Mineralogical and isotopic study of magnesite veins in the Evia and Gerakini ultramafites (Greece)
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Data di Pubblicazione:
2021
Citazione:
Mineralogical and isotopic study of magnesite veins in the Evia and Gerakini ultramafites (Greece) / M. Bussolesi, G. Grieco, E. Tzamos, A. Cavallo, P. Marescotti, L. Crispini, A. Kasinos, A. Zoubulis. ((Intervento presentato al convegno RawMat2021 International COnference on Raw Materials and Circular Economy tenutosi a Atene nel 2021.
Abstract:
Magnesite ore deposits are the main source of Mg for the industry and are used in the
production of various kinds of magnesia. They are closely associated to ophiolite
geological contexts, and are usually hosted within variously altered harzburgites and
dunites.
Greece hosts exploitable ophiolite-related magnesite deposits in two areas, located in
the Evia island and in the Chalkidiki peninsula. In the present contribution we take into
consideration magnesite veins at Kymasi (Evia) and Gerakini (Chalkidiki). The Kymasi
magnesites are hosted in peridotites in the tectonic unit of the Pelagonian Zone of
Northern Evia. Gerakini is located in the Vardar Zone ophiolite belt, and forms the
Gerakini-Ormylia ophiolite complex.
Both areas host major magnesite deposits, mainly comprising shallow stockwork-type
ores hosted within variably altered dunites and harzburgites locally intruded by
pyroxenitic and gabbroic veins.
At Kymasi, field work was focused on a well exposed network of magnesite veins that
show the following zoning from core to rim: a thick massive magnesite central portion,
a serpentinized hydraulic breccia with magnesite cement and a partially dolomitized
peridotite. The host rock is unaltered peridotite. All contacts are irregular and sharp.
At Gerakini sampling was focused on two active open pits, Ugo and Antonium.
Magnesite samples show a variety of textures, comprising massive magnesite,
cauliflower magnesite, fibrous magnesite and brecciated magnesite. Host rocks are
serpentinized dunites.
XRD data show that, differently from Kymasi, at Gerakini magnesite veins contain a
variable amount of dolomite up to 16%.
Mineral chemistry data show that, at Kymasi, high-Cr spinels occur in the breccia,
while partially dolomitized peridotite and unaltered peridotite spinels are lower in Cr.
The isotopic analyses show very similar δ18O and δ13C values in Kymasi and
Gerakini, also consistent with other ophiolite-related magnesite mineralizations in the
Balkans. The isotopic values suggest that the CO2 was originated from the
decarboxylation of organic matter present in the sediments of the area.
Considering the origin of the CO2 and the shallow nature of the stockwork
mineralization, it can be concluded that both Kymasi and Gerakini magnesites were
formed by infiltration of CO2-rich meteoric waters which interacted with peridotites.
The interaction caused the leaching of Mg, which was transported by the fluids through
preferential pathways, possibly reactivating older shear zones, and finally deposited in
the form of magnesite once it reached saturation at shallow depths.
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Elenco autori:
M. Bussolesi, G. Grieco, E. Tzamos, A. Cavallo, P. Marescotti, L. Crispini, A. Kasinos, A. Zoubulis
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