Seismic imaging across fault systems in the Abitibi greenstone belt – an analysis of pre- and post-stack migration approaches in the Chibougamau area, Quebec, Canada

Abstract

Abstract. Two high-resolution seismic reflection profiles acquired north and south of Chibougamau, located in the northeast of the Abitibi subprovince of Canada, help understand historic volcanically hosted massive sulfide (VMS) deposits and hydrothermal Cu–Au mineralization found there. Major faults crossed by the profiles include the Barlow fault in the north and the Doda fault and the Guercheville fault in the south, all targets of this study that seeks to determine spatial relationships with a known metal endowment in the area. Common-offset DMO corrections and common-offset pre-stack time migrations (PSTMs) were considered. Irregularities of the trace midpoint distribution resulting from the crooked geometry of both profiles and their relative contribution to the DMO and PSTM methods and seismic illumination were assessed in the context of the complex subsurface architecture of the area. To scrutinize this contribution, seismic images were generated for offset ranges of 0–9 km using increments of 3 km. Migration of out-of-plane reflections used cross-dip element analysis to accurately estimate the fault dip. The seismic imaging shows the thickening of the upper-crustal rocks near the fault zones along both profiles. In the northern seismic reflection section, the key geological structures identified include the Barlow fault and two diffraction sets imaged within the fault zone that represent potential targets for future exploration. The south seismic reflection section shows rather a complicated geometry of two fault systems. The Guercheville fault observed as a subhorizontal reflector connects to a steeply dipping reflector. The Doda fault dips subvertical in the shallow crust but as a steeply dipping reflection set at depth. Nearby gold showings suggest that these faults may help channel and concentrate mineralizing fluids.

Preface: State of the art in mineral exploration

“…The authors apply dip moveout corrections (DMO) and pre-stack time migration (PSTM) algorithms to obtain images of the main faults in the area, as well as identifying two diffraction sets that could be targeted in future exploration efforts. In their analysis, Cheraghi et al (2021) confirm that both techniques, DMO and PSTM, are very sensitive to irregularities in the acquisition geometry, in this case produced by the crooked footprint of the profiles as well as gaps of shots or receivers during the acquisition. This is, unfortunately, a common challenge in land seismic exploration, which can lead to misinterpretation of out-of-plane reflections.…”

Reflection seismic imaging across a greenstone belt, Abitibi (Ontario), Canada

“…Table 1 presents the geometrical attributes of the Swayze East survey. Cheraghi et al (2021) showed the effect of offset distribution for a crooked-line survey in a crystalline rock environment on common-offset Kirchhoff-style DMO No. of sweeps 1…”

“…Another criterion could be the complexity of the subsurface architecture (i.e., dip and strike) wherever a crooked survey is acquired. These criteria define whether common midpoints (CMPs) contribute constructively or destructively after wave equation DMO or PSTM application (Cheraghi et al., 2021). In comparison, the weighting of the wave field in a receiver location by considering neighbouring traces makes the CM imaging algorithm independent from the geometry of the source–receiver pairs, as well as dip and strike of the geological formations (Hloušek et al., 2015a).…”

“…Cheraghi et al. (2021) showed the effect of offset distribution for a crooked‐line survey in a crystalline rock environment on common‐offset Kirchhoff‐style DMO corrections or PSTM. Their case study indicates that the offset range has a dominant effect on the quality of the imaging illumination of these methods; therefore, we first determined the longest offset range that could contribute constructively to imaging without generating any artefact.…”

“…Besides the velocity model, the performance of PSTM in crystalline rock environments depends strongly on the geometry and especially how common midpoints (CMPs) contribute to the illumination of steeply dipping structures (Cheraghi et al., 2021). In many cases, the irregularity of the survey (i.e., crooked pattern and irregular spatial distribution of CMPs) affects the proper subsurface imaging (Canning & Gardner, 1998).…”