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Variability in fluid sources in the fluorite deposits from Asturias (N Spain): Further evidences from REE, radiogenic (Sr, Sm, Nd) and stable (S, C, O) isotope data

Sánchez Pérez-Cejuela, Virginia and Cardellach, Esteve and Corbella, Mercè and Vindel Catena, Elena and Martín Crespo, Tomás and Boyce, Adrian J. (2010) Variability in fluid sources in the fluorite deposits from Asturias (N Spain): Further evidences from REE, radiogenic (Sr, Sm, Nd) and stable (S, C, O) isotope data. Ore geology reviews, 37 . pp. 87-100. ISSN 0169-1368

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Abstract

Fluorite deposits in Asturias (Iberian Peninsula, N Spain) are hosted in Permo-Triassic and Paleozoic rocks.
The three main districts of Berbes, La Collada and Villabona preferentially occur along the margins of a
Mesozoic basin and comprise veins and stratabound mineralization composed of fluorite, barite, calcite,
dolomite, quartz and sulphides. Although the geological framework is similar and fluorite dominates in all
deposits, variability in sources and processes has led to each area having its own distinctive characteristics. Sr
isotope data of fluorite, calcite and barite (87Sr/86Sr=0.7080 to 0.7105) are compatible with a mixing
between seawater and an evolved groundwater that interacted with basement rocks. Sm/Nd ratios in
fluorites from Villabona district provide an isochron age of 185±28 Ma (Late Triassic–Late Jurassic),
consistent with other hydrothermal events in the Iberian Peninsula and Europe. The total REE content of
fluorite increases from Berbes to Villabona by an order of magnitude (0.4 to 9.3). The La/Lu ratio in fluorites
decreases from a mean value of 0.36 in Berbes, 0.17 in La Collada to 0.09 in Villabona indicating a strong
fractionation between LREE and HREE.
Calculated δ18O of fluids ranges from 0.3 to +7.4‰ during barite precipitation, from +0.8 to +4‰ during
quartz formation and around +3‰ during carbonate deposition. The δ34S of barite (+17 to +56‰), is
explained by sulphate reduction processes (either thermochemically or bacterially mediated) in a system
closed with respect to sulphate. The δ34S of sulphide (+0.6 to −32‰) is compatible with these processes
although bacterial processes must have dominated at Villabona. Organic matter was an important source of C
in the fluids especially in Villabona (δ13C=−14.8 to −2.5‰ in calcites and from −7.9 to −2.2‰ in
dolomites). Differences in host rock and position within the basin, and the lithology of the basement, seem to
have exerted a strong control on the chemistry of mineralizing fluids providing each district with distinctive
characteristics.


Item Type:Article
Uncontrolled Keywords:Fluorite; Sr isotopes; Sm–Nd isochron; Stable isotopes; Asturias Spain
Subjects:Sciences > Geology > Crystallography
Sciences > Geology > Petrology
ID Code:16195
Deposited On:11 Sep 2012 11:39
Last Modified:11 Sep 2012 11:39

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