Since alkali sulphide solutions are frequently considered to be ore carriers, their action on minerals of the country rock, particularly iron-containing ones, was investigated. All experiments were made at temperatures of 300 degrees C. in gold-lined bombs. The time of each was approximately one week. Numerous alteration products were obtained; many of them were positively identified. Others, due to the minute quantities obtained could not be recognized. Solutions of H 2 S and NaHS commonly alter the iron in the original minerals to pyrite, while Na 2 S produces iron oxides and black FeS. Other minerals produced were marcasite, quartz, chalcedony, opal, analcite, albite?, chlorites, acmite, sericite?, chrysotile, anhydrite, sulphur, and gold crystals. Kaolin minerals and nontronite were probably among the alteration products.