Kiruna Mine Research Articles

Testing the P/S Amplitude Seismic Source Discriminant at Local Distances Using Seismic Events Within and Surrounding the Kloof Gold Mine, South Africa, and the Kiruna Iron Ore Mine, Northern Sweden

ABSTRACT We investigate the utility of the P/S amplitude discriminant for small seismic events recorded at local distances on surface seismic networks using (1) mining-related events from within the Kloof gold mine in South Africa; and (2) mining-related events and earthquakes within and adjacent to the Kiruna iron ore mine in northern Sweden. For the Kloof mine, seventy-five source mechanisms characterized by moment tensor solutions obtained using high-frequency in-mine seismic data are used to evaluate three mine-related source types, isotropic (crush), compensated linear vector dipole (crush-slip), and double-couple (DC; pure slip). For the Kiruna mine region, 270 events are used to evaluate earthquake sources, chemical explosions, and mine-related seismic events (primarily isotropic). For the Kloof mine events, we find that average P/S amplitude ratios measured in the 2–6 Hz frequency band discriminate between isotropic and DC events, and if only pure-slip events with a DC component of >60% are considered, the effective frequency band can be extended from 2 to 8 Hz. For the Kiruna region events, P/S amplitude ratios effectively discriminate earthquakes from chemical explosions in the 4–6 Hz and 10–28 Hz frequency bands. Our findings further show that average P/S amplitude ratios for mine-related events and earthquakes separate at frequencies of 10 Hz and higher. A comparison of amplitude ratios for crush and pure-slip events located within a depth range of 1 km in the Kloof mine, and a comparison of amplitude ratios of shallow (<10 km depth) and deep-focus (>20 km depth) earthquakes in the Kiruna region, indicate that the P/S amplitude discriminant is not influenced significantly by source depth. These findings thus suggest that the P/S amplitude discriminant, originally developed for larger events recorded at regional and teleseismic distances, can be extended to smaller events recorded at local distances.

Study of the Impact of Hard Rock Pillar Behavior on the Raise Caving Mining System

Raise caving is a novel mining method with an active stress control approach, which is suitable for deep mining environments. The application of raise caving is investigated for LKAB’s Kiruna mine. This mining method consists of two different phases. In the de-stressing phase, inclined de-stressing slots are created with a minimum amount of infrastructure and long-raise bore holes. The de-stressing slots provide stress shadows for subsequent large scale mining activities. These slots are separated by massive pillars, with width to height ratios of up to 10 and a length of several hundreds of meters, which are required to control stresses and seismicity and prevent hangingwall caving. Due to the stress redistribution in the mine, pillars and abutment areas become highly stressed. In the so-called “production phase”, which follows the de-stressing phase, large scale mineral extraction is conducted. As pillars are highly stressed after the de-stressing phase, it is important to de-stress them in the production phase to be able to extract them in a safe manner. Overall, pillars play a decisive role for the success of the raise caving mining method. Hence, studies on pillars and their impact on the raise caving mining method are of great importance. The first part of the contribution outlines the importance of pillars in the raise caving mining method on a conceptual basis. Numerical simulations for different mine layouts and different pillar behavior are then conducted to study the impact of pillar behavior on the system. The stress redistribution in the mining system and the infrastructure stability, with the help of the RCF-value, are analyzed. For this purpose, simulations with a linear elastic material behavior are a well-suited method. Consequently, the de-stressing of the pillar due to crushing cannot be analyzed with a linear elastic model. To do so, a method for de-stressing the pillar has to be implemented into the simulation. The behavior for pillars with a different width to height ratio is implemented with the help of pre-calculated stress-strain curves from available knowledge on pillar strength and behavior. Since mining is a progressive process, the sequence of mining plays an important role for the stress development in pillars and abutment areas and is also included in the simulations. Different ways for pillar de-stressing are outlined and discussed. Furthermore, the influence of stoping in the production phase is discussed in this contribution.

