Final Pit Research Articles

Enhancing the performance of integer models for addressing the long-term production planning problem in open pit mines by decision variable fixation based on parametric analysis of the final pit limit

Enhancing the performance of integer models for addressing the long-term production planning problem in open pit mines by decision variable fixation based on parametric analysis of the final pit limit

Delimitation of the Final Pit in Open Pit Mines Using the Pseudoflow Maximum Flow Algorithm: A Comparative Analysis of 1×5 and 1×9 Arcs

Delimitation of the Final Pit in Open Pit Mines Using the Pseudoflow Maximum Flow Algorithm: A Comparative Analysis of 1×5 and 1×9 Arcs

Pit Slope Configuration for Open Pit Mining – A Case Study

To achieve stable pit wall slopes, it is imperative to obtain a fair knowledge of the rock mass characterisation before designing the pit. Insufficient knowledge of the competency of the country rock could lead to using unsupported slope configuration in the design process which can consequently lead to slope failure. In this study, the geomechnical properties of the Bremen-Nkosuo concession are analysed using Bieniawski’s classification scheme to determine the Rock Mass Rating (RMR) for defining safe pit slope configuration of the Nkosuo pit. The findings show that the rockmass are best described as ‘fair’ for the two main lithologies existing at the concession. Subsequently, localised adjustment factors are applied to the calculated RMR to arrive at Mining Rock Mass Ratings (MRMR). These MRMR values are correlated with 50 m fixed stack height and 1.2 safety factor to determine optimum Bench Slack Angle (BSA) of 54° and 57° for host sedimentary and granitic rocks respectively. For individual benches, optimum slope design configurations were 10 m, 800, and 6.6 m respectively for bench height, bench face angle and catch berm for metasedimentary rocks. Likewise, that for granitic formation were 10 m bench height, 800 face angle and 6.0 m catch berm width. These configurations are in conformance with mineral and mining regulations of Ghana. Slope stability assessment was performed which included Slope Mass Rating (SMR), Kinematic and Limit equilibrium analysis. From the analysis, multi-bench scale slope instability occurrence was found to be rare but single-double scale could be possible at the western wall of the planned pit with probability of failure of about 0.4. Presplit and trim shots perimeter blasting techniques are recommended to maintain the integrity of the final pit walls at certain areas.

Slope geometry optimization considering groundwater drawdown scenarios at an open-pit phosphate mine, southeastern Brazil

The design of open-pit mines should balance safety and economy. However, safe geotechnical conditions generally involve redesigning the geometry of slopes and groundwater drawdown, significantly increasing the costs of mining operations. The use of numerical models to simulate groundwater drawdown and slope stability can be an alternative to assess cost–benefit trade-offs for decision-making. This study documents a mining plan using groundwater drawdown scenarios that illustrate how geotechnical, economic, and environmental indicators can be combined to obtain optimum slope geometry for open-pit mining. The optimization approach analyzed different scenarios of groundwater drawdown for the final pit of a phosphate mine to improve the pit slopes stability. The groundwater simulation scenarios included the combination of deep horizontal drains and pumping wells. Stability analyses using the limit equilibrium method were used to obtain the bench, inter-ramp, and overall factors of safety of different representative sections. The factors of safety obtained, the drawdown costs and the water table elevation of each section were selected as indicators for obtaining the optimal drawdown scenario using a multi-objective tool. The groundwater control system obtained with 11 horizontal drains and 1 pumping well was considered the most adequate from the geotechnical and economic perspectives. Slope geometry optimization obtained with this drawdown scenario led to adequate inter-ramp and overall safety factors for the final pit design, reducing the barren-to-ore ratio to 0.38, much less than the present ratio (≈ 3). The results are important for optimizing the slope geometry of open-pit mines and can be replicated in other regions.

