The formation of ore deposits in the Lavrion Pb-Zn-Ag district was associated with Miocene detachment that accommodated orogenic collapse and exhumation of high-grade nappes across the ductile-brittle transition. This district consists of (1) low-grade porphyry Mo style, (2) Cu-Fe skarn, (3) high-temperature carbonate replacement Pb-Zn-Ag, and (4) vein and breccia Pb-Zn-Ag mineralization. The vein and breccia mineralization locally contains high-grade silver in base metal sulfides that are cemented by fluorite and carbonate gangue. The rare earth element contents of these gangue minerals, chondrite-normalized patterns, and fluid inclusion studies suggest that they precipitated from a low-temperature hydrothermal fluid. Primary and pseudosecondary fluid inclusions in fluorite and calcite are characterized by a wide range of homogenization temperatures (92°–207°C) and salinities of up to 17.1 wt % NaCl equiv. Secondary fluid inclusions only represent <5 vol % of the total fluid trapped. Fluids extracted from inclusions in fluorite have values of δD = –82.1 to –47.7‰ (Vienna-standard mean ocean water [V-SMOW]) and δ18O = –10.4 to –5.1‰ (V-SMOW). These data and low ratios of Cl/Br measured by crush-leach analyses for fluids in fluorite (102–315) and calcite (162–188) are compatible with the ore fluid being the result of mixing of meteoric water with evaporated seawater. These data suggest that fluids leading to the deposition of late Pb-Zn-Ag–rich vein- and breccia-style mineralization in Lavrion were related to circulation of mixed evaporated seawater and meteoric fluids that was enhanced by brittle deformation. This contrasts with the fluids of magmatic origin related to the formation of low-grade porphyry Mo, Cu-Fe skarn, and high-temperature carbonate replacement deposits spatially related to the Plaka granodiorite.