COALI

CONSULTANT'S COMMENT

Another punch •In the wallThe existing variety of mining methods sometimes causes confusion evenamongst experienced mining professionals, let alone analysts, investors,suppliers and the broader community,

SOME MINES have developed theirunique mining or development methodsto reflect some specific mining and

geological conditions or production require-ments. Some mines go a step further andimplement special equipment and tools tomeet the challenges of increasing miningcomplexity.

With commodity prices hitting rock bottomall mining companies and contractors facethe necessity to cut the production cost, asthe unpronounced slogan of the miningboom "more tonnes at all costs" is no longerapplicable. One of the keys to survival inthese tough times is optimisation of theexisting mining methods and scrupulousevaluation of new ones.

As the community becomes more environ-mentally aware it is important that everyoneone can obtain enough knowledge about min-ing methods and operations to make informedand well weighted decisions about new minedevelopments. It may be harder to do if theterms are confused or misused, especiallywhen pronunciation is similar, but the mean-ing can be very different.

Here are some attempts at explaining a fewpopular mining terms:

Room and pillar - one of the oldest andmost traditional underground mining methodsand is suitable for flat or slightly inclineddeposits. Pros: does not require substantialdevelopment. Cons: incurs significant lossesof mineral in pillars. Have caused surface sub-sidence in the past due to deterioration of roofsupport and pillars in coal mines. Solutions:can be integrated with cut and fill techniques(Post Room and Pillar mining) or used insome other modified forms.

Longwall mining - underground mining ofcoal with mechanised roof support, mecha-nised coal extraction - a shearer (or a ploughin the past). Pros: better ground control andrecovery comparing to room and pillar mines.Cons: low utilisation and mine and surfacesubsidence. Solutions: further development ofthe method and backfill techniques.

Shortwall mining - underground miningof coal similar to longwall , but with shorterwidth of blocks, usually under 100 metres.

Highwall mining - a mining methodwhere a high wall mining system (essentiallyan auger) is placed against the highwall in anopen cut coal mine to enable additional recov-ery of coal without overburden removal orunderground development. Pros: faster recov-ery of coal. Cons: still seen as a supplemen-tary method; coal losses; ground controlissues. Solutions: consideration of backfilltechniques and further development of thetechnology.

Punch longwall mining - a longwall min-ing system implemented through an existingopen cut mine. Pros: lower development cost.Cons: needs to retain and maintain the opencut surface infrastructure throughout the lifeof underground operations; surface subsi-dence. Solutions: minimisation of the foot-print once the open cut operations are com-pleted; development of the backfill tech-niques.

Strip mining - a traditional open cut min-ing method where overburden (waste) isremoved ahead of coal (or other mineral) andwhen upon extraction of coal the face is back-filled with the previously removed waste.Pros: enables for simultaneous extraction ofseveral faces and large production output.Cons: requires substantial overburden removalexpenditures upfront; causes significant dis-turbance to all surface and near surface envi-ronment. Solutions: better environmental andgroundwater modelling; compulsory rehabili-tation of land.

Narrow-vein mining - a method devel-oped for rich but small orebodies when thefeasibility of the mine often dictates smalldrives and small equipment. Pros: lower capi-tal cost and minimal environmental impact.Cons: operations in confined space; sensitivityto cut-off grades. Solutions: strict safety con-trol; fmer drilling and geological mapping;further optimisation of the mines.

Block caving - a method developed forlarge orebodies with low grades, when largetonnage of orebearing mineral needs to beextracted andprocessed. Requires large under-ground equipment and substantial develop-ment work. Pros: enables extraction of lowgrade deposits. Cons: Ground control issues;

By Dmitry Przhedetsky

causes significant mine subsidence. Solutions:more precise geotechnical studies along withfurther development of backfill techniques.

Top coal caving - in essence a longwallmining when due to a large thickness of a coalseam and more advanced system of conveyorsand roof support additional (to the shearer)extraction of coal is possible from the goafside due to natural caving of the coal in thetop part of the seam. On thicker seams it canbe combined with an additional advancingshearer caving the coal in the front of the sec-ond shearer located at a lower level. Pros:potentially lower cost of coal due its breakagethrough natural forces. Cons: ground controlrequirements and subsidence problems.Solutions: further development of precisiontechniques and consideration of backfill.

In-situ leaching - a mining method usedpredominantly for underground chemicalextraction of uranite (Triuranium octaoxide)through a system of injection wells andextraction wells. Pros: does not require con-ventional mining operations, i.e. no excava-tion is conducted during the entire life ofmine. Cons: occasional inconsistencies of therecovery process; potential for chemical con-tamination of ground water; long neutralisa-tion time of leachates and by-products.Solutions: advanced geological and hydrogeo-logical studies; finer hydrogeological model-ling and control.

While there isn't sufficient space to providea complete description of all mining methodsin practice, the expertise is available throughmining consulting firms capable of explainingeach method to the community. Knowledgeand understanding of mining is the best toolto mitigate frictions in the society inconspicu-ously or conspicuously "driven by the minetrucks and shuttle cars." 0

* Dmitry Przhedetsky (M Eng (Mining), FAusIMM) is a

director of Rock Cognition Pty Ltd. Contact him at:

dmitry@rockcognition.com.au

AIM: AUSTRALIAN JOURNAL OF MINING JULY I AUGUST 2009 25