Although sideritized limestone of the Macumber Formation hosts the Ba (Cu, Pb, Zn, Ag) Walton deposit of Nova Scotia, siderite is an uncommon gangