Publication: Sources and composition of fluids associated with fluorite
deposits of Asturias (N Spain)
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Publication Date
2009
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Blackwell Publishing
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Abstract
The fluorite deposits of Asturias (northern Iberian Peninsula) are hosted by rocks of Permo-Triassic and Palaeozoic
age. Fluid inclusions in ore and gangue minerals show homogenization temperatures from 80 to 170C and the
presence of two types of fluids: an H2O–NaCl low-salinity fluid (<8 eq. wt% NaCl) and an H2O–NaCl–CaCl2 fluid
(7–13 wt% NaCl and 11–14 wt% CaCl2). The low salinity and the Cl ⁄ Br and Na ⁄ Br ratios (Cl ⁄ Brmolar 100–700
and Na ⁄ Brmolar 20–700) are consistent with an evaporated sea water origin of this fluid. The other end-member
of the mixture was highly saline brine with high Cl ⁄ Br and Na ⁄ Br ratios (Cl ⁄ Brmolar 700–13 000 and Na ⁄ Brmolar
700–11 000) generated after dissolution of Triassic age evaporites. LA-ICP-MS analyses of fluid inclusions in fluorite
reveal higher Zn, Pb and Ba contents in the high-salinity fluids (160–500, 90–170, 320–480 p.p.m. respectively)
than in the low-salinity fluid (75–230, 25–150 and 100–300 p.p.m. respectively). The metal content of the
fluids appears to decrease from E to W, from Berbes to La Collada and to Villabona. The source of F is probably
related to leaching of volcanic rocks of Permian age. Brines circulated along faults into the Palaeozoic basement.
Evaporated sea water was present in permeable rocks and faults along or above the unconformity between the
Permo-Triassic sediments and the Palaeozoic basement. Mineralization formed when the deep brines mixed with
the surficial fluids in carbonates, breccias and fractures resulting in the formation of veins and stratabound bodies
of fluorite, barite, calcite, dolomite and quartz and minor amounts of sulphides. Fluid movement and mineralization
occurred between Late Triassic and Late Jurassic times, probably associated with rifting events related to the
opening of the Atlantic Ocean. This model is also consistent with the geodynamic setting of other fluorite-rich
districts in Europe.