Monitoring of seismic activity in near-wall rock masses of open pits using seismic recorders in deep boreholes beyond the final pit boundary

Monitoring of seismic activity in near-wall rock masses of open pits using seismic recorders in deep boreholes beyond the final pit boundary

Detection and diagnosis of gear-tooth pitting damage by the Average-Log-Ratio ALR algorithm

Computation of the Average-Log-Ratio (ALR) gear-damage detection algorithm is carried out using accelerometer recordings of the vibration response from a spur-gear-pair pitting test. ALR computed from gear rotational-harmonic amplitudes up to the fifth tooth-meshing harmonic shows monotonically increasing ALR with increasing pitting damage. ALR computations using rotational-harmonic amplitudes between adjacent tooth-meshing harmonics show maximum ALR values moving to lower rotational- harmonic ranges with increasing radial pit size, in agreement with an earlier-derived analytical relationship between radial pit size and transmission-error rotational-harmonic amplitudes. The final rotational-harmonic range with maximum ALR value is in good agreement with that predicted analytically from the observed final pit size, thereby providing additional experimental confirmation of this analytically derived relationship.

Open Pit Optimization Using the Floating Cone Method: A New Algorithm

Three-dimensional block models are the most frequently used tool for estimating mineral resources and reserves within a mineral deposit. In open pit mining, the basis of mine design and the long term mining schedule is calculation of the ultimate pit limit. The ultimate pit limit is the pit with the highest profit value. Over the years, different algorithms have been developed that enable us to calculate the final pit: floating or mobile cone, floating cone II and its corrected forms, floating cone III, the Korobov algorithm and its corrected form, the Lerchs–Grossmann 2D algorithm (dynamic programming), and the Lerchs–Grossmann 3D algorithm (graph theory). All these algorithms have advantages and disadvantages. The floating cone method stands out for its simplicity, speed, and easy implementation, even for calculating a pit with a variable slope angle. The main drawback of this method is that it is unable to examine all possible combinations. For this reason, the algorithm does not consistently give optimal results, which is why it has required improvements over time. However, the improved methods still have some problems. To overcome these problems, a new algorithm called the floating cone IV method will be demonstrated in this paper.

Исследования детонационных характеристик эмульсионных взрывчатых веществ, применяемых на железорудных карьерах

The paper outlines the main trends in the development of blasting operations used in iron ore mining. It is pointed out that due to the tendency to raise the weight of blast charges, an increasing negative effect of the seismic blast action is observed on the surrounding rock masses and protected facilities. In order to identify efficient ways to reduce seismic impact on the final pit outline and the protected facilities, a set of field tests was performed on the detonation characteristics of emulsion explosives for the conditions of iron ore open pits. The paper demonstrates that petering-out of detonation is observed for the extended charge of explosives. Analysis of causes for the detonation failure showed that it can be related to non-observance of the technology to charge watered boreholes, failures to meet the technological process when manufacturing the emulsion explosivuseful minerals, explosives, protected facilities, seismic action, detonation, emulsion explosives, charge, deflagration, booster, primer, environmentes, blast hole collapses caused by premature firing of the neighboring holes that have bigger delays. Analysis of the research results into the detonation characteristics of emulsion explosives showed that the probability of shifting from detonation to a low-velocity mode or deflagration is related to the length of the emulsion charge, the distance from the booster and probability is increasing at the lower (reverse) method of firing the charge. It is concluded that in order to increase the reliability of detonation of the emulsion explosives it is required to minimize the length of the emulsion part of the charge and to use combined firing methods of the blast charges.

