International Journal of Mining and Mineral Engineering (21 papers in press)
Implementation of Industry 4.0 technologies in the mining industry a case study
by Arnesh Telukdarie
Abstract: In modern mining, it is imperative to have a real-time flow of information between enterprise level and shop floor systems. The gaps that exist between these spheres make it difficult for managers to have timely information for optimum decision making. A mining company needs instantaneous visibility on production, quality, cycle times, machine status, and other important operational variables to achieve optimum and effective operations. With the implementation of Industry 4.0 technologies at a Mine, the integration of fragmented shop floor and the enterprise level systems enables seamless communication in delivering optimum operations. This research demonstrates Industry 4.0 technologies as the mechanisms for integrating business systems, manufacturing systems and processes. The Industry 4.0 methods researched are deployed using Software Development Lifecycle (SDLC) process at a mining company to integrate systems such as manufacturing, plant, business partners, and SAP ERP. The results introduce a semi-smart Mine with real-time visibility of the overall mining status.
Keywords: Industry 4.0; Internet of Things; Industrial Internet of Things; Cyber Physical Systems; Big Data; ERP.
Effect of aggloflotation of coal slimes by use Flomin C9606 as a collector
by Richard Kasomo, Sammy Ombiro
Abstract: In many coal preparation plants and concentrators, coal slime (ultra-fine coal) form the major challenge due to difficulties in processing and upgrading. Several techniques are currently being devised in coal and mineral industries to aid in beneficiation of the coals in their finer sizes. Most of the ultra-fine coal particles are processed by oil agglomeration, selective flocculation or hydrophobic flocculation flotation techniques. In this research the main focus was hydrophobic flocculation flotation to utilize the ultrafine coal particles. In the study, the conventional flotation batch tests were conducted to determine the best collector and the best dispersant for this coal, then Flocculation experiments were carried out followed by the flotation. The effects of fundamentals parameters such as the type and dosages of flocculating reagents, the impeller stirring speed and the grinding fineness were also investigated. The optimum conditions for research were as follows: Flomin C9606 was determined to be the best collector, sodium Hexametaphosphate as the best dispersing agent, the impeller speed was determined to 1500rpm, and the best grinding fineness was achieved at 30 minutes. When the sample was processed by the flow sheet consisting of one stage rougher and one stage cleaner, the ash content of the raw coal was reduced from 22.73%, (raw coal) to 6.39%. This was achieved by four stage flotation cleaning with the solid combustible matter recovery of 86.28%. The overall ash reduction was 73.57% which met the minimum requirement to be used as a clean coal product in industries. It was therefore concluded that hydrophobic flocculation flotation using Flomin C9606 was capable of cleaning ultra-fine coal to obtain the clean coal product.
Keywords: Coal slimes; hydrophobic flocculation flotation; Flomin C9606; Froth flotation.
Impact of hydraulic fracturing and borehole spacing on gas drainage along coal seam
by Huayong Lv
Abstract: Hydraulic fracturing is a technology employed to improve coal seam permeability and gas drainage. This study uses theoretical analysis and field testing to examine the mechanisms of hydraulic fracturing of a coal seam, including the initiation conditions of boreholes and cracks, main crack forms, and expansion and extension processes. RFPA2D-flow software was used to develop a numerical simulation of double-hole hydraulic fracturing, from crack initiation to expansion and extension in the coal body. The numerical simulation revealed characteristics and evolution of the stresses, water pressure and acoustic emission around the boreholes and estimated the permeability improvement range of fracturing holes under conditions of different hole spacing. Results of a field industrial test showed that the daily gas drainage pure flows increased by 5.817.6 times, the average gas drainage velocity reached 3.76 m3/min (maximum 10 m3/min), the gas drainage rate of the working face reached 57.32%, and the influence radius of single-hole hydraulic fracturing is approximately 5 m. This study demonstrates that hydraulic fracturing and permeability improvement technology can greatly improve the gas drainage rate of boreholes in a coal seam.
Keywords: Hydraulic fracturing; Crack expansion and extension; Pressure relief and permeability improvement; Gas drainage.
