THE STATE OF MINE CLOSURE: CONCEPTS, COMMITMENTS, AND COOPERATION

摘要

The objectives for closure of a typical hard rock mine include minimizing long term environmental liability, attaining regulatory compliance, and maintaining geotechnical stability, while closing as quickly and cost effectively as possible in a manner that returns the land to a safe and stable configuration for post-mining uses. Some of the key features that must be considered during decommissioning and closure of a mine could include any underground workings, a tailings impoundment, an open pit, surface waste rock piles, and spent leach pads. The environmental concerns surrounding each of these features have changed dramatically over the years with varying economic consequences to mine closure. Of particular interest is the heap leach operation and the related features of an open pit, waste rock piles, and the spent leach pads. The open pit has become a center of controversy due to its physical aspects and the potential for becoming a temporary or permanent water impoundment. The resultant quality of the pit lake and its subsequent classification becomes important as to "waters of the state". The primary concern with waste rock piles is the potential for oxidation of reduced sulfides and the release of acid and metals contained in the drainage. Lastly, there is the spent leach pad and its draindown solution which contains cyanide, metals, and other inorganic constituents. Although the fear of cyanide prompted the initial regulations related to rinsing of spent leach pads, it is the potential release of metals and other inorganic constituents that have become the major regulatory focus over the years. The environmental issues related to closure of underground workings, tailings impoundments, and conventional milling operations present similar challenges but appear to be less of an issue to the public and the regulatory agencies.