Periodic Assessment of Seismicity to Assess the Ground Support Requirements on Potential Fault Headings - Case Studies

Abstract

ABSTRACT: Vale's Coleman Mine, an underground mining operation initiated in 1970, is renowned for producing nickel, copper, and precious metals. Situated approximately 45 km northeast of Sudbury, Ontario, this mine is seismically active and has encountered seismic events with a local magnitude of up to 3.8 and is mining at depths of 2.0 km, presenting a significant hazard to workers and assets. To address this challenge, the mine conducts long-term, medium-term, and short-term seismic analyses, geological mapping, and monitoring to determine the necessary controls and mitigation strategies (support systems, seismic standoffs, equipment selection). This study outlines the methodology used to assess three critical headings within the mine: two fresh air raise access headings, 5200L and 5850L, and a footwall drift, 6050L, all situated within the 170 Ore body, at approximately 1.6 km from surface. Geologists previously mapped one of the faults in the 5200L heading using diamond drilling and on-site inspections. In the case of the 5850L heading, the potential for a fault was deduced from an abnormal surge in seismic activity beyond anticipated levels. In contrast, the fault in the 6050L heading was identified through a combination of seismic evaluations and visual inspections. The study provides a comprehensive account of the methodologies employed, the data analyses undertaken, and the measures implemented during the mining process for these headings. As a result, faults have been conclusively identified in all three headings, guiding the selection of appropriate ground support measures to mitigate the seismic risk effectively. This research contributes valuable insights into the challenges and strategies associated with seismic hazard management in underground mining operations. 1. INTRODUCTION Coleman, one of Vale Base Metals' most productive mines, has operated for over 50 years. The mine specializes in producing nickel-copper-PGE ore (Landry and Reimer, 2019). Its ore veins are complex in formulation, formed by a meteorite impact and later deformed by endogenic tectonism around 1.85 billion years ago (Stephan and Ian, 1974). Various mining methods have been employed at Coleman to optimize ore recovery, including underhand and overhand cut-and-fill, post-pillar cut-and-fill, and bulk mining methods such as vertical retreat, slot-slash, upper retreat, and underhand bulk mining. Due to its complexity, seismicity management has been one of the critical components to ensure a safe environment for workers while Coleman completes its development and extraction. The previous publications by Yao et al. (2014), Landry and Reimer (2019) report the ground support design and challenges from Coleman mine due to the combination of brittle solid host rock (UCS∼200MPa), high horizontal stress fields, with regions yielded and with unconfined conditions. These conditions make the mine prone to rock bursts and falls of ground, which can involve the host rock, ore, or sandfill. To address these issues, ground control, geomechanics, and geology teams have been collaborating to investigate the problems, develop mitigation strategies, and implement safer and more efficient mining practices.