100 years of mining research: 100 years of mining research: phoenix, arizona; february 28 - march...
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
Practical final pit depth considering the Practical final pit depth considering the
future underground mining- A case studyfuture underground mining- A case study
Title of paper:Title of paper:
Authors:Authors:
1- Ezzeddin Bakhtavar; Urmia University of Technology
2- Kazem Oraee; University of Stirling, Stirling, UKUniversity of Stirling, Stirling, UK
3- Kourosh Shahriar; Amirkabir University of Technology
4- Farhad Samimi Namin, Zanjan University
100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
In some cases it is considered that the most suitable and economical
method for the exploitation of an ore deposit (such as the investigated
case study) is to combine open-pit and underground methods.
In this regard, the most critical problem is the determination of optimal
final pit depth with considering the underground alternative.
Here, to determine optimal final open-pit depth of Gol-e-Gohar Area 3
mine (case study) a method, which was recently introduced on the basis
of economical block models of open-pit and underground, was used.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
The main idea of the applied model was concluded from the initial
algorithm of Nilsson.
In order to reduce the shortcomings of the Nilsson algorithm and to
accomplish some modifications, a number of essential requirements
were added to the algorithm, for instance, to take into consideration to
a suitable crown pillar.
The target of the model can be achieved by comparison between the
obtained values of various scenarios of combined mining.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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In this method, it is necessary to split up the future pit volume into
several level-cuts (independent pit).
100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
Considering and below each level-cut, an underground option can be
included, but after to bear in mind the most effective crown pillar.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
At most, a crown pillar with a height as a multiple of blocks height
considering the selected underground mining method and geotechnical
investigations must be contemplated.
The main part of the present method is associated with selection of a
combined mining scenario includes maximum NPV.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
1.1. General description of the siteGeneral description of the site Ore complex located in Kerman province of Iran and includes six areas.
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Gol-e-Gohar Iron Ore complex
100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
The Area 3 zone is approximately 1730 meters above sea level in an area of
planar desert topography.
Length of the Gol-e-Gohar Area 3 ore body is about 2200 m (N-S).
Average width of the ore body is nearly 1800 m (E-W).
Thickness of overburden and waste rock above the ore zone varies from 95
to 560 m.
Depth of the ore body varies from 95 m at the north end to 600 m at the
southern end.
Ore body thickness varies from 15 to 130 m with an average of 40 m.
The indicated resources have been estimated to be 496 Mt and an Inferred
resource of 147 Mt.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
2.2. Technical considerations of the open-pit optionTechnical considerations of the open-pit option A bench height of 15 m (Therefore, the block height of 15 m used in
the block model)
Pit slopes of 45 degrees in ore and waste rock and 32 to 33 degrees in
dry overburden
A safety berm height of 2 m
A drainage ditch width of 2 m
The required width of the haul road is 26 m with a grade of 10%.
Four shovels with 9-m3 buckets for use primarily in ore and 15-m3
buckets for use in overburden.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
During the production stage, 13 to 29 hauling tracks with capacity of 136
ton will be required.
Other mining support equipments: one wheel dozer, four track dozers, two
motor graders, one water truck, one ANFO / emulsion truck, and etc.
Four rotary blast hole drills
Burden by spacing in ore is 5.5m*7m
Burden by spacing in all waste rock zones is 5.5m*6m
Burden by spacing in dry and wet overburden zones are 8m*10m and
8m*9m, respectively.
Sub-drilling is 1.5 m in ore and waste rock and 2.5 m in overburden.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
3.3. Selection of a suitable underground optionSelection of a suitable underground option During the selection of a low cost and productive underground method
the following assumptions are considered and finally “room and pillar”
has been chosen.
o Backfilling of openings will not be economically viable; therefore
mining will be by room and pillar or open stoping methods.
o Due to the potential height of the mining, multiple levels would be
required, separated by sill pillars.
o Due to the plunge of the ore body (approximately 20 degrees to the
south) and the potential for low friction contacts (gouge and broken
zones) between the ore zone and hanging wall / foot wall rocks, it is
assumed that pillars left in place will be continuous ribs generally
oriented in a N-S direction (i.e. along dip).
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
4.4. Technical considerations of the underground optionTechnical considerations of the underground option A room width of 10 m
Pillar height varies from 60 m at 100-m depth to 9 m at 400 m depth.
A 60% of ore extraction and recovery
The rock support consists of bolts, screen and concrete (for waste).
A sill pillar thickness of 6.7 m
One production shaft with a diameter of 6.71 m, one service shaft with
a diameter of 7.62 m, and one exhaust ventilation shaft with a diameter
of 7.62 m
Two crusher stations (each crusher can crush 900 ton/hr)
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
Conveyor belts at the bottom of the crusher will transport the ore to a
1000-ton bin.
