The Gays River Formation of the Lower Windsor Group in the vicinity of the Gays River Zn–Pb deposit was completely dolomitized via a volume for volume transformation prior to mineralization. Premineralization porosity was the precursor limestone porosity, comprising fenestrae, dissolution molds, and intercrystalline, intraskeletal, and growth pores, which remained essentially unchanged through dolomitization. Regionally, the dolomites (one replacement and one cement) overlapped with sediment compaction and dissolution of aragonite. The dolomites are characterized by low δ18OPDB values (−14 to −4; average −8), slightly radiogenic 87Sr/86Sr ratios (0.70778–0.70900), and locally high percentages of FeCO3 and MnCO3 (up to 13.5 and 9.5 mol%, respectively). The presented petrographic and geochemical data compiled with existing fluid-inclusion microthermometry data suggest dolomitization by hot brines, in a burial setting. High Fe and Mn concentrations south of the studied area, with progressive depletion towards the northeast and northwest, suggest either a northward flow of an Fe- and Mn-rich fluid or interaction with local sources of Fe and Mn, during single or multiple flows. By preserving the host-rock permeability, dolomitization played a role in ground preparation but was not genetically associated with the Zn– and Pb–rich fluid that mineralized the Gays River deposit.