Abstarct: Exploitation of mines needs remarkable investment and having an incorrect understanding of effective factor may cause failures in project. One of the most important properties of mextal deposits is grade, thus, because exploration of mextal deposits is complex and costly, there is not a comprehensive knowledge on the deposit grade. In this study, geostatistical simulation was used to create the grade models of Siriz iron ore mine. The estimated model yielded the reserve tonnage and average grade, 23.4 (Mt) and 32.666 (%) respectively, while the average obtained tonnage and grade from geostatistical simulation models yielded, 23.191 (Mt), 32.680 (%) respectively. Also the simulated models showed overestimate about 0.9 %. The economical model was created and then the final limit for estimated and simulated models was determined. Comparison between the estimated model and the simulated models revealed that the results of Net Present Value (NPV) and Stripping Ratio (SR) from estimated model is lower than the simulated ones about 2.37 % and 1.31 % respectively. But the total extractable ore and production cost (per unit recovered mextal) of the estimated model is more than the simulated models about 16.64 % and 2.9 % respectively. To increase the safety margins of investment, the risk of investment was quantified. NPV is the most important criterion indicating the project attractiveness for investor. The average NPVs of simulated models and estimated model are 78.97 (M$) and 77.10 (M$) respectively. The effect of grade uncertainty was shown clearly by comparison between the final limits of simulated models and estimated model.