Lost-ore mining—A supplementary mining method to sublevel caving

Sublevel caving (SLC) is a mass mining method having high productivity and high safety. However, this method often causes a considerable amount of permanent ore loss. Interestingly, all lost ores are buried in the broken waste rocks that come mostly from the caved hanging wall and partly from the ore body in which ore and waste rock are originally situated together. To mine out such lost ores from the broken waste rocks and increase ore recovery in SLC mines, a new mining method called lost-ore mining is introduced as a supplementary method to SLC, and a simple mechanics analysis is used to explain why the lost-ore could be mined out. Using this lost ore mining method, the Malmberget mine had recovered 7.5 million tons of lost iron ores from many old production drifts, as reported in the year 2016. Similarly, the Kiruna mine had mined out 2.6 million tons of iron ores from the old production drifts, according to a report in 2012. At last, some suggestions on how to use this new method are proposed.

Analysis of a Potential Correlation between Seismicity and Production in Kiruna Mine on a Mine-wide and an Extraction Block Scale

The creation of cavities in the underground results in stress redistributions and energy changes in the rock mass. Zones with increased stresses and zones with lower stresses develop. The energy changes manifest themselves amongst others in changes in potential energy, absorption of energy in the formation of fracture zones, and release of energy such as seismic energy. To prevent damage to infrastructure and personnel, it is important to understand the mechanisms of energy changes as a result of mining. As far as seismic energy release is concerned, it is important to understand to relationship between large scale mineral extraction and mining induced seismicity. One coarse way to do this is to correlate for specific areas the cumulated tons of mined rock multiplied by the depth of extraction and multiplied by the gravitational acceleration to get the unit of energy, which is a rough assessment of the mining-induced energy changes, with the cumulated released seismic energy, which is derived from the seismic monitoring system. This correlation is studied for Kiruna Mine on a mine-wide scale and on an extraction block scale for the years 2014 to 2020. The results show that there is a reasonable correlation between the mining-induced energy changes and the seismic energy release not only on a mine-wide scale but also on an extraction block scale. Periods of decreased seismic energy release are followed either by a period of increased seismic activity or by one or a series of large seismic event. Accordingly, periods of decreased seismic activity can be considered as an indicator for a likely increase in future seismic activities. More detailed investigations should be made to find out the cause for the lack of energy release. A disadvantage of this method is that it does not reveal the exact area and reason for the decrease in seismicity. Therefore, additional rock mechanics analysis is needed to understand the background of the change in energy release.

Early diagenesis of anthropogenic uranium in lakes receiving deep groundwater from the Kiruna mine, northern Sweden

The uranium (U) concentrations and isotopic composition of waters and sediment cores were used to investigate the transport and accumulation of U in a water system (tailings pond, two lakes, and the Kalix River) receiving mine waters from the Kiruna mine. Concentrations of dissolved U decrease two orders of magnitude between the inflow of mine waters and in the Kalix River, while the concentration of the element bound to particulate matter increases, most likely due to sorption on iron‑manganese hydroxides and organic matter. The vertical distribution of U in the water column differs between two polluted lakes with a potential indication of dissolved U supply from sediment's pore waters at anoxic conditions. Since the beginning of exposure in the 1950s, U concentrations in lake sediments have increased >20-fold, reaching concentrations above 50 μg g-1. The distribution of anthropogenic U between the lakes does not follow the distribution of other mine water contaminants, with a higher relative proportion of U accumulating in the sediments of the second lake.Concentrations of redox-sensitive elements in the sediment core as well as Fe isotopic composition were used to re-construct past redox-conditions potentially controlling early diagenesis of U in surface sediments. Two analytical techniques (ICP-SFMS and MC-ICP-MS) were used for the determination of U isotopic composition, providing an extra dimension in the understanding of processes in the system. The (234 U)/(238 U) activity ratio (AR) is rather uniform in the tailings pond but varies considerably in water and lake sediments providing a potential tracer for U transport from the Kiruna mine through the water system, and U immobilization in sediments. The U mass balance in the Rakkurijoki system as well as the amount of anthropogenic U accumulated in lake sediments were evaluated, indicating the immobilization in the two lakes of 170 kg and 285 kg U, respectively.

