Abstract
Rare earth elements (REEs) have become increasingly important to our modern society due to their strategical significance and numerous high technological applications. Regolith-hosted heavy rare earth element (HREE) deposits in South China are currently the main source of the HREEs, but the ore-forming processes are poorly understood. In these deposits, the REEs are postulated to accumulate in regolith through adsorption on clay minerals. In the Zudong deposit, the world’s largest regolith-hosted HREE deposit, clay minerals are dominated by short, stubby, nanometer-scale halloysite tubes (either 10 or 7 Å) and microcrystalline kaolinite in the saprolite and lower pedolith and micrometer-sized vermicular kaolinite in the humic layer and upper pedolith. A critical transformation of the clay minerals in the upper pedolith is coalescence and unrolling of halloysite to form vermicular kaolinite. Microcrystalline kaolinite also transformed to large, well-crystalline vermicular kaolinite. This transformation could result in significant changes in different physicochemical properties of the clay assemblages. Halloysite-abundant clay assemblages in the deep regolith have specific surface area and porosity significantly higher than the kaolinite-dominant clay assemblages in the shallow soils. The crystallinity of clay minerals also increased, exemplified by decrease in Fe contents of the kaolinite group minerals (from ~1.2 wt% in the lower saprolite to ~0.35 wt% in the upper pedolith), thereby indicative of less availability of various types of adsorption sites. Hence, halloysite-abundant clay minerals of high adsorption capacity in deep regolith could efficiently retain the REEs released from weathering of the parent granite. Reduction in adsorption capacity during the clay transformation in shallow depth partially leads to REE desorption, and the released REEs would be subsequently transported to and adsorbed at deeper part of the soil profile. Hence, the clay-adsorbed REE concentration in the lower pedolith and saprolite (~2500 ppm on average) is much higher than the uppermost soils (~400 ppm on average). Therefore, weathering environments that favor the release of the REEs in the shallow soils but preservation of halloysite in the deep regolith can continuously adsorb REEs in the clay minerals to form economically valuable deposits.
Acknowledgments
We thank the kind assistance of Xiao Fu for EPMA, Lily Chiu for PSA, Maria Lo for ICP-OES analysis, and Frankie Chan from the EMU for TEM analysis. Youjun Deng from the Texas A&M University is acknowledged for the kind provision of his soil mineralogy laboratory manual. Daniel E. Harlov is thanked for his constructive comments and language polishing on the manuscript. Editorial handling by Editor Hongwu Xu, Associate Editor Andy Madden, and constructive comments by Kenzo Sanematsu and an anonymous reviewer are gratified.
Funding This study was supported financially by a major research plan program of the National Natural Science Foundation of China on regolith-hosted REE deposits in South China and by China University of Geosciences (Wuhan) to M.-F.Z.
References cited
Aoudjit, H., Elsass, F., Robert, M., and Righi, D. (1996) Mica weathering in acidic soils by analytical electron microscopy. Clay Minerals, 31(3), 319–332.10.1180/claymin.1996.031.3.03Search in Google Scholar
Bailey, S.W. (1990) Halloysite—A critical assessment. Sciences Géologiques, bulletins et mémoires, 86(1), 89–98.Search in Google Scholar
