Integrated interpretation of 3D seismic data to enhance the detection of the gold‐bearing reef: Mponeng Gold mine, Witwatersrand Basin (South Africa)

Abstract

A B S T R A C TWe present an integrated approach to the seismic interpretation of one of the world's deepest gold ore body (Carbon Leader Reef) using three-dimensional seismic data, ultrasonic velocity measurements at elevated stresses, and modified instantaneous attribute analysis. Seismic wave velocities of the drill-core samples (quartzite, shale, and conglomeratic reef) from the mine are sensitive to uniaxial stress changes, i.e., they slowly increase with increasing pressure until they reach maximum value at ß25 MPa. For all the samples, seismic velocities are constant above 25 MPa, indicating a possible closure of microcracks at stress corresponding to 1.0 km-1.5 km. A reflection coefficient of 0.02 computed between hanging wall and footwall quartzites of the Carbon Leader Reef ore body suggests that it may be difficult to obtain a strong seismic reflection at their interface. Our modified seismic attribute algorithm, on the other hand, shows that the detection of the lateral continuity of the Carbon Leader Reef reflector can significantly be improved by sharpening the seismic traces. Three-dimensional seismic data reveal that faults with throws greater than 25 m that offset the Carbon Leader Reef can clearly be seen. Faults with throws less than 25 m but greater than 2-m throw were identified through horizon-based attribute analysis, while most dykes and sills with thickness less than 25 m were invisible. The detection of the lateral continuity of the Carbon Leader Reef reflector and its depth position is greatly improved by integrating the modified instantaneous attributes with controls from borehole observations. The three-dimensional visualization and effective interpretation of the Carbon Leader Reef horizon shows a host of structurally complex ore body blocks that may impact future shaft positioning and reduce its associated risks.

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

“…Previous publications and recorded exploration drilled cores show the thickness of the Witwatersrand Supergroup to be approximately 5 km (Manzi et al, 2015). The thickness of the layers associated with the Witwatersrand Supergroup package on the reprocessed 2021 pre‐stack depth migration (PreSDM) data has a thickness of ∼4.5 km, which corresponds to the expected thickness of the supergroup.…”

“…The PreSDM was applied with velocity ranges of 4000–6900 m/s, choosing the velocity model with the most coherent reflections. The velocities used were derived from the physical properties studies conducted in the Witwatersrand Basin (Manzi et al, 2015). The effectiveness of PreSDM in complex hard rock environment is well documented by various authors (e.g., Bradford et al, 2006; Buske et al, 2009; Hu and Stoffa, 2009; Manzi et al, 2012b; Storch et al, 2021).…”

Recycling of Paleoplacer Gold through Mechanical and Postdepositional Mobilization in the Neoarchean Black Reef Formation, South Africa

“…In addition to the underground mapping, we carefully applied a series of 3D seismic attributes (Manzi et al 2013(Manzi et al , 2015 to the 3D reflection seismic data to enhance detection of faults (or fractures) and dikes affecting the BRF, with vertical displacements below the traditional resolution criteria (fig. 4a).…”

Broadband seismic source data acquisition and processing to delineate iron oxide deposits in the Blötberget mine‐central Sweden

“…Seismic methods have recently opened up new possibilities in the mineral exploration industry with promising examples reported worldwide, especially during the past 10 years (e.g. Koivisto et al ., 2012; Manzi et al ., 2012, 2015; Buske et al ., 2015 and references therein; Malehmir et al ., 2017, 2018; Balestrini et al ., 2020; Malehmir et al ., 2020 and references therein; Papadopoulou et al ., 2020, Polychronopoulou et al ., 2020). Given the commonly complex nature and small target size of deposits hosted within hardrock environments, seismic exploration in such settings may benefit from high‐resolution imaging provided by broadband data acquisition and processing workflows (ten Kroode et al ., 2013; Cordery, 2020).…”