Questions

1. A coal mine is using the room and pillar mining method to mine a seam. The rooms are 6m wide driven on 25m centres. Entries and entry crosscuts have the same dimensions. If no barrier pillars are left, calculate the percentage recovery both with and without pillar recovery.

2. A mining recovery rate of 60% is required in an underground coal mine using the room and pillar mining method. All entries and cross cuts are 6m wide. Pillar recovery is not undertaken and barrier pillars are not used. Determine the pillar dimension to provide the required recovery, assume square pillars

3. A retreat longwall coal mining system utilises twin accesses on both the intake and return sides of a panel whose face width is 250m. If the access drives are 4.5m wide and chain pillars are 40m wide and square between the accesses determine the extraction ratio for the following cases:
a) Panel under development
b) Panel under production

It may be assumed that a barrier pillar of 40 m width is left to protect the main mine entries and that the panel length is 2km.

4. The diagram below illustrates the amount of coal that is left intact after mining in pillars and the amount of coal that is extracted in the rooms. If a1 = 20m, a2 = 22.5 m, b1 = 5m and b2 = 4.5m determine the recovery ratio in a 2.5 m coal seam.

5. The hauling speed of a shearer whilst cutting a coal face bi-directionally is 7 m/min. A web of 1 m is cut with a cut height of 3.5 m.
a. How long does the shearer take to cut a complete strip of coal if the face length is 275m?
b. If the coal has a density of 800 kg/m3 how many tonnes of coal are cut in a single strip?
c. Assuming a turnaround time of 30 minutes following each strip of coal cut and assuming an effective 50 minute hour, how many strips can be mined over a 8 hour shift and how many tonnes are produced?

6. A room and pillar mining operation uses 5m wide rooms and 35m square pillars to extract a 3m thick coal seam.
a. Determine the extraction ratio for the workings
b. If the workings are located 450m below ground and the overlying strata has an average density of 2500 kg/m3 (assume g = 9.81 m/s2) what is the vertical stress on the virgin seam?
c. If the stress concentration factor following mining can be expressed in the form 1/(1-ER) where ER is the extraction ratio determine the stress on the remaining pillars
d. If the formula

Pillar Strength (Mpa) = 7.2 p0^.46/m^0.66

Can be applied where p = pillar width (m) and m = pillar height (m), determine the pillar strength

e. Determine the factor of safety against failure for the pillar.

7. An LHD has a bucket capacity of 4.5m³. The material being handled has a loose density of 2000 kg/m3 and the bucket fill factor is 0.9. Loading time including manoeuvring is 23 seconds and dump time is 12 seconds including manoeuvring. Acceleration and deceleration are equal at 0.3 m/s2. The one way haulage distance is 250m and the maximum speed of the unit is 2.5 m/s. Determine the following:

a) The acceleration and deceleration times
b) The acceleration and deceleration distances
c) The maximum speed haulage distance (it can be assumed that the maximum speed is the same for the full and empty elements of the run)
d) The fixed cycle time
e) The variable cycle time
f) The total cycle time
g) If the machine has an availability of 50 minutes per hour how many cycles per hour can be achieved
h) The productivity of the unit per hour

8. An ore body dips at 80° and has a vertical depth of 120m. The top of the ore body is 200m from the surface and surface mining operations have been discarded in favour of underground operations. The strike length of the deposit is 450m. The ore body varies from 8m to 20m and averages 15m. Grades are as follows:
Lead = 10% (90% recovery)
Zinc = 15% (85% recovery)
Silver = 120 g/t (60% recovery)
Gold = 2 g/t (50% recovery)
What is the total ore resource in tonnes, assume an SG of 3.6, and what is it worth at today's metal prices in A$?
Note: to calculate the worth of an ore body recovery must be considered. Recovery as quoted in the above figures means mill recovery

9. The following describes a mineral deposit. For the deposit you are required to select a suitable mining method for the deposit based on the information given and to describe the mining system in detail. The following should be included in the answer/report:
a. Describe suitable surface connection(s).
b. Detail development requirements
c. Detail Production requirements including a full description of the method selected.
d. Number of production unit's required/rate of production.
e. Describe loading/haulage requirements
f. Equipment
g. Briefly describe ventilation/drainage requirements
h. Personnel
i. Safety

As well as any other salient points as required by the mining system.For economic analysis use current market prices in A$ for the commodity as required. Accurate costings are not an essential aspect to the project but some notional costings should be undertaken to illustrate the viability of the method detailed.

A massive silver/lead/ zinc deposit approximately 250 m in width and 1,500m long ranging in depth from 300m below surface to 900m below surface. Angle of dip is 70°. The deposit grades 2g/tonne silver, 1.5% lead and 2% lead. The deposit is remotely located, however an airstrip can be developed. Additionally the site is located 15km from a rail route to a suitable port facility located 500km distant and 5km from a sealed two lane road.