The worth of a mineral project is the value of the project's future cash flows. Cash flow is an sccounting term that represents the balance of all cash revenues minus cash operating and capital costs at the end of a year for the project. The worldwide project evaluation methods are those, which recognize time value of money, such as the net present value (NPV) and internal rate of return (IRR). Discount rate is examined as a fundamental means of reflecting risk in discounted cash flow analysis. The article gives various kinds of discount rates of mineral projects, including risk-adjusted discount rate and weighted average cost of capital. It describes the way of calculating the rate for a mining company by capital asset pricing model (CAPM). As an example author demonstrates calculation process of the risk-adjusted discount rate for the only Polish mining company, which is presently quotating at the Warsaw Stock Exchange - a copper plant KGHM "Polska Miedź" S.A. The text depicts also risk-adjusted discount rates that are commonly used in mineral industry, in various stages of project development and country risk premiums. Then it tries to give a risk-adjusted discount rate for Polish non-ferrous metals industry and at the end presents a problem of using different rates for the same project - one for the valuation and one for development-timing decision.