Epitaxic and syntactic intergrowth of structural related spinels, minerals of hӧgbomite supergroup, nežilovite and rinmanite from Pelagonian massif, Macedoniaтезисы доклада

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[1] Epitaxic and syntactic intergrowth of structural related spinels, minerals of hӧgbomite supergroup, nežilovite and rinmanite from pelagonian massif, macedonia / V. N. Ermolaeva, N. V. Chukanov, D. A. Varlamov et al. // Proceedings of XXXVI International Conference Magmatism of the Earth and related strategic metal deposits. — GEOKHI RAS Moscow, 2019. — P. 77–79. Minerals of the spinel group, högbomite supergroup (MHS), nežilovite and rinmanite were found in the Pelagonian massif, Macedonia in two types of metasomatic rocks enriched in chalcophile elements (As, Sb, Pb, Zn). Minerals of the spinel group (gahnite, franklinite) and hetaerolite (so-called “spinellides”) form isometric grains or graphic intergrowths, and MHS occur as subparallel aggregates of thin plates. Gahnite often forms partial or full pseudomorphs after franklinite and hetaerolite grains (Ermolaeva et al., 2016). Detailed research of compositional variations of MHS from non- sulphide endogeneous Pb-Zn-Sb-As associations occurring in the Pelagonian massif shows that chemical variability of these minerals is beyond that accepted in their nomenclature. In particular, Mn4+ or Sb5+ may play the role of the main charge-balancing high-valent cations (Ermolaeva et al., 2018). Often regular intergrowths of earlier zinc shpinels with later MHS are observed. Obviously, the presence of spinel module in MHS structures promoted the formation of epitaxic intergrowths of MHS with gahnite and franklinite individuals. In turn, MHS often form close epitaxiс and syntactic intergrowths with nežilovite. Outer zone of these parallel intergrowths of nežilovite and MHS are composed by zincohögbomite, which confirms that the latter was formed after nežilovite and other MHS. The latest mineral in intergrowths of this type is apparently Sb-analogue of zincohögbomite. The formation of parallel intergrowths of MHS with nežilovite is caused by the similarity of a-parameters of unit cells of these minerals (5.74 Å for zincohögbomite-2N6S (Chukanov et al., 2015), 5.90 Å for zincovelesite-6N6S (Chukanov et al., 2018), and 5.85 Å for nežilovite (Bermanec et al., 1996)), as well as commensurability of c-parameters of unit cells of zincovelesite-6N6S (55.87 Å) and nežilovite (22.81 Å). Zincovelesite-6N6S also forms close intergrowths with rinmanite Mg2Fe4Zn2Sb2O14(OH)2, one more oxide structurally related to MHS. The formation of parallel intergrowths of these minerals is also caused by the proximity of a-parameters of unit cells (5.99Å for rinmanite, 5.90 Å for zincovelesite-6N6S), as well as commensurability of c-parameters of rinmanite (9.35Å) and zincovelesite-6N6S (55.87 Å).

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