What Governs the Spatial and Temporal Distribution of Aftershocks in Mining-Induced Seismicity: Insight into the Influence of Coseismic Static Stress Changes on Seismicity in Kiruna Mine, Sweden

ABSTRACTStrong mining-induced earthquakes are often followed by aftershocks, similar to natural earthquakes. Although the magnitudes of such in-mine aftershocks are not high, they may pose a threat to mining infrastructure, production, and primarily, people working underground. The existing post-earthquake mining procedures usually do not consider any aspects of the physics of the mainshock. This work aims to estimate the rate and distribution of aftershocks following mining-induced seismic events by applying the rate-and-state model of fault friction, which is commonly used in natural earthquake studies. It was found that both the pre-mainshock level of seismicity and the coseismic stress change following the mainshock rupture have strong effects on the aftershock sequence. For mining-induced seismicity, however, we need to additionally account for the constantly changing stress state caused by the ongoing exploitation. Here, we attempt to model the aftershock sequence, its rate, and distribution of two M≈2 events in iron ore Kiruna mine, Sweden. We could appropriately estimate the aftershock sequence for one of the events because both the modeled rate and distribution of aftershocks matched the observed activity; however, the model underestimated the rate of aftershocks for the other event. The results of modeling showed that aftershocks following mining events occur in the areas of pre-mainshock activity influenced by the positive coulomb stress changes, according to the model’s assumptions. However, we also noted that some additional process not incorporated in the rate-and-state model may influence the aftershock sequence. Nevertheless, this type of modeling is a good tool for evaluating the risk areas in mines following a strong seismic event.

Exploring Kiruna iron ore fields with large-scale, semi-airborne, controlled-source electromagnetics

Abstract The Kiruna mine is the largest underground iron ore mine in the world and provides a large portion of the iron ore produced within the EU. To facilitate the mineral exploration for such deep deposits, a novel semi-airborne controlled-source electromagnetic (CSEM) system was developed in the DESMEX project. In this approach, the transmitter is positioned on the ground, while the magnetic field is measured airborne with the support of additional ground observations of five components of the EM field. Such a set-up takes advantage of both ground and airborne techniques. High-moment transmitters are installed on the Earth’s surface, enabling injection of strong primary EM fields in the subsurface. The airborne receivers in turn ensure efficient, fast and spatially dense surveying. The semi-airborne EM system was validated in several field experiments in Germany. However, none of the tests were done at an active mineral exploration site. Here, we present the first results of the semi-airborne EM survey conducted at the Per Geijer iron ore deposit near Kiruna to explore the spatial and depth distribution of the ore body. The sophisticated 3D conductivity model matches the well-known surface geology and other geophysical information yet brings new insights into the general model of the ore body.

Numerical modeling for a simulated rockburst experiment using LS-DYNA

Ground support systems are commonly used to mitigate the potential consequences of rockburst in burst prone mines. To assess the capacity of ground support systems when subjected to dynamic loading, simulated rockburst tests using blasting were conducted at the Kiruna Mine. In this study, a numerical simulation for one of the field tests was conducted using the LS-DYNA code to investigate the dynamic response of the ground support systems including shotcrete and rockbolts. The numerical results showed a similar particle vibration pattern and a crack pattern to those of the field measurements. The effects of the detonator position and the charge configuration on the dynamic response of ground support systems are also discussed. Numerical results indicated that the peak particle vibrations on the tested panel increase along the direction of detonation propagation. It is difficult to use different charge concentrations in one borehole to investigate the effect of different dynamic loads on the dynamic response of support systems. Numerical results also indicated that 2D numerical modeling for simulated rockburst experiments could overestimate the dynamic response of ground support systems.

Development of an Underground Haulage System Evaluation Tool for Feasibility Studies

The mining industry faces many difficult challenges, for example, lower ore grades, smaller and deeper deposits, and longer transportation distances. In the past, there have been remarkable innovations in both equipment and the types of mining methods for which it is used, which have resulted in economies of scale. This has led to an increased use of bulk mining methods, like sublevel and block caving, which has increased productivity and reduced costs. Haulage alone plays a major role. Current haulage techniques are a significant cost driver, which account for between 15 and 30% of the overall capital investment (capex) in a mine and are an increasingly part of the operating costs (opex). The paper introduces a simulation tool of main haulage system in underground mining. Therefore, performances and the costs of the three most common underground main haulage systems, rail, truck, and conveyor, are calculated using a developed modeling tool. The tool was applied and validated in a case study carried out with the LKAB Kiruna Mine in northern Sweden.

