Fluid inclusion and geochemical evidence for fluid mixing in the genesis of Ba-F (Pb-Zn) lodes of the Spanish central system

Fluid inclusion data and geochemical evidence lead to a genesis of Ba-F (Pb-Zn) lodes of the Spanish Central System as related to fluid mixing of hot (>300 ~ low saline ( 2.8 molal), Na-K-Ca-Mg brines of phraeatic origin. Ore formation took place at relative low depth and temperatures (from 270 to 120~ in a regime of increasingfoz, (Ca + Mg)/Na ratio and pH of the fluids towards the surface. Such evolution destabilizes the chloride metal complexes, allowing for the precipitation of Zn and Pb carried by the deep solution. Vertical fluorite-baryte zonation is explained in terms of mineral solubilities. Fluorite deposition in the deeper mineralized zone is related to a slig~ht increase of inCa 2+ of the fluid in the lower part of the fluid mixing zone; further increase of inCa 2+ and mMg 2+ towards the surface promotes fluorite dissolution. Increase offo~ in the shallow part of the hydrothermal system promotes the oxidation of ZH2S to ZSO2, resulting in baryte formation. We propose an ore genesis related to fluid mixing in shallow hydrothermal systems associated with an extension of Permo-Triassic age. Such interpretation is in agreement with the present day ideas for the genesis of many of the Ba-F deposits in the Hercynian Belt of Europe.