CFD simulations of DPM flow patterns generated by vehicles in underground mines for different air flow and exhaust pipe directions
by Ramakrishna Morla, Shivakumar Karekal, Ajit Godbole
Abstract: In this paper, an attempt is made to model Diesel Particulate Matter (DPM) flows generated by Load Haul Dumpers (LHDs) and trucks in an underground mine environment for different DPM flow and intake air flow directions and exhaust pipe directions. Field experiments were conducted and used to validate the computational fluid dynamics (CFD) models and to map the DPM flow patterns. The results obtained show that if the DPM and the intake air co-flow (flow in the same direction), the DPM was predominantly confined to the middle of the roadway. Alternatively, if the DPM and the intake air counter-flow (flow in opposite directions), the DPM tends to spread over the entire cross-section of the roadway. In the latter case, the vehicle operator will be more susceptible to exposure to high concentrations of DPM. Further, the DPM concentration near the vehicle was dependent on exhaust pipe location and direction. If the exhaust pipe is located at the rear or the top of the vehicle, the vehicle operator may be susceptible to exposure to high concentrations of DPM. If the exhaust pipe is located at the bottom of the vehicle, the operator is less likely to be exposed to high concentrations of DPM. Finally, in all cases, at 10 m downstream of the vehicle the DPM particles tend to spread over the entire cross section of the roadway, and downstream loading bays generally contained very high concentrations of DPM.
Keywords: Coal mines; DPM; Diesel-operated LHD; CFD simulation.
Mechanical Behavior and Failure Characteristics of Cemented Paste Backfill under Lateral Unloading Condition
by Hongjian Lu, Peng Liang
Abstract: A key issue associated with mine backfill design using the stage open stoping with the subsequent filling method is the determination of mechanical behaviour and failure characteristics of the cemented paste backfill (CPB). Especially for CPB under lateral unloading conditions during the excavation of secondary stope. In this research, a series of lateral unloading tests with RFPA3D were conducted to investigate the relationships among the cement-tailings ratio (1:4 and 1:8), lateral unloading stress (0MPa, 0.2MPa, 0.4MPa, 0.6MPa, 0.8MPa and 1.0MPa), mechanical behavior, failure modes and AE (acoustic emissions) characteristics. Similar mechanical behaviour of all the CPB specimens was obtained. With different cement-tailings ratios and preloading stress values, the ultimate failure modes of CPB specimens show different forms. Additionally, increasing the preloading stress value caused a rising of AE counts. The results of this study can provide a significant reference for the backfill design and study of underground mining.
Keywords: cemented paste backfill; mechanical behaviour; failure characteristics; lateral unloading; numerical simulation.
Selection of an optimal electric monorail loading technique in underground mining using analytic hierarchy process and Yagers technique
by Webby Banda
Abstract: The electric monorail transport system has found wide application in decline development. However, the loading mechanism in this haulage system still possesses a great challenge to its overall optimal efficiency. It has been demonstrated that high loading time is the main pitfall to high advance rates in monorail application. In this paper, the analytic hierarchy process and Yagers multiple criteria decision making techniques were used to select the optimal loading mechanism in the electric monorail transport system among three loading alternatives, namely, electric loader, conventional load haul dump unit and pneumatic loading system. Results of the two methods show that the electric loading technique is the optimal monorail loading system for efficient decline development in narrow vein deposits. Additionally, sensitivity analyses under the two techniques show that the electric loader system is always selected as the optimal solution to
Keywords: Monorail; Analytic hierarchy process; Yager’s; Decline; Narrow vein deposits.
Investigating the effects of gemstone mining on the environs: a case study of Komu in Southwestern Nigeria
by Moshood Onifade, Adeyemi Aladejare, Bayo Adewumi
Abstract: Mining engineering practice involves the extraction of minerals from the earth with significant effect to the environment. Though this operation is important to living better lives but causes more damage to the landscape than ever before. This research examines the effects of gemstone mining by investigating soil and water samples collected from different locations of a mining community in Nigeria taking into consideration the concentration of heavy metals and micro nutrients, physiochemical parameters and cation exchange capacity present in these samples. These concentrations were compared with the World Health Organization (WHO) standards. The concentrations of heavy metals, micro nutrients and physiochemical parameters obtained from the sample locations varies from one location to another. The results for heavy metals concentration obtained from the soil samples are 0.30, 0.90, 0.09, 0.995 and 39.40 mg/kg for lead (Pb), copper (Cu), cadmium (Cd), zinc (Zn) and iron (Fe) respectively. The values of micro nutrients concentration in the soil are 4.90, 5.295 and 0.97 mg/kg for sodium (Na), magnesium (Mg) and aluminium (Al) respectively with sequence, Mg > Na > Al. The results of physiochemical parameters obtained from the water samples are 7.495 mg/L, 187.00 mg/L, 233.414 mg/L, 70.00 mg/L, 16.52 mg/L, 6.28 mg/L, 14.65 mg/L and 10.25 mg/L respectively for pH, hardness, chloride, alkalinity, total solids, total dissolved solids, total suspended solids, sodium and potassium. When the results of soil and water analysis were compared with WHO standards, it was found that the values obtained were lesser than the WHO acceptable limit for certain heavy metals. However, the concentrations of Cd and Fe in the soil samples are higher than the WHO permissible limit in soil which implies that the soil is toxic and not good for agriculture purposes.
