Sunshading is a powerful tool for the enhancement of edges in images. Given the azimuth and elevation of a source illumination, it calculates the reflectance from a surface which is composed of the data to be interpreted. It is a standard tool used in the interpretation of geophysical potential field data. In the great Oulad Abdoun phosphate basin, inclusions of sterile hardpan — so-called “disturbances” — are hard to detect as they interfere with phosphates. Their resistivity is above 200 Ohm⋅m against 80 to 150 Ohm⋅m for a phosphate-rich mineral. A Schlumberger resistivity survey over an area of 50 hectares was carried out. The geologic setting was successfully modeled on the basis of sunshaded maps of disturbances. A new field procedure was tested to deal with the extended edges of anomalous zones of phosphate deposit disturbances. Phosphate reserves were estimated more reliably.

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