Mineralogy of the Plio-Pleistocene potassic and ultrapotassic volcanic rocks from the Republic of Macedonia

Ultra- to high potassic volcanic rocks of Plio-Pleistocene age (3.24-1.47 Ma) crop out in the Vardar
zone. On the basis of chemical composition, they are classified as phonotephrites to ultrapotassic shoshonites
and latites, including also high-Mg latites. They contain pheno- and microphenocrysts of olivine,
clinopyroxene, phlogopite, ± leucite. The groundmass consists of poikilitic Ba-Na sanidine and Ba-Ti
phlogopite, ± Sr-rich oligoclase (up to 3 wt.% SrO), anorthoclase and Mg-bearing calcite, all enclosing
microlites of clinopyroxene, phlogopite, Ti-magnetite, ± leucite. The olivine phenocrysts are zoned,
forsterite-rich (up to Fo 93), and display a positive correlation between Fo component and NiO and negative
one between the same component and MnO. The clinopyroxenes are diopside-augites, and some of them are
rich in Al (up to 5.4 wt.% Al2O3), which correlates positively with Ti. On the other hand, Ti correlates
negatively with Mg# and Si. The micas are essentially phlogopites rich in Ti (up to 12 wt.% TiO2). In some
localities they are also highly enriched in Ba (up to 8.3 wt.% BaO) approaching to the Ti-kinoshitalite
composition. Ba in micas correlates positively with Ti and Al, but negatively with K, Mg# as well as with Si.
A positive correlation between Ba and Sr and negative one between Ba and Si/Al ratio is observed in both
sanidine and plagioclase. The leucite microphenocrysts are sometimes replaced by Na-sanidine, zeolites
(laumontite, phillipsite, etc.) and clays or by nepheline and amorphous nephelinic masses. The obtained
mineralogical features of the Macedonian ultrapotassic rocks assign them to the Roman Province Type rocks.