Mining activities often produce long-term environmental pollution and create many problems comprising acid drainage generation and discharging heavy metals to the surface and groundwater resources. The principal environmental concerns associated with waste rock dumps result from the oxidation of sulfide minerals, mainly pyrite within the from dwaste materials, when such minerals are exposed to atmospheric oxygen and/or water, they undergo rapid oxidation that produces acid waters. There are many mechanisms to make available oxygen within the waste dumps. Diffusion in the gaseous and aqueous phase through pores in the waste materials is the dominant mechanism for transporting the atmospheric oxygen from surface to the depth where the oxidation takes place. In this paper, oxygen diffusion and pyrite oxidation processes within the dump materials has been modeled using a finite volume code called PHEONICS in Sarcheshmeh copper mine. The analytical solution has been used to calibrate the numerical model. Both analytical and numerical methods show that the diffusion coefficient has an important role in pyrite oxidation and pollution generation. The results obtained from the numerical modeling further show that the pyrite reached to 13.8 % in surface samples of waste dumps after 4 years of the beginning of the oxidation process. It increased gradually with depth and reached to its initial percent (18.5 %) at a depth of 2.5 m within the dump where no oxygen is available to oxidize pyrite. The results obtained from such studies can be used in designing appropriate methods in order to minimize environmental pollution and their impacts to water resources.