ABSTRACT: Acid mine drainage occurs as a result of reactions with water and sulphide minerals such as pyrite.As a result of these reactions water gains acidic properties and significant water pollution problems couldrise. The study area located in Ortakent (Koyulhisar) has an active Pb-Zn-Cu mining site. The corelationand factor analyses applied to determine mineral-water reactions controlling the chemical compositionof groundwater clearly show effects of sulphide mineral bearing volcanic rocks. Sulfide minerals produceacid and groundwater contains high concentrations of SO4 and Fe. Low pH values are also responsiblefor dissolved metals (Al, Fe, Mn SO4, Pb, Zn) in the groundwater and river. Al, Fe and Mn concentrationsin the acidic waters in the study area exceed the limits of Ministry of Health-2005 Standard. In addition,several springs have SO4 and Pb concentrations higher than the limits of drinking water standards. Solidand liquid mine wastes contribute on the trace element contamination of water as well. Geochemicalmodelling showed that mostly heavy toxic metals in the acidic waters may exist largely in the form of freemetal and metal-sulphate. It is understood that the trace elements contained in the groundwater and rivercould introduce high risks to human, animals and plants.