The study of postvolcanic alterations of rock materials by acid-sulphate solution (mass change, isotope geochemistry) are of special interest because it allows answers to various questions. For example, the nature of hydrothermal solutions can be investigated in order to give helpful hints for ore deposits. Of special interest is the zonal distribution of the alteration products indicating the change of solution chemistry in the direction of solution wich is caused by the solution-rock reaction. This observation can be used to find ore bodies situated in central or other certain zones of alteration. Special topics of this investigation are the mass transfere, the geochemical and the isotope aspects during the alteration by acid-sulphate solutions.