A mining investment is a risky business because of uncertainties that exist in the reserve evaluation and economical analysis. The main uncertainties are involved in the amount of overburden and reserve, ore grade, capital and operating costs, recovery, dilution, commodity prices, gross revenue and profit/loss, also in economical analysis, determining if the feasibility of orebody utilizes the cut-off grade technique. This technique assumes that operation cost and commodity price remain constant although they may vary. The modern approach in the evaluation of the mineral resources is based on determining the frequency distribution of each variable involved in the calculations and find the result within some confidence interval. At the end, the net present worth that will be achieved will be obtained as a probability distribution, so a decision maker can decide the probability of feasibility of the project. Lower limit and upper limit of the NPV can also be indicated by the distribution. In other words, the distribution can indicate the probability for which project become feasible.