Strategic mine planning of surface mining projects incorporating sustainability concepts

Transcription

1 6th International Conference on Sustainable Development in the 645 Strategic mine planning of surface mining projects incorporating sustainability concepts C. Roumpos and E. Papacosta Public Power Corporation of Greece S.A., Mines Division, Greece ABSTRACT Long-term strategic mining planning and scheduling is a critical stage for the design and development of surface mining projects. It requires an integrated approach and optimization based on all available technical (mineral deposit characteristics, geological, geotechnical and hydrogeological data), economic, environmental or social parameters. Many of these parameters are crucial for the viability and sustainability of the mining project. Within this context, the quantification of the main parameters effect on mine design and scheduling incorporating sustainability concepts is very important for a successful mine planning. The objective of this paper is the development of a framework for the strategic mine planning of surface mining projects considering parameters of sustainability, their interrelationships and their influence on the optimization model as well as on mine development. A case study with a description of the proposed model in a surface lignite mine development is presented. 1. INTRODUCTION Mining projects are dynamic complex systems, with a long-term horizon, affected by many uncertainty and risk sources. Project uncertainties may relate to geological-mineral deposit characteristics, technical, environmental, social, economic or other factors. Especially in surface mines, which extend over very large areas and usually have a long life the long-term strategic mine planning should take into account these uncertainties. The planning stage is critical for the successful development of the mining projects (Roumpos and Spanidis, 2003; Roumpos et al., 2006). Strategic open pit mine planning, incorporating stochastic optimization techniques in mine design and production scheduling, allows modeling and direct integration of the project uncertainties and provides a framework for the optimization of life-of-mine planning (Dimitrakopoulos, 2011). Public acceptance of surface mining operations in relation to sustainable development may also affect the viability of the corresponding projects (Pavloudakis et al., 2012). Modeling and evaluation of the exploitation strategy of such projects in the strategic mine planning and scheduling phase should incorporate sustainability issues connected with activities that take place throughout the whole mine life cycle, from the first exploratory stages to the post mining period (Roumpos et al., 2005). A holistic approach model for the mine planning of surface mining projects should be based on an integrated approach to the long-term strategic mining planning and development, taking into account the latest technical, environmental, economic and social data with regards to the operation of surface mines (Roumpos et al., 2011). Within this context, the critical role of sustainability parameters on the strategic mine planning of surface mining projects can be described by dividing the mine planning model into the following interrelated sub-models: - Mineral deposit geologic hydrogeologic - geotechnical model. - Mine development and scheduling model. - Environmental impact assessment model. - Financial - mining economics - market model.

2 646 6th International Conference on Sustainable Development in the In this paper the effect of sustainability parameters on the mine planning sub-models is described. A case study, clarifying some critical issues of the analysis, is presented concerning the mine planning of Mavropigi Mine. 2. SUSTAINABLE MINE PLANING OF SURFACE MINING PROJECTS The critical effect of sustainability parameters on the strategic mine planning of surface mining projects is presented, examining every submodel of the mine planning model. 2.1 Mineral deposit - geologic- geotechnical - hydrogeological model The mineable ore reserves estimation process is a very important subject for the mine planning and design phase of the mining project. It is a core component of any surface mining project, affecting the life of the project, the annual production rate of the mine, the life of the corresponding mineral processing or other facilities and the viability of the overall project (Roumpos et al., 2009). The role of reserve estimation is also crucial in setting sustainable targets in the context of managing the mining industry s greatest asset (Weatherstone, 2005). Quality parameters of run-off-mine ore are also very important in strategic mine planning. They also affect the economic viability of the project, the efficiency of the processing facilities, the environmental performance of the project or the decision for the mining sequence. Mine planning activities should take into account the efficient use of mineral resources. It is, therefore, essential a reliable mineral deposit model, based on the geologic and fault model of the deposit and on exploration drill holes data. This model should be based on conventional and geostatistical grade and tonnage assessment techniques, incorporating errors and uncertainties related to the exploration data or other uncertainties concerning the spatial tonnage or grade distribution variability. It should also be revised periodically, adding the new knowledge acquired during the mining project. The model can be used for the optimization of final pit limits as well as for the optimization of long and short-term of mine development. Geotechnical analysis is also a very important issue of the mine planning process. Geotechnical model affects the overall mining ratio (volume of waste per ton of ore) and therefore the cost and the economics of the project. It also plays a critical role in strategic mine development. Geotechnical investigations should start in the early exploration phase of the deposit and a geotechnical model should be available in the mine planning phase in order to be used into the mine planning optimization processes, ensuring geotechnical stability of the excavation and dumping process and safe mining operations. The geotechnical parameters of surface mining projects contribute to sustainable mine planning design of the projects. Hydrogeological analysis is also an essential issue for the mine planning process. Hydrogeological investigations referring to groundwater and surface water problems that will be encountered during the mining project should also start from the early exploration phase and continue to after mining closure phase. In surface mining projects the hydrogeological model is an integral part of mine planning process as it is related to geotechnical model and also affects the dewatering planning of the mine, the environmental impact of the project, the water balance of the mining area and the environmental reclamation of the mine. It is clear that the hydrogeological parameters are also critical in the sustainability of mine development parameters and in the viability of the project. 2.2 Mine development and scheduling model Strategic mine development and scheduling model is the most important part of mine planning activities. It is a complex, multi-objective optimization problem incorporating technical, environmental, economic, social or other constraints. The main optimization model includes the selection of the mining method or the combination of mining methods, the location of the opening phase of the surface mine and the sequence of the excavations and the waste dumping and waste management, the optimization of bench design, the optimization of the production

