The average grades of copper mines are dropped by extracting high-grade copper ores. This matter has drawn considerations to processing methods which not only extracts low-grade copper ores but also decreases adverse environmental impacts. Hydrometallurgical methods are the most applicable ones which affect the optimum policy of cut-off grades determination. In this research, an optimum cut-off grades modeling is developed with the objective function of net present value (NPV) maximization. The costs of processing methods and associated environmental costs are also involved in the model. Next, limiting and balancing cut-off grades of processing methods are calculated through Lagrange multiplier optimization method. Finally, an iteration algorithm is exercised to compute the maximum amount of NPV as well as concentration and leaching optimum cut-off grades. The results show that the concentration and leaching optimum cut-off grades policy makes an improvement on overall NPV by 35% in comparison with the traditional approaches of cut-off grades determination. The adverse environmental impacts of low-grade ores dumping are also reduced by using hydrometallurgical methods