New insights from legacy seismic data: reprocessing of legacy 2D seismic data for imaging of iron‐oxide mineralization near Sishen Mine, South Africa

Abstract

Two overlapping legacy seismic profiles, 130 km long end to end, were shot in the 1990s over the Kuruman Hills on the western margin of the Kaapvaal Craton in southern Africa. The 6‐s profiles were aimed at investigating the crustal structure of the western Kaapvaal Craton as well as to locate potential continuation of the Witwatersrand gold‐bearing horizons beneath the cover rocks, the latter of which was unsuccessful. In this study, the legacy seismic data are reprocessed and used to image the iron‐oxide (mainly haematite) mineralization found in the Kuruman Formation of the Griqualand‐West Supergroup, which outcrops along the two seismic profiles. The seismic profiles are located close to the Sishen open pit iron mine, where one of the world's largest iron ore concentrations (986 Mt) is mined. The reprocessed and merged seismic data are combined with magnetic, magnetotelluric, borehole and outcrop data to constrain the interpretation, and all indicate the mineralization host rocks to have ∼500 m thickness and 950 m depth. The seismic data further reveal seismic reflections associated with multiple iron ore horizons, which are affected by a first‐order scale syncline and numerous near‐vertically dipping (∼65–80°) normal and reverse faults of various orientations and throws, thus providing insight into the structurally controlled iron ore mineralization in the area. Seismic tomography and magnetotellurics characterize the sediments to have a velocity ranging between 5000 and 6000 m/s and a resistivity of <10 Ωm. The seismic imaging of the syncline and associated structural disruptions is important for future mining purposes and plans in the area as these structures might have preserved iron‐oxide mineralization from erosion. The reprocessed data thus provide information that could be incorporated in potential future underground mine planning in the area, improving the resource evaluation of the iron‐oxide deposit. Legacy seismic data are thus shown to hold intrinsic quality and possible untapped potential that can be realized via data reprocessing.

Cost‐effective in‐mine seismic experiments to image platinum deposits and associated geological structures at Maseve platinum mine, South Africa

“…21 m. Theoretically, this implies that two or more geological features within 21 m of each other will not be resolved as separate features. However, smaller features could still be detected, but this will depend on signal‐to‐noise ratio of the data, the velocity field and the migration algorithm used for migration (Manzi et al ., 2014; Westgate et al ., 2020).…”

Seismic delineation of the gold‐bearing structures in the South Rand goldfield (South Africa): A comparison of pre‐stack time and depth migration approaches on legacy seismic data

“…The two unconformities (U1 and R1) are clearly mapped due to the high acoustic impedance contrast between the overlying Karoo strata with low velocities (∼4000 m/s) and densities (∼2.10 g/cm 3 ) and the underlying Ventersdorp basaltic lavas with high velocities (∼6400 m/s) and densities (∼2.90 g/cm 3 ) (Westgate et al, 2020). The contact between the Ventersdorp basaltic lavas and the underlying Central Rand Group quartzite with relatively lower velocities (∼5400 m/s) and densities (∼2.67 g/cm 3 ) also exhibit a significant acoustic impedance contrast (Manzi et al, 2015).…”

“…Moreover, a better understanding of the velocity fields from hard rock environment has shown significant improvement in depth imaging of complex geological structures. Several authors (e.g., Malehmir et al, 2019; Manzi et al, 2019; Westgate et al, 2020) have demonstrated, through various case studies from hard rock environments, how legacy reflection seismic data can be revisited and reprocessed to improve the quality of the data and delineate the complex geological structures that host mineral deposits. The objective of this study is to reprocess the 18 km long, 6 s two‐way time (TWT), legacy 2D reflection seismic profile acquired in 1993 near Burnstone mine in the South Rand goldfield of the Witwatersrand Basin (South Africa).…”

Moving towards deep underground mineral resources: Drivers, challenges and potential solutions

“…The journey from initial consideration, proof-of-concept, proof-of-value to adoption is long but constitutes almost half of the roadmap to a dominantly automated context (Global Mining Guidelines Group, 2019). The history of mining is extensive, and particularly in South Africa where underground mining has generated enormous amounts of irreplaceable data (e.g., Manzi et al, 2015;Westgate et al, 2020;Zhang et al, 2021b;Nwaila et al, 2022). However, legacy data can be difficult to comprehend, as metadata, reference data and other supplementary information are incomplete, missing or not machine readable.…”