3 6th International Conference on Sustainable Development in the 647 rate meeting short and long-term tonnage and grade targets, the optimization of mining equipment reliability and utilization and the stockpile management and blending procedures. The model should be optimized taking into account the operation of a number of mines of a mining center and incorporating the interlinking ore and waste handling systems. Mine development flexibility is a very important issue concerning the complexity and uncertainties that a surface mining project faces through mine lifetime. Strategic long term planning requires a cyclical reassessment of exploitation options, in the context of anticipated changes in the near- and long-term business operating environment (Smith, 2012). It is obvious that in the optimization process of a surface mine development and scheduling problem sustainability parameters should be incorporated in all stages of the project, throughout the whole mine life cycle, from the first exploratory stages to the post mining period. These parameters, which are also related with the parameters of the other three mine planning sub-models, may include: - The recovery and efficient utilization of the mineral resource. - The optimal environmental and ecological planning of the mining operation as well as the landscape and environmental reclamation of the mine, minimizing the volumes of waste outside dumps. - The economic performance of the mining project. - The social acceptance of the project and the contribution to long-term viability of the local and regional economies. - The minimization of risk in all stages of mining operation. The above-mentioned parameters should be taken into account into integrated optimization of mine development and scheduling model. 2.3 Environmental impact assessment model Surface mines are complex operations that can affect numerous environmental constituents in various ways. The environmental impact assessment model aims at the sustainable environmental planning and development of the mining project throughout the entire mine life cycle. The type and magnitude of environmental impacts of surface mining projects are closely related to various site-specific physical, chemical, ecological, socioeconomic and cultural characteristics, which must be thoroughly identified, analyzed and modeled. The corresponding model requires the identification of inflows and outflows of the mining system defining appropriately the boundaries of the system, the determination of the best available environmental management practices as well as the definition of environmental monitoring and sustainable development indicators. Environmental and social issues often have a direct impact on the economics of the mining project. They may be related to the following parameters: - Land acquisition requirements essential for mining excavations and waste dumping development. One of the main parameters in the optimization of mine development is the minimization of the waste outside dumping areas, minimizing the land acquisition requirements and consequently the corresponding cost as well as the environmental impact of the surface mining project. Land acquisition processes may be crucial in mine operation causing delays in mine development or changes in the direction of mining operation. Therefore, a land acquisition planning should be incorporated into the mine planning procedures. - Relocation of infrastructures affected by the project. An appropriate management model for large technical projects is also required from the initial phase of mine planning activities (Roumpos et al., 2011). The large technical projects may necessitate significant modifications-revisions of the mine limits and of its development schedule. They are also related to the environmental and sustainability planning of the mining project and have a direct effect on the economics of the project. - Environmental protection and land reclamation planning of the mined out and waste

