Clays and Clay Minerals

, Volume 43, Issue 5, pp 569–585 | Cite as

Mechanism of Illitization of Bentonites in the Geothermal Field of Milos Island Greece: Evidence Based on Mineralogy, Chemistry, Particle Thickness and Morphology

  • George E. Christidis


Hydrothermal alteration has caused illitization along a 40m vertical profile in the Tsantilis bentonite deposit, Eastern Milos, Greece which consists principally of a Wyoming-type montmorillonite and authigenic K-feldspar. The product K-bentonite which contains illite/smectite, kaolinite, K-feldspar, quartz, sulphates and sulphides exhibits an unusual tendency for increase of expandability with depth.

Mineralogy and I/S textures were determined with X-ray diffraction and SEM and TEM methods respectively and chemistry using X-ray fluorescence. Illitization is characterized by a 5- to 6-fold increase of K and release of Si, Fe, Mg Na, and Ca from the parent rock, indicating a K-influx (K-metasomatism) in the system.

The I/S particle morphology is characterized by both flaky and lath-like particles, the former dominating in the range 100-50% expandable layers (R0 ordering) and the latter in the range 50-10% expandable layers (R1 and R > 1 ordering). Flaky particles are also abundant in samples with R1 ordering and abundant kaolinite, indicating that the latter might affect illitization. The I/S particles are classified in populations with thickness multiples of 10 A, their thickness being probably smaller than the coherent XRD domain. As the reaction proceeds, particles grow thicker and more equant. The distribution of I/S particle dimensions forms steady state profiles showing log-normal distribution; however, sensu stricto Ostwald ripening is unlikely. It seems that the reaction proceeds toward minimization of the surface free energy of I/S, being affected principally by temperature and K-availability. The spatial distribution of expandability implies that the heating source was probably a mineralized vein with T < 200°C, directed away from the bentonite, suggesting that illitization might be used as an exploration guide for mineral deposits.

Key words

Bentonite Hydrothermal alteration Illitization Illite/smectite Kaolinite Neoformation Ostwald ripening Solid state transformation 


