The case of the carbonatite-like dyke of the Madenska River complex at the Kriva Lakavica section in the Republic of Macedonia: oxygen and carbon isotopic constraints

Abstract

The oxygen and carbon isotope compositions of carbonate samples from the carbonatite-like dyke of the Madenska River complex at the Kriva Lakavica section, samples of calcite skarns from the Damjan Fe-ore deposit and the Sasa Pb-Zn ore deposit, and samples of marbles from the Pohorje Mountains were analyzed to provide critical evidence in favor of the magmatic or sedimentary origin of this carbonatite-like dyke. We suggest that the carbonatite-like dyke is not a "normal" carbonatite, but instead represents melted carbonates, which can be associated with an unexposed, deep-seated, causative magmatic body. This dyke has a fluidal texture and carries xenoliths of ultramafic rocks that can be up to 35 cm in size. Its isotopic composition plots between primary unaltered carbonatites and marine carbonates, and ranges between 13.79‰ and 18.89‰ for δ 18 O VSMOW and between -1.22‰ and 1.31‰ for δ 13 C VPDB . These values are significantly lower than those observed in carbonatites analyzed during this study and range between 6.53‰ and 8.10‰ for δ 18 O VSMOW and between -5.82‰ and -4.32‰ for δ 13 C VPDB , which is the primary isotope signature of most magmatic carbonatites. Similarly high δ 18 O and δ 13 C values were found in skarns of the Damjan Fe deposit close to the Madanska River complex and in the Sasa Pb-Zn deposit, as well as in highgrade regional metamorphic calcitic marbles of the Pohorje massive. The emplacement levels of the carbonatite-like dyke, due to several tectonic processes, are uncertain. The type of country rocks (sedimentary carbonates, ultramafic, mafic, and granitic rocks), hydrothermal alternation, and metasomatic and regional metamorphic processes seem to be the most important parameters that affect the O and C isotopic patterns found in the Kriva Lakavica carbonatitelike dyke and in the investigated samples.