Abstract: 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 °C), low saline (<0.6 molal), Na-K deep fluids and cool (<100 °C), oxidized, more 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 °C) in a regime of increasing f_O2, (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 slight increase of mCa²⁺ of the fluid in the lower part of the fluid mixing zone; further increase of mCa²⁺ and mMg²⁺ towards the surface promotes fluorite dissolution. Increase of f_O2 in the shallow part of the hydrothermal system promotes the oxidation of ΣH₂S to ΣSO4=, 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.