Problems of ore density determinations at Nanisivik mines

Abstract

One of the difficulties of ore reserve calculations is the determination of the factor to convert a volume to be mined into a tonnage to feed the mill. This factor is normally referred to as 'tonnage factor', 'density' or 'specific gravity'. At Nanisivik , a zinc-lead mine located in Canada's High Arctic problems occurred with the tonnage factor when,2½ years after start-up, a stockpile of 91 000 tonnes of ore had accumulated on paper, while actually only 11 000 tonnes could be identified. These stockpile differences indicated that the ore density of 4.4 t/m3 was probably no longer appropriate. The influence of survey errors in measuring were evaluated. Density calculations were carried out on 345 samples taken underground. The moisture content of the ore in the millfeed was used to calculate the density for two periods of about one year. Ultimately it was concluded that the actual density was around 4.0. This figure was then adopted and ore reserves were adjusted accordingly.