Mineralogy of limonite in lead-zinc gossans

Differential thermal analysis was applied to 112 specimens of gossan limonite obtained from cappings over lead-zinc ores of highly varied geologic setting and primary mineralogy. It was hoped that variations in the proportions of lepidocrocite and goethite in gossan limonite would show a dependency on the type or grade of original ore or on the degree of transportation of the iron oxides.Rather than revealing new outcrop criteria of value in the search for ore, this study showed that differential thermal analysis cannot, as formerly thought, be used for reliable identification of the hydrous ferric oxide minerals.No lepidocrocite was found in any of the gossan specimens analyzed; the predominance of goethite in leached lead-zinc outcrops is explained in terms of the conditions under which the two minerals, goethite and lepidocrocite, are synthesized in the laboratory.An application of thermal analysis to study of hematite-goethite-jarosite assemblages in oxidized copper ore outcrops is suggested.