La Recherche De Phosphates Par Radiometrie Aeroportee*

Abstract

As a rule, deposits of phosphates contain radioactive elements. Studies made in the laboratory of samples from North America and north Africa had shown that this radioactivity is due to the presence of uranium, and occasionally of thorium, either in the form of vaandate or in a diffuse state. Surface measurements carried out with a portable scintillometer had enabled some deposits to be outlined, but radiometric prospecting was only a supplementary method at this stage. From the results of these surface studies, it could be considered that the relations emitted by phosphates were sufficiently intense to be detected from a certain altitude. Consequently, a scintillometer was installed aboard a helicopter, and experimental tests were carried out on the known deposit of Djebel Honk, Algeria. Three profiles, flown perpendicular to the existing layers at 45 metres, permitted us to ascertain the validity of the method, and to define the working standards. Despite the small width of these outcrops (30 metres at most), it was established that “helicopter radiometry” could be used for phosphate exploration. Fourteen thousand kilometres of profiles were flown in northern Algeria. Since the phosphate deposits known in this area are located at the contact of the Cretaceous and Eocene (Dano‐Maestrichtian, Thanetian, Ypresian), a systematic coverage of these geological series was undertaken. It was then possible to draw up a rapid inventory of the series. Airborne radiometry, and helicopter radiometry in particular, now seems to be the most efficient, quickest, and least expensive method that can be applied to systematic phosphate exploration.