Banfield, J.F., and Eggleton, R.A. (1990) Analytical transmission electron microscope studies of plagioclase, muscovite, and K-feldspar weathering. Clays and Clay Minerals, 38(1), 77–89.10.1346/CCMN.1990.0380111Search in Google Scholar
Bao, Z., and Zhao, Z. (2008) Geochemistry of mineralization with exchangeable REY in the weathering crusts of granitic rocks in South China. Ore Geology Reviews, 33(3), 519–535.10.1016/j.oregeorev.2007.03.005Search in Google Scholar
Barrett, E.P., Joyner, L.G., and Halenda, P.P. (1951) The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms. Journal of the American Chemical Society, 73(1), 373–380.10.1021/ja01145a126Search in Google Scholar
Berger, A., Janots, E., Gnos, E., Frei, R., and Bernier, F. (2014) Rare earth element mineralogy and geochemistry in a laterite profile from Madagascar. Applied Geochemistry, 41, 218–228.10.1016/j.apgeochem.2013.12.013Search in Google Scholar
Blum, A.E., and Stillings, L.L. (1995) Feldspar dissolution kinetics. Reviews in Mineralogy and Geochemistry, 31, 291–351.Search in Google Scholar
Bobos, I., Duplay, J., Rocha, J., and Gomes, C. (2001) Kaolinite to halloysite-7 Å transformation in the kaolin deposit of São Vicente de Pereira, Portugal. Clays and Clay Minerals, 49(6), 596–607.10.1346/CCMN.2001.0490609Search in Google Scholar
Borst, A.M., Smith, M.P., Finch, A., Marquis, E., Estrade, G., Kynicky, J., Xu, C., and Geraki, K. (2018) Structural state of REE in ion adsorption deposits: A XANES/EXAFS study of laterites from Madagascar and China. Proceedings of the Resources for Future Generations Conference, Vancouver.Search in Google Scholar
Carr, R., Chaikum, N., and Patterson, N. (1978) Intercalation of salts in halloysite. Clays and Clay Minerals, 26(2), 144–152.10.1346/CCMN.1978.0260210Search in Google Scholar
Cheshire, M.C. (2011) Isotopic and geochemical composition of the Georgia kaolins: Insights into formation and diagenetic conditions. Ph.D. thesis, 244 p. Indiana University.Search in Google Scholar
Cheshire, M.C., Bish, D.L., Cahill, J.F., Kertesz, V., and Stack, A.G. (2018) Geochemical Evidence for Rare-Earth Element Mobilization during Kaolin Diagenesis. ACS Earth and Space Chemistry, 2(5), 506–520.10.1021/acsearthspacechem.7b00124Search in Google Scholar
Churchman, G., and Carr, R. (1975) The definition and nomenclature of halloysites. Clays and Clay Minerals, 23(5), 382–388.10.1346/CCMN.1975.0230510Search in Google Scholar
Churchman, G., Aldridge, L., and Carr, R. (1972) The relationship between the hydrated and dehydrated states of an halloysite. Clays and Clay Minerals, 20(4), 241–246.10.1346/CCMN.1972.0200409Search in Google Scholar
Churchman, G., and Gilkes, R. (1989) Recognition of intermediates in the possible transformation of halloysite to kaolinite in weathering profiles. Clay Minerals, 24(4), 579–590.10.1180/claymin.1989.024.4.02Search in Google Scholar
Churchman, G., Davy, T., Aylmore, L., Gilkes, R., and Self, P. (1995) Characteristics of fine pores in some halloysites. Clay Minerals, 30(2), 89–98.10.1180/claymin.1995.030.2.01Search in Google Scholar
Deng, Y., White, G.N., and Dixon, J.B. (2014) Soil mineralogy laboratory manual, 201 p. Department of Soil and Crop Sciences. Texas A&M University.Search in Google Scholar
Elliott, W.C., Gardner, D.J., Malla, P., and Riley, E. (2018) A new look at the occurrences of the rare-earth elements in the Georgia kaolins. Clays and Clay Minerals, 66(3), 245–260.10.1346/CCMN.2018.064096Search in Google Scholar
