Report: Mangoola Open Cut Coal mine and rehabilitation site
Jose F. Martin Duque, Alec Roberts, Korbinian Kraus, Nigel Stace
Mangoola Open Cut Coal mine is located approximately 20 km western direction from Muswellbrook. The exploration of Mangoola began in the early 2000’s as they found coal in a very shallow depth. Mangoola mine is owned and operated by Glencore.
Mangoola mine produces thermal coal principally for export, with 25% being supplied to AGL for local use at the Hunter Valley Coal-powered thermal power stations Liddell and Bayswater. The mine employs 294 people. The mine has really high visibility, as they promote trips to the mine by schools, and the public. They receive more than 700 visitors in a year.
In Mangoola the coal is very close to the surface, which makes truck and shovel mining the adequate mining procedure (not dragline seen at other open cut mines in the Hunter). On a total area of 10,200 ha, with the mine currently 2299 ha in size, the vast amount of 13.5 MT per annum is harvested. But what to do with the land after being mined?
The magic words are good mine rehabilitation. Good progressive rehabilitation is necessary for a mine in order to stay accepted in the community.
In Mangoola 380 ha have already been rehabilitated and it is planned to treat 100 ha per year over the next 5 years. The mine also has an additional 3000 ha of offsets and approximately 4,800 ha setup for grazing.
The mine owners Glencore are required to lodge a security bond with the NSW Government to cover the full cost of rehabilitation. The size of the rehabilitation security bond is set each year, and varies from year to year depending on the amount of land requiring rehabilitation. Currently $54 million is held as a rehabilitation deposit.
Progressive rehabilitation allows the mine owner to reduce the amount of security bond held by the government. Progressive rehabilitation involves the staged restoration of disturbed areas during the mine operation, instead of large-scale works at the end of the mines life. Progressive rehabilitation is undertaken at Mangoola, with the driver for this being the size of the security bonds. The mine has an annual rehabilitation and land management plan which includes the management of the buffer lands. The Environment manager meets weekly with operations staff to ensure mine operations and rehab are in synch.
With the help of Software such as GIS and GEOFLUV – Natural Regrade geomorphologists can create a landscape that comes very close to natural territory. They can plan hills, valleys and everything else natural landscape has. One of the mines goals is to produce a sustainable landform and drainage design with the mining planning working towards a final geomorphic landform design. The mine also uses the best practice Landscape Evolution Model SIBERIA to test landform stability.
The mine says that it is economically worthwhile to do GeoFluv, because even if it would be more expensive, it has high community acceptance. They also specifically recognize the advantages of geomorphic-based progressive rehabilitation: reduction of dust, bond release, liability, commitment, and cost saving by the absence of drop structures (down drains) in the final design.
With the shallow depth of operation, the cost of extracting the coal is less than other sites, however the rate of progressive rehabilitation in greater (as more ground is covered to extract the same amount of coal).
External contractors are used for the rehab preparation which is:
Bulk shaping is done using a GPS guided dozer (D6). Top soil stockpiles are kept onsite for use within a couple of weeks to maintain topsoil viability. Where possible, top soil is placed directly in its target location.
Following the application of gypsum, the land is deep ripped and approximately 100m of mulch is applied and then a sterile cover crop of oats and Japanese millet is hand sown. Hand sowing is an effective method compared to other techniques as no heavy vehicles are required onsite and can be done at short notice. The mine land was originally 700 ha of grassland with the remaining land light woodland. The plan is to put back the ecological communities that were once here.
A seed collection program in the buffer lands and offsets provides a good source of viable indigenous plant and tree species seed which are then hand sown into the rehab.
Salvaged timber with hollows are placed upright (stag trees) presumably for birds of prey. Big rocks are placed on the land and together with the stage trees deliver some shadow and shelter for animals and vegetation. All this creates an artificial landscape that improves the quality of the land and decreases the negative effects of the coal mining.
Nesting boxes are placed throughout the rehab and offsets to encourage wildlife. Tiger orchids have been transplanted to more established trees and stag trees.
The GeoFluv landforms have a main role in the design of the valleys. It is what we could term an adapted version of GeoFluv, in which large mines try to simplify procedures of rehabilitation, to include them in mine production but keeping the principles of the method. The mining plan works towards the final landform (which is the most difficult part to achieve).
Rehab is a rather slow an ongoing business, it takes a while until the first success can be seen. However, Mangoola can act as a kind of role model for other mines. They started five years ago with moving and replanting parts of the mine. In Mangoola birds and other animals start to repopulate the land again, which is a sign of successful rehab.
Compared to other mines in the Hunter Valley, Mangoola is doing a very good job. In general, the mine is a VERY good example of progressive rehabilitation and also the consideration of landforms, soils, revegetation, and fauna.
For more information see:
Kelder, I, Waygood CG & Willis, T 2016, 'Integrating the use of natural analogues and erosion modelling in landform design for closure', in AB Fourie & M Tibbett (eds), Proceedings of the 11th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 99-106.
In the news
17 May 2019 Newcastle Mine Rehabilitation Conference seeks to answer crucial questions - Hunter Business Review