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Fractionation and Rare-Element Mineralization of Kenticha Pegmatite, Southern Ethiopia

에티오피아 남부 켄티차 페그마타이트의 분화양상과 희유원소 광화작용

  • Kim, Eui-Jun (Korea Institute of Geoscience and Mineral Resources) ;
  • Kim, Soo-Young (Korea Institute of Geoscience and Mineral Resources) ;
  • Moon, Dong-Hyeok (Korea Institute of Geoscience and Mineral Resources) ;
  • Koh, Sang-Mo (Korea Institute of Geoscience and Mineral Resources)
  • Received : 2013.05.03
  • Accepted : 2013.09.20
  • Published : 2013.10.28

Abstract

The Kenticha rare-element (Ta-Li-Nb-Be) mineralized zone is located in ophiolitic fold and thrust complex of southern Ethiopia and was firstly discovered by joint exploration program of Ethiopia-Soviet in 1980s. It includes Dermidama, Kilkele, Shuni Hill, Kenticha, and Bupo pegmatites from south to north. The Kenticha pegmatite intruded parallel to NS-striking serpentinite and talc-chlorite schist, and is exposed approximately 2 km length and 400-700 m width. The Kenticha pegmatite is internally zoned and subdivided into lower quartz-muscovite-albite granite, intermediate muscovite-quartz-albite-microcline pegmatite, and upper spodumene-quartz-albite pegmatite, based on their mineral assemblage. The major, trace elements (e.g., Rb, Li, Nb, Ta, and Ga), and element ratios (e.g., K/Rb, Nb/Ta, Mg/Li, and Al/Ga) suggest that the fractionation and solidification of pegmatite have progressed from the lower towards upper pegmatite. In contrast, unlike general magmatic fractionation, Mg/Li ratios of the Kenticha pegmatite tend to be increased towards the upper pegmatite. It may result from post-magmatic hydrothermal alteration and/or interaction with upper ultramafic rock. Rare-element mineralization in Kenticha pegmatite concentrates on the upper pegmatite, which contains up to 3.0 wt % $Li_2O$, 3,780 ppm Rb, 111 ppm Cs, 1,320 ppm Ta, and 332 ppm Nb. Ore minerals in Kenticha pegmatite mostly include tantalite, spodumene, and lepidolite, and tantalite has an association with coarser quartz-spodumene and relatively fine sacchroidal albite. The tantalite is classified into Mn-tantalite as a function of $Mn^*[Mn/(Mn+Fe)]$ and $Ta^*[Ta/(Ta+Nb)]$ values. Its compositions ($Mn^*$, $Ta^*$, and Nb/Ta) between coarse and fine tantalites are different and the former is strongly enriched in Ta and depleted in Nb compared to latter one. In conclusion, rare-element mineralization in the Kenticha pegmatite may has occurred in the latest stage of magmatic fractionation.

