Model experiments were performed on the solubility of sulfide ores from the Kyzyl-Tashtyg deposit in distilled water and fulvic-acid (FA) solutions of different concentrations. It has been established that the oxidation of sulfide minerals in ores under atmospheric conditions might produce acid drainage waters with toxic heavy metals (Cu, Zn, Cd). The influence of natural organic acids depends on the capability of ore and host rock to neutralize the acidity of solutions. If carbonate content is enough at the first stage, a considerable increase in the pH value of FA-free solutions ensures Fe and Cu removal into the solid phase, whereas the formation of metal fulvate complexes hinders this process. However, when the rocks exhaust their neutralizing potential, all the solutions remain acidic for >100 days of leaching. In this case, FAs, on the contrary, inhibit the oxidation of the surface of sulfide minerals and reduce the removal of heavy metals into the solution.