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 . Regardless of the environment, natural resources can be in a dangerous condition and adverse consequences will happen on the planet . Mining provides the necessary materials for human progress and also take away environment health and human life by increasing the pollutions . Hence, in many countries environmental impacts of mining operations have been studied and different standards for pollution from mining activities have been determined . 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 . 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) . 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 . 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 . Economically, the main thing about UPL is outside the specified range, exploitation and any mining operation are not economic . 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 . 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 . 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 . 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 . 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 , moving cone II , dynamic programming , korobov. Lerch and Grossmann method is able to calculate the optimum in all cases  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 $/year should spend for improving the environment of mine and decreasing the pollution. Suggesting scenario for designed mine is mentioned below. a) Creating Green belt surrounding the pit to control dust and noise pollution , b) Phytoremediation by planting absorb plant c) Using zeolite to clean up polluted waters; each ton zeolite can clean up 2456 m3 polluted water  d) Using geotextile to seal off floor of tailing dam Error! Reference source not found., e) Using zeolite at the base of tailing dam to clean up penetrated contaminated water  f) Doing water spraying to control dusts around the min g) Using suitable drilling machine to reduce air pollution  h) Using optimized blasting method to reduce fly rock and dusts The next step is using environmental impact assessment (Folchi Matrix Method) to compare impact of Classic pit and Green pit. EIA is process and review of investigation and the formal study of the effects of a proposed project on environment, human and social welfare. Figure 3 shows results of EIA of Classic pit and Green pit. Results show decreasing negative impacts of mining on environment in Green Pit. Figure 3- EIA Result of Classic pit & Green Pit Gray Color is related to Green Pit, Black color is related to Classic Pit 5. Results Table 2 shows statistical comparison of Classic pit and Green pit. Applying environmental cost in Green pit leads to decreasing 9.16% of waste tonnage, 0.38% of ore tonnage, 0.14% of revenue and 9.09% of stripping ratio and increasing 0.3% of Pb grade and 0.22% of Zn grade. Table 2- Statistical Comparison Between Classic Pit & Green Pit Mining Cost ($/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. 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