Dioctahedral Tosudite in Hydrothermally Altered Pliocene Rhyolitic Tuff, Neutla, Mexico

Abstract

Abstract--Dioctahedral tosudite, a regular interstratification of dioctahedral chlorite-dioctahedral smectire, occurs associated with kaolin in the hydrothermal area of Delgado, Neutla, Mexico. Its composition corresponds to the formula: (Si13.77A12.23)AlsO4o(OH)a "Cao.39Nao.oaKLo6" (A13 vgFe+ 3o ogFe + 2o o6Mgo.26)(OH)~2.It forms as thin irregular flakes up to 5 #m in size. Adsorbed and cation hydration interlayer H20 is lost at 81 ~ and 184~ dehydroxylation is intense at 496*(7 and weak at 656~ with recrystallization at 970~ and 989~ Infrared analysis shows OH-stretching at 3605 cm-~ assigned to the AI--OH-A1 group and at 3628, 3500, and 3365 cm -t. Also, OH-bending occurs at 822 cm -~, deformation of the H20 molecule at 1630 cm -~, Si-O stretching at 1020 cm -~, and bending at 482 cm -t, displaced by A1 substitution and increase of the Si--O distance. The characteristic basal spacing of 29.49 ,~ for the air-dry mineral is changed to 31.32 ,~ when solvated and to 23.23/~ upon heating; do6o = 1.496/~. The interstratification is a regular 1 : 1 dioctahedral chlorite-dioctahedral smectite, R = 1, with coefficient of variability 0.73% for the airdried mineral and 0.76% for the solvated one.

Occurrence of tosudite in the Guezouman, Tarat and Tchirezrine 2 formations, hosts of uranium deposits in Niger (Tim Mersoï basin)

“…Tosudite is related to an alteration process which post-dated the burial diagenesis of the basin, the physical-chemical conditions of which are poorly constrained. In this respect, two main types of geological environments have been reported for the natural occurrence of tosudite: (1) areas that experienced hydrothermal activity related to circulation of acidic solutions at temperatures generally >200°C (Shimoda, 1969;Brown et al, 1974;Nishiyama et al, 1975;Creach et al, 1986;Merceron et al, 1988;Daniels & Altaner, 1990;Pablo-Galan & Chavez-Garcia, 1994;Hillier et al, 1996;Harrison et al, 2004); and (2) areas FIG. 8.…”

“…According to the recommendation of Bailey (1982), the CV should be <0.75 for regular interstratifications. In this study, the CV is very small (0.03-0.13) and permits the name tosudite to be used for this mineral, which is a regularly ordered 50:50 mixed-layer chlorite-smectite (Brown et al, 1974;Pablo-Galan & Chavez-Garcia, 1994;Nishiyama et al, 1975).…”

Clays at the Natural Nuclear Reactor at Bangombé, Gabon: Migration of Actinides

“…Dioctahedral and di-tri chlorites are located within the argile de pile and within the sandstones immediately adjacent (within a meter) to the reactor. The dioctahedral and di-tri chlorites could have been formed during a hydrothermal event [16,17] such as that which occurred during the reactor's operation. Alternatively, chlorite compositions in and near the argile de pile may merely reflect the very high-Al nature of the argile de pile and thus, could result from a later event.…”