A two-boom electric-hydraulic drill jumbo
A crawler-mounted, Single-boom, electric hydraulic bench drill will
drill 12.5-m long, 64-mm diameter holes on a 1.2-m by 1.4-m burden
and spacing pattern.
Each bench hole will contain 1 m of water gel explosives followed by
8.5 m of ANFO prills and 0.3 m of collar stemming materials.
50-ton trucks and 16-ton loaders.
A total of 17 trucks and 15 loaders
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
4.4. Economical considerations of the open-pit and underground Economical considerations of the open-pit and underground
A)A) Estimation of the annual incomes Estimation of the annual incomes The actual production of the processing plant was determined to be 6
Mt/year considering a loss of 5% of concentrate to dust in the plant. To produce the actual targeted 6 Mt of concentrate, the annual tonnage of
processed ore will be in the range of 8.7 Mt. The price for concentrate is US$0.235 per Fe unit in concentrate based on
US$16/t at 68% Fe.
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Characteristic Open-pit underground
Annual concentration (ton) 6000000 6000000
Price of Fe unit (US$) 0.235 0.235
Annual income 96585000 96585000
Table- Annual incomes achieving from open-pit and underground mining
100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
B)B) Estimation of the costs Estimation of the costs The total operating cost was estimated to be equal to 554.65 (US$ million).
Here, operating cost is divided into three groups of mining, processing, and
general and administration.
“Processing” cost as well as “general and administration” cost are the same
in both open-pit and underground.
An average process operating cost was estimated to be US $3.00/ton per
feed ore.
General and administration cost was estimated to be equal to 2.3 (US$
million/year).
Therefore, the operating cost of processing plant for open-pit and
underground mining is calculated to be 26.17 and 24.7 (US$ million/year),
respectively.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
Ascendant trend of operating cost per each tonnage of produced ore in regard to
different open-pit mine sizes, is assessed (following Figure).
As it is clear in following Figure, in relation to an open-pit mine including 130
Mt of ore, mining operating cost is US$2.28 per each tonnage of produced ore.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
During the three years of overburden removal, operating cost of mine is
taken into account to be US$0.4 per each tonnage of overburden removal.
Therefore, before ore production and during development stage mining cost
will be 13.666 (US$ million/year).
On the basis of an open-pit mine with maximum production capacity of
130.87 Mt of ore capital cost is considered to be 100.712 (US$ million).
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
All estimations for the underground costs are in US dollars, using 2002
prices, and have an error of estimate of 25%. A 15% contingency has been
added to all cost estimates.
The Capital costs include:o 124.962 (US$ million) for underground mobile mining equipment,o 17.34 (US$ million) for miscellaneous mine equipment,o 36.453 (US$ million) for shaft development and installations,o 33.119 (US$ million) for mine development,o 2.2 (US$ million) for mine construction,o 2.919 (US$ million) for miscellaneous mine operating,o 5.23 (US$ million) for staff and labour.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
As it shown in following Figure, the total operating cost for direct operating and
maintenance supplies and labour for stope and production development, room
and pillar mining has been estimated to be 4.47 (US$/ton, Milled).
Therefore, mining cost of the room and pillar will be 36.9 (US$ million/year).
On the basis of the room and pillar mine with maximum production capacity of
122.455 Mt of ore capital cost is considered to be 208.142 (US$ million).
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
It is first necessary to identify several scenarios of combined mining on the
basis of the benches height of 15-m in open-pit.
Each scenario includes three components of open-pit, a crown pillar, and
underground.
Crown pillar stability will be dependent on numerous parameters including
rock type, rook quality, rock strength, overburden depth, water influence,
in-situ rock stress, and pillar geometry.
In the next step, through the economical comparison between the
scenarios, the most profitable one can be selected.
It is notable that the main assessment is done according to the constructed
economical block models of open-pit and underground mining.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
Open-pit depth (m)
As it shown in following Figure, considering a discount rate of 12%, a net
present value of 63 (US$ million) is achieved due to the related scenario of
285-m depth of open-pit. It means that the optimal final open-pit depth considering the room and
pillar mining to be equal to 285 m achieving a 63 (US$ million) of net
present value.
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
Due to the significance of determining the optimal open-pit depth
considering an underground option for Gol-e-Gohar Area 3 ore body, an
effective method was used.
In this regard, according to the benches height of 15-m several scenarios of
combined mining of open-pit and room and pillar were initially
considered.
Then, with considering a discount rate of 12% the related NPV of each
scenario was determined.
After that, during an economical comparison between the scenarios, the
most profitable one was selected.
In this relation, the optimal open-pit depth was assessed to be equal to 285
m, which achieves a total NPV of 63 (US$ million).
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100 YEARS OF MINING RESEARCH:100 YEARS OF MINING RESEARCH: Phoenix, Arizona; February 28 - March 03, 2010
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