Keywords: Gemstone mining; environment; pollution; WHO standards; soil analysis; water analysis.
Evaluation of the vibration accelerations of drill bit for the well rotative-vibration drilling using the cavitation hydrovibrator
by Olexiy Nikolayev, Yuriy Zhulay, Yuri Kvasha, Nikolai Dzoz
Abstract: Cavitation hydrovibrator is one of the promising devices to intensify drilling of geological prospecting and production wells. Cavitation hydrovibrator transforms the stationary flow of drilling mud into a discrete-pulsed flow of increased power. The mud oscillating flow in hydrovibrator is converted into high-frequency (1 000 Hz 20 000 Hz) vibrations of the drill bit. A method for determining the longitudinal vibrations of a drill string with bit has been developed. The method is based on the results of experimental studies of the dynamic interaction between longitudinal oscillations of the drilling string with rock massive by mathematical modeling this process with use finite-element discretization of drilling string. An obtained satisfactory convergence of the computed vibration accelerations of the drill bit and experimental data confirms the adequacy of the developed mathematical model and the ability with its help to determine the rational operational modes of the hydrovibrator.
Keywords: rotative-vibration well drilling; high-frequency downhole cavitation hydrovibrator; drill bit; longitudinal acceleration;.
Special Issue on: ISCSM 2018 Advances in Continuous Surface Mining
Percussive Cutting of Hard Rocks with Point Attack Picks: Dependency of Specific Energy Consumption and Number of Blows per Unit Length of Cut Groove on Impact Energy and Cutting Parameters
by Taras Shepel, Carsten Drebenstedt
Abstract: The development of sustainable technological solutions for the non-blasting excavation of hard rocks remains at the forefront of efforts of many researchers and engineers worldwide. This paper discusses the applicability of the percussive cutting method with the use of point attack picks for hard rock excavation applications. Based on laboratory test results, regression models describing dependencies of the specific energy consumption and the number of blows per unit length of cut groove on the impact energy and cutting parameters were developed. Several hard rocks such as sandstone, granodiorite and dolomite samples with respective uniaxial compressive strengths of 139 MPa, 205 MPa and 79 MPa, were used in the cutting tests. The study has demonstrated that effective cutting of rocks used in the tests is possible if the single impact energy exceeds 20-30 Joules per mm of cut depth. The currently achievable maximum cutting speed is discussed.
Keywords: percussive cutting; hard rock; point attack pick; specific energy consumption; number of blows per unit length; impact energy; cutting parameters; non-blasting excavation; regression models.
Structural Analysis of Greek and Bulgarian Coals by Solid-State 13C Nuclear Magnetic Resonance (NMR) Spectroscopy
by Christina Apostolidou, Andreas Georgakopoulos
Abstract: In this study thirty-two peat, xylite-rich and matrix lignites, and sub-bituminous coal samples from representative lignite and sub-bituminous coal basins of Greece and Bulgaria were used to investigate how their NMR differences reflect the organic matter origin, genesis conditions and coalification process in each one of these basins. The evolution of the major organic structural units in the samples was identified by using high-resolution, solid-state 13C Nuclear Magnetic Resonance Spectroscopy (NMR), using a spectrometer with cross-polarization and magic-angle spinning. Solid- state 13C CP/MAS NMR is considered as a very powerful method for determining the chemical structure of complex organic substances such as coals of various ranks. To investigate a possible influence of paramagnetic species on the CPMAS-NMR spectra of the samples, Electron Paramagnetic Resonance (EPR) spectroscopy was also applied. Similarities were observed between the spectra of coals of similar rank or of similar forming conditions. The peat lignite and lignite sub-bituminous coal transition is marked by pronounced differences in the NMR spectra, as do the different lithotypes of lignite i.e., matrix and xylite-rich. Determination of the coal organic constituents offers valuable knowledge about the chemical and thermal behavior of coals in order to investigate major issues associated with coal mining, combustion, and post-combustion processes.