Keywords

Kenticha rare-element mineralized zone;pegmatite;fractionation;tantalite

Acknowledgement

Grant : 해외 희유금속자원 탐사 및 부존잠재성 평가

Supported by : 한국지질자원연구원

References

  1. Abraham, A., Hassen, N., Yemane, T., Genzebu, W., Seyid, G., Mehari, K, and Alemu, T (1992) The geological evolution of the proterozoic of southern Ethiopia. Abstr Vol 29th Intern Geological Congress, Kyoto, Japan, p.13.
  2. Beus, A.A., Berengilova, V.V., Grabovskaya, L.I., Kochemasov, G.G., Leont' eva, L.A. and Sitnin, A.A. (1968) Geokhimicheskie poiski endogennykh mestorozhdemii redkikh elementov (na primere tantala); Nedra Moscow, 264p. (in Russian) (English translation: Geochemistry exploration for endogenic deposits of rare-elements (citing tantalum as an example), in Geological Survey of Canada Library, Ottawa, Ontario.
  3. Breaks, F.W., Selway, J.B. and Tindle, A.G. (2003) Fertile peraluminous granite and related rare-element mineralization in pegmatite, Superior Province, Northwest and Northeast Ontario: Operation Treasure Hunt. Ontario Geological Survey Open File Report 6099, 179p.
  4. Cerny, P. (1989) Exploration strategy and methods for pegmatite deposits of tantalum; in Lanthanides, tantalum, and niobium. Springer-Verlag, New Your, p.274-302.
  5. Ethiopian Mapping Agency (1988) Geological map of Adola area (1: 100,000).
  6. Genzebu, W., Hassen, N. and Yemane, T. (1994) Geology of the Agere Mariam area. Ethiopian Institute of Geological Surveys, memoir 8. Ethiopian Institute of Geological Surveys, Addis Ababa, 23p.
  7. InvestmentMine (2013) http://www.infomine.com/investment/metal-prices/tantalite-ore.
  8. Kazmin, V. 1972. Geology of Ethiopia. Explanatory Note to the Geological Map of Ethiopia, Scale 1:2,000,000, UNDP.
  9. Kesler, S.K., Gruber, P.W., Medina, P.A., Keoleian, G.A., Everson, M.P. and Wallington, T.J. (2012) Global lithium resources: Relative importance of pegmatite, brine, and other deposits. Ore Geology Reviews, v.48, p.55-69. https://doi.org/10.1016/j.oregeorev.2012.05.006
  10. Kozyrev, V., Girma, K., Bekele, W.M. and Teweldemedhin, T. (1982) Regional geological and exploration work for gold and other minerals in the Adola gold fields. Internal report (unpubl) Ethiopian Mineral Resource Development Corp. Ministry of Mines and Envergy, Addis Ababa, 260p.
  11. Kster, D., Romer, R.L., Tolessa, D., Zerihun, D., Bheemalingeswara, K., Melcher, F. and Oberthr, R. (2009) The Kenticha rare-element pegamtite, Ethiopia: internal differntiation, U-Pb age and Ta mineralization. Miner. Deposita, v.44, p.723-750. https://doi.org/10.1007/s00126-009-0240-8
  12. Poletayev, J.A., Verbvsky, O.N., Teweldemedhin, T., Musa, E., Alemayehu, B. and Manaye, Y. (1991) The geolgoy and rare metal potential of the Kenticah pegmatite deposit. Internal report (unpub) Ethiopian Mineral Resource Development Corp, Ministry of Mines and Energy, Addis Ababa, 113p.
  13. Polinares (2012) Fact Sheet: Tantalum. Polinares working paper, n.36, 13p.
  14. Roskill Information Services Ltd. (2009) The economics of tantalum. v.10, 152p.
  15. Teklay, M., Kroner, A., Mezger, K. and Oberhansli, R. (1998) Geochemistry, Pb-Pb single zircon ages and Nd-Sr isotope composition of Precambrian rocks from southern and eastern Ethiopia: implications for crustal evolution in East Africa. J. Afr. Earth Sci., v.26, p.207-227. https://doi.org/10.1016/S0899-5362(98)00006-2
  16. Trueman, D.L. and Cern yo, P. (1982) Exploration for rare- element granitic pegmatites; in Granitic pegmatite in science and industry. Mineralogical Association of Canada, Short Course Handbook 8, p.463-493.
  17. Worku, H. (1996) Geodynamic development of the Adola Belt (southern Ethiopia) in the Neoproterozoic and its control an gold mineralization. Ph.D. thesis, Tech. Univ. Berlin, 156p.
  18. Yibas, B., Reimold, W.U., Armstrong, R., Koeberl, C., Anhaeusser, C.R. and Phillips, D. (2002) The tectonostratigraphy, granitoid geochronology and geological evolution of the Precambrian of southern Ethiopia. J. Afr. Earth Sci., v.34, p.57-84. https://doi.org/10.1016/S0899-5362(01)00099-9
  19. Zerihun, D., Garbarino, C. and Valera, R. (1995) Granite pegmatite system in Kenticha (Adola, Sidamo, Ehtiopia) rare metal pegmatite belt: petrochemistry, regional pegmatite zoning and classification. SINET Ethiopian J. Sci., v.18, p.119-148.

Cited by

  1. Alternative beneficiation of tantalite and removal of radioactive oxides from Ethiopian Kenticha pegmatite–spodumene ores vol.24, pp.7, 2017, https://doi.org/10.1007/s12613-017-1456-8