Assessment of undergorund mining of Nussir copper deposit: With special emphasize on cut-off and mining method
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The narrow steeply dipping strata bound sediment hosted copper deposit, Nussir, located in Kvalsund community, Finmark, Norway, have been subject to an assessment of underground mining. Resources classified as Indicated, within a 0,9%Cu cut-off limit have been identified as suitable for sublevel open stoping mining method, accessed by 590m long tunnel from fjord, a 2000m haulage tunnel in footwall progressing westward along strike and two individual ramps separated by 1280m along strike. Stopes are dimensioned 40m long and 3m wide on average with 62m and 102m height, with two and three sublevel drifts respectively. The stoping layout s stability rely on 5m rib pillars, 8m sill pillars and yielding pillars in stope centre, calculated from geotechnical data and empirical design methods. The retreating mining method implies narrow ore mining practices, utilizing small mechanized equipment, developing drifts along strike in two directions from ramp. Stopes are planned produced by up-and-downward drilling of 20m holes carefully planned within the narrow mineralisation, blasted carefully to avoid dilution from stope walls. Dilution causing head grade drop and obtaining of available treatment capacity, must be expected and dealt with. Cable bolting of the on average 60⁰ dipping hangwall from drifts, is necessary to avoid caving. Dillution, estimated as dependent on mineralisation thickness, have been added to the stope resources obtained by wireframe evaluation of block model in DataMine. A planned production schedule of development tunnels and stoping, producing 3Mt in 6 years time, is the basis for a financial model with 245million NOK in capital expenditures and 177NOK/tonne in mining costs. The planned mining operation gives a Net Present value of 32million NOK. Project value is considered highly sensitive to changes in copper price, mining costs and copper grade.