Moment tensor inversion with three-dimensional sensor configuration of mining induced seismicity (Kiruna mine, Sweden)

Mining induced seismicity is an undesired consequence of mining operations, which poses significant hazard to miners and infrastructures and requires an accurate analysis of the rupture process. Se ...

Effects on nutrient regime in two recipients of nitrogen-rich mine effluents in northern Sweden

The question of the limiting nutrient(s) for production of phytoplankton and macrophytes was explored in two contrasting freshwater systems receiving N- and P-rich mine effluents from the Boliden and Kiruna mine sites, northern Sweden. For both sites, total N (TN), total P (TP) and TN:TP mass ratios in water, sediment and macrophytes were used to examine (1) spatial variations within the systems, (2) differences between the systems and (3) seasonal variations. The TN concentration from the discharge point at the Kiruna site was about seven times higher than at the Boliden discharge point, while the TP concentration was 10 times lower than in the discharge point at the Boliden site. The majority of the studied lakes showed elevated biomass of phytoplankton, with maximum values found in Lake Bruträsket (Boliden). Mining activities have affected the nutrient regime of the two recipients by contributing to elevated TN and TP concentrations and TN:TP mass ratios as well as elevated production of phytoplankton and macrophytes compared to the reference sites. Depending on the NH4 concentration in the effluent at the Boliden site, water column TN:TP mass ratios shifted from being >22, indicating P-deficiency, to between 9 and 22, indicating a transition from N- to P-deficiency (co-limitation). However, water column TN:TP mass ratios at the Kiruna site always indicated P-deficiency, while TN:TP mass ratios of macrophytes indicate that both sites may vary from N- to P-limitation. The study suggests that for the design of efficient monitoring programmes and remediation measures, it is important to consider the major N and P species in water, phytoplankton, sediment and macrophytes.

A solution approach for optimizing long- and short-term production scheduling at LKAB’s Kiruna mine

We present a mixed-integer program to schedule long- and short-term production at LKAB’s Kiruna mine, an underground sublevel caving mine located in northern Sweden. The model minimizes deviations from monthly preplanned production quantities while adhering to operational constraints. Because of the mathematical structure of the model and its moderately large size, instances spanning a time horizon of more than a year or two tend to be intractable. We develop an optimization-based decomposition heuristic that, on average, obtains better solutions faster than solving the model directly. We show that for realistic data sets, we can generate solutions with deviations that comprise about 3–6% of total demand in about a third of an hour.

Utilizing a Value of Information Framework to Improve Ore Collection and Classification Procedures

This case study utilizes a value of information decision framework to provide mine managers guidance regarding the purchase of ore grade scanners. LKAB's Kiruna mine produces three types of iron ore to meet long-term contractual agreements on a monthly basis. There is a priori uncertainty regarding the ore type in any given mineable section of the orebody. In addition, there is extracted ore type uncertainty that is introduced by the mining process. These uncertainties are better understood by obtaining more precise (real-time) information. In addition, a better understanding of the uncertainties can improve the quality of operational decisions and increase the overall profitability of the mine. This case study provides a framework for measuring the economic impact of information purchases in a mining context and discusses the implications of those findings.

Using aggregation to optimize long-term production planning at an underground mine

Motivated by an underground mining operation at Kiruna, Sweden, we formulate a mixed integer program to schedule iron ore production over multiple time periods. Our optimization model determines an operationally feasible ore extraction sequence that minimizes deviations from planned production quantities. The number of binary decision variables in our model is large enough that directly solving the full, detailed problem for a three year time horizon requires hours, or even days. We therefore design a heuristic based on solving a smaller, more tractable, model in which we aggregate time periods, and then solving the original model using information gained from the aggregated model. We compute a bound on the worst case performance of this heuristic and demonstrate empirically that this procedure produces good quality solutions while substantially reducing computation time for problem instances from the Kiruna mine.

Implementing a Production Schedule at LKAB's Kiruna Mine

LKAB's Kiruna Mine, located in northern Sweden, produces about 24 million tons of iron ore yearly using an underground mining method known as sublevel caving. To efficiently run the mills that process the iron ore, the mine must deliver planned quantities of three ore types. We used mixed-integer programming to schedule Kiruna's operations, specifically, which production blocks to mine and when to mine them to minimize deviations from monthly planned production quantities while adhering to operational restrictions. These production schedules save costs compared to schedules produced manually by meeting desired production quantities more closely and reducing employee time spent on preparing schedules.

