Record details

    Geochemistry of agates: a trace element and stable isotope study
Statement of responsibility
    J. Götze, M. Tichomirova, H. Fuchs, J. Pilot, Z.D. Sharp
    Fuchs, H.
    Götze, J.
    Pilot, J.
    Sharp, Z. D.
    Tichomirova, M.
Source title - serial
    Chemical geology (including isotope geoscience)
    Vol. 175, no. 3-4
    p. 523-541
    8 obr., 2 fot., 4 tab., 2 s.bibl.
    Zkr. název ser.: Chem. Geol. (Isotope Geosci.)
Subject group
    hydrotermální alterace
    izotopy C
    izotopy H
    izotopy stabilní
    podkrkonošská pánev
    prvky stopové
    roztok vodný
    skupina SiO2
    vzácné zeminy
Geographical name
    Brazílie-Rio Grande do Sul
    Frýdštejn (Jablonec nad Nisou)
    Kyje (Jičín)
    Nová Paka (Jičín)
    Velká Británie-Scotland
Abstract (in english)
   Agate samples of acidic, intermediate and basic volcanics from 18 localities around the world and of different age (Precambrian to tertiary) were studied by trace element and stable isotope analysis to provide information about the process of agate formation and the origin of mineral-forming fluids. trace element data are similar for agates from acidic and basic volcanics. The general chondrite-normalized REE distribution pattern is characterized by a slope from La to Lu with enriched LREE and a positive Eu anomaly in some samples. The similarity in the shape of the REE patterns between agates and the parent volcanic rocks suggests that the element are mobilized by circulating fluids during syn- and postvolcanoc alteration of the volcanic wall rocks. Observed positive Eu anomalies in agates probably originate from feldspar alteration. Deuterium and oxygen isotope analyses of agates and associated quartz incrustations (delta: -44%. to -130%.;delta18O: +16.4%.
   to 33.4%.) reveal variations in isotopic composition between samples of different localities but also within single agate samples (up to 10% for delta18O). In general, oxygen isotope compositions become heavier as volcanic host rocks grow more acidic. Furthermore, agates have higher delta18O values than associated quartz incrustations. Variations within single agate samples can be explained either by kinetic effects during isotope fractionation (e.g. the formation of agate from a noncrystalline precursor) or by mixing processes of meteoric and magmatic fluids
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    23. 8. 2007
Import date
    8. 8. 2012