Selecting an optimal rock transportation system at Trojan mine using the Analytic Hierarchy Process
Date
2020
Authors
Karembera, Philip Tafadzwa
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Abstract
Trojan nickel mine’s Mineral Reserves within the current mining area (35/0 lift) are getting depleted due to extraction, with a remaining life of 3.2 years at the projected Life of Mine (LOM) plan extraction rate of 40,000 tpm. To extend the LOM of Trojan mine, 37/0 lift and 39/0 lift are currently being developed to replace 35/0 lift, which will add an additional two years to Trojan mine’s life at the projected LOM plan ramp up depletion rate of about 65,000 tpm. Eventually, Trojan mine has plans to further ramp up to the plant capacity of 90,000 tpm as it targets to extract deeper levels of the deposit. However, the 37/0 lift and 39/0 lift Mineral Reserves have low grade ore averaging 0.71% nickel and the ore is transferred through 37/0L and 39/0L haulages, respectively. Since these two haulages are located at elevations lower than that of 35/0 lift, it implies that the extraction of 37/0 lift and 39/0 lift Mineral Reserves will be done at an increased operating cost. In addition to the low ore grade and higher operating cost at an increased depth, the price of nickel has been relatively low, with the current forecast nickel price being US$12,000 per tonne of nickel in concentrate. The price of nickel once soared by 400% to a record high of US$54,000 per tonne of nickel in concentrate in May 2007, and dropped to just under US$9,000 per tonne in October 2008 and has remained subdued ever since. In order to optimise value from the extraction of the low grade ore from lower levels coupled with increased cost due to increased extraction depth and lower nickel price, an optimal rock transportation system has to be selected. The selected transport system will eventually be used in 37/0L,37/0L and future main haulages. The operating cost of rock transportation at Trojan mine accounts for about 20% of total mining cost. In all upper levels up to 35/0L rail haulage has been the sole means of transporting rock from chutes to main ore and waste passes but no formal study has been conducted at the mine to investigate the viability of other alternative rock transportation systems such as belt conveyor or truck systems. It was therefore the aim of this study to analyse and select the optimal rock transportation system to use in the all future haulages at Trojan mine. To do this analysis, the Analytic Hierarchy Process (AHP) was used to select the optimal rock transportation system amidst multiple conflicting criteria. An AHP model was developed in Microsoft Excel® and used to rank the selected transportation alternatives against three major categories of evaluation criteria namely; economic, environmental and technical. The AHP technique uses matrix and vector algebra as the basis of its methodology framework and therefore the technique was chosen due to its simplicity. In addition to its simplicity, the technique has the ability to detect inconsistency and estimate the degree of inconsistency which means that its results are reliable. From the AHP analysis, the belt conveyor system was found to be the optimal material transportation system. This was followed by the rail and truck systems. To validate the AHP results, a Discounted Cashflow Analysis (DCF) was done for the three transportation systems. According to the DCF analysis, the belt conveyor system has the highest NPV of US$83.5 million, followed by the truck system with a NPV of US$79.9 million and lastly the rail system with a NPV of US$79.5 million. The DCF results confirmed that the belt conveyor system is the optimal material transportation system. Therefore, it is recommended that the mine uses the belt conveyor system for future haulages. However, it is recommended that the pair-wise comparisons be extended to the senior company executives as they are the key decision makers
Description
A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2020