Abstract
Abstract. Among numerous minerals determined at Nežilovo, Pelagonian Massif, North Macedonia, ardennite-(As) has been discovered in two different associations and studied by means of optical microscopy, electron microprobe analysis (EMPA), and single-crystal and powder X-ray diffraction methods. The refractive indices of ardennite-(As) from Nežilovo are α=1.537(2), β=1.579(1) and γ=1.741(1), where γ corresponds to the c direction. The optical axial angle is 2Vx=49(1)∘. EMPA of the investigated samples yields the following empirical formulae: [Mn3.272+Ca0.73]Σ4.00[Al4.18Mg1.24Fe0.29Mn0.193+Zn0.10]Σ6.00(Si4.73Al0.27)Σ5.00(As0.96Si0.03V0.01)Σ1.00O22 [OH5.36(H2O)0.64]Σ6.00 for ardennite-(As) and (K0.95Na0.04Ba0.02)Σ1.01(Al1.44Fe0.303+Mg0.20Mn0.03Ti0.02 Zn0.01)Σ2.00(Si3.21Al0.79O10) (OH1.97O0.03)Σ2.00 for the associated red mica. The unit cell parameters of ardennite-(As) determined by X-ray powder diffraction are a=8.757(2) Å, b=5.836(2) Å, c=18.578(2) Å and V=941.97 Å3. The unit cell parameters of ardennite-(As) were also determined by single-crystal X-ray diffraction and are a=8.760(1) Å, b=5.838(1) Å, c=18.582(2) Å and V=950.30 Å3. Regularities of isomorphism in ardennite-related minerals are discussed. The presence of ardennite-(As) in association with 2M1 and 3T phengite polytypes provides evidence for three separate stages of formation. Conditions at which ardennite-(As) crystallized have been estimated based on compositional features of associated micas.
Highlights
Ore occurrences at the village of Nežilovo, Pelagonian Massif, North Macedonia, attract the attention of geologists and mineralogists because of the unusual associations of numerous rare and new oxygen-bearing minerals of chalcophile elements (Pb, Zn, Sb, Cu, As)
Bermanec et al.: Ardennite-bearing mineral association related to sulfide-free ores
This paper describes a new locality of ardennite-(As) in the Pelagonian Massif, North Macedonia, and discusses solid solution series between ardennite-(As) and structurally related minerals
Summary
Ore occurrences at the village of Nežilovo, Pelagonian Massif, North Macedonia, attract the attention of geologists and mineralogists because of the unusual associations of numerous rare and new oxygen-bearing minerals of chalcophile elements (Pb, Zn, Sb, Cu, As). The uniqueness of the formation hosting these occurrences (called “mixed series”) is a result of complex multistage metamorphism and metasomatic transformations of different sediments with very diverse and peculiar chemical composition (see Stojanov, 1960, 1967– 1968; Majer and Mason, 1983; Arsovski and Dumurdzhanov, 1984). An extensive description of the metamorphic conditions in the Pelagonides has been given by Most (2003). M. Bermanec et al.: Ardennite-bearing mineral association related to sulfide-free ores
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