Keywords: 13C CPMAS NMR spectroscopy; coalification; Greek and Bulgarian coals.
A cloudbased near real time slope movement monitoring system
by Chrysanthos Steiakakis, Georgia Papavgeri, Nick Steiakakis, Zach Agioutantis, Paul Schilizzi
Abstract: A near real time cloud-based data management system for geotechnical monitoring that can efficiently record, transfer, store, manage, process, analyze and evaluate monitoring data and generate easy to view and use information is presented. The database structure and manual of the system functionalities for addressing issues during data upload and processing, record handling for multisensory devices, data visualization using common reference dates, data error correction and parametric handling of import files are presented in detail. New features that are in development include a more robust warning system and a journaling system for visual observations are briefly presented. The system can reliably and quickly generate information about excessive movements, alarm levels in every day mine or other construction monitoring operations.
Keywords: geotechnical monitoring; visualization; web application; data management system; cloud-based system.
Ultimate pit limit determination for fully mobile in-pit crushing and conveying systems
by Edward Hay, Micah Nehring, Peter Knights, Mehmet Kizil
Abstract: Fully-mobile in-pit crushing and conveying systems have different pit shape requirements to traditional truck haulage systems due to linear bench and flat floor constraints imposed by conveyor systems. As the shape of a pit is largely based on the ultimate pit limit, it is desirable to have the additional shape requirements of fully mobile in-pit crushing and conveying systems included in the ultimate pit limit determination process. This paper discusses and highlights why there are different requirements for these systems, and what they are. A method of including these extra requirements during ultimate pit limit determination is presented. A case study has been included that shows the method working successfully, with scheduling of the pits to further highlight fully mobile in-pit crushing and conveying viability. This case study shows that through the reduced mining costs, a fully mobile in-pit crushing and conveying pit can return a higher Net Present Value than the traditional truck and shovel pit for the same deposit. The development of this method provides the opportunity for the metalliferous industry to accurately determine ultimate pit limits for mines considering the use of fully mobile in-pit crushing and conveying systems.
Keywords: in-pit crushing and conveying; IPCC; mine planning; ultimate pit limit; UPL; FMIPCC; pit optimisation.
Lignite Mine Monitoring and Mapping Using Freely-Available Radar and Optical Satellite Imagery
by Marianthi Stefouli, Antigoni Panagiotopoulou, Eleni Charou, Yiota Spastra, Emmanuel Bratsolis, Nicholas Madamopoulos, Stavros Perantonis
Abstract: A methodology for monitoring and mapping Lignite Mining areas using Sentinel-1 and Sentinel-2 ESA Copernicus satellite systems is presented. A Stochastic Regularized Super-Resolution Reconstruction (SRSR) for the enhancement of the Sentinel-2 optical data is developed and a Land Monitoring/Change Analysis based on the enhanced Sentinel-2 images is performed. Additionally, the ground motion is monitored using the Sentinel-1 radar data via the Rheticus Service. The proposed methodology is tested on the Amyntaio lignite mine in Ptolemais basin, Greece, for Sentinel images obtained from 2014 to 2018. The Amyntaio area has been of particular interest, as a landslide event occurred on June 10th, 2017, causing major operational disruption and a severe economic loss to the Public Power Plant Cooperation of Greece SA. The methodology proves to be useful for facilitating mapping and monitoring mining and post-mining areas facing similar problems with the Amyntaio lignite site.rn
Keywords: Keywords: Lignite; Surface Mining; Landslides; Radar; Sentinel-1; Ground Motion; Rheticus service; Multispectral; Sentinel-2; Super-Resolution Reconstruction; Lorentzian Estimator; BTV Regularization; Self Organizing Maps; Land Cover Change Analysis.rn.
