English abstract
This thesis presents findings from a comprehensive geochemical and geophysical investigations for uranium and associated minerals in a few selected though limited areas of the Sultanate of Oman. Based on the knowledge that Proterozoic basins produce ~ 30-40% or even more of the global uranium production, the Proterozoic basement of Dhofar assumes significance with possible uranium targets, which were identified in reconnaissance investigations that were carried out in the late 1970s. The objective of this study was to re-investigate several of the uranium anomalies found in this region, particularly in the Neoproterozoic rocks of southern Oman and some members of the Huqf Super group in Al Wasta region in addition to further potential sites. An association of shales rich in organic carbon and rocks with hydrocarbon accumulations presents possible geochemical traps for an initial pre-concentration of uranium. Accordingly, five different locations (Area-I, Area-II, Area-III, Area-IV and Area-V) were investigated including the basement outcrops at Mirbat (Dhofar) and NW of Muhut (central Oman), shale outcrops near Rakhyut (Dhofar near Yemeni border-Area-I) and fault intersections near Marmul (~ 170 km NE of Salalah-Area-II), plus the salt dome of Qarat Kibrit (oil acting as possible geochemical Uranium trap, while mobile brines are potential uranium carriers-Area-III), a silicified volcanic unit exposing radiation halos, typically seen in roll-front deposits, at Al-Ashkharah (South of Sur-Area-IV), and a radiogenic placer (heavy minerals containing zircon) in the siliciclastic Ordovician Amdeh formation, SE of Muscat (West of Al-Amirat-Area-V). The methods of investigation comprise in-situ and laboratory XRF analyses, geophysical methods consisting of gamma ray spectroscopy, very low frequency electromagnetic (VLF-EM) and magnetic surveys and gravity only in Murmul.The XRF and gamma-ray spectroscopy surveys in fields (Area-I, U Loc-1 to U Loc-4), detected only very weak uranium anomalies, some areas in Dhofar (Near Oman-Yemen) border yielded an elevated uranium concentrations of 30-40 ppm from small-scale anomalies (highly mobile when affected by weathering) which are uneconomic. Further, the geophysical surveys in U Loc-2 explored concealed faults underneath a plateau with depth in the range 10 m– 80 m. These faults were believed to have acted as conduits to the U-carrying fluids that emplaced U in its present location or near the surface. In addition, gamma ray and XRF analyses revealed a U-Th decoupling, indicating a high mobility of uranium than thorium. Further, the results from Marmul, Qarat Kibrit salt dome (near Adam) and Al-Ashkharah fields represent weak uranium anomalies. In the case of the Qarat Kibrit salt dome, the geophysical study figured out the precise spatial location of the salt unit and probable trend of a subsurface fault at an estimated depth from different methods range 10 m- 60 m. However, no enrichment of radiogenic elements was recorded here. Finally, the placer deposits of Al-Amirat (Area-V) have shown moderate enrichments for radiogenic uranium (~ 90 ppm) and thorium (~ 900 ppm), however, the basement outcrops did not indicate uranium enrichment and basically showed background values for the respective igneous/metamorphic rocks. Results of interpretation of VLF-EM and magnetic signals have revealed the possible mineralized structures as deep as 9 m- 44 m, emphasizing the need for further detailed investigations. Among the five different areas investigated, it may be stated that the possible occurrence of uranium of low grade and moderately high concentration of thorium could be seen near Al-Amirat (Area-V) though not commercially viable. In all the other areas of investigation, the geophysical signals particularly total magnetic field and VLF-EM have identified the subsurface faults and established their depth.
