We've got mine waste rock dumps covered

Dr Peter Golos (Research Scientist), Dr Carole Elliott (Research Scientist)

The mining industry transforms natural landscapes, leaving novel features such as rock dumps and tailings dams behind.

Mine closure obligations in Western Australia require partial or full repair of ecosystems and their biodiversity to ensure the long-term stability of mine waste landform structures. Establishing vegetation cover on post-mine landforms is a necessary step to fulfill these obligations.

A waste rock dump revegetation trial in the foreground with a tailings storage facility in the background at Nifty mine site in the Great Sandy Desert. Photo Peter Golos

What vegetation community is to be restored? A simple question with a complex decision-making process. For some mine sites, the regulators have indicated what vegetation community needs to be restored, such as a threatened ecological community that has been directly impacted by mining operations. For other mine sites there is no specific vegetation community indicated, but the pre-mine ecosystem is usually targeted for restoration.

It can be extremely challenging to restore the original plant community, as soil quality is usually degraded. Sandplain and sand dune vegetation may be replaced by a waste rock dump. Sand loving plants may find it hard to grow on a rock pile, so alternative stony hill plants may be more successful. Therefore, analysis of the soils and topography of the site are crucial to choose the most suitable vegetation community to be restored.

Revegetation trial plots to determine the effects of topsoil sourced from different landforms, the addition of waste rock and subsoil in layers and/or blends on top of waste rock dump at Telfer. Field trials that test and demonstrate improved restoration outcomes will support the goals of The Decade. Photo: Peter Golos

Topsoil is the most important substrate used in installing the livable layer for plants on a waste rock dump (i.e. the cover system). This living layer contains seeds, microbes and fungi that are crucial for plant establishment and ecosystem function. Research has found the quality of the topsoil is dependent on the landform, harvesting method and storage history. Its value may be reduced requiring topsoil being supplemented with additional seed or tube stock plantings.

Waste rock can also be a useful substitute for these cover systems in ensuring a stable mine waste landform. Mine waste rock dumps often have steep slopes from which topsoil is easily eroded.

The solution – mixing topsoil with waste rock – can create a stable mine waste landform. Waste rock mixed with topsoil can provide micro sites as an added benefit for more favourable seedling emergence. Blending waste rock with topsoil extends the area that can be restored, making sure that nothing is wasted!

The waste material produced in mining is often chemically and physically different to natural soils. Some types of waste rock and tailings are toxic and need to be encapsulated deep within the waste landforms with more benign substrates used as a cover.

Seeding trial on waste rock dump in plot with 20 cm of topsoil on waste rock (pictured) and plot with no topsoil layer (below). Seedling emergence and survival from sown seed was significantly lower in plots without topsoil. Photo: Peter Golos

Seeding trial on waste rock dump in plot with 20 cm of topsoil on waste rock (above) and plot with no topsoil layer (pictured). Seedling emergence and survival from sown seed was significantly lower in plots without topsoil. Photo: Peter Golos

Restoring mine waste effectively across Western Australia often requires research and restoration trials to develop improved soil cover designs and suitable plant communities (e.g. Telfer, Nifty, Koolanooka and Karara mine sites).

The waste material available varies widely in characteristics, both within and between mine sites, requiring different solutions for cover designs, blends of topsoil, subsoil and mine waste with the aim of developing a cover system that will successfully restore a self-sustaining vegetation community.

Glasshouse trial on the effect of cover system design. Root growth reached the bottom of 50 cm topsoil column (pictured) while root growth is largely confined to topsoil layer in 20 cm topsoil on 30 cm tailings waste column (below). Photo: Arielle Fontaine

Glasshouse trial on the effect of cover system design. Root growth reached the bottom of 50 cm topsoil column (above) while root growth is largely confined to topsoil layer in 20 cm topsoil on 30 cm tailings waste column (pictured). Photo: Arielle Fontaine