Aspects on the Illitization of the Kinnekulle Bentonites

Abstract

Abstract--Earlier interpretations of the conversion of the virgin smectite of the Ordovician Kinnekulle K-bentonites into the present mixed-layer illite/smectite imply that it took place through charge increase of the smectite with subsequent uptake and fixation of potassium. Recent analyses show that the layer charge of the smectite component of the I/S is in fact low and they suggest that neoformation of a separate illite phase took place. Pytte's kinetic model gives good agreement with the actual conversion rate for an activation energy of about 25-27 kcal/mole, depending on the adopted rate parameters, temperature history and assumed potassium source. In the KinnekuUe case the rate-controlling factor appears to have been the supply of potassium, which is concluded to have required large-scale, heat-induced groundwater convection.

Report on THMC Modeling of the Near Field Evolution of a Generic Clay Repository: Model Validation and Demonstration

“…Fairly extensive studies have been conducted to evaluate the occurrence of illitization in bentonite and clay formation; some of these studies are listed in Table 5-2 and a brief summary of each study is given below. Illitization is clearly evidenced in geological system (Wersin et al, 2007), as exemplified by several natural analogue studies (Pusch and Madsen, 1995;Kamei et al, 2004;Cuadros, 2006;Casciello et al, 2011). Illite/smectite mixed-layer clay is commonly observed in the clayey sediments, and typically the deep formation contains more illite than shallow formation (Cuadros, 2006), which lead to a conclusion that smectite is gradually transformed to illite during diagenesis.…”

“…Illite/smectite mixed-layer clay is commonly observed in the clayey sediments, and typically the deep formation contains more illite than shallow formation (Cuadros, 2006), which lead to a conclusion that smectite is gradually transformed to illite during diagenesis. Pusch and Madsen (1995) investigated the illitization of kinnekulle bentonite, a 5 m thick illite/smectite interlayers with upper and lower part having 50-70% illite and the central part 30-50% illite. This indicates that illitization proceeds from the surrounding environment and moves toward the center.…”

Reactive plasticity for clays: application to a natural analog of long-term geomechanical effects of nuclear waste disposal

“…The leading metamorphic mechanism in clays in the range of analog temperature has been identified as illitization of smectite in the upper Pierre Shale at Walsenburg, CO (Pytte and Reynolds, 1989), Murakami clay (Kamei et al, 1990) and in Kinnekulle clay (Pusch and Madsen, 1995). However, this mechanism does not seem to fit the findings at sites of Orciatico (Leoni et al, 1986) or Skye .…”

“…A mechanism alternative to the one-step rehydration is dissolution/precipitation proposed by Nadeau et al (1985), Whitney and Velde (1993), Pusch and Madsen (1995) and Hetzel et al (1994). In this reaction, clay particles composed of certain number of platelets break off, dissolve in water, acquire an adsorbed water layer, flocculate into larger clusters and eventually precipitate on solid substrate.…”

“…A number of studies of natural analogs, consisting in intrusion of hot magmatic mass into clays have been conducted concentrating on mineralogical changes (see, e.g. Pytte and Reynolds, 1989;Ferry et al, 1987;Kamei et al, 1990;Pusch and Madsen, 1995). They suggest massive illitization of smectitic parent clay in the temperature of analogy.…”