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Question: 1.

For the following situations determine the effective noise level in dB(A)

a. A rock drill produces a sound pressure level of 90 dB(A) in a heading. If two more drills were to operate in the heading what would be the expected noise level?

b. Currently a conveyor operator works for a shift length of 8 hours and is subjected to a noise exposure of 85 dB(A) over the shift. If this worker works a double shift at his normal work station what will be his noise exposure for that day?

c. A continuous miner operator sitting on the machine is exposed to a noise level of 93 dB(A) when sat 3m from the noise source. If this operation were to be made a line of site remote operation with the operator being an equivalent distance of 18m away from the noise source what would his noise exposure be?

d. Determine the equivalent 8 hour noise exposure level for a worker exposed to an equivalent continuous sound pressure of 86dB(A) over a 12 hour shift?

Question: 2.

An analysis of air samples taken in a return airway indicates the following gas concentrations:

Carbon dioxide: 0.2 percent, Hydrogen Sulphide: 2 ppm, Sulphur Dioxide: 1 ppm. Determine the threshold limit values, TWA and STEL for the mixture.

Question: 3.

Using the Brief and Scala method determine the TLV-TWA for Carbon Dioxide for an 11 hour shift if the TWA-TLV for an 8 hour shift is 0.5%

Question: 4.

Develop a spreadsheet based application to determine the optimum diameter for a ventilation shaft for a ventilation flow rate of 200 m3/s. It may be assumed that the cost of power is Au$ 0.45 kWhr.

The following apply
Shaft sinking
Set up and decommissioning costs $ 1,000,000
Excavation cost $ 450/m3
Fittings and Lining $ 500/m
Shaft Data
Shaft depth 1000m
Friction factor 0.006 kg/m3
Air density 1.2 kg/m3
Fan efficiency 70%
Shaft life 20 years
Annual rate of interest 10%
Use Chapter 5 and 9 provided as a reference

Question: 5.

Calculate the Net Values for gold ore containing 1.3 g/t, 4.5 g/t , 8.0 g/t and 15.7 g/t. Use the input values given below.

Input Values

Mill Recovery Rate

93%

Mill Concentrate Grade

20g/t Au

Smelter Loss

0.7 g/t of Au pulp

Refining Loss

0.25 g/t of Au dorey

Head Grade

1.3 g/t, 4.5 g/t , 8.0 g/t , 15.7 g/t

Au price

$12.50 /g

By-product credit (Ag)

$45.00/t

Production costs (excluding stripping)

$103.00/t

Mining costs

$25.20/t

Milling costs

$95.00/t

General/Administration

$3.20/t

Shipment of mill pulp to mint

$8.20/t of Au pulp

Smelting cost

$45/t of Au dorey

Shipment of dorey to refinery

$45/t of dorey Au

Refining cost

$12.00/t of dorey Au

Selling & Delivery costs

$3.20/g Au metal

General Plant costs

$0.84/g of Au

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