Question 1: 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 underdevelopment

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 3km.

Question 2: A room and pillar mining operation uses 5m wide rooms and 35m square pillars to extract a 3m thick coal seam.

a. If the workings are located 250m 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? 

b. If the stress concentration factor following mining can be ex pressed in the form 1/(1-ER) where ER is the extraction ratio determine the stress on the remaining pillars ?

c. If the formula ? 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.

Question 3: 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 (70% recovery)

Gold = 5 g/t (80% 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 The following describes a mineral deposit.

Question 4: For the deposit the candidate is required to select a suitable mining method for the deposit based on the information given and to describe the mining system in detail.

The candidate should include in their answer the following:

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

Question 5:

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. Project Description Your company has secured a mining lease in the Hunter Valley region.

The lease is 5 km in width East to West and 4 km in length North to South. Other than a railway running straight down the Eastern side of the lease, North to South, no other surface infrastructure requires protection from subsidence. The mines department has indicated that 100 m measured on the surface requires to be left on either side of the railway to avoid subsidence.

Also that a line drawn at 37° should be drawn down to each of the two coal seams on the lease from this subsidence free zone. Any coal inside these two lines should be considered to be sterilised and cannot be mined.

It can be assumed that the surface is level. Seam 1 is 3.5 m in thickness and is at a depth of 450m below surface, seam 2 is 600m below surface and is 7.5m thick. The seams are parallel and level. The SG of coal for the upper seam is 0.8 and the lower seam is 0.83.