PERFROMANCE OF THE LTA COVER TO LIMIT THE PRODUCTION OF ACID MINE DRAINAGE: RESULTS FROM SEVEN YEARS OF MONITORING

CIM Montreal 2003
Abdelkabir Maqsoud, Michel Aubertin, Dominique Beaudry,
Abstract The mining industry contributes significantly to the Canadian economy. Mining operations, however, produce various types of wastes (tailings, waste rock, treatment sludge) that must be managed properly to protect the environment. Acid Mine Drainage (AMD) from mine wastes is probably the most challenging environmental problem facing the mining industry. AMD results from naturally occurring processes when sulphide minerlas are exposed to water and air. When the mining wastes have the potential to produce AMD, the reactive wastes have to rehabilitate, without the possibility of impacting the environment through effluent release or solid migration. This challange was the one facing Barrick Gold corp. at the Les Terrains Aurifères (LTA) Property, Malartic, Québec, Canada.

LTA Property ceased its remaining milling activities in 1994. During the latest years of mining, the mill processed a sulphide ore from Bousquet mine which has acid generating potential. After an extensive technico-economical study, the closure option selected for the LTA tailings pond by Barrick (about 50 ha) was the construction of a multilayered cover with capillary barrier effects (CCBE) to prevent the production of Acid Mine Drainage (AMD). The CCBE, constructed during the winter 95-96 and the summer 96, is made of three layers: a bottom layer made of 0.5 m of sand, a 0.8 m moisture-retaining layer made of non acid generating tailings, and a 0.3 m top layer made of a sand and gravel. After the construction, the cover was instrumented to monitor his performance. The parameters evaluated are oxygen-consumption through the cover, the volumetric water content and the suction in the different layers.

This paper presents the main results obtained from the monitoring program undertaken seven years ago. First, a brief description of the site and of the CCBE is presented. The main monitoring intruments used are then described and their location on the site are presented. The hydraulic behavior of the CCBE since the construction follows. Finally, a discussion on the performance of the cover to limit the production of AMD at the LTA site ends the paper.
Keywords: Acid mine drainage, Cover with capillary barrier effects, Rehabilitation, Oxygen flux, Hydraulic behavior, Reuse of tailings, Instrumentation, Mining environment, Mine tailings, Monitoring
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