a 2D orthogonal array, and a 3D array, we show the possibility of monitoring and estimating the horizontal location of the drill bit.