Going green in the Hunter

Miners, now more than ever before, are focused on corporate and social responsibility, and the impact their operations will have long after they stop mining. One miner is making leaps forward in investigating how it can repurpose its old mines for agricultural uses.

Glencore Coal’s Liddell mine has commenced a third cattle grazing trial following positive results from two trials conducted on their land previously used for mining.

Glencore began their first cattle grazing trial at the Liddell mine in December 2012. Trials at the mine, located halfway between Singleton and Muswellbrook in NSW Upper Hunter Valley, sought to determine whether rehabilitated pastures can sustain cattle grazing to an extent similar to before the land was mined.

The trail had three main objectives: to analyse and compare livestock, soil and vegetation results to an un-mined pasture; to establish guidelines on ways to create and maintain rehabilitation areas; and to prove cattle grazing as a rehabilitation suitable option for use on previously mined land.

The initial trial involved monitoring adjoining natural and rehabilitated mines measuring 70 hectares each, with the rehabilitated land having not been sown between three and ten years. Two groups of 30 Charbray steers were used in the trial, positioned on either the natural or rehabilitated land at a stocking rate of one steer per 2.4 hectares; a range over the recommendations of year round stocking by the NSW Department of Primary Industries.

In June 2014, after 18 months, the trial identified an overall weight gain of cattle grazed on rehabilitated pasture. At the beginning of the trial the cattle had an average weight of 406kg and at the end weighed an average of 662kg; a 250kg increase per animal. This, in turn, generated higher financial yields, with each steer selling for nearly $220, close to 25% more in price than cattle grazed on natural land.

Cattle reportedly grazed more frequently on the rehabilitated pasture due to the higher feed quality of the land which contained legumes and introduced tropical pasture species. In contrast, the natural land was mainly comprised of native and natural grasses which tend to have lower feed quality for cattle.

Results from topsoil analysis was varied. While natural pastures were more acidic, rehabilitated pastures maintained an alkaline nature. Higher levels of sodicity and salinity were found in the rehabilitation pastures.  

Stock water quality in both pastures was acceptable for grazing cattle.

The second phase of the trial showed minor differences from the first. Conducted over 12 months, between November 2014 and December 2015, using 20 steers, it found cattle grazed on rehabilitation pastures still gained weight, although the difference was less than the first trial, with an average of 14kg. This time, natural land maintained a better feed quality as legumes and single super was used in both pastures. Agricultural operations in the Hunter Valley often use this method to improve the quality of their pastures.

The cattle from the natural and rehabilitation pastures received good returns overall; however, as cattle from both pastures were sold at a flat rate, returns from each treatment could not be evaluated.

Despite the positive results of both trials the results are not yet definitive, with a third trial starting last month to determine trends over a long period of time.

Previous rehabilitation initiatives have been successful in Australia, with the nearby Mt Owen coal mine receiving international acclaim for its efforts. The mine conducts ongoing rehabilitation of forests, pasture, and native woodlands in post-mined land to establish sustainable pasture and create habitats for native wildlife. Land that began rehabilitation during the 1990s has since developed native vegetation similar to that of the adjacent Ravensworth State Forest. This restored area has also seen the return of native animals such as gliders and quolls.

Members from the International Mining for Development Centre (IM4DC) inspected these rehabilitated areas in March 2015. Director of University of Queensland’s Centre for Mined Land Rehabilitation Professor David Milligan said that the mine showcases the best in rehabilitation application.

Mangoola, another Glencore mine in the Hunter Valley, has included natural landform into its mine rehabilitation program and aims to return the entire post-mined land to the natural environment that surrounds it. Mangoola’s operations manager Tony Israel acknowledged how monitoring the effect of mining on the environment is an overall value of Glencore.

“For us at Mangoola it’s part of our site values managing the impacts we have on the environment and in the community,” he said.

In 2011 Mangoola began to transform the land into native animal habitats and for agriculture. Within the last four years over 145 hectares of natural landform has been created, with Glencore expanding this reform to its Bulga and Ravensworth mines.

To keep up to date with Australian Mining, subscribe to our free email newsletters delivered straight to your inbox. Click here.