Question 1. A mine has been sealed for some time following a fire. The atmosphere has stabilised and a typical analysis is
|
CO2
|
1.0%
|
CH4
|
3.7%
|
|
O2
|
17.1%
|
H2
|
0.0%
|
|
CO
|
0.03%
|
N2
|
78.2%
|
Determine
a. Graham's ratio and its implication
b. Trickett's ratio and its implication
Question 2. Detail the design and construction of a pressure balance stopping
Question 3. For the fan curve for static pressure provided in the above chart determine the static pressure/quantity curve if the fan were working at 1300 rpm.
Question 4. Blast fume clearance time
For the following
Face dimensions 6 m high by 6 m wide
Face advance 4.2 m
Length of development before blast 700m
Rock density 2.8 tonnes/m3
ANFO factor 2.5 kg/m3 rock broken
Face ventilation 20m3/s
NO2 gas production rate 3.5 kg per tonne of ANFO
NO2 TWA is 3 ppm
Determine
1. Volume of rock to be blasted
2. Tonnes of rock to be blasted
3. ANFO used
4. Fume throw back distance
5. Volume of fumes immediately after the blast
6. Volume of NO2 gas produced
7. Concentration of NO2 in fume throw back zone immediately after the blast
8. Concentration of fumes after they have spread throughout the drive but before they have entered the decline
9. Time for diluted fumes to fill the drive
10. Time for fumes to be diluted below TWA concentration
11. Total time for fumes to clear
12. Repeat steps 9, 10 and 11 of the above for a face ventilation rate of 35 m3/s
Question 5. In the sections below a number of fictitious ore deposits, each with different characteristics are defined. Based on the information provided, propose up to three mining methods for mining the orebody in order of preference if applicable (note in some cases it may not be possible to provide 3 mining methods). Also summarise the most important reasons, factors, characteristics or conditions that were most influential in your first choice of mining method. The assignment is to be no more than a single page of A4 for each deposit. Also note dot point presentation is suitable. Marks for the assignment will be based on the suitability of the first choice mining method and the reasons for selecting this method and on the conciseness of the reasoning. It should also be noted that there is no one single method of mining each deposit.
Deposit 1:
This is a large, massive, low grade copper orebody. The grade is uniform with an average of 1.0% copper. The average thickness of the deposit is 200m, with a dip of 70° and a mean depth approximately 600m below surface. The average strength in the ore zone is strong and the ore is highly fractured with a weak fracture strength. The country rock is stronger and is less fractured than the ore zone. The RQD of the orebody is 35%, whilst the country rock has an RQD of 60%. Joint surface in the orebody are uncemented, whilst in the country rock there is evidence of gypsum in the joints.
Deposit 2:
The orebody is highly irregular in shape, varying in thickness from less than 1 m to 5m. The dip averages 80° but is highly irregular varying from vertical to a dip of 45°. The orebody ranges in depth from 250m below surface to 1000m deep and is continuous. The average grade is 100 g/tonne but is also highly irregular. The ore and country rock are weak with UCS < 50 MPa and highly fractured.
Deposit 3:
A tabular, narrow vein steeply dipping gold deposit. Grade averages around 18 g/tonne but is variable. Ore body width varies from 2 to 3 m and dip between 70 to 80°. The orebody ranges in depth from 50m below surface to 800m depth. The ore is strong, 200 MPa, with very little fracturing. The footwalls and hanging walls are strong, UCS 200MPa, also with very little fracturing
Deposit 4:
A flat, tabular, platinum deposit located some 600m below surface. The deposit varies between 0.6 and 1.2m thick, with dip being 4° from the horizontal. Ore grade is uniform at 7 g/tonne. The ore and country rock are very strong at 350 MPa both having bedding parallel to the dip pf the orebody.
Deposit 5:
A seam like deposit of potash, ranging in thickness from 2.5 to 3.5 m. the total area of the deposit is 10km2. It outcrops at surface at the northern end of the mine lease and dips in a southerly direction at 10°. The floor strata is a mudstone and the roof consists of a well consolidated sandstone.
Deposit 6:
A coal seam 2.5 m thick, located 900m underground. Dip is about 2°. The mining lease is located in mixed rural and urban area. The coal is underlain by a reasonably competent mudstone and overlain by a series of typical coal measures strata. Underlying and overlying the seam are a number of very thin < 20cm thick coal seams within 200m of the seam to be mined.
Deposit 7
A massive porphyry style deposit located at altitude in Arizona. Average grade of the deposit is 0.5 g/t Au and 0.8 g/t Cu. The deposit has a UCS of 200MPa and is highly fractured; country rock is similar in nature. The deposit has a large foot print area 800m by 800m and is located 300m from surface and open at depth.
Deposit 8
A coal seam 8 m thick, located 250m underground. Dip is horizontal. The mining lease is located in rural area. The coal is underlain by a reasonably competent mudstone and overlain by a series of typical coal measures strata.