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
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Mill Recovery Rate
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93%
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Mill Concentrate Grade
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20g/t Au
|
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Smelter Loss
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0.7 g/t of Au pulp
|
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Refining Loss
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0.25 g/t of Au dorey
|
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Head Grade
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1.3 g/t, 4.5 g/t , 8.0 g/t , 15.7 g/t
|
|
Au price
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$12.50 /g
|
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By-product credit (Ag)
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$45.00/t
|
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Production costs (excluding stripping)
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$103.00/t
|
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Mining costs
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$25.20/t
|
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Milling costs
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$95.00/t
|
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General/Administration
|
$3.20/t
|
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Shipment of mill pulp to mint
|
$8.20/t of Au pulp
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Smelting cost
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$45/t of Au dorey
|
|
Shipment of dorey to refinery
|
$45/t of dorey Au
|
|
Refining cost
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$12.00/t of dorey Au
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|
Selling & Delivery costs
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$3.20/g Au metal
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General Plant costs
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$0.84/g of Au
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