Eswaran, H., and Bin, W.C. (1978) A study of a deep weathering profile on granite in peninsular Malaysia: II. Mineralogy of the clay, silt, and sand fractions. Soil Science Society of America Journal, 42(1), 149–153.10.2136/sssaj1978.03615995004200010033xSearch in Google Scholar
Giese, R. (1988) Kaolin minerals; structures and stabilities. Reviews in Mineralogy and Geochemistry, 19, 29–66.Search in Google Scholar
Hart, R.D., Gilkes, R.J., Siradz, S., and Singh, B. (2002) The nature of soil kaolins from Indonesia and Western Australia. Clays and Clay Minerals, 50(2), 198–207.10.1346/000986002760832793Search in Google Scholar
Hart, R., Wiriyakitnateekul, W., and Gilkes, R. (2003) Properties of soil kaolins from Thailand. Clay Minerals, 38(1), 71–94.10.1180/0009855033810080Search in Google Scholar
Hinckley, D.N. (1962) Variability in “crystallinity” values among the kaolin deposits of the coastal plain of Georgia and South Carolina. Clays and Clay Minerals, 11(1), 229–235.10.1346/CCMN.1962.0110122Search in Google Scholar
Huang, D., Wu, C., and Han, J. (1989) REE geochemistry and mineralization characteristics of the Zudong and Guanxi granites, Jiangxi Province. Acta Geologica Sinica (English edition), 2(2), 139–157.Search in Google Scholar
Huang, J., Sun, S., and Zhang, J. (2013) Detection of trends in precipitation during 1960–2008 in Jiangxi province, southeast China. Theoretical and applied climatology, 114(1-2), 237–251.10.1007/s00704-013-0831-2Search in Google Scholar
Inoue, A., Utada, M., and Hatta, T. (2012) Halloysite-to-kaolinite transformation by dissolution and recrystallization during weathering of crystalline rocks. Clay Minerals, 47(3), 373–390.10.1180/claymin.2012.047.3.08Search in Google Scholar
Jeong, G. Y. (1998a) Formation of vermicular kaolinite from halloysite aggregates in the weathering of plagioclase. Clays and Clay Minerals, 46(3), 270–279.10.1346/CCMN.1998.0460306Search in Google Scholar
Jeong, G. Y. (1998b) Vermicular kaolinite epitactic on primary phyllosilicates in the weathering profiles of anorthosite. Clays and Clay Minerals, 46(5), 509–520.10.1346/CCMN.1998.0460504Search in Google Scholar
Jige, M., Takagi, T., Takahashi, Y., Kurisu, M., Tsunazawa, Y., Morimoto, K., Hoshino, M., and Tsukimura, K. (2018) Fe-kaolinite in granite saprolite beneath sedimentary kaolin deposits: A mode of Fe substitution for Al in kaolinite. American Mineralogist, 103, 1126–1135.10.2138/am-2018-6478Search in Google Scholar
Joussein, E., Petit, S., Churchman, J., Theng, B., Righi, D., and Delvaux, B. (2005) Halloysite clay minerals—a review. Clay Minerals, 40(4), 383–426.10.1180/0009855054040180Search in Google Scholar
Jozefaciuk, G. (2009) Effect of the size of aggregates on pore characteristics of minerals measured by mercury intrusion and water-vapor desorption techniques. Clays and Clay Minerals, 57(5), 586–601.10.1346/CCMN.2009.0570507Search in Google Scholar
Kosmulski, M. (2018) The pH dependent surface charging and points of zero charge. VII. Update. Advances in Colloid and Interface Science, 251, 115–138.10.1016/j.cis.2017.10.005Search in Google Scholar PubMed
Li, Y.H.M., Zhao, W.W., and Zhou, M.-F. (2017) Nature of parent rocks, mineralization styles and ore genesis of regolith-hosted REE deposits in South China: An integrated genetic model. Journal of Asian Earth Sciences, 148, 65–95.10.1016/j.jseaes.2017.08.004Search in Google Scholar
Li, M.Y.H., Zhou, M.-F., and Williams-Jones, A.E. (2019) The genesis of regolith-hosted heavy rare earth element deposits: Insights from the world-class Zudong deposit in Jiangxi Province, South China. Economic Geology, 114(3), 541–568.10.5382/econgeo.4642Search in Google Scholar
