Green Pit: Ultimate Pit Limit With Regard To Environmental Costs C

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Green Pit: Ultimate Pit Limit With Regard To Environmental Costs
Case Study: Lead-Zinc Deposit
Hesam Faghih Jouybari1, Ramin Doostmohammadi2, Farhad Samimi Namin3
1
MSc student of Environmental Sciences, University of Zanjan, Iran. [email protected]
2
Assistant professor of Mining Engineering Faculty, University Of Zanjan, Iran.
3
Assistant professor of Mining Engineering Faculty, University Of Zanjan, Iran.
Abstract
In the past two decades, the people's concern gradually increased to maintain environmental quality
and this phenomenon has influenced the design of mining activities. Since Iran is a developing
country and needs to develop mines for growing, so it is necessary to identify and study
environmental aspects of the mining industry for the sustainable development. The main objective of
this research is evaluation of open pit mine design with regard to environmental costs of open pit
mining method. In this study, it is assumed that using environmental costs in pit design could have
positive effects on environment. Since mine owners is not required themselves to perform reclamation
phase after extracting ores in iran, so it needs to apply environmental costs to perform improvement
operations parallel to extracting operations. Environmental costs in Green pit, is just used to reduce
negative effects of mining on environment. The case study is a lead-zinc deposit that is similar to
Angouran Lead-Zinc deposit. Audit fees are in accordance with paragraph (c) of Article 104 and
Article 134 of Iran's Third Development Plan. Deposit modeling is done by Datamine software and
ultimate limit is obtained by NPV Scheduler software. Declining revenue, profit, waste tonnage, ore
tonnage, strip ratio and increasing in-situ and recovered product grade has resulted in the ultimate pit.
Environmental impact assessment has been used to compare the performance of green pit. The results
of Folchi method showed that negative effects of mining, has been decreased in Green pit.
Key words: Green Pit, Ultimate Pit Limit, Environmental Costs, Environmental Impact Assessment,
Lead-Zinc Deposit.
1. Introduction
Development of the mining sector is the most important tools in the vision of economic development
of any country. Conservation of natural resources and environment is the base of sustainable
development [1]. Regardless of the environment, natural resources can be in a dangerous condition
and adverse consequences will happen on the planet [2]. Mining provides the necessary materials for
human progress and also take away environment health and human life by increasing the pollutions
[2]. Hence, in many countries environmental impacts of mining operations have been studied and
different standards for pollution from mining activities have been determined [3]. Since Iran is a
developing country and needs to develop mines for growing, so it is necessary to identify and study
environmental aspects of the mining industry for the sustainable development. Iranian mine owners
are not required to implement their reclamation processes at the end of mine life, so it needs to be
thought a new design of mine and its legal requirements. According to the rules of procedure of
paragraph (c) of article 104 and 134 of iran's third development plan, all industrial units should
consider environmental issues as their economic issues and they should know the cost of maintaining
the environment as their internal costs [3]. So far, Applying environmental costs in design of open-pit
mines had been much less important and it was not considered in mine design. In this study, it is
mentioned to the amount and method of calculating the environmental costs of Lead-Zinc deposit that
is similar to Angouran Lead-Zinc deposit of Zanjan. Then it is compared changing of Ultimate Pit
Limit of Classic Pit and Green Pit by using technical design parameters and environmental impact
assessment (Folchi method) [4].
2. Importance of Ultimate Pit Limit (UPL) in Open-Pit Mines
Determining the UPL is one of the most important issues of open-pit mines. Before extracting ores in
open-pit mining method, it is necessary to determine the size and shape of UPL to determine amount
of storage, amount of stripping, location of surface facilities such as access roads, tailing depot and
processing factory [5]. Open pit mining is an important general mining method that mineral deposit
will be mined via pits. The shape of mining area at the end of mining operation or final limits of a
mine must be designed before starting the operation. According to the designed final pit limits, mining
operational parameters such as width, length and depth of mined pit, opening track ways, location of
waste dump, stripping ratio, mine life, minable ore tonnage, waste tonnage and production scheduling
can also be determined [5]. Economically, the main thing about UPL is outside the specified range,
exploitation and any mining operation are not economic [5]. UPL is related to some parameters such
as: ore grade, cut-off grade, mining cost, stripping cost, processing cost, efficiency and price of
mineral ore that because of changing this parameters or accessing some new exploring information, it
may lead to change this UPL in mine life time [5]. Therefore, the design of algorithms for massive
computations is performed by a computer program is necessary for mine design. To determine the
UPL, various techniques are used such as hand-drawn, computer-aided design and optimal design [5].
