Abstract: The calculation method of the profit-maximizing cutoff grade， i.e.， the break-even grade， is first discussed and an equation is given. The influence of cutoff grade on optimum pit limit and total profit is analyzed through a case study. The findings are as follows: for given economic parameters， the cutoff grade used both in pit limit design and in production can be selected in a relatively wide range. When the cutoff grades in both design and production change in these respective ranges， the total profit of the optimum pits is almost equal to that at the break-even grade. For different concentrate prices， these selection ranges only differ a little， though the volume and the total profit of the optimum pits differ a great deal.

Key words: open pit mine, pit limit, total profit, cutoff grade, case study