Microseismic monitoring system of the pit’s board array based on seismic sensors in deep boreholes beyond the final pit contour

Microseismic monitoring system of the pit’s board array based on seismic sensors in deep boreholes beyond the final pit contour

Stochastic Final Pit Limits: An Efficient Frontier Analysis under Geological Uncertainty in the Open-Pit Mining Industry

In the context of planning the exploitation of an open-pit mine, the final pit limit problem consists of finding the volume to be extracted so that it maximizes the total profit of exploitation subject to overall slope angles to keep pit walls stable. To address this problem, the ore deposit is discretized as a block model, and efficient algorithms are used to find the optimal final pit. However, this methodology assumes a deterministic scenario, i.e., it does not consider that information, such as ore grades, is subject to several sources of uncertainty. This paper presents a model based on stochastic programming, seeking a balance between conflicting objectives: on the one hand, it maximizes the expected value of the open-pit mining business and simultaneously minimizes the risk of losses, measured as conditional value at risk, associated with the uncertainty in the estimation of the mineral content found in the deposit, which is characterized by a set of conditional simulations. This allows generating a set of optimal solutions in the expected return vs. risk space, forming the Pareto front or efficient frontier of final pit alternatives under geological uncertainty. In addition, some criteria are proposed that can be used by the decision maker of the mining company to choose which final pit best fits the return/risk trade off according to its objectives. This methodology was applied on a real case study, making a comparison with other proposals in the literature. The results show that our proposal better manages the relationship in controlling the risk of suffering economic losses without renouncing high expected profit.

Determination of the optimal transition point between a truck and shovel system and a semi-mobile in-pit crushing and conveying system

One of the most challenging aspects in semi-mobile in-pit crushing and conveying (SMIPCC) system design is determining the optimum depth at which to change from a purely truck-based haulage system to a conveyor-based haulage system. We used scenario analysis to determine the optimum transition depth between a truck and shovel (TS) system and a SMIPCC system. Traditional pit-limit algorithms were used to generate the final pit limit on a copper deposit, which was then divided into four pushbacks. The final operating pushbacks (phases) were designed for both TS and SMIPCC. The end depths for each phase are viewed as candidate transition points to switch from the TS to SMIPCC haulage system. Economic calculations were applied for five different scenarios, including adopting SMIPCC from the outset (pure SMIPCC), after the first, second, and third phases, and finally not using the SMIPCC system (pure TS) at all. The analysis indicates that the second scenario, at a depth of 335 m, results in the lowest cumulative discounted cost (CDC). In this case, the CDC is 17.6% lower than that for the pure TS scenario and 10.7% lower than for the pure SMIPCC system scenario.

Mathematical relationship between ultimate pit limits generated by discounted and undiscounted block value maximization in open pit mining

Ultimate pit limit is an important aspect of open pit mining. The optimal ultimate outline determines the tonnage of extractable ore, the volume of waste to be removed, the location of the subsidiary facilities, the location of ore and waste stockpiles, the life time of the mine and the estimated net present value (NPV) of the entire mining operation. Traditionally, there are two major approaches to optimizing the ultimate pit limit. One seeks to determine the ultimate pit using undiscounted profit maximization and the other by determining the optimal mining sequence of all blocks and discounting the value of the blocks. The outline with the highest cumulative NPV will be chosen as the final pit limit. For each of these approaches, different algorithms are presented. The aim of this paper is to present an analytical investigation about the mathematical relationship between sets of blocks of ultimate pits generated by each of these approaches in an ore body. This investigation is in fact the mathematical proof of the theorem that a discounted ultimate pit is smaller than or equal to the undiscounted pit. The results show that the discounted pit is always a subset of the undiscounted pit.

Continuous Monitoring and Improvement of the Blasting Process in Open Pit Mines Using Unmanned Aerial Vehicle Techniques

The current techniques used for monitoring the blasting process in open pit mines are manual, intermittent and inefficient and can expose technical manpower to hazardous conditions. This study presents the application of unmanned aerial vehicle (UAV) systems for monitoring and improving the blasting process in open pit mines. Field experiments were conducted in different open pit mines to assess rock fragmentation, blast-induced damage on final pit walls, blast dynamics and the accuracy of blastholes including production and pre-split holes. The UAV-based monitoring was done in three different stages, including pre-blasting, blasting and post-blasting. In the pre-blasting stage, pit walls were mapped to collect structural data to predict in situ block size distribution and to develop as-built pit wall digital elevation models (DEM) to assess blast-induced damage. This was followed by mapping the production blasthole patterns implemented in the mine to investigate drillhole alignment. To monitor the blasting process, a high-speed camera was mounted on the UAV to investigate blast initiation, sequencing, misfired holes and stemming ejection. In the post-blast stage, the blasted rock pile (muck pile) was monitored to estimate fragmentation and assess muck pile configuration, heave and throw. The collected aerial data provide detailed information and high spatial and temporal resolution on the quality of the blasting process and significant opportunities for process improvement. The current challenges with regards to the application of UAVs for blasting process monitoring are discussed, and recommendations for obtaining the most value out of an UAV application are provided.

