Mineral potential for incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites in the Islamic Republic of Mauritania (phase V, deliverable 87)

Abstract

Review of PRISM-I documents and the National inventory of mineral occurrences suggests that resources of U, Th, Nb, Ta, Be, rare earth elements (REEs) and fluorite are known in Mauritania and have been exploited in the past at the Bou Naga alkaline complex. Several different deposit types are indicated by the available data. Pegmatitic veins are recorded in several areas of the Archean and Paleoproterozoic portions of the Rgueïbat Shield and are prospective for resources of Li, Be, Nb, Ta, U, Th, and REEs. Over 150 beryl pegmatites are known in the Khnefissat and Inkebden areas of the Chami greenstone belt, and additional concentrations of pegmatites are known in the Guelb Nich Sud area of the Sebkhet Nich greenstone belt and in the northeastern part of the Amsaga Complex. Due to the small size of these deposits, they are unlikely to be economic unless additional value can be gained by processing contained minerals for their industrial uses. Potential for incompatible element deposits associated with alkaline granites, syenites, and phonolites of the Tigsmat el Khadra Complex exists in the Paleoproterozoic portion of the Rgueïbat Shield in northern and northeastern Mauritania. The small alkaline complex at Tabatanet is associated with a magnetic and radiometric anomaly and consists of a probable vein-type deposit that extends for 500 m. The hyperalkaline granite at Tigsmat may have REE enrichments in associated placers but appears to be of low potential. Two other areas at el Mrhader and at el Hajar have indications of potential based on geophysics and high scintillometer readings. All of these prospects and past mining at Bou Naga indicate potential for mineralization related to alkaline igneous rocks. A third major possibility for U, Th, REE, and other incompatible elements exists in association with carbonatite complexes, known to be present in Mauritania. Deposits of this type can host a wide array of valuable metals and industrial minerals (for example, Phalabora carbonatite complex, South Africa; Hicks Dome carbonatite complex and associated fluorite deposits of the Illinois-Kentucky Fluorspar District of the U.S. Midcontinent) and are most common in cratonic areas that have undergone rifting. PRISM-I studies suggest the presence of a carbonatite at Guelb er Richat and a coincident high thorium geophysical anomaly. The co-location of Guelb er Richat on prominent ENE trending structures with two separate swarms of kimberlite intrusions suggest that this structure is seated in the sub-Taoudeni cratonic basement and could localize the emplacement of additional carbonatite (and kimberlite) bodies. USGS review of PRISM-I data suggests that there is abundant documentation of the Bou Naga alkaline complex and to a lesser degree, the Guelb er Richat carbonatite complex, but that all other occurrences of U, Th, REE, and associated elements are poorly described, and poorly understood (Taylor, 2007)