World demand for the rare-earth elements (REE), crucial for a growing number of high-technology and environmental applications, has risen rapidly in the last half decade. We report and describe a major deposit of light rare-earth elements (LREE) within the Khanneshin carbonatite complex of southern Afghanistan. The deposit is located in a remote and rugged part of the complex’s central intrusive vent, in a region previously identified by Soviet geologists in the 1970’s. Two types of LREE-enriched rocks are present: Type-1 concordantly mineralized barite-strontianite alvikite, and Type-2 igneous dikes of coarse-grained carbonatite enriched in fluorine and /or phosphorus. Type-1 mineralized alvikite averages 22.25 wt. % BaO, 4.27 wt. % SrO, and 3.25 wt. % ∑LREE2O3 ( sum of La, Ce, Pr, and Nd oxides). Type-2 igneous dikes average 15.45 wt. % BaO, 5.95 wt. % SrO, and 3.36 wt. % ∑LREE2O3. A magmatic origin is clearly indicated for the Type-2 LREE-enriched dikes, and Type-1 LREE mineralization probably formed in the presence of LREE-rich hydrothermal fluid. It is possible that both types of LREE mineralization may be pene-contemporaneous having formed in a carbonate-rich magma, in the marginal zone of the central vent, highly charged with volatile constituents (i.e. CO2, F, P2O5) and strongly enriched in Ba, Sr, and the LREE. Based on several assumptions, and employing simple geometry for the zone of LREE enrichment, we estimate that at least 1.3 Mt (million metric tonnes) of LREE2O3 is present in the Khanneshin complex.
Discipline Categories: Economic GeologyPreferred Presentation Type: Oral