A Real-Time Event-Driven Database Productivity and Maintenance Planning tool for Continuous Surface Mining Operations
by Zach Agioutantis, Stamatini Delmadorou, Nikos Steiakakis, Chrysanthos Steiakakis, Stergios Papaterpos
Abstract: This paper presents a data management application driven by real time events, which has been developed as a Productivity and Maintenance Planning software application to be used in the surface lignite mines in northern Greece. The mines operate using a continuous mining system comprised of multiple bucket wheel excavators, belt conveyors, spreaders and stackers. There is a control center for each mine, comprising of Aspect Servers, OPC servers and a SCADA system which interfaces with PLCs at each equipment unit in the field. The overall data management infrastructure is installed on the main network system and draws data from the OPC servers at each mine. In order to collect the data, the application is developed using event driven functionality as well as data polls. Data can then be modified by the control tower personnel. The application generates reports on a daily basis for production monitoring, productivity, equipment performance and utilization as well as various maintenance tasks. The system has been in operation at the surface lignite mines in northern Greece since 2011 and has been embraced by mine personnel for decision making and planning.
Keywords: SCADA; OPC; PLC; database; continuous mining system; productivity; maintenance; belt conveyors.
Exploring the effect of physical, human and technical factors on Bucket Wheel Excavators Efficiency: A Fuzzy Cognitive Map Approach
by Maria Menegaki, Theodoros Michalakopoulos, Christos Roumpos
Abstract: Several parameters, e.g. characteristics of the excavated material, number and thickness of lignite layers, bucket wheel capacity, experience of personnel, etc., affect the efficiency of bucket wheel excavators (BWEs). In this paper, the FCM (Fuzzy Cognitive Map) approach is used to explore the factors affecting the efficiency of BWEs as well as their interlinkages and interdependencies, based on an extensive review of scientific literature and expert intervention. The main goal is to provide a transparent and flexible model and propose a different simulation approach for complex mining systems that can interconnect the factors influencing systems behaviour. The implementation of the proposed model revealed significant differences in BWEs efficiency under favourable and hostile conditions. This is a first step towards simulations intended to help mining practitioners, bridging the gap between pure qualitative and quantitative approaches.
Keywords: bucket wheel excavators; efficiency of BWEs; fuzzy cognitive mapping; soft modelling; learning algorithms.
Surface Mining in Western Macedonia, Greece: Fugitive Dust (PM10) Emissions and Dispersion
by Athanasios Triantafyllou, Symela Andreadou, Nikolaos Moussiopoulos, Stylianos Garas, Ioannis Kapageridis, Georgios Tsegas, Christos Diamantopoulos, Christos Sachanidis, Ioannis Skordas
Abstract: In the operation of large open-pit lignite mines (extracting and handling excavation materials) a series of significant fugitive dust emission sources are recorded. The quantification of the emissions of each source and the investigation of atmospheric dispersion are subjects of great interest for the development and implementation of air quality management systems in the neighbouring residential areas. The study aims to investigate and locate the fugitive dust sources in the surface mines operated in Western Macedonia in NW Greece, and quantify their contribution to the total fugitive dust (PM10) emissions produced by the mines activities. The contribution of each emission source recorded was quantified. An effort was also made to investigate the dispersion of fugitive dust emitted from each individual mine and source activity and assess the contribution of the mining activities to the air quality of the surrounding areas, by using a three-dimensional, nestable, prognostic meteorological, and air pollution model. The results can contribute to the implementation of measures and scenarios for the air quality management in the area.
Keywords: Fugitive dust; PM10 emissions; dust dispersion; surface mining; lignite; continuous mining.
Assessment of Social and Environmental Risks on Opencast Coal Mines
by Natalija Pavlovic, Dragan Ignjatovic, Vladimir Pavlovic
Abstract: The opening and development of large opencast coal mines with complex continuous mining systems is subject to a large number of risks. The process of assessing social and ecological risks is based on the analysis and determination of the probability of occurrence, the operation reliability of the opencast mine and the required costs to minimize the impact of risk. Social risks are related to sustainable development, harmonization with the local community and government legislation. Environmental risks can be controlled, when it comes to sustainable mining, and partially uncontrolled, in relation to natural disasters. Together they represent a serial stochastic process with probabilities which define the reliability of the mine. Detailed quantitative and qualitative risk analyses of opencast coal mine Tamnava-West Field have been examined and compared, with a commentary on the obtained results.
