[en] Full text: The Pimpama River drainage system is located 80 km south of Brisbane, in southeast Queensland. The coastal plain of the lower catchment developed during the last several thousands of years as a result of sea level fluctuations and changing fluvial regimes which provided ideal conditions for the formation of sedimentary pyrite (FeS₂). The hydrolysis of this pyrite and the consequent production of sulfuric acid is triggered and controlled by a complex mixture of natural and human factors such as rainfall patterns and seasonality, human changes to tidal regime, and current agricultural and residential activities. The production of acid and subsequent leaching of metals from the pyrite-rich sediments represent the main environmental issue of this coastal setting. Here we report some results of an X-ray diffraction (XRD) study aimed at identifying changes in the mineralogy of the floodplain sediments which have been affected by the local production of sulfuric acid. The XRD traces were run on samples of powder using a Philips PW 1050 diffractometer equipped with a cobalt anticathode. The identification and quantification of mineral phases was assisted by several computer programs: 1) TRACES (plot of traces and locate peaks), 2) JADE (search-match program) and 3) SIROQUANT (quantification program)