Zincocromita en un skarn del Grupo Minero Los Guindos, Córdoba: primer registro en Argentina

ESPECHE, MARÍA JOSÉ; LIRA, RAÚL; GUERESCHI, ALINA BEATRIZ

Córdoba

Congreso; XIII Congreso de Mineralogía, Petrología Ígnea y Metamórfica, y Metalogénesis (XIII MINMET-IV PIMMA); 2019

Asociación Mineralógica Argentina y Comisión de Petrología (COMPETRO) de la Asociación Geológica Argentina

Zincochromite occurs as a 200 μm sized single crystal included in an idiomorphic clinopyroxene (Di83Hd16Jo1) grain partially replaced by Cr-rich epidote, from a garnet-clinopyroxene skarn product of partial replacement of a deformed pre-Devonian pegmatite, in contact with a marble with amphibolite lenses, near of Veta Pampa scheelite skarn mine in Los Guindos mining group, Pampa de Olaen, Córdoba, Argentina. The basement is represented by gneisses, migmatites, marbles, amphibolites and ultramafic rocks of Neoproterozoic-Cambrian age and intruded by Cambrian-Ordovician granitoids. Microprobe analysis revealed ZnO contents from 17 to 19 wt. %, Cr2O3 from 57 to 60 wt. % and FeO (t) from 20 to 23 wt. %. Non-significant Al2O3 contents are reported (< 1 wt. %). V2O3 contents average 0.20 wt. %. The core of the crystal is slightly enriched in Zn+2 and varies gradually to higher Fe+2 in the rim. The Cr/Fe+3 ratio does not correlate with Zn/Fe2+ A-site substitution from core to rim. Molar proportions show that the core of the chromian spinel crystal corresponds to zincochromite (ZnCr2O4 ~48% molar) that gradually changes into a Zn rich-chromite (ZnCr2O4 ~42% molar) in the rim. A primary magmatic (ultramafic) versus a metasomatic (skarn) origin, or both, is matter of debate.