Among these methods, optimal design methods based on a specific algorithm to determine the UPL
are important. Using a computer to design the optimal limit of open-pit mines usually starts with
building a block model of the deposit. For this purpose, first gangue and ore is considered as a big
block so that all areas of the mineralization. Then the next step is to divide it into smaller blocks and
assigning an estimated grade to each one. The blocks may have different shapes and sizes. Block
models of the deposit with respect to split it into smaller blocks is divided to four models [6]. These
models are three-dimensional regular and irregular model, two-dimensional regular and irregular
model. Among of all, three-dimensional regular model, in which all dimensions are equal, is more
common [6]. The height of the blocks in the model are generally designed to measure the step height
are considered but their horizontal dimensions depend on the exploration and sampling interval.
Optimum design of open-pit mines is a complex subject that requires a lot of computation. After the
invention and development of computer, many algorithms presented for determining the optimum pit
limit that the main goal of all algorithms is to find a set of blocks that if they be extracted, achieved
profit will be maximum under technical and economic limits. The most important algorithms for the
optimal design of ultimate pit include: Lerch and Grossmann [7], moving cone II [8], dynamic
programming [9], korobov[10]. Lerch and Grossmann method is able to calculate the optimum in all
cases [5] and NPV Scheduler software is using the same method to determine the optimal pit limit.
3. Benefit of Mine Design With Regard to Environmental Costs
Environment is a public commodity that belongs to the public and preserving it for present and future
generations is their certain right. Environmental costs include internal costs and external costs.
Internal costs include costs for preventing the pollutions, waste disposal, changing production system
for decreasing pollutions and redundancy technology. External cost is effect of environment pollution
on the entire society that less attention is being. It is necessary for governments to use some tools such
as legislation, establishing taxes and penalties to control the costs. In order to reduce the pollution of
the environment, particularly in the natural resources and water resources, industrial units are
responsible for implementing technical standards of their environment and take action to reduce
pollution. If the unit doesn’t perform the necessary action to reduce damage to the environment, it is
considered for them some penalties to reduce pollutions according the standards. Regulations in third
development plan focuses on the case of environmental crime and considers environmental costs as
current fees. The penalties collected commensurate with damage inflicted on environment and
deposited into general revenue to use it for safety implementation of environment. This causes
decreasing the damages to environment by government and this can be an incentive factor for
environmental standards. But unfortunately, there are two bad things about collecting penalties from
industrial units. Frist, the pollutant units just desire to pay penalties and they don’t fix pollution issues.
Second, according to executive regulations of iran's third development plan government should spend
these penalties for environment improvement, but usually nothing happens. So it feels the need to
bring up a new solution for mining industry. Green Pit design is the suggested solution for decreasing
negative aspect of mining activities. In Green Pit, it needs to calculate environmental costs on basis of
environmental scenario of each deposit. Environmental scenario can be adopted from environmental
situation of similar deposit or can be predicted. Environmental cost that is calculating in this research,
include activities such as mining operations, processing and smelting factory. After calculating
environmental cost, it needs to apply this cost in mine design. This cost is just for improvement of
designed mine that should be parallel to mining activities. Improvement plans parallel to mining
operations could lead to decreasing negative impacts of mining on environment.
4. Green Pit Design
Firstly, block model of Lead-Zinc deposit is made by Datamine software. Figures 1 and 2 show the
ore body and block model that is designed by Datamine software.
