Variability in fluid sources in the fluorite deposits from Asturias (N Spain): Further evidences from REE, radiogenic (Sr, Sm, Nd) and stable (S, C, 0) isotope data

摘要

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 (~(87)Sr/~(86)Sr= 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.