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Abstract

Equity Silver Mines Ltd. has scheduled pit closure by the third quarter of 1992. In preparation for this event, detailed plans have been developed to insure there is a smooth transition for release of the workforce and that environmental concerns are addressed. Socio-economic and mine closure plans have been completed to serve as guides for termination of operations. A socio-economic study, funded by Equity Silver and the Township of Houston, B.C., was developed to assess impact of mine closure and looked at means to mitigate this impact. The mine closure plan, which will be the focus of this paper, was developed to serve as a guide for both Equity Silver Mines Ltd. and government agencies. It has under gone several reviews and revisions prior to being accepted as a final document. Of particular importance is the ongoing care and maintenance of facilities required to collect and treat acid rock drainage (A.R.D.) formed by oxidation of sulphides present in the mined waste rock. A.R.D. treatment facilities, which will operate for an indefinite period, will require ongoing funding to sustain their operation. Bonding has been put in place to develop sufficient interest to cover the annual cost of these facilities. The initial estimate for the bond was based on escalating historical environmental costs which resulted in a fund larger than originally anticipated. On the basis of this higher cost, the company decided to reslope the waste dump and install a compacted clay cover to mitigate the quantity of A.R.D. produced. Studies indicated that the clay cover would significantly reduce water infiltration into the waste dump and would also eliminate much of the oxygen transfer required to fuel the acid generation process.