THE DURICO-BEIRAO (PORTUGAL) ANTIMONY-GOLD DISTRICT - PARAGENETIC AND GEOCHEMICAL EVOLUTION, METALLOGENIC IMPLICATIONS

The veins of this Hercynian district occur within the epimetamorphic series of the Durico-Beirao anticlinorium, along the edges of a straight Carboniferous syncline. A comparative paragenetic study, microprobe analyses of arsenopyrite and sphalerite, and a preliminary fluide inclusion study improve the knowledge to the metallogenic process. Pure or Ag-bearing gold is concentrated in the veins during all metallogenic process, in the different stages: with arsenopyrite-pyrite, or jamesonite, or berthierite-stibnite I, or galena-fuloppite-pyrargyrite-stibnite II-carbonates (late hydrothermal remobilization stage), or Sb-oxides (weathering). The presence of discrete W-Sn minerals in the first stage of the Sb-Au veins supports the possibility of a genetic link with the W-Sn deposits related to nearby granites. The Pb-Zn-Ag veins located in the south-eastern margin of the district present epithermal characters, and are probably more recent. The Durico-Beirao district can thus be compared to other Hercynian metallogenic provinces (French Massif Central, Central Marocco), considered as examples of geochemical interference between Pb and Sb by metallogenic superimposition. As consequences for exploration, these results suggest a southward extension of the Sb-Au district and the presence of Ag-rich gold in the Pb-Zn stage.