Continuous closure

Tommi Kauppila, Geological Survey of Finland, PO Box 1237, 70211 Kuopio, Finland; tommi.kauppila(at)tk.fi

As described in other sections, mine closure is a long process that starts early in the mining project and continues with what often is a long post closure monitoring period to verify the stability of the site and attainment of the closure goals. The process is guided by the Closure Management Plan that is continuously updated to match the stage of the project and the remaining life-of-mine and liabilities. In addition to the regular reviews of the CMP, mines invariably employ what is commonly called continuous closure, i.e., perform closure actions throughout the operating period of the mine. Another commonly used term is concurrent rehabilitation but this is somewhat more limited in scope.

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Figure 1. The green arrows show examples of continuous closure actions.

The earliest phase of continuous closure actions is in the design and construction phase when closure-related structures are designed and constructed. These typically include water management structures, closure-related features of tailings management facilities and other waste areas, constructed structures for post closure effluent treatment etc.

Long term monitoring programs and field tests are commonly initiated early in the production phase when tailings, waste waters, and dewatering waters become available. Long term tests are usually employed to learn about the stability and reactions of the waste materials that are to be stored on site or used for mine backfill or other construction works. Similarly, tests of alternative cover structures and materials for the waste facilities are often started early in the operating period.

Systematic collection, management, and processing of environmental and socio-economic monitoring data also can be seen as part of continuous closure. The aim is to learn more about the environmental risks and to gradually reduce the uncertainties surrounding the eventual closure actions. It is good practice to include such activities as part of the CMP, targeted to specified issues with knowledge gaps. Any changes from the original designs or operating parameters also must be documented throughout the project as well to be able to base the eventual closure actions on solid understanding of the facilities to be closed.

The best known and most visible continuous closure actions are those in which certain facilities or parts of facilities are closed during the mining period when they reach their end of life. This is what the term ‘concurrent rehabilitation’ usually refers to. The most common of such early closed facilities are probably the initial open pits that are no longer in production and tailings and other waste facilities, or individual cells of the facilities that have been filled to capacity. These early closure actions, when accompanied by appropriate monitoring, provide invaluable information on the performance and costs of the closure methods and engineering options selected. They also allow testing of various technical options in a larger scale than what would otherwise be possible. Closure of certain facilities early in the project is usually economical and logistically easy because the resources are in place (human, equipment, management) and there is cash flow to facilitate the activities. In addition, early closure helps in preventing unwanted processes such as extensive oxidation of sulphide minerals in the waste materials or pit walls.