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Investigations in 1965 located veins containing radioactive material in the Halaban Group on the east side of a granite pluton at Jabal Aja near Ha'il. Later study extended the known area of radioactivity to a total length of about 30 km. Mineralogic studies indicated that the samples were low in uranium and that the radioactivity was due principally to thorium in niobium-bearing minerals. Two samples were reexamined to identify the sources of radioactivity, but X-ray and alpha plate studies did not reveal the radioactive minerals, even though uranium mineralization was indicated by the alpha plates. Further sampling is suggested to isolate the sources of radioactivity, This study indicates that niobium occurrences are related to alkaline intrusives in many areas of western Saudi Arabia. These areas should be investigated for their possible niobium and rare earth contents; their uranium content is apparently too low to be of economic interest. INTRODUCTION Location and previous work The Ha'il area (fig. 1) is in the northeastern Hijaz quadrangle (Brown and others, 1963) about in the center of 7-2^ an area sampled by Hummel and Hakim (19& ) and Meissner and Petty (written commun., 1970). In their mineral reconnaissance survey Hummel and Hakim collected two samples (2334d and 2335a) about 10 km north of Ha'il and just east of Jabal Aja (fig. 2) that contained as much as 0.29 percent Nb90c. These samples " D were collected from veins that measured as much as 1 m wide. V.J. Flanigan (written commun.) stated that an aerial scintillation survey made in 1966-67 showed an anomaly of twice background over the Ha'il sample localities and other anomalies over the granite pluton at Jabal Aja. Meissner and Petty (written commun., 1970) further investigated these niobium-rich localities in the Ha'il area and other anomalous radioactive sites. They determined that the many aeroradiometric anomalies over the granite are caused by the large volume of slightly radioactive granite to give a large mass effect and that localized radiation on the ground is only slightly above background. The radioactive material is confined to veins and plugs. Other veins of about the same size as those sampled by Hummel and Hakim were discovered and sampled by Meissner and Petty 9 km south of the sample 2335a locality and also 17 km northwest; the approximate length of an anomalously radioactive zone is thus about 30 km.

A summary of niobium and rare earth localities from Ha'il and other areas in western Saudi Arabia: a preliminary study