Assessing seismicity for three different mining periods at the Lucky Friday mine

ABSTRACT: The Lucky Friday mine (Idaho, US) uses narrow underhand mining methods to extract stacked subvertical, tabular high-grade (silver, lead, zinc) ore veins from the Gold Hunter (GH) deposit within the Wallace Formation. This study analyzes seismic response patterns across three distinct mining periods at the mine: traditional Lucky Friday Underhand Longwall (LFUL) at 720 tpd (2014-2016), reduced-rate LFUL at 110 tpd (2017-2019), and Underhand Closed Bench (UCB) at 630 tpd (2020-2021). Through comprehensive analysis of magnitude, timing, location, and production relationships, we evaluated how mining methods and extraction rates influence seismic behavior. Results show that reduced mining rates led to decreased maximum magnitudes and longer return periods for large events, while the UCB method also achieved longer return periods despite maintaining high production rates. Overall, the UCB method demonstrated better seismic risk management, with 87% of seismic energy released during off-shift periods compared to 37% during traditional LFUL. While seismic events in pillars and along faults persisted across all periods, the UCB method showed reduced stope-related seismicity while maintaining production rates near LFUL levels. These findings provide valuable insights into deep mining operations seeking to optimize extraction methods for improved seismic risk management while maintaining productive output.