Please use this identifier to cite or link to this item:
|Title: ||In situ LA-ICP-MS trace element analysis of magnetite as a vector towards mineral exploration: A comparative case study of Fe-skarn deposits from SW Iberia (Ossa-Morena Zone)|
|Authors: ||Maia, Miguel|
Trace element analysis
|Issue Date: ||2022|
|Publisher: ||Journal of Geochemical Exploration|
|Citation: ||Maia, M., Barrulas, P., Nogueira, P. M., Mirão, J., & Noronha, F. (2022). In situ LA-ICP-MS trace element analysis of magnetite as a vector towards mineral exploration: A comparative case study of Fe-skarn deposits from SW Iberia (Ossa-Morena Zone). Journal of Geochemical Exploration, (Version of Record 7 January 2022). https://doi.org/10.1016/j.gexplo.2021.106941|
|Abstract: ||The Azenhas and Alvito Fe-deposits are located at SW of the Iberian Variscan belt, in a wide Fe-Zn ore district
(Montemor-Ficalho Belt), part of the Ossa-Morena Zone. Both deposits are dominantly composed of magnetite
ores that display distinct ore formation processes and, at the Azenhas deposit, massive magnetite ores are mainly
hosted in amphibolites (Middle Cambrian – Ordovician), with a genesis arguably associated with metamorphic-
metasomatic reactions promoted by fluid circulation through several thrust faults that led to and expressive
tectonic pilling. Contrastingly, the Alvito massive magnetite ores are formed by the emplacement of a gabbro-
dioritic suite in contact with calcite-dolomite marbles, constituting a typical calcic exoskarn Fe-skarn deposit.
Primary and secondary magnetite were identified and characterized, and further selected for in situ laser ablation
coupled inductively mass spectroscopy (LA-ICP-MS) trace element analysis. Results show that primary magnetite
(Mag I) from the Azenhas deposit is discriminated by higher concentrations of Mg, Cr, Mn, Zn, Co, and Sn,
whereas secondary magnetite (Mag II) is depleted in most trace elements, although displaying relatively higher
concentrations of V, Ga, Mo, and Pb. The application of TMg-Mag geothermometer reinforced the discriminatory
indexes, with Mag I displaying higher-temperature estimations (ca. 770 ◦C) when compared to Mag II (ca.
420 ◦C), thus suggesting that primary ores are associated to higher temperature processes than previously
Characterization of the ores from Alvito deposit revealed primary magnetite characterized by abundant
ilmenite and Al-spinel oxy-exsolutions which led to high measured Al concentrations in magnetite. The trace
element content indicates high-temperature hydrothermal magnetite, underlining the contribution of hot hy-
drothermal fluids from the igneous body emplacement, also supported by the TMg-Mag geothermometer (ca.
685 ◦ C). The anomalous presence of Co (max. 156 ppm) and Ni (max. 100 ppm) concentrations in Mag I from
Alvito, along with pentlandite-magnetite assemblages, suggest that prone conditions were sustained for the
development of Ni-bearing ores and that magnetite composition could be an interesting geochemical proxy for
the exploration of such mineralization.
The Mn + Al versus Ti + V discriminant diagram shows that primary ores from both deposits plot in the skarn
field. The combination of magnetite analyses with whole-rock geochemistry and field geology, allowed us to
define criteria that can be applied in the discrimination of Fe-deposits and contribute to improve the geological
models of the studied ore deposits, thus beneficiating future exploration in SW Iberia|
|Appears in Collections:||GEO - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.