Final recovery at Inco's Little Stobie Mine: a case study

CIM Bulletin, Vol. 87, No. 976, 1994

S. Espley and G. Tan, Inco Limited, Ontario Division, Copper Cliff, Ontario

Inco's Little Stobie Mine is a low-grade nickel operation producing approximately 4000 tons per day. Backfill has never been an economical option at the mine; therefore, the only viable type of mining in the upper zones has been by sub-level cave. This mining method allows for the draw-down of a rock cover into the empty slopes to provide stability to the over-all rock mass. In the lower areas of the mine, bulk blasthole mining methods have taken place, without rock fill, resulting in extremely large open stapes. As the mine reaches its final stage of recovery, it is inevitable that the hang-ingwall of the large voids will undergo tensile failure via spoiling. This paper deals with the collaborating efforts of Inco's Rock Mechanics group and the Little Stobie mining operations toward the successful recovery of the ore zone remnants such that the inevitable failure, and time of failure, of the rock mass is "controlled". Within the mining scheme, several key requirements had to be met to satisfy the operations: (I) production rates; (2) good blast fragmentation; and (3) secure putting-horizons. A full-scale rock mechanics study was carried out involving: numerical modelling studies; pulling ellipse analyses; blast design, monitoring and analyses; laser profiling; and time domain reflectometry (TDK) instrumentation. The final recovery scheme, employing a controlled failure, involves recommendations on: (1) blasting techniques; (2) support systems; (3) mining sequences and scenarios; and (4) monitoring systems.

Keywords: Rock mechanics, Inco Limited, Little Stobie Mine, Rock failure, Numerical modelling, Blast designs.