Implementing a Production Schedule at LKAB?s Kiruna Mine

LKAB's Kiruna Mine, located in northern Sweden, produces about 24 million tons of iron ore yearly using an underground mining method known as sublevel caving. To efficiently run the mills that proc...

Ore characterisation for––and simulation of––primary autogenous grinding

In this work, the purpose was to study the impact of variations in feed ore properties on the performance of a primary autogenous grinding circuit by ore characterisation and simulation. Samples were selected to represent various points in the production system; ore faces with different drillability, grinding circuit feed, mill charges and waste rock. The investigation was carried out at the LKAB Kiruna mine in northern Sweden.The result clearly shows that self-breakage occurs ahead of the mill since the ore hardness, or resistance to breakage, increase with the distance from the mining face. Ore from a location, which by the mine is characterised as “hard to drill”, has the lowest resistance to breakage, and the surrounding rock is clearly harder than the magnetite ore. Validation of a simulation model for the primary autogenous grinding circuit reveals that the differences between simulated and experimental data are small. Therefore, the model is used to simulate the influence of variations in feed ore characteristics on the circuit performance. The simulations show that the net throughput from the circuit at a coarse–hard feed will be ≈10% higher compared to a situation when the feed is fine–soft. Moreover, a fine and soft feed results in a coarser particle size distribution of the mill discharge, compared to a coarse and hard material. However, it is the amount of coarse material in the feed, which is the most influential factor.

Handbook for grease applications

The process of finding the ultimate grease is described in this report using an example from railway applications. This example includes steps such as a requirement list, field tests, laboratory tests and an evaluation method. The example deals with the problems discovered in a field test performed to determine the best grease for tapered roller bearings in railway wagon wheels and to increase the knowledge of grease lubrication. Seven different fully formulated commercial greases were examined in the wheel bearings of one ore wagon, used for transporting ore commercially by railway from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. The steps performed in this study are recommended in all problems associated with finding the optimal grease for different types of applications.

A new method for determining the mechanical stability of lubricating greases

Mechanical stability is of central importance when dealing with the long-term service-length of grease-lubricated roller bearings. Poor stability will lead to consistency degradation of the grease, because of mechanical forces between the rolling parts of the bearing. The result can be leakage of grease through seals, or at worst a total failure of the bearing. The present investigation was initiated because present-day methods for prediction of mechanical stability show weak correlation with real service-length. The aim of the project was to develop a useful alternative. In order to fulfil this, both field tests and laboratory tests were carried out. In the field tests, nine different commercial greases were examined in the wheel bearings of five ore waggons, used for transporting ore by railroad from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. The test ore waggons travelled a distance of about 300,000 km during a period of 3 years. Small samples of greases were taken, on eight different occasions, for consistency testing. After the end of the test period, the damage on the bearings was also studied. In the laboratory tests, new undestroyed greases of the same brand as in the field tests were examined using conventional methods, such as the V2F, the Roll Stability Test and the Grease Worker. Comparisons between the field tests and these laboratory tests indicate poor correlation. In addition to these conventional methods, the relevance of the shear strength of the greases to the prediction of the mechanical stability was also tested. The shear stress τ L depends on the applied pressure p, thus τ L= τ 0+ γ· p where τ 0 is the shear stress at atmospheric pressure. γ is a property of the lubricant in the same way as viscosity or density. It was found that γ correlates well with the mechanical stability in service. Increased γ values lead to a decrease in the mechanical stability. One reasonable explanation is that high γ values correspond to high shear stresses in the grease, and thus severe conditions for the thickener.

Grease lubrication of roller bearings in railway waggons. Part 1: field tests and systematic evaluation to determine the optimal greases

Describes a comprehensive field test to determine the best grease for spherical roller bearings in railway waggon wheels and increase the knowledge of grease lubrication. Nine different fully‐formulated commercial greases were examined in the wheel bearings of five ore waggons, used for transporting ore commercially by railroad from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. After the end of the test period, the wear and electrical damage, as well as the rust on the bearings, were also studied. In order to find out the optimum grease for this application, draws up a specification of requirements and uses a systematic approach to development of an evaluation method that could be applied to greases in actual service.