This study was carried out to understand the formation of acid mine drainage(AMD) by pyro-phyllite(so-called Napseok)-rainwater interaction (weathering), dispersion patterns of heavy metals, and patterns of mixing with non-polluted water in the Tongnae pyrophyllite mine. Based on the mass balance and reaction path modeling, using both the geochemistry of water and occurrence of ghe secondaty minerals (weathering products), the geochemical evolution of AMD was simulated by computer code of SOLVEQ and CHILLER. It shows that the pH of stream water is from 6.2 to 7.3 upstream of the Tongnae minw. Close to the minem the pH decreases to 2. Despite being diluted with non-polluted tributaries, the acidiry of mine drainae water maintains as far as downstream. The results of modeling of water-rock interaction show that the activiry of hydrogen ion increases (pH decreases), the concentration of HCO₃decreases associated with increasing H+ activity, as the reaction is processing. The concentration of SO₄2- first increases minutely, but later increases rapidly as pH drops below 4.3. The concentrations of cations and heavy metals are controlled by the dissolution of reactants and re-dissolution of derived species (weathering produts) according to the pH. The continuous adding of reactive minerals, namely the progressively sequence; gochite, then Mn-oxides, then boehmite, then kaolinite, then Ca-nontronite, then Mg-nontronite, and finally chalcedony. The results of reaction paty modeling agree well with the field data, and offer useful information on the geochemical evolution of AMD. The results of reaction path modeling on the formation of AMD offer useful information for the estimation and the appraisal of pollution caused by water-rock interaction as geological environments. And also, the ones can be used as data for the choice of appropriate remediation technique for AMD.
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