4 648 6th International Conference on Sustainable Development in the dumping areas. These activities are closely connected with mine planning procedures, with the land uses prior to mining operation and the planned land uses of the reclaimed areas. They should also take into account the transportation and deposition of the byproducts of the mining project. They start from the early stages of deposit exploration and expand many years after the mine closure and affect directly the social acceptance as well as the economic performance of the mining project. - Archaeological investigations in the mining area. Surface mining projects offer an opportunity to conduct Archaeological fieldwork by funding the Archaeological research prior to mining operations and thus to contribute to sustainable mining operation concerning the Archaeological findings. On the other hand inappropriate planning of Archaeological investigation taking place in the region surface mine may cause significant delays or changes in the mine development. 2.4 Financial - mining economics - market model This model is related with the financial, mining economics and market parameters that are usually taken into account in the mine optimization model. They may refer to objective function, to the criteria and economic analysis for investment decision - making or to the constraints of the model. The basic economic parameters of the mining project are directly connected with the parameters of the other mine planning submodels. They mainly include the escalation of capital and operating mining cost through all phases of mining project, from the exploration to post mining activities, the commodity prices, the interest rates and the financial engineering and risk analysis model. The economic analysis model could also be integrated by incorporating the evaluation technique of real options or the game theory analysis taking into account the competition of other mining projects. 3. CASE STUDY An analysis of the described mine planning model concerning the strategic mine planning of the Mavropigi surface lignite mine is presented in this section. 3.1 Mine location - Description of the Mavropigi lignite deposit The Mavropigi mining field is located in the northern part of the west boundary of the Ptolemais mining area (Fig. 1). The area of the mine covers approx. 11 km 2. In the NW-SE direction, it extends over approx. 5 km from the Ptolemais power station to the Komanos village and in the NE-SW direction from the former opencast mines of North Field and Komanos, to the mountain front where pre-tertiary slates and limestone layers occur near the surface. The mining field includes administrative buildings of the opencast mines, industrial facilities and parts of the Ptolemais power station. Inside the planned mining area, the Mavropigi village is located in the southwest of the field. From the beginning of the mining operations at the end of 2002 until the end of 2012, 51.8 Mt of lignite was produced. The remaining exploitable lignite reserves amount to Mt. The main mine equipment consists of 8 bucket wheel excava- Figure 1: Ptolemais lignite basin and the Mavropigi Mine.

5 6th International Conference on Sustainable Development in the Strategic mine planning of Mavropigi mine The main issues concerning the strategic mine planning of Mavropigi mine include the following: Figure 2: Fault system - initial and final pit limits of the Mavropigi mine. tors and 3 spreaders, transferred from the exhausted mines of North Field and Komanos as appropriate for the Moavropigi deposit (Kolovos, 2006) and the annual lignite production of the mine is approximately 8 Mt (Pagonis et al., 2009). After a zone of very small thicknesses of the lignite-bearing series in the south, the thickness grows towards the northwest where it mainly ranges between 50 and 150 m, while it rises up to approximately 200 m towards the southwestern mountain boundary. The increase in thickness of the lignite-bearing layers is accompanied by a division into a multitude of split seams. In a graben settling down to the north and opening towards the Proastio field, the lignite-bearing series reaches a thickness of 200 to 250m in the planned mining area. The overlying strata thicknesses mainly range between 10 and 50m. The mining field is separated by NW-SE striking faults into individual fault blocks (Fig. 2). Towards the mountain front it is limited by one or several faults with dips towards the mine. Furthermore, sandy-gravelly layers of the overburden strata locally incorporate consolidated layers. Excavation pit limits Strategic mine planning and scheduling of Mavropigi mine has been modified since the initial phases of the mining project. The pit limits in the initial mining study of Mavropigi mine (Rheinbraun Engineering & Public Power Corporation of Greece, 2006) did not include Mavropigi Village (Fig. 2). Figure 3 shows the mine development sequence (A-B-C-D-E) mainly by the use of continuous mining equipment and the areas of exhausted mines North Field and Komanos mine planned for waste material outside dumping (areas of outside dump 1 (2 spreaders) and 2 (1 spreader) respectively). In a revision of mine planning, based on the decision for a new power plant construction, and on the new exploration, geotechnical, environmental, social and economic data, the pit limits in the area of Mavropigi village were extended, increasing the mineable lignite reserves of the deposit and consequently the increasing the contribution to the sustainability of the mining project concerning the efficient utilization of the lignite deposit and to the to long-term viability of the local and regional economies. Also, the need for covering part of the production needs of the adjacent Kardia surface lignite mine, the exploitation of low depth deposit of Komanos village, which initially was part of the lignite deposit of Mavropigi mine, was assigned to Kardia mine (Fig. 2). This part of the deposit was planned to be excavated by non-continuous mining equipment. Lignite production rate-excavations sequence In the initial mining study the annual production rate of the mine was ~ 6 Mt, covering the feeding needs of Ptolemais Power Plant. The demand for higher annual production rates (8-10 Mt) covering the needs of other power plants of the lignite center, necessitated the application of a rapid mine development plan with significant modifications in the excavations sequence of the mining sectors (Fig. 4), introducing the applica-