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  1. Ahn, J. H., and P. R. Buseck. 1990. Layer-stacking sequences and structural disorder in mixed-layer illite/smectite: Image simulations and HRTEM imaging. Am. Miner. 75: 267–275.Google Scholar
  2. Altaner, S. P, J. Hower, G. Whitney, and J. L. Aronson. 1984. Model for K-bentonite formation: Evidence from zoned K-bentonites in the disturbed belt, Montana. Geology 12: 412–415.CrossRefGoogle Scholar
  3. Baronnet, A. 1982. Ostwald ripening in solution. The case of calcite and mica. Estud. Geol. 38: 185–198.Google Scholar
  4. Baronnet, A. 1984. Growth kinetics of the silicates. A review of the basic concepts. Fortschr. Miner. 62: 187–232.Google Scholar
  5. Bennett H., and G. J. Oliver. 1976. Development of fluxes for the analysis of ceramic materials by X-ray Spectrometry. Analyst. 101: 803–807.CrossRefGoogle Scholar
  6. Bethke, G. M., and S. P. Altaner. 1986. Layer by layer mechanism of smectite illitization and application to a new rate law. Clays & Clay Miner. 34: 136–145.CrossRefGoogle Scholar
  7. Beutelspacher H., and H. W. van der Marel. 1968. Atlas of Electron Microscopy of Clay Minerals and Their Admixtures. Amsterdam: Elsevier, 333 pp.CrossRefGoogle Scholar
  8. Boles, J. R., and S. G. Franks. 1979. Clay diagenesis in Wilcox Sandstones of Southwest Texas: Implications of smectite diagenesis on sandstone cementation. J. Sed. Pet. 49: 55–70.Google Scholar
  9. Brusewitz, A. M. 1986. Chemical and physical properties of Paleozoic potassium bentonites from Kinnekulle, Sweden. Clays & Clay Miner. 34: 442–454.CrossRefGoogle Scholar
  10. Chai, B. H. T. 1974. Mass transfer of calcite during hydro-thermal recrystallization. In Geochemical Transport and Kinetics. A. W. Hoffmann, B. J. Giletti, H. S. Yoder Jr., and R. A. Jund, eds. Washington: Carnegie Inst, 205–218.Google Scholar
  11. Christidis, G. 1992. Origin, physical and chemical properties, of the bentonite deposits from the Aegean Islands of Milos, Kimolos and Chios, Greece. Ph.D. thesis. Univ. Leicester, UK. 472 pp.Google Scholar
  12. Christidis G., and A. C. Dunham. 1993. Compositional variations in smectites: Part I: Alteration of intermediate volcanic rocks. A case study from Milos Island, Greece. Clay Miner. 28: 255–273.CrossRefGoogle Scholar
  13. Christidis G., and T. Marcopoulos. 1993. Kaolinite generating processes in the Milos bentonites and their influence on the physical properties of bentonites. Bull. Geol. Soc. Greece (in press).Google Scholar
  14. Christidis G., P. W. Scott, and T. Marcopoulos. 1995. Origin of the bentonite deposits of Eastern Milos, Aegean, Greece: Geological, mineralogical and geochemical evidence. Clays & Clay Miner. 43: 63–77.CrossRefGoogle Scholar
  15. Eberl, D. D. 1978. The reaction of montmorillonite to mixed-layer clay: The effect of interlayer alkali and alkaline earth cations. Geochim. Cosmochim. Acta. 42: 1–7.CrossRefGoogle Scholar
  16. Eberl, D. D., G. Whitney, and H. Khoury. 1978. Hydro-thermal reactivity of smectite. Am. Miner. 63: 401–409.Google Scholar
  17. Eberl, D. D., and J. Srodon. 1988. Ostwald ripening and interparticle-diffraction effects for illite crystals. Am. Miner. 73: 1335–1345.Google Scholar
  18. Eberl, D. D., J. Srodon, and H. R. Northrop. 1986. Potassium fixation in smectite by wetting and drying. In Geochemical Processes at Mineral Surfaces. J. A. Davis and K. F. Hayes, eds. Amer. Chem. Soc. Symp. Ser. 323: 296–326.Google Scholar
  19. Eberl, D. D., J. Srodon, M. Kralik, B. E. Taylor, and Z. E. Peterman. 1990. Ostwald ripening of clays and meta-morphic minerals. Science 248: 474–477.CrossRefGoogle Scholar
  20. Eberl, D. D., B. Velde, and T. McCormick. 1993. Synthesis of illite-smectite from smectite at earth surface temperatures and high pH. Clay Miner. 28: 49–60.CrossRefGoogle Scholar
  21. Fyticas, M. 1977. Geological and Geothermal and Study of Milos Island. Ph.D thesis. Univ. Thessaloniki, Greece, 228 pp. (in Greek).Google Scholar
  22. Fyticas M., F. Innocenti, N. Kolios, P. Manetti, R. Mazzuoli, G. Poli, F. Rita, and L. Villari. 1986. Volcanology and petrology of volcanic products from the island of Milos and neighbouring islets. J. Volcanol. Geotherm. Res. 28: 297–317.CrossRefGoogle Scholar