Keywords: mining risks; probability; risk assessment; environmental risks; social risks; Tamnava-West Field; quantitative analysis; risk management; floods.
Alkali activation of low-alumina mine tailings for more sustainable raw material supply
by Mahroo Falah, Robert Obenaus-Emler, Paivo Kinnunen, Mirja Illikainen
Abstract: Each year, the mining industry generates a significant amount of mine tailings (MTs). The disposal of MTs has environmental impacts, such as air pollution and the release of heavy metals to surface and underground waters. The EU funded project Integrated mineral technologies for more sustainable raw material supply (ITERAMS) includes the development of alkali-activated materials from low-alumina MTs, which is supported by a Cu/Ni mine located in northern Finland. Initially, the compressive strengths of alkali-activated products were investigated using different alkali activator solutions. Based on the final strength of the prepared and cured samples, sodium silicate (Na2SiO3) was selected as the activator and subsequently used for further experiments. The alkali-activated MTs were prepared by mixing different concentrations of Na2SiO3 solutions and water with MTs powder. A curing temperature of 40
Keywords: Alkali-activated; Tremolite; Microstructure; Compressive strength.
Current State and Development of Continuous Systems on EPS Opencast Lignite Mines
by Dragan Ignjatovic, Vladimir Pavlovic, Slobodan Mitrovic, Branko Jevtic
Abstract: Currently, opencast coal mines of Electric Power Industry of Serbia (EPS) produce about 40 million tons of coal per year within two basins (Kolubara and Kostolac basins) and five opencast mines (Field C, Field D, Field G, Tamnava West Field and Drmno). On that basis, 70% of Serbias electric power is being produced in Serbia. Since some opencast mines are undertaking closure procedure, it is necessary to open replacement capacities in order to maintain coal production. This paper shows the current state, development perspectives, opening plans for new opencast mines and planned continuous mining systems which are foreseen to operate in the future time period.
Keywords: opencast mines; EPS; continuous systems; lignite; ECC systems; ECS systems; Kolubara basin; Kostolac basin; mining dynamics; continuous equipment.
Design and approval third party audit of material handling and mining equipment
by Przemyslaw Moczko, Damian Pietrusiak, Eugeniusz Rusinski
Abstract: Specialised mining and material handling equipment such as stackers, reclaimers, bucket wheel excavators, spreaders, etc. require special attention during the design and manufacturing stages. Due to the complexity of such equipment, it is possible that introduced defects may occur as structure faults, which will adversely affect their performance. The third party audit conducted by Independent Expert plays an important role in the entire delivery process. Although the use of a third party auditor is recommended by different standards, it is not a mandatory step that will ensure a design and manufacturing crosscheck. It appears, however, that more and more new and complex industrial projects utilize this process. An Independent Expert can check the design, supervise manufacturing, erection and performance tests and finally approve the delivered structure. Such a check and approval procedure is introduced in order to improve the quality of the entire deliverable of the project. Although it may slightly increase the initial costs of the project, it is very beneficial as it decreases future investments and downtimes of equipment. In case of equipment with a service life of about 30 years, the use of a third party auditor can realize very significant savings. In this paper, the authors present recommended scope of third party audit of mining and material handling equipment and their experiences gained as the Independent Expert during many projects completed in this field.
Keywords: mining; material handling; machines; structures; third party audit.
Application of Mine Planning Software to Resources Estimation of the Lava Lignite Deposit in Servia Greece
by Ioannis Kapageridis, Athanasios Apostolikas, Efstratios Koundourellis
Abstract: The use of mine planning software in the evaluation and estimation of mineral resources and reserves is well established nowadays in the mining industry for the design and scheduling of surface mines and it is a requirement for the reporting of mineral resources and reserves according to international reporting codes. This paper describes the application of mine planning software in the estimation and modelling procedures of the operational lignite mine of LARCO GMMSA at the Lava deposit in Servia, Kozani. All stages of exploration data analysis, geological modelling, grade estimation, resources reporting, mine design and optimisation, and reserves calculation of the mining operations are explained. Data integration, advanced 3D graphics and specialised modelling algorithms all within a user-friendly environment contribute to the successful implementation of mining industry accepted procedures to the effective planning and estimation of the surface lignite mine.
Keywords: mine planning; mineral resources estimation; lignite mining.