6 650 6th International Conference on Sustainable Development in the Figure 4: Mine development sequence after the modifications of pit limits and production targets. Figure 3: Mine development sequence in the initial strategic planning of the Mavropigi mine. tion of non-continuous mining equipment to a large extent in various areas and incorporating the production flexibility of the project. As a consequence, there was a need for a new area for dumping the waste material excavated by non-continuous equipment (outside dump 3). The site that was selected for the construction of the new power plant had been planned for the outside dump 2 of waste material (Fig. 3). Because of this selection, the area of outside dump 2 was changed (Fig. 4). Further changes of mining sectors sequence due to land acquisition and the consequent geotechnical problems Land acquisition of a small area (L) (Fig. 5) in front of excavation face became a crucial issue in excavation development of the Mavropigi mine. The delays in the acquisition of that area caused production problems and imposed significant changes in the direction of excavations. A flexible planning of the mine included the changes of the mining direction shown in Figure 5. The new excavations sequence formulated excavations face geometry with adverse geotechnical effects. A new geotechnical investigation of the south-west final perimeter slope of the excavations revealed the movement model, identified the risk factors, improved the geological and fault model and suggested a safe slope inclination in for excavating the deep lignite seams in that area with safe mine operations. The occurrence of the limestone in the upper benches of the mine also imposed the use of continuous mining equipment in the west boundaries of the mine. In that area, hard rock conglomerate material also exists, so the planning of the excavations with the combination of continuous and noncontinuous mining equipment in different mining areas is a critical issue for the efficient use of the main mine equipment and the appropriate mine development. Hydrogeological problems in the western mine perimeter require a water management planning. As a result of these changes in mine excavation planning and based on the outcome of the new geotechnical investigations, the estimation of the volume of waste material that will be dumped to the outside dump area 1 increased. An increase is also anticipated for the final levels of the outside dump area 1 (avoiding new dumping areas) as well as the delay of the installation of spreaders in the inside dump of the mine.

7 6th International Conference on Sustainable Development in the 651 issues concerning the development of Mavropigi mine. Figure 5: Further changes in mine development sequence after land acquisition problems and geotechnical investigation of south-west final perimeter slope. Concerning the areas of archaeological interest at the south part of the Mavropigi mine (Fig. 5), a major archaeological fieldwork was funded and started in 2008, prior to mining operations that identified a number of areas of archaeological interest, contributing to sustainability of mining operations. The appropriate planning of archaeological investigations did not cause any delays in mine development. 4. CONCLUSIONS Strategic mine planning surface mining projects is a complex, multi-objective optimization problem that requires an integrated approach with the incorporation of technical, environmental, economic, social or other issues. In the optimization process of a surface mine development and scheduling problem sustainability parameters should be incorporated in all stages of the mining project, throughout the whole mine life cycle, from the first exploratory stages to the post mining period. In this paper, the critical role of sustainability parameters on the strategic mine planning of surface mining projects was described by dividing the mine planning model into interrelated sub-models, with a discussion of some critical REFERENCES Dimitrakopoulos, R., (2011). Strategic Mine Planning under Uncertainty. Stochastic Optimization for Strategic Mine Planning: A Decade of Developments, Journal of Mining Science, Vol. 47, No. 2. Kolovos. C., (2006). Technical Aspects Regarding the Opening of a New Mine with Old Already-Existing Equipment, Energy Sources, Part B: Economics, Planning, and Policy, 1, pp Pagonis, G., Ch. Roumpos, K. Liakoura and N. Paraskevis, (2009). Revised mine planning of Mavropigi mine, Public Power Corporation of Greece (in Greek). Rheinbraun Engineering & Public Power Corporation of Greece, (1996). Technical Mine Master Plan, unpublished report, 600 p. Roumpos, Ch., F. Pavloudakis and M. Galetakis, (2005). Modelling and evaluation of open-pit lignite mines exploitation strategy, 2nd Int. Conference on Sustainable Development Indicators in the Minerals Industry (SDIMI 2005), May 18th - 20th, 2005, Aachen, Germany, pp Roumpos, Ch., K. Liakoura and M. Leontidis, (2006). Strategic mine planning framework for continuous surface mining systems operation, 8th International Symposium Continuous Surface Mining (ISCSM), Aachen, Germany, September, pp Roumpos, Ch., F. Pavloudakis and M. Galetakis, (2009). Optimal production rate model for a surface lignite mine. Proceedings of the 3rd AMIREG International Conference: Assessing the Footprint of Resource Utilization and Hazardous Waste Management, 7-9 Sept. 2009, Athens, Greece: pp Roumpos, Ch., K. Liakoura and N. Paraskevis, (2011). A model for management of large technical projects in surface lignite mines, Mineral Wealth, 159/2011, pp (in Greek). Smith, G.L., (2012). Strategic long term planning in mining, The Journal of The Southern African Institute of Mining and Metallurgy, Vol. 112, pp Weatherstone, N., (2005). The role of the mineral reserve estimator in promoting sustainable development in the mining industry, Applied Earth Science (Trans. Inst. Min. Metall. B) Vol. 114, pp. B14- B21.