• Musa Manzi
  • Wits University
  • South Africa
Abstract

South Africa hosts some of the world’s richest ore bodies, the gold-bearing conglomerates of the Witwatersrand Basin. These ore bodies extend to depths exceeding 3.5 km, the greatest mining depths in the world by far. The deep mines are also characterized by high-stress levels that give rise to intensive mining-induced fracturing within the rock mass, resulting into rockbursting. Rockbursts have remained one of the most serious and least understood problems facing deep mining operations. In this paper we demonstrate how the reflection seismic method has been successfully used to explore some of the world’s largest gold deposits and map the gross structural architecture that controlled the formation of these ore bodies and support mine planning, and improve safety. We further demonstrate how reflection seismics can be combined with source parameters of mining-induced earthquakes to improve mine safety. We analysed more than 2000 seismic events (main events and aftershocks) with local magnitudes between -3.0 and 3.0 that caused damage to the surrounding stopes in the deep underground gold mines. Superposition of large seismic events (> 1.5 ML) on the reflection seismic data suggests that sub-vertical structures (faults and dykes) are most likely to trigger seismicity. The integration of source parameters and reflection-seismic defined structures indicates that mining activities may lead to a burst or a slip on pre-existing geological structures. We argue that the integration of reflection seismics with mine seismology may increase mine safety and make it possible to explore and mine successfully at depths exceeding 3.5 km.

About the speaker

Manzi holds a BSc degree (2007) in physics and maths, BSc honours degree (2008) and PhD degree (2013) in geophysics (all from the University of the Witwatersrand). After completing his PhD, he joined Wits University where he currently holds a geophysics-lectureship position in the School of Geosciences and director of the Seismci Reaserach Centre.