Abandoned mine workings are part of the heritage of Western Australia. Workings can be found in and around towns and cities and the resultant rough terrain can be attractive to trail bike and motor cross riders. For prospectors and fossickers, the attraction is discovering mineral wealth or samples. Old workings and town sites are also a lucrative source of historic paraphernalia for collectors and dealers.
Old mine workings – stay out and stay alive!
Why are old mine workings a serious hazard?
If a mine is abandoned or put into care and maintenance, operators need to:
- prevent (as far as practicable) subsidence and access to dangerous areas
- remove or dispose of hazardous substances
- ensure any equipment left behind is secured and in good condition.
Historically, however, mines were constructed and maintained to be safe only while they were in operation. The abandonment process, if performed, was not always done well. Even when a mine is closed properly, the effects of time can reduce the effectiveness of the precautionary measures.
What are some of the hazards?
Mine openings
If you get too close to an open edge of workings, there is the potential to fall into the open pit or quarry, or down a steep opening. The weathered ground around these areas can subside or break away under vibrations from a vehicle or under a person’s weight. Vegetation and dirt can also form a false floor over underground mine openings and obscure the hazard.
Deadly gases and lack of oxygen
Lethal concentrations of methane, carbon monoxide, hydrogen sulphide and sulphur dioxide can accumulate in underground workings. Through the process of weathering (oxidation), certain minerals can literally consume a significant proportion of the oxygen normally present in the atmosphere.
These processes can result in pockets of still air with little or no oxygen being encountered. By the time people feel ill, they may be unable to react appropriately to remove themselves from the hazard.
Cave-ins
Old mine workings are potentially unstable and can cave in at any time. The effects of blasting when the mine was operating followed by the effects of weathering can weaken what was once strong rock. Work done to stabilise rock walls may also become less effective over time.
Unsafe structures
Old and disused underground or surface support timbers, ladders, buildings, pumps, tanks, and other mining related structures may seem safe but can easily collapse or crumble under a person’s weight.
Unstable explosives
Deteriorating explosives that have been left in place on abandoned operations are occasionally encountered. Unused or misfired explosives can be deadly. This is particularly true for old explosives containing nitroglycerine, which can become unstable, with a very small disturbance triggering an explosion.
Highwalls
Highwalls are created when the sides of hills or material from pits (below the natural surface) are removed during mining. Rock walls resembling cliffs remain at the point where the mining excavation ceased. These highwalls can be unstable and prone to collapse.
Waste rock heaps
Waste heaps from the mining process can become unstable when steep slopes are saturated by water from mine sources, the watertable or rainfall. In addition, landslips can engulf or injure people, damage roads and buildings, and block the paths of creeks causing upstream flooding. Waste rock heaps should never be used as recreational jump sites.
Waste rock heaps should never be used as recreational jump sites.
Water hazards
Many abandoned mines fill with water over time. Do not swim or dive in flooded old mine workings because:
- the water may be very salty or acidic, causing skin irritation, or contain microorganisms that can cause illness and infection
- there may be unseen hazards from abandoned equipment or rock falls
- extreme temperature gradients are possible within the body of water, which may cause muscle cramps or other physical problems in the swimmer.