Engineered open pit mine backfilling

Flambeau Mining Company (Flambeau), a wholly owned subsidiary of the Kennecott Corporation, developed an open pit copper mine near Ladysmith, Wisconsin. Site reclamation involved backfilling of the open pit. This paper describes the backfill program with respect to the geotechnical characteristics of the materials to be backfilled and the field testing undertaken to evaluate compaction methods and equipment considering variables such as degree of weathering, moisture content, and lift thickness. In addition, the geochemical testing and oxygen transport work completed to define stockpiled waste rock characteristics and the alkali addition rates to use during backfilling, and to predict equilibrated pore water quality are addressed. The paper also describes the quality assurance plan developed for construction and the results of backfilling work.