Consultant’s Comment: Another punch in the wall-1
The variety of mining methods can cause confusion even amongst experienced mining professionals, let alone analysts, suppliers and the broader community.
Image courtesy of Austar Coal
By Dmitry Przhedetsky
Some mines have developed their unique mining or development methods to reflect some specific mining and geological conditions or production requirements. Some mines go a step further and implement special equipment and tools to meet the challenges of increasing mining complexity.
With commodity prices hitting rock bottom all mining companies and contractors face the necessity to cut the production cost, as the unpronounced slogan of the mining boom “more tonnes at all costs” is no longer applicable. One of the keys to survival in these tough times is optimisation of the existing mining methods and scrupulous evaluation of new ones.
As the community becomes more environmentally aware it is important that everyone one can obtain enough knowledge about mining methods and operations to make informed and well weighted decisions about new mine developments. It may be harder to do if the terms are confused or misused, especially when pronunciation is similar, but the meaning can be very different.
Here are some attempts at explaining a few popular mining terms:
Room and pillar – one of the oldest and most traditional underground mining methods and is suitable for flat or slightly inclined deposits. Pros: does not require substantial development. Cons: incurs significant losses of mineral in pillars. Have caused surface subsidence in the past due to deterioration of roof support and pillars in coal mines. Solutions: can be integrated with cut and fill techniques (Post Room and Pillar mining) or used in some other modified forms.
Longwall mining – underground mining of coal with mechanised roof support, mechanised coal extraction - a shearer (or a plough in the past). Pros: better ground control and recovery comparing to room and pillar mines. Cons: low utilisation and mine and surface subsidence. Solutions: further development of the method and backfill techniques.
Shortwall mining – underground mining of coal similar to longwall, but with shorter width of blocks, usually under 100 metres.
Highwall mining – a mining method where a high wall mining system (essentially an auger) is placed against the highwall in an open cut coal mine to enable additional recovery of coal without overburden removal or underground development. Pros: faster recovery of coal. Cons: still seen as a supplementary method; coal losses; ground control issues. Solutions: consideration of backfill techniques and further development of the technology.
Punch longwall mining – a longwall mining system implemented through an existing open cut mine. Pros: lower development cost. Cons: needs to retain and maintain the open cut surface infrastructure throughout the life of underground operations; surface subsidence. Solutions: minimisation of the footprint once the open cut operations are completed; development of the backfill techniques.
Strip mining – a traditional open cut mining method where overburden (waste) is removed ahead of coal (or other mineral) and when upon extraction of coal the face is backfilled with the previously removed waste. Pros: enables for simultaneous extraction of several faces and large production output. Cons: requires substantial overburden removal expenditures upfront; causes significant disturbance to all surface and near surface environment. Solutions: better environmental and groundwater modelling; compulsory rehabilitation of land.
Narrow-vein mining – a method developed for rich but small orebodies when the feasibility of the mine often dictates small drives and small equipment. Pros: lower capital cost and minimal environmental impact. Cons: operations in confined space; sensitivity to cut-off grades. Solutions: strict safety control; finer drilling and geological mapping; further optimisation of the mines.
Block caving – a method developed for large orebodies with low grades, when large tonnage of orebearing mineral needs to be extracted and processed. Requires large underground equipment and substantial development work. Pros: enables extraction of low grade deposits. Cons: Ground control issues; causes significant mine subsidence. Solutions: more precise geotechnical studies along with further development of backfill techniques.
Top coal caving – in essence a longwall mining when due to a large thickness of a coal seam and more advanced system of conveyors and roof support additional (to the shearer) extraction of coal is possible from the goaf side due to natural caving of the coal in the top part of the seam. On thicker seams it can be combined with an additional advancing shearer caving the coal in the front of the second shearer located at a lower level. Pros: potentially lower cost of coal due its breakage through natural forces. Cons: ground control requirements and subsidence problems. Solutions: further development of precision techniques and consideration of backfill.
In-situ leaching – a mining method used predominantly for underground chemical extraction of uranite (Triuranium octaoxide) through a system of injection wells and extraction wells. Pros: does not require conventional mining operations, i.e. no excavation is conducted during the entire life of mine. Cons: occasional inconsistencies of the recovery process; potential for chemical contamination of ground water; long neutralisation time of leachates and by-products. Solutions: advanced geological and hydrogeological studies; finer hydrogeological modelling and control.
While there isn’t sufficient space to provide a complete description of all mining methods in practice, the expertise is available through mining consulting firms capable of explaining each method to the community. Knowledge and understanding of mining is the best tool to mitigate frictions in the society inconspicuously or conspicuously “driven by the mine trucks and shuttle cars.”
* Dmitry Przhedetsky (M Eng (Mining), FAusIMM) is a director of Rock Cognition Pty Ltd. Contact him at: firstname.lastname@example.org