Abstract. To discover or delineate mineral deposits and other geological
features such as faults and lithological boundaries in their host rocks,
seismic methods are preferred for imaging the targets at great depth. One
major goal for seismic methods is to produce a reliable image of the
reflectors underground given the typical discontinuous geology in
crystalline environments with low signal-to-noise ratios. In this study, we
investigate the usefulness of the reverse time migration (RTM) imaging algorithm
in hardrock environments by applying it to a 2D dataset, which was acquired
in the Ludvika mining area of central Sweden. We provide a how-to solution
for applications of RTM in future and similar datasets. When using the RTM
imaging technique properly, it is possible to obtain high-fidelity seismic
images of the subsurface. Due to good amplitude preservation in the RTM
image, the imaged reflectors provide indications to infer their geological
origin. In order to obtain a reliable RTM image, we performed a detailed
data pre-processing flow to deal with random noise, near-surface effects, and
irregular receiver and source spacing, which can downgrade the
final image if ignored. Exemplified with the Ludvika data, the resultant RTM
image not only delineates the iron oxide deposits down to 1200 m depth as
shown from previous studies, but also provides a better inferred ending of
sheet-like mineralization. Additionally, the RTM image provides
much-improved reflection of the dike and crosscutting features relative to
the mineralized sheets when compared to the images produced by Kirchhoff
migration in the previous studies. Two of the imaged crosscutting features
are considered to be crucial when interpreting large-scale geological
structures at the site and the likely disappearance of mineralization at
depth. Using a field dataset acquired in hardrock environment, we
demonstrate the usefulness of RTM imaging workflows for deep targeting
mineral deposits.
3D reflection seismic imaging of the iron-oxide deposits in the Ludvika mining area (Sweden) using a focusing pre-stack depth migration approach