Mechanism Of Illitization Of Bentonites In The Geothermal Field Of Milos Island Greece- Evidence Based On Mineralogy, Chemistry, Particle Thickness And Morphology

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Journal Article: Mechanism Of Illitization Of Bentonites In The Geothermal Field Of Milos Island Greece- Evidence Based On Mineralogy, Chemistry, Particle Thickness And Morphology

Abstract
Hydrothermal alteration has caused illitization along a 40m vertical profile in the Tsantilis bentonite deposit, Eastern Miles, 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 (RO 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 YS 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 degrees C, directed away from the bentonite, suggesting that illitization might be used as an exploration guide for mineral deposits.

Author 
G. E. Christidis








Published Journal 
Clays and Clay Minerals, 1995





DOI 
Not Provided
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Citation

G. E. Christidis. 1995. Mechanism Of Illitization Of Bentonites In The Geothermal Field Of Milos Island Greece- Evidence Based On Mineralogy, Chemistry, Particle Thickness And Morphology. Clays and Clay Minerals. (!) .