  23. Glasmann, J. R., P. D. Lundegard, R. A. Clark, B. K. Penny, and I. D. Collins. 1989. Geochemical evidence for the history of diagenesis and fluid migration: Brent Sandstone, Heather Field, North Sea. Clay Miner. 24: 255–284.CrossRefGoogle Scholar
  24. Govindaraju, K. 1989. Geostandards Newsletter 13: Spec. Issue, July 1989.Google Scholar
  25. Giiven, N. 1974. Electron Optical investigations on mont-morillonites-I. Cheto, Camp-Bertaux and Wyoming mont-morillonites. Clays & Clay Miner. 22: 155–165.CrossRefGoogle Scholar
  26. Giiven N., and R. W. Pease. 1975. Electron Optical investigations on montmorillonites-II: Morphological variations in the intermediate members of the montmorillonite-bei-dellite series. Clays & Clay Miner. 23: 187–191.CrossRefGoogle Scholar
  27. Harvey, C. C., and P. R. L. Browne. 1991. Mixed-layer clay geothermometry in the Wairakei geothermal field, New Zealand. Clays & Clay Miner. 39: 614–621.CrossRefGoogle Scholar
  28. Howard, J. J., and D. M. Roy. 1985. Development of layer charge and kinetics of experimental smectite alteration. Clays & Clay Miner. 33: 81–88.CrossRefGoogle Scholar
  29. Hower J., E. V. Eslinger, M. E. Hower, and E. A. Perry. 1976. Mechanism of burial metamorphism of argillaceous sediment: 1. Mineralogical and chemical evidence. Bull. Geol. Soc. Am. 87: 725–737.CrossRefGoogle Scholar
  30. Huang, W. L., J. M. Longo, and D. R. Pevear. 1993. An experimentally derived kinetic model for smectite-to-illite conversion and its use as a geothermometer. Clays & Clay Miner. 41: 162–177.CrossRefGoogle Scholar
  31. Huff, W. D., and A. G. Türkmenoglu. 1981. Chemical characteristics and origin of Ordovician K-bentonites along the Cincinnati Arch. Clays & Clay Miner. 29: 113–123.CrossRefGoogle Scholar
  32. Inoue A., and M. Utada. 1983. Further investigations of a conversion series of diochahedral mica/smectites in the Shinzan hydrothermal alteration area, Northeast Japan. Clays & Clay Miner. 31: 401–412.CrossRefGoogle Scholar
  33. Inoue A., N. Kohyama, R. Kitagawa, and T. Watanabe. 1987. Chemical and morphological evidence for the conversion of smectite to illite. Clays & Clay Miner. 35: 111–120.CrossRefGoogle Scholar
  34. Inoue A., B. Velde, A. Meunier, and G. Touchard. 1988. Mechanism of illite formation during smectite-to-illite conversion in a hydrothermal system. Am. Miner. 73: 1305–1334.Google Scholar
  35. Jagodzinski, H. 1949. Eindimensionale Fehlordnung in Kristallen und ihr Einfluss auf die Rontgeninterferenzen. I. Berechnung des Fehlordnungsgrades aus der Rontgeninten-sitaten. Acta Crystallogr. 2: 201–207.CrossRefGoogle Scholar
  36. Jahren, J. S. 1991. Evidence of Ostwald ripening related recrystallization of diagenetic chlorites from reservoir rocks offshore Norway. Clay Miner. 26: 169–178.CrossRefGoogle Scholar
  37. Kalogeropoulos, S. I. and P. Mitropoulos. 1983. Geochemistry of barites from Milos island (Aegean Sea), Greece. N. Jb. Miner. Mh. 13–21.Google Scholar
  38. Keller, W. D., R. C. Reynolds, and Inoue, A. 1986. Morphology of clay minerals in the smectite-to-illite conversion series by scanning electron microscopy. Clays & Clay Miner. 34: 187–197.CrossRefGoogle Scholar
  39. Lanson B., and D. Champion. 1991. The I/S to illite reaction in the late stage diagenesis. Am. J. Sci. 291: 473–506.CrossRefGoogle Scholar
  40. Liakopoulos, A. 1987. Hydrothermalisme et mineralizations metalliferes de l’ile de Milos (Cyclades, Grece). Ph.D thesis. Univ. Pierre and Marie Curie, Paris, 276 pp.Google Scholar
  41. Lifshitz, I. M., and V. V. Slyozov. 1961. The kinetics of precipitation from supersaturated solid solutions. J. Phys. Chem. Solids. 19: 35–50.CrossRefGoogle Scholar
  42. Lindgreen H., and P. L. Hansen. 1991. Ordering of illite-smectite in Upper Jurassic claystones from the North Sea. Clay Miner. 26: 105–125.CrossRefGoogle Scholar
  43. Mering J., and A. Oberlin. 1971. The smectites. In The Electron Optical Investigation of Clays. J. A. Gard, ed. Mineralogical Society: London, 193–229.Google Scholar