Liu, X., Chen, Y., Wang, D., Huang, F., and Zhao, Z. (2016) The metallogenic geomorphic condition analysis of the ion-adsorbing type rare earth ore in the eastern Nanling region based on DEM data. Acta Geoscientica Sinica, 37(2), 174–184 (in Chinese with English abstract).Search in Google Scholar
Lu, Y., Wang, R., Lu, X., Li, J., and Wang, T. (2016) Reprint of Genesis of halloysite from the weathering of muscovite: Insights from microscopic observations of a weathered granite in the Gaoling Area, Jingdezhen, China. Applied Clay Science, 119, 59–66.10.1016/j.clay.2015.08.024Search in Google Scholar
Ma, C., and Eggleton, R.A. (1999) Cation exchange capacity of kaolinite. Clays and Clay Minerals, 47(2), 174–180.10.1346/CCMN.1999.0470207Search in Google Scholar
Meunier, A., and Velde, B. (1976) Mineral reactions at grain contacts in early stages of granite weathering. Clay Minerals, 11(3), 235–240.10.1180/claymin.1976.011.3.05Search in Google Scholar
Miller, W., and Keller, W. (1963) Differentiation between endellite-halloysite and kaolinite by treatment with potassium acetate and ethylene glycol. Clays and Clay Minerals, 10, 244–253.10.1346/CCMN.1961.0100120Search in Google Scholar
Moldoveanu, G., and Papangelakis, V. (2016) An overview of rare-earth recovery by ion-exchange leaching from ion-adsorption clays of various origins. Mineralogical Magazine, 80(1), 63–76.10.1180/minmag.2016.080.051Search in Google Scholar
Padrones, J.T., Imai, A., and Takahashi, R. (2017) Geochemical behavior of rare earth elements in weathered granitic rocks in northern Palawan, Philippines. Resource Geology, 67(3), 231–253.10.1111/rge.12123Search in Google Scholar
Papoulis, D., Tsolis-Katagas, P., and Katagas, C. (2004) Progressive stages in the formation of kaolin minerals of different morphologies in the weathering of plagioclase. Clays and Clay Minerals, 52(3), 275–286.10.1346/CCMN.2004.0520303Search in Google Scholar
Pasbakhsh, P., Churchman, G.J., and Keeling, J.L. (2013) Characterisation of properties of various halloysites relevant to their use as nanotubes and microfibre fillers. Applied Clay Science, 74, 47–57.10.1016/j.clay.2012.06.014Search in Google Scholar
Radoslovich, E. (1963) The cell dimensions and symmetry of layer-lattice silicates. VI. Serpentine and kaolin morphology. American Mineralogist, 48, 368–378.Search in Google Scholar
Robertson, I.D., and Eggleton, R.A. (1991) Weathering of granitic muscovite to kaolinite and halloysite and of plagioclase-derived kaolinite to halloysite. Clays and Clay Minerals, 39(2), 113–126.10.1346/CCMN.1991.0390201Search in Google Scholar
Rudnick, R.L., and Gao, S. (2003) Composition of the continental crust. In H.D. Holland, and K.K. Turekian, Eds., Treatise on Geochemistry, 3, 1–64. Elsevier.10.1016/B0-08-043751-6/03016-4Search in Google Scholar
Sanematsu, K., and Watanabe, Y. (2016) Characteristics and genesis of ion-adsorption type deposits. Reviews in Economic Geology, 18, 55–79.Search in Google Scholar
Sanematsu, K., Kon, Y., Imai, A., Watanabe, K., and Watanabe, Y. (2013) Geochemical and mineralogical characteristics of ion-adsorption type REE mineralization in Phuket, Thailand. Mineralium Deposita, 48(4), 437–451.10.1007/s00126-011-0380-5Search in Google Scholar
Sanematsu, K., Kon, Y., and Imai, A. (2015) Influence of phosphate on mobility and adsorption of REEs during weathering of granites in Thailand. Journal of Asian Earth Sciences, 111, 14–30.10.1016/j.jseaes.2015.05.018Search in Google Scholar
Simandl, G. (2014) Geology and market-dependent significance of rare earth element resources. Mineralium Deposita, 49(8), 889–904.10.1007/s00126-014-0546-zSearch in Google Scholar