Figure 1- Block model of Lead-Zinc Deposit in Datamine software
Figure 2- Ore body of Lead-Zinc Deposit in Datamine software
Then, Environmental cost should be calculated according to executive regulation of iran’s third
development plan and environmental scenario. Environmental cost is equal to 4.07 $/tonne extracted
rock. After adding this cost to mining cost in NPV Scheduler software and running it, upl will obtain.
Mining cost is 0.5 $/tonne in classic pit and 4.07 $/tonne in Green pit. After obtaining upl in classic
pit and Green pit, statical comparison should be done. Table 1 shows importing parameters in NPV
Scheduler software for Lead-Zinc mine.
Table 1- Importing Parameter for NPV Scheduler Software
Pb price ($/tonne)
2149
Zn price ($/tonne)
1894.5
Pb sell cost ($/tonne)
300
Zn sell cost ($/tonne)
300
Mining cost ($/tonne)
0.5
Dilution (%)
0
Recovery (%)
100
Mining cost adjustment factor
1
Concentration cost
40
Leaching cost
360
Final pit slope
45
Working days
365
Average mine production (tonne/ year)
800000
Annual discounting rate (%)
15
According to these calculations, this mine 8791200 $/year should spend for improving the
environment of mine and decreasing the pollution. Suggesting scenario for designed mine is
mentioned below.
a) Creating Green belt surrounding the pit to control dust and noise pollution [11],[12]
b) Phytoremediation by planting absorb plant[14]
c) Using zeolite to clean up polluted waters; each ton zeolite can clean up 2456 m3 polluted
water [15]
d) Using geotextile to seal off floor of tailing dam Error! Reference source not found.,[18]
e) Using zeolite at the base of tailing dam to clean up penetrated contaminated water [15]
f) Doing water spraying to control dusts around the min[19][20]
g) Using suitable drilling machine to reduce air pollution [20]
h) Using optimized blasting method to reduce fly rock and dusts
The next step is using environmental impact assessment (Folchi Matrix Method) to compare impact of
Classic pit and Green pit. EIA is process and review of investigation and the formal study of the
effects of a proposed project on environment, human and social welfare. Figure 3 shows results of
EIA of Classic pit and Green pit. Results show decreasing negative impacts of mining on environment
in Green Pit.
Figure 3- EIA Result of Classic pit & Green Pit
Gray Color is related to Green Pit, Black color is related to Classic Pit
5. Results
Table 2 shows statistical comparison of Classic pit and Green pit. Applying environmental cost in
Green pit leads to decreasing 9.16% of waste tonnage, 0.38% of ore tonnage, 0.14% of revenue and
9.09% of stripping ratio and increasing 0.3% of Pb grade and 0.22% of Zn grade.
Table 2- Statistical Comparison Between Classic Pit & Green Pit
Mining Cost ($/tonne)
0.5 (classic pit)
4.57 (Green pit)
Number of blocks in ultimate pit
3452
3256
Waste tonnage
25541719
23200159
Ore tonnage
13669037
13616998
Profit ($)
4314905869
4161323103
Revenue ($)
4881518889
4874471425
Processing cost ($)
546761497
544679900
Strip ratio
1.87
1.7
Estimated life time (year)
17.09
17.02
Zn -insitu Product (%)
18.775
18.816
Pb-insitu product (%)
4.14
4.153
Zn – Recovered product (%)
17.836
17.876
Pb- Recovered product (%)
3.933
3.945
6. Conclusion
According to EIA results of Green Pit, it is seen that designing open-pit mine with regard to
environmental costs lead to decreasing negative impacts of mining on Health and safety, water
quality, air quality, use of territory, aboveground, underground and landscape.
Environment is a public good. This is not fair that society pays the cost of hurting the environment by
industrial units. Today, managers realized that if environmental cost identify correctly, it could lead to
more profit. By using Green Pit design the so-called win-win occurs; because in Green Pit design, it
should be done improvement operation parallel to mining operation and environmental protection
agency (EPA) won’t fine the mine. Environmental penalty that EPA considered for polluted unit is
1% of revenue. But in Green Pit design, the mine’s costs for improvement is 0.14% of revenue. So
using Green Pit is economic and its profit is for mine and society. Mine pays less money and society
live in less polluted environment.
7. Reference
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