Modern miners have recognised their significant role in contributing to worldwide sustainable development in this way and in particular the requirement to manage their operations in such a way as to minimise the unwanted long-term, adverse environmental impacts of their industry and so retain their social licence to operate.

The minesite’s effect on the landscape after closure is much longer than its life during operations. As a result, this requires closure objectives for post-mining landforms at the site should all be based on sound geomorphological and ecological principles for long-term performance.

In order to achieve these objectives, planning for closure should begin as early as practicable in the mine’s life, ideally in the initial conceptual development of the project. This should include setting clear closure objectives for the site to achieve prior to the operating company relinquishing the site.

Over the past 40 or so years, the rehabilitation of mining’s terrestrial landforms has become a well-researched practice.

However, mining restoration of open cut operations typically ceases at the edge of pit voids. This is in spite of the fact that open pit/open cast mining has left a legacy of thousands of mining pit voids across Australia and even more across the world. Europe has pit void legacies extending back from Neolithic peat extraction in wetlands to Roman mines for coal and metals.

Backfilling and rehabilitation is often the simplest way to deal with remaining pit voids. However, where backfilling of pits is not an economic or feasible option and the pit extends into the water table then a pit lake will form as the pit fills with ground and surface waters.

These lakes displace the terrestrial ecosystems that existed prior to mining, replacing these ecosystems with aquatic eco-systems of varying value and sustainability.

Water quality will be key in both determining the risk and liability the pit lake presents to the broader environment.

Understanding the physical and geochemical processes at work in the pit lake that develops at mine closure increases a miner’s chances of being able to successfully and economically manage problems that may arise with water quality.

Investigating these processes early in the life of the mine will maximise opportunities and minimise closure costs. If potential pit lake issues are detected early, especially during the initial mine planning stages, there is a greater opportunity to remedy them.

Enabling legislation is more likely to result in acceptable pit lakes by setting outcomes, such as water quality and pit wall safety characteristics, without constraint of mine planners on how these objectives can best be achieved.

Hugh Jones is senior consultant and Dr Clint McCullough is principal environmental scientist at Golder Associates.

This article first appeared in the June 2012 issue of Australian Longwall magazine.