Molybdenum ore is mined by block caving methods at Molycorp’s Questa Mine. AAI has provided geotechnical consulting services to the mine since 1979 as follows:
- Evaluation of decline rock support requirements, and recommendations and implementation of a shotcrete and rockbolt system.
- Evaluation of ground stability and support requirements on the undercut, grizzly, and haulage levels as well as within the access decline and raises.
- Draw control program.
- Design of D block.
- Support design and stabilization of a large underground storage bin.
- Stability and support monitoring through the mine.
- The comprehensive design and evaluation program conducted in this mine has led to the formulation of a ground support strategy which matches the required ground support system to rock quality and location relative to the cave and associated abutment loads.
- D Orebody Natural Slope Stability Instrumentation
- Design and installation of TDR cables and inclinometers
Development of a new orebody, the D Orebody, began in 1999 at twice the depth of previous mining. AAI was called upon for the design and evaluation of ground support on the Grizzly and Haulage Levels beneath the planned cave. Three-dimensional numerical analysis of stress conditions was conducted for critical stages of the cave evolution. The three-dimensional geometry of the cave was modeled over the planned course of mining. The local three-dimensional geologic structure was explicitly defined in the model to assess the damage potential of transient abutment stresses in different rock types.
AAI completed a comprehensive subsidence study for the Questa block caving molybdenum mine for Molycorp, Inc. in support of the Mine Closure/Closeout Plan ultimately submitted to the New Mexico Energy, Minerals and Natural Resources Department, Mining and Mineral Division and the New Mexico Environmental Department. The study comprised investigation of historical block caving subsidence at the Questa Mine and elsewhere, instrumentation and monitoring of subsidence over a new block cave at Questa, core drilling, laboratory core testing, field mapping, geotechnical characterization, and, ultimately, predictive modeling of future subsidence associated with the long-term mine plan.