Singer, A., Zarei, M., Lange, F., and Stahr, K. (2004) Halloysite characteristics and formation in the northern Golan Heights. Geoderma, 123(3-4), 279–295.10.1016/j.geoderma.2004.02.012Search in Google Scholar
Singh, B. (1996) Why does halloysite roll?—A new model. Clays and Clay Minerals, 44(2), 191–196.10.1346/CCMN.1996.0440204Search in Google Scholar
Singh, B., and Gilkes, R. (1991) Weathering of a chromian muscovite to kaolinite. Clays and Clay Minerals, 39(6), 571–579.10.1346/CCMN.1991.0390602Search in Google Scholar
Singh, B., and Gilkes, R. (1992) An electron optical investigation of the alteration of kaolinite to halloysite. Clays and Clay Minerals, 40(2), 212–229.10.1346/CCMN.1992.0400211Search in Google Scholar
Soma, M., Churchman, G., and Iheng, B. (1992) X-ray photoelectron spectroscopic analysis of halloysites with different composition and particle morphology. Clay Minerals, 27, 413–421.10.1180/claymin.1992.027.4.02Search in Google Scholar
Tazaki, K. (1981) Analytical electron microscopic studies of halloysite formation processesmorphology and composition of halloysite. In M.M. Mortlan and V.C. Farmer, Eds., Proceedings of the 6th International Clay Conference 1978, p. 573–584. Elsevier.Search in Google Scholar
Velde, B. (1985) Clay Minerals: a physico-chemical explanation of their occurrence. Elsevier.Search in Google Scholar
Wada, K. (1959a) An interlayer complex of halloysite with ammonium chloride. American Mineralogist, 44, 1237–1247.Search in Google Scholar
Wada, K. (1959b) Oriented penetration of ionic compounds between the silicate layers of halloysite. American Mineralogist, 44, 153–165.Search in Google Scholar
Wada, K. (1961) Lattice expansion of kaolin minerals by treatment with potassium acetate. American Mineralogist, 46, 78–91.Search in Google Scholar
White, A.F., Bullen, T.D., Schulz, M. S., Blum, A.E., Huntington, T.G., and Peters, N.E. (2001) Differential rates of feldspar weathering in granitic regoliths. Geochimica et Cosmochimica Acta, 65(6), 847–869.10.1016/S0016-7037(00)00577-9Search in Google Scholar
Wilson, M., Deer, W., Howie, R., and Zussman, J. (2013) Sheet Silicates: Clay Minerals. Rock-Forming Minerals, vol. 3C, p. 724. Geological Society, London.Search in Google Scholar
Wouatong, A., Kitagawa, R., Takeno, S., Felix M, T., and Daniel, N. (1996) Morphological transformation of kaolin minerals from granite saprolite in the western part of Cameroon. Clay Science, 10(1), 67–81.Search in Google Scholar
Wu, C., Huang, D., and Guo, Z. (1990) REE geochemistry in the weathered crust of granites, Longnan area, Jiangxi Province. Acta Geologica Sinica (English edition), 3, 193–209.Search in Google Scholar
Xie, Y., Hou, Z., Goldfarb, R.J., Guo, X., and Wang, L. (2016) Rare earth element deposits in China. Reviews in Economic Geology, 18, 115–136.10.5382/Rev.18.06Search in Google Scholar
Yamaguchi, A., Honda, T., Tanaka, M., Tanaka, K., and Takahashi, Y. (2018) Discovery of ion-adsorption type deposits of rare earth elements (REE) in Southwest Japan with speciation of REE by extended X-ray absorption fine structure spectroscopy. Geochemical Journal, 52(5), 415–425.10.2343/geochemj.2.0531Search in Google Scholar
Zhao, Z., Wang, D., Chen, Z., Chen, Z., Zhwng, G., and Liu, X. (2014) Zircon U-Pb age, endogenic mineralization and petrogenesis of rare earth ore-bearing granite in Longnan, Jiangxi province. Acta Geoscientica Sinica, 35(6), 719–725.Search in Google Scholar
© 2020 Walter de Gruyter GmbH, Berlin/Boston
