Isotope geochemistry of Los Santos (Spanish Central System) calcic scheelite skarn: constraints on the source of the fluids and tungsten

The Los Santos mineralization is the largest tungsten-bearing skarn of the Iberian Peninsula. Its is a complex skarn that share many features with equivalent tungsten-bearing calcic mesozonal reduced ones elsewhere. The mineralization is related with a hedenbergite-rich skarn superimposed by a younger amphi-bole-rich one in the contact with monzogranites, that are also pervasively replaced by a plagioclase-rich endoskarn; all these metasomatic rocks host disseminated scheelite. δ18O composition of the silicate minerals indicates that homogeneous deep fluids of likely magmatic/metamorphic origin were dominant in the formation of both the early and late skarns. The Sr and Nd isotope composition and the REE contents of the scheelite suggest that the tungsten derived from the nearby rocks (granitoids and siliciclastic sediments) and a deep, unexposed, highly evolved granite equivalent to those hosting the widespread W-Sn mineralization in the Variscan Belt of Iberia.