Operator influence on the loading process at LKAB’s iron ore mines A. Gustafson1, H. Schunnesson1, J. Paraszczak2, G. Shekhar1, S. Bergström3, and P. Brännman3 Affiliation: 1Luleå University of Technology, Sweden. Synopsis Université Laval, Quebec City, The loading process in sublevel caving mines entails loading material from the drawpoint using load haul Canada. dump machines that transport the material to orepasses or trucks, depending on the mine conditions. Luossavaara Kiirunavaara AB, Sweden. When each bucket is drawn from the drawpoint, a decision must be made as to whether loading should continue or be stopped and the next ring blasted. The decision to abandon the drawpoint is irrevocable, as it is followed by the blasting of the next ring. Abandonment of the drawpoint too early leads to ore Correspondence to: losses and inefficient use of ore resources. Loading beyond the optimal point increases dilution as well A. Gustafson as mining costs. The experience of the LHD operators is an important basis for manual drawpoint control. However, it has been difficult to establish which specific factors manual drawpoint control is based on. To try to Email: shed more light on these factors we analysed the operators’ experiences at LKAB’s Kiirunavaara and [email protected] Malmberget iron ore mines. The operators in the two mines completed a questionnaire on the current loading practices and the process of deciding to abandon ’normal’ rings, opening rings, and rings with Dates: loading issues. Received: 12 Oct. 2018 It was found that in both case study mines, most decisions on the abandonment of drawpoints are Revised: 29 Oct. 2019 made by the operators. The more experienced operators tend to make more decisions themselves rather Accepted: 5 Dec. 2019 than rely on support from the existing support functions. Published: March 2020 Keywords How to cite: loading process, operator influence, decision control, sublevel caving, load haul dump machine, draw control. Gustafson, A., Schunnesson, H., Paraszczak, J., Shekhar, G., Bergström, S., and Brännman, P. Operator influence on the loading- process at LKAB’s iron ore mines. The Southern African Insitute of Introduction Mining and Metallurgy The process of loading in the sublevel caving (SLC) mining method is difficult, as a large amount of DOI ID: material is loaded from a drawpoint with a small cross-section, while at the same time material flows http://dx.doi.org/10.17159/2411- down from the top of the drawbell, filling the void left by the material removed (Dunstan and Power, 9717/376/2020 2011) (Figure 1). Then, the loaded material is either hauled by load haul dump (LHD) machines to orepasses or dumped into trucks, depending on production conditions. Loading at the drawpoint begins after a production ring is blasted and clearance is given for loading. The blasted material swells and fills the drawpoint to form a muckpile; the spread and angle of the muckpile’s slope vary during loading. According to Kvapil (2008), for good extraction, an ideally blasted ring creates a muckpile which fills the drawpoint, as shown in Figure 2. Sublevel caving includes a series of unit operations: drilling, blasting, loading, and transportation Figure 1—Loading at a drawpoint (Dunstan and Power, 2011) The Journal of the Southern African Institute of Mining and Metallurgy VOLUME 120 MARCH 2020 191 ◀ Operator influence on the loading process at LKAB’s iron ore mines delivering of mining-related information is vital for today’s highly mechanized mining operations. The ore recovery, dilution, and extraction rate are determined and controlled at the drawpoint. Here, the overall production plans depend on a fundamental decision – as each bucket is drawn, the operator must decide to either continue loading or to abandon the drawpoint. A decision to abandon the drawpoint is irrevocable, since it is followed by the blasting of the next ring. Premature abandonment of the drawpoint leads to ore losses and inefficient use of ore resources. Continuing to load beyond the optimum point, however, results in increased dilution and increased production costs. Decisions to stop or to continue loading must consider factors such as the current ore grade, extraction ratio, indication of remaining ore above the loading point, metal price, cut-off grades, processing costs, and the possibility of recovering the remaining ore at lower levels. In other words, the SLC loading process depends on various mining, geological, and economic parameters. In order to balance these vastly different. but equally important parameters, a set of rules and guidelines must be established (Shekhar, Gustafson, and Schunnesson, 2016). This is generally termed the ‘draw control strategy’. A draw control strategy incorporates the