  44. Muffler, P. L. J., and D. E. White. 1969. Active metamorphism of Upper Cenozoic sediments in the Salton Sea Geothermal Field and the Salton Trough, southeastern California. Bull. Geol. Soc. Am. 80: 157–182.CrossRefGoogle Scholar
  45. Nadeau, P. H., and R. C. Reynolds. 1981. Burial and contact metamorphism in the Mancos Shale. Clays & Clay Miner. 29: 249–259.CrossRefGoogle Scholar
  46. Nadeau, P. H., J. M. Tait, W. J. McHardy, and M. J. Wilson. 1984a. Interstratified XRD characteristics of physical mixtures of elementary clay particles. Clay Miner. 19: 67–76.CrossRefGoogle Scholar
  47. Nadeau, P. H., M. J. Wilson, W. J. McHardy, and J. M. Tait. 1984b. Interstratified clays as fundamental particles. Science 225: 923–925.CrossRefGoogle Scholar
  48. Nadeau, P. H., M. J. Wilson, W. J. McHardy, and J. M. Tait. 1984c. Interparticle diffraction: A new concept for interstratified clays. Clay Miner. 19: 757–769.CrossRefGoogle Scholar
  49. Newman, A. C. D., and G. Brown. 1987. The chemical constitution of clays. In Chemistry of Clays and Clay Minerals. A. C. D. Newman, ed. London: Mineralogical Society, 1–128.Google Scholar
  50. Ramseyer K., and J. R. Boles. 1986. Mixed-layer illite/smectite minerals in tertiary sandstones and shales, San Joaquin Basin, California. Clays & Clay Miner. 34: 115–124.CrossRefGoogle Scholar
  51. Reynolds, R. C. 1989. Principles and techniques of quantitative analysis of clay minerals by X-ray powder diffraction. In Quantitative Mineral Analysis of Clays. D. R. Pevear and F. A. Mumpton, eds. CMS workshop lectures. 1: 4–36.Google Scholar
  52. Robertson, H. E., and R. W. Lahann. 1981. Smectite to illite conversion rates: effects of solution chemistry. Clays & Clay Miner. 29: 129–135.CrossRefGoogle Scholar
  53. Rosenberg, P. E., J. A. Kittrick, and S. U. Aja. 1990. Mixed layer illite/smectite: A multiphase model. Am. Miner. 75: 1182–1185.Google Scholar
  54. Singer A., and P. Stoffers. 1980. Clay mineral diagenesis in two African lake sediments. Clay Miner. 15: 291–307.CrossRefGoogle Scholar
  55. Srodon, J. 1980. Precise identification of illite/smectite in-terstratiflcations by X-ray diffraction. Clays & Clay Miner. 28:401–411.CrossRefGoogle Scholar
  56. Srodon J., and D. D. Eberl. 1984. Illite. In Micas. S. W. Bailey ed. Washington D.C.: Mineralogical Society of America, 13: 495–538.CrossRefGoogle Scholar
  57. Srodon J., D. J. Morgan, E. V. Eslinger, D. D. Eberl, and M. R. Karlinger. 1986. Chemistry of illite/smectite and end-member illite. Clays & Clay Miner. 34: 368–378.CrossRefGoogle Scholar
  58. Srodon J., F. Elsass, W. J. McHardy, and D. J. Morgan. 1992. Chemistry of illite-smectite inferred from TEM measurements of fundamental particles. Clay Miner. 27: 137–158.CrossRefGoogle Scholar
  59. Steefel, C. I., and P. van Cappellen. 1990. A new kinetic approach to modeling water-rock interaction: The role of nucleation, precursors and Ostwald ripening. Geochim. Cosmochim. Acta 54: 2657–2677.CrossRefGoogle Scholar
  60. Sucha V., I. Kraus, H. Gerthofferova, J. Petes, and M. Serekova. 1993. Smectite to illite conversion in bentonites and shales of the East Slovak Basin. Clay Miner. 28: 243–253.CrossRefGoogle Scholar
  61. Veblen, D. R., G. D. Guthrie Jr., K. J. T. Livi, and R. C. Reynolds. 1990. High-resolution transmission electron microscopy and electron diffraction of mixed-layer illite smectite: Experimental results. Clays & Clay Miner. 38: 1–13.CrossRefGoogle Scholar
  62. Velde B., and E. Nicot. 1986. Diagenetic clay mineral composition as a function of pressure, temperature and chemical activity. J. Sed. Pet. 55: 541–547.Google Scholar
  63. Whitney, G. 1990. Role of water in the smectite-to-illite reaction. Clays & Clay Miner. 38: 343–350.CrossRefGoogle Scholar
  64. Whitney G., and R. Northrop. 1988. Experimental investigation of the smectite to illite reaction: Dual reaction mechanisms and oxygen-isotope systematics. Am. Miner. 73: 77–90.Google Scholar

Copyright information

© The Clay Minerals Society 1995

Authors and Affiliations

  • George E. Christidis
    • 1
  1. 1.Technical University of CreteDepartment of Mineral Resources EngineeringChania, CreteGreece

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