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An integrated underground mining and processing system for massive sulphide ores

University of British Columbia

A conceptual framework for the consideration of underground processing to improve the economics and environmental performance of underground hard rock mining has been developed from a previous phase of research at UBC. This research included identifying the opportunity for and benefits of underground waste rejection and disposal. Several enabling mineral processing technologies including electronic sorting were shortlisted for evaluation. This project represents the second phase of research into underground processing with INCO at UBC. The motivation for underground pre-concentration is discussed, and precedents for the concept are presented. Liberation criteria for evaluation of the amenability of an ore to underground pre-concentration have been identified. Fundamental design criteria and supporting technologies for underground pre-concentration are discussed, and the framework of an idealized integrated underground mining and processing system is presented. The work is considered both unique and valuable in that the contribution of the research is a feasible and practical new mining system that has been developed from previously vague and disparate concepts through the application of a combination of research and engineering skills. Using the conceptual framework thus developed, a case study into underground pre-concentration has been undertaken for the Main (MOB) and 153 Orebodies (153) at INCO's McCreedy East Mine in Sudbury, Ontario. Fieldwork and sampling, mineralogical evaluation, conceptual process design and costing have been completed, leading to the development of a system design which has been integrated into the existing mining scenario. Mineralogical results indicate that the liberation and separability characteristics of both ores as blasted is good: for the 153 ore, 55% of the tons mined could be rejected underground at a Cu recovery of 97%, resulting in a concentrate grade of 22% from a feed grade of 13% Cu. The system design comprises rejection of a coarse barren oversize at the orepass, transport of ore to the pre-concentrator by haul truck, pre-concentration of the ore through dense media separation and hoisting of the pre-concentrate to surface by hydraulic transport. For the MOB ore, 22% of the tons mined could be rejected underground through sorting at 97% Ni recovery, resulting in a concentrate grade of 2.93% from a feed grade of 2.44% Ni. Preconcentration is achieved through combined conductivity sorting and magnetic separation. Pre-concentrated MOB ore would be hauled and hoisted to surface conventionally using the existing hoisting system. Waste products are coarse and competent and appear to be suitable for use as rockfill or as a source of aggregate for cemented fill. Substantial savings will be achieved through reduced underground haulage, hoisting, surface transport, milling and tailings disposal tonnages. Operating cost savings are of the order of 16% for the MOB and 24% in the case of the 153 orebody. In addition to this, further revenue could be generated through eliminating milling and smelting recovery losses in Cu, Ni and precious metals from the 153 ore: the pre-concentrate appears to be of a quality suitable for introduction as feed to the smelter or matte converter. Results from the metallurgical testwork, process design, system layout, and a 30% capital and operating cost estimate are presented. A preliminary financial evaluation over the present life-of-mine, based on a total estimated system cost of CDN$30.8 million indicates an NPV of CDN$134 million, and an IRR of 79% at a discount rate of 11%. A brief evaluation of operational, economic and environmental impacts at the case study mine is also presented. A third phase of research and testwork is recommended comprising the following key objectives: 1) Bench scale testwork on alternative process technologies including coarse-particle flotation and autogenous grinding and classification. 2) Evaluation of the rheology and pumpability of the pre-concentrate for the purposes of hydraulic hoist design. 3) Research and testwork on the mechanical properties and rheology of a cemented backfill using pre-concentration rejects, and the modeling of the impact of introducing such fill on the geotechnical behaviour of an orebody at depth. 4) Assessment of the long term stability of the process plant excavations in different stress and geotechnical situations. 5) Further investigation of the comminution and liberation behaviour of the ores. 6) Piloting of the conductivity sorting and dense media separation technologies on representative samples of the McCreedy ore. 7) Further case studies on ores of different mineralogy and geotechnical properties Integration of the results of this third phase of research with the results presented in this thesis will provide a comprehensive tool for assessing the feasibility and impact of implementing underground pre-concentration for a range of mining scenarios presently considered uneconomic or technically unfeasible due to geotechnical considerations.

Thesis/Dissertation

application/pdf

2009-11-28

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http://hdl.handle.net/2429/15958

Mining Engineering

University of British Columbia

UBCV

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