AbstractFluid 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 fO2, (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 fO2 in the shallow part of the hydrothermal system promotes the oxidation of , 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.
Proterozoic Carbonate-hosted Morro Agudo Sulfide Pb-Zn District, Brazil: Mineralogical and Geochemical Evidence of Fluid Mixing during the Ore Stage
