Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Jaromír Ulrych, Edvín Pivec, Pavel Povondra, Jiří Bendl

Geochemical and isotope characteristics of representative carbonates in young alkaline volcanites from northern Bohemia

Journal of the Czech Geological Society, volume 42 (1997), issue 1-2, 26 - 32

Carbonates of young alkaline volcanics from northern Bohemia have carbon of primary magmatic character with a shift to light isotopes, in association with fractionation processes. The oxygen isotopes show equilibration with meteoric - hydrothermal water at low temperatures. Representative samples reveal the following characteristics:
- dolomites associated with melilititic lamprophyres - polzenites of the Osečná Complex are characterized by high REE, high La/Yb ratio, and by δ¹³C values in the primary magmatic range (carbonatite affinity), but with δ¹⁸O values and ⁸⁷Sr/⁸⁶Sr ratios corresponding to lower-temperature processes and some crustal contamination
- calcites in phlogopitite, originated as alteration product of olivine melilitolite of the Osečná complex by late-magmatic fluids, are characterized by very low REE, low La/Yb ratio, low δ¹³C values and by ⁸⁷Sr/⁸⁶Sr ratio corresponding to the parental rock; high δ¹⁸O values indicate lower-temperature origin
- calcites from the contact zone of polzenite dyke with sandstones of the Czech Cretaceous Basin, with geochemical characteristics typical for sedimentary origin, are characterized by low REE, low La/Yb ratio and very high δ¹³C, δ¹⁸O values, and ⁸⁷Sr/⁸⁶Sr ratios
- rhodochrosite-dolomite-calcite series of post-magmatic hydrothermal origin, associated with base metal ore vein in the Roztoky Volcanic Centre of the České středohoří Mts., is characterized by moderate REE contents and Yb/La ratios, high Sr and Ba contents and by ⁸⁷Sr/⁸⁶Sr ratio reflecting some crustal contamination; δ¹³C values indicate probably minor admixture of sedimentary C in carbon of deep-seated origin, while the O isotope data point to participation of a low δ¹⁸O fluid of meteoric derivation.