Figure 2—Muckpile spread for a vertical ring (Kvapil, 2008) sequencing and scheduling of development, production, and material handling systems, with the dual objective of minimizing mining costs and dilution (Smith and Rahal, 2001). A good draw of material. Each unit operation generates a large amount of control strategy creates an optimal balance of ore dilution and ore data that is used to plan the subsequent processes and monitor recovery, balancing production demands with loading procedures the mining operation. The systematic recording, storing, and and resource efficiency. Table I Loading issues in SLC (Shekhar, Gustafson. and Schunnesson, 2016) Loading issue Problem Source of issue Effect Poor brow condition Uneven material flow, scattered muck profile, Blasting damage from development and/ Poor ore recovery and increased difficulty approaching drawpoint or poor mine support (Bull and Page, 2000; dilution Kvapil, 2008) Brow failure Loading cannot be done, next set of rings Poor support and /or blasting damage from Poor ore recovery re-drilled production blast (Baase, Diment’ and Petrina, 1982; Bull and Page, 2000; Kvapil, 2008) Bridging Preferential flow of dilution and eventual ring Toe left due to poor blasting, which grows Poor ore recovery and increased freezing (Bull and Page, 2000) dilution Walls Over-compaction of caved material Overcharging or double ring blasting Poor ore recovery (Brunton, 2009) Ring freezing No flow or interrupted flow of material Over-burdening or over-consolidation of waste Poor ore recovery (Gustafsson, 1998; Bull and Page, 2000) Rib formation Unbroken or partially broken ore around Poor drilling and blasting or poor mine design Poor ore recovery the side holes (Bull and Page, 2000) Hangups Uneven flow of material with premature Poor fragmentation (Kvapil, 2008) Increased dilution dilution by fine waste material Wedge failures/ large-scale Damage to pre-drilled production holes and Discontinuous caving or other stability issues More support and re-drilling required cave slides underground infrastructure (Bull and Page, 2000) Overhangs Damage to holes and structures Delayed caving of material More support and re-drilling required (Bull and Page, 2000; Gustafsson, 1998) Blast-hole damage Delay in blasting and loading Blasting damage or poor geological Re-drilling required conditions (Brunton, 2009) Overcharging Increased consumption of explosives Cracks or openings in the holes Increased explosive cost and back-break (Brunton, 2009) Air blast No material flow initially and damage Delayed caving (Bull and Page, 2000) Increased support costs to structures ▶ 192 MARCH 2020 VOLUME 120 The Journal of the Southern African Institute of Mining and Metallurgy Operator influence on the loading process at LKAB’s iron ore mines Loading at the drawpoint can be halted or delayed due to a The questionnaire contained 34 questions; 24 were closed variety of loading issues (Cokayne, 1982), adversely affecting questions (with alternative answers) and 10 were open questions the resource efficiency. These issues include poor mine design (the respondent composed the answer). The questionnaires were or poor drilling or blasting practices, as listed in Table I. At handed to the operators in person and answered right away in the Swedish mining company Luossavaara Kiirunavara AB the presence of the interviewer. This ensured that a large number (LKAB), loading at the drawpoint is sometimes stopped early of questions were answered. because of loading issues such as hangups, brow failure, pillar The questionnaire aimed at investigating: failure, intrusions, poor fragmentation, or ring freeze (Shekhar, ➤ The organizational structure of the mines Gustafson, and Schunnesson, 2016). ➤ The general loading process Many decisions (how much to load from a drawpoint, the ➤ The decision process in abandoning a normal ring identification of different loading issues, and the action taken, ➤ The decision process in abandoning an opening ring etc.) are based on the LHD operator’s personal experience and ➤ The decision process in abandoning a ring with loading practical knowledge. This experience is today an important issues foundation for manual drawpoint control. However, it is difficult ➤ The person responsible for abandoning a ring with loading to define which factors manual drawpoint control is based on. issues The purpose with this study is to investigate the experience ➤ The differences between operators, depending on loading of the LHD operators in in LKAB’s Kiirunavaara and Malmberget experience. mines to obtain a better understanding of current loading practices and the decision-making processes involved in abandoning ‘normal’ rings, opening rings, and rings with Mine site descriptions loading issues (e.g.