Aims of Coal Mining
1. Quality
2. Recovery
3. Cost
Success to Date
1. Quality has been adequate, although there are frequent problems with dilution and moisture
2. Recovery, 90.5% in 2006, is unacceptable for a mine that enjoys thick seams and little structural disturbance
Causes of High Coal Loss
1. Complacency
2. Laziness
3. Poor training
4. Poor supervision
5. Lax contract provisions
Lax Contract Provisions
1. “for coal that is exposed and subsequently becomes irrecoverable, the contractor will be made liable for the cost of uncovering the coal
2. Although inadequate, this has not often been enforced.
3. At present, the contractor is paid the same money for hauling 1 bcm of coal at 1,26 t/m3 to the dump as for hauling 1 bcm of OB at 2.2 t.m3. This is an incentive !
Seam Geometry
1. Thick Seam (+20 m)
2. Medium Seam (5-20 m)
3. Thin Seam (1-5 m)
4. Steep/Gentle Seam Dip Angle
Cleaning of Coal Roof
1. Excavation of overburden to withing 0.5 m of the coal roof
2. ‘Touching’ of coal every 30-40 m2 to ensure that minimal OB is left
3. Final clean up by small excavator
4. Must be done promptly to avoid having to clean high faces later
5. Considering the implementation of a ‘sign-off’ by Adaro supervision
Thickness of Cut
1. Current SOP states 3m mining thickness
2. This is quite variable in practice
3. Recent estimate of coal lost in fines is 0.10 tonnes per m2
4. Equipment currently in use is more than capable of digging 4 m lifts
Size of Equipment
1. For coal roof and floor cleaning, 30 tonne excavator is adequate, 20 tonne excavator is somewhat lacking in reach
2. For coal mining, coal geometry will determine preferred equipment size, from maybe 40 tonne for the thinnest seams to For coal roof and floor cleaning, 30 tonne excavator is adequate, 20 tonne excavator is somewhat lacking in reach
3. For coal mining, coal geometry will determine preferred equipment size, from maybe 40 tonne for the thinnest seams to 300 tonne for the thick seams
Faults and Intrusions
1. For coal that is affected by faulting, washouts or intrusions, smaller equipment must be used and mining restricted to daylight hours only
2. Thickness of cut may also be reduced to increase selectivity
Partings Removal
Where partings thickness is 100 mm or more, it needs to be removed