Providing practical geotechnical and geomatics solutions for small mine operators - slope failure and successful remediation at the Enchanted Designs Ammolite mine in Alberta


Lucy Philip, Stantec; Alex Amies, Stantec; Tom Chant, Enchanted Designs Ltd; Connor Emigh, Enchanted Designs Ltd

Ammolite is an iridescent biogenic gemstone made of the fossilized shells of ammonites. It is typically used in jewelry. Ammolite deposits are found in the Bearpaw Formation that extends from Alberta to Saskatchewan in Canada and south to Montana in the USA. Historically, a few commercial mining operations have developed along the banks of the St. Mary River, in an area near the city of Lethbridge. During July 2017, there was a pit slope and waste dump failure of the entire east face at the newly developed mine in pre-production. The slope failure resulted in a Stop Work Order (SWO) being issued by Occupational Health and Safety (OHS). Between the time of failure and the OHS inspection, Enchanted Designs started construction of a a toe berm to act as support for the failure; however, following the OHS inspection the SWO prevented completion of the stabilizing toe berm due to worker safety. Enchanted Designs needed to address the SWO and propose stabilization measures for the mine and waste dump slope in a manner that was safe to workers, acceptable to OHS and on a timescale minimizing work stoppage.  This paper presents the geology; the operating conditions at the mine; the background and evolution of the failure; assessment of likely causes of failure; post-failure site observations; investigation difficulties due to safety issues; remote access laser scanning to obtain topographic surfaces for stability analysis; stability back analysis to estimate material parameters and stability forward analysis to develop the solutions to stabilize the slope safely and have the SWO lifted. An observation and surveillance program is also described, to minimize future risks. Lessons learned and suggestions for similar small operations are presented.
Keywords: Slope Failure, geomatics, safety