Mineralogy and chemistry of ochre sediments from an acid mine drainage near a disused mine in Cornwall, UK

Ochre sediments from acid mine drainage in Cornwall have been investigated using X-ray diffraction, thermal methods, infrared spectroscopy, X-ray phot oelectron spectroscopy: transmission electron microscopy and chemical metho ds in order to determine their mineralogical and chemical composition. Fres h sediments consist of ferrihydrite and goethite. Large fractions of these minerals are dissolved by the ammonium oxalate treatment reflecting their p oorly crystalline structure. Fresh sediments contain large amounts of surfa ce-adsorbed SO4 (up to 9.3%) which is readily desorbed by the PO4 treatment . Goethite is the only mineral present in relatively older sediments and th e mineral is well crystallized with rod-shaped morphology. Environmental co nditions, such as pH and SO4 content, are not favourable for the presence o f schwertmannite at the site. Iron minerals appear to be precipitating arou nd filamentous algae and the shape of algae is preserved in the Fe oxide ma trix. The ubiquitous presence of algae in close association with Fe mineral s indicate their possible role in the crystallization of Fe oxides.