Genesis and evolution of the San Manuel iron skarn deposit (Betic Cordillera, SW Spain)

Gonzalez-Perez, Igor ; Gonzalez-Jimenez, Jose M. ; Gervilla, Fernando ; Fanlo, Isabel (Universidad de Zaragoza) ; Tornos, Fernando ; Colas, Vanessa (Universidad de Zaragoza) ; Arranz, Enrique (Universidad de Zaragoza) ; Hanchar, John ; del Mar Abad-Ortega, Maria ; Moreno-Abril, Antonio J. ; Carrion, Maria ; Noval, Samuel

Resumen: The San Manuel magnesian skarn is an iron deposit hosted in dolomitic marbles from a tectonic slice imbricated within the Ronda peridotites, in the westernmost part of the Betic Cordillera, Spain. According to the dominant mineral assemblage, the skarn is subdivided into three different zones, (1) forsterite +/- calcite skarn, (2) calcite +/- chlorite +/- serpentine skarn, and (3) Ca-amphibole skarn. The main ore in the skarn is a similar to 2.5 m thick, massive ore body situated in the middle of the sequence. In this paper, we firstly report a comprehensive major to trace element composition, texture, microstructure, and mineralogy characterization for zoned magnesioferritemagnetite grains of the San Manuel deposit using a combination of (1) laser ablation inductively coupled plasma mass spectrometer, (2) focused ion beam combined with transmission electron microscopy, and (3) electron back-scattered diffraction. We have defined four different magnesioferrite-magnetite generations. A complete sequence of zoning includes cores of magnesioferrite (Mag-1; MgO up to 10.6 wt%) overprinted by three successive generations of magnetite, namely Mag-2, Mag-3, Mag-4. Mag-2 (MgO < 4 wt%), hosts composite forsterite +/- calcite +/- chlorite inclusions, consistently with high Si, Ca, and Sr (average: 8204 ppm, 8980 ppm, and 49 ppm respectively) contents detected by in situ laser ablation inductively coupled plasma (LA-ICP-MS). Mag-3 replacing former Mag-1 and Mag-2 includes nanometric spinel and gahnite exsolutions detected by focused ion beam combined with a transmission electron microscope (FIB-TEM), which is consistent with its high Al, Ti, V, and Ga (average: 5073 ppm, 368 ppm, and 20 ppm, respectively) trace element concentration. Mag-4 is the Fe-richest magnetite (up to 94.16 wt% FeOtotal) forming the outermost rims in magnetite grains, and exhibiting the lowest total trace element contents. Approaches in temperature estimations employing magnetitespinel exsolutions in Mag-3 suggest that the minimum temperature of the prograde stage reached temperatures below 700 degrees C, whereas Mag-4 should be formed during the retrograde stage. Magnetite microstructure studied by electron backscatter diffraction (EBSD) suggests Mag-4 formation under fluid-assisted dynamic conditions, which is consistent with the tectonic evolution of the emplacement. We propose that the San Manuel deposit formed by pulsed hydrothermal fluids derived from anatexis of crustal rocks during peridotite emplacement, promoting reequilibration processes that led to the magnesioferrite-magnetite zoning.

Idioma: Inglés

DOI: 10.1016/j.oregeorev.2021.104657

Año: 2022

Publicado en: ORE GEOLOGY REVIEWS 141, 104657 (2022), [21 pp]
ISSN: 0169-1368

Factor impacto JCR: 3.3 (2022)

Categ. JCR: GEOLOGY rank: 5 / 48 = 0.104 (2022) - Q1 - T1
Categ. JCR: MINING & MINERAL PROCESSING rank: 6 / 20 = 0.3 (2022) - Q2 - T1
Categ. JCR: MINERALOGY rank: 8 / 29 = 0.276 (2022) - Q2 - T1

Factor impacto CITESCORE: 6.2 - Earth and Planetary Sciences (Q1)

Factor impacto SCIMAGO: 1.172 - Economic Geology (Q1) - Geology (Q1) - Geochemistry and Petrology (Q1)

Financiación: info:eu-repo/grantAgreement/ES/MCIU/RTI2018-099157-A-I00
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PRE2019-088262
Financiación: info:eu-repo/grantAgreement/ES/MINECO/RYC-2015-17596

Tipo y forma: Article (Published version)

Área (Departamento): Área Petrología y Geoquímica (Dpto. Ciencias de la Tierra)
Área (Departamento): Área Cristalografía Mineralog. (Dpto. Ciencias de la Tierra)