The significance of secondary iron and manganese oxides in geochemical exploration is suggested by their common occurrence as coatings or concretions and as discrete particles of colloidal dimensions in soils and stream sediments and by their strong scavenging of important ore metals from the weathering zone. Chemical fractionation techniques are available to partition secondary oxides and their associated metals into different mineral phases and chemical forms by partial selective extraction. A knowledge of the distribution of metals in various chemical combinations is valuable to geochemical exploration in providing a proper selection of sample medium and extraction procedure and in helping evaluate the significance of metal anomalies. Studies of secondary Fe and Mn oxides and their relationships to the geochemistry of heavy metals should be further strengthened.

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