Abstract The carbonate Vegadeo Fm (Lower-Middle Cambrian, NW Spain) hosts abundant Zn-Pb mineralization. Minor stratiform ore showings occur in mineralogically and geochemically undisturbed limestones of the Lower Member. They are interpreted as related to diagenetic processes, with sulfur derived from the abiogenic reduction of sulfates interbedded in the carbonates and lead leached from the nearby detrital rocks. The major mineralization, stratabound deposits in the Upper Vegadeo Fm and discordant replacements (Rubiales-type), occurs in relationship with pervasive epigenetic silicification and minor hydrothermal breccias. They are interpreted as of Late Variscan age. Here, the mineralization seems to be formed by reaction of the hosting carbonates with low-saline (<7 wt% NaCl eq.) water-rich fluids that circulated along major lithologic contacts or extensional faults. Isotopic composition of the hydrothermal fluids falls within the field of low-grade metamorphic or basinal waters (δ 18 0=-1.0 to +6.3%; δD=-43 to -31%0). The ore-forming process occurred at temperatures between 150 and 250°C and at low fluid pressures (<500 b). Lead isotopes suggest that most of the base metals were derived from the hydrothermal remobilization of the diagenetic ores in a “lead-frozen” system. Some of the sulfur appears to have had the same source, but there was also a significant input from biogenically-reduced sulfur from the enclosing shales. These Variscan ores have many of the descriptive features of carbonate-hosted deposits, but the fluid compositions, P-T conditions of formation, and tectonic setting were fundamentally different. They can be interpreted as equivalent to MVT deposits, but formed in the internal zones of orogenic belts.