Effective solution of the long-term open pit production planning problem using block clustering

Production planning of an open pit mine is defined as determining the extraction sequence of blocks in the final pit limit with the goal of maximizing Net Present Value (NPV) while considering the constraints imposed on the mining system. Mathematical programming models are used to optimize long-term open pit production planning problems. In real mines with several thousands of blocks and several scheduling periods, however, these methods lose their efficiency by increasing the number of decision variables, and it is almost impossible to solve and obtain a solution in a reasonable time using current solvers. In this paper, a new method based on block clustering was proposed to reduce the model size. In the first step, blocks are aggregated in clusters called “mother clusters” using the concept of clustering as a mathematical programming problem and solved using Genetic Algorithm (GA). In the second step, the mother clusters are converted to the mining clusters considering the practicality issues. The results of implementing the proposed method on a real deposit showed that block clustering could decrease the number of binary variables from 476,100 to 5,652. This led to a significant reduction in solution time from 372 hours to 23.4 seconds compared to the original block model. The clustering strategy was also able to realize more than 82% of the NPV obtained from scheduling original blocks.

Influence of water level in mine sequencing applied to strategic mining planning

Abstract Developing mine sequencing involves a number of factors and a large amount of information, and consequently the profitability of the project will strongly depend on the production schedule. A mining project may be conditioned to non-optimal sequencing, which may affect the economic results of the project and also lead to an inadequate utilization of the mineral resources. The conventional method of mining sequencing is divided into three main steps: first, the delineation of the final pit; second, subdivision of the final pit in operational pushbacks (mining advances) and third, sequencing the blocks in each of these pushbacks, taking into consideration mine, processing plant and market capacities. However, there are some aspects that are not usually incorporated in production scheduling, including ore mining below groundwater level. The objective of this study is to demonstrate the relevance and impact on the results of the Net Present Value (NPV) from groundwater level as a constraint related to the need for its drawdown, also considering grades and Stripping Ratio (SR) variability during mining sequence for a phosphate mine. The results show a difference of U$ 140 million for the evaluation considering and not considering groundwater level, without considering other restrictions.

Analysis of the impacts of slope angle variation on slope stability and NPV via two different final pit definition techniques

Abstract The traditionally and widely used Lerchs-Grossmann algorithm presents well-known limitations that newer propositions attempt to overcome. The direct block schedule (DBS) methodology, which has gained relevance with computational advances, obtains the final pit as a natural result of production sequencing, different from Lerchs-Grossmann-based algorithms. This process flow applies constraints in the final pit definition stage attempting to provide a more realistic result and to minimize risks. Slope instability is a common and inherent risk to open pit mining and may affect the project's net present value (NPV). A study of the impacts of slope angle variations on safety indexes and final pit NPV provides an auxiliary tool for the overall slope angle definition process. This article presents a case study in which the effects of variations of the overall slope angle on the safety factor (SF) and project NPV were analyzed. A total of 25 pits were generated by each studied final pit definition methodology, and each pit had the sections with the varied slope angles analyzed in the stability assessment, resulting in a total of 150 slopes analyzed. A comparison between the results obtained by the two different methodologies implemented in commercial software is presented. The results show no relationship between the NPV and the overall slope angle using the DBS methodology. An analysis of the results for each geotechnical sector obtained by the traditional methodology was conducted and may contribute to the trade-off analysis between the best slope angle to achieve a reasonable SF and the maximum NPV.

Managing Geologic Uncertainty in Pit Shell Optimization Using a Heuristic Algorithm and Stochastic Dominance

Optimizing final pit limits for stochastic models provides access to geologic and economic uncertainty in the pit optimization stages of a mining project. This paper presents an approach for optimizing final pit limits for a highly variable and geologically complex gold deposit. A heuristic pit optimizer is used to manage the effect of geological uncertainty in the resources within a pit shell with multiple uncertainty rated solutions. The uncertainty rated pit shells follow the mean-variance criterion to approximate the efficient frontier for final pit limits. Stochastic dominance rules are then used in a risk management framework to further eliminate sub-optimal solutions along the efficient frontier. This results in a smaller set of final pit shells that could be further analyzed for production scheduling. Additionally, the original solutions are analyzed for changes in the mining limits and two regions are targeted as potential regions for further exploration.

Prediction of Haul Units’ Requirements for the Open Pit Mines Operating Towards Closure

The determination of haul units is one of the important steps in the equipment selection process. The process should aim at minimizing the operational costs and create an optimal match for the haulage system. When open pit mines operating towards closure, reducing the operational costs results in significant gaining, and the savings can be used to implement some of the closure plans. In this paper, the prediction of haul units for an open pit mine which operates towards the final pit limit was analysed using discrete event simulation and multiple linear regressions. The result shows that the changes in production rate have significantly impact on the number of haul units in operations. The obtained P-value suggests that there is a strong correlation between the haul units’ requirement, production rates, and haul distances. This reveals that the prediction of haul units’ requirements can be achieved using a developed regression model. It was observed that, the approach of using discrete event simulation and multiple linear regressions is useful in integrating fleet size decision in a multi-period production schedule.

FINAL PIT PLANNING COAL MINING IN 16 PHASE 2 SEAMS IN PT. KTC COAL MINING & ENERGY, KECAMATAN. PALARAN, SAMARINDA, EAST KALIMANTAN

Mining stage design which is a complex problem in terms of three-dimensional geometry that is always changing, then in this thesis the pit limit, mine sequence design or mining stages are in accordance with the tolerance stripping ratio recommended by the company and the production equipment to be used in order to obtain production targets the optimal. The research was conducted using software to design the final pit and block model method to calculate the volume. The results of the research that have been carried out obtained 752,930 MT of mined reserves and Over Burden (OB) volumes of 4,439,394 BCM and Stripping Ratio (SR).

A two-step approach to incorporate cut-off grade and stockpiling in oil sands mine planning optimization framework

In achieving maximum benefit in oil sands mining, the time and sequence of removing ore, dyke material and waste from the final pit limit is essential to the long-term production schedule. In-pit waste management strategy requires the simultaneous construction of dykes with the advancement of mining operations. This paper seeks to determine: (1) the time and sequence for removal of ore, dyke material and waste to maximize Net Present Value (NPV); (2) the quantity of dyke material required for dyke construction to minimize construction costs; and (3) the impacts of stockpiling and stockpile reclamation with limited time duration. An Integrated Cut-Off Grade Optimization (ICOGO) model was used to generate an optimum cut-off grade policy and a schedule for mining ore and waste, as well as overburden, interburden and tailings coarse sand dyke materials in long-term production planning. Subsequently, a Mixed Integer Linear Goal Programming (MILGP) model was developed to generate a detailed production schedule for removal of ore, waste and dyke materials from the final pit limit. The cut-off grade profile and schedule generated by the ICOGO model are used as guides to define the grade constraints and production goals required by the MILGP model. The developed models feature stockpiling with limited duration for long-term production scheduling. The models were applied to an oil sands case study to maximize the NPV of the operation. In comparison, whereas the ICOGO model solved the optimization problem faster, the MILGP model results provided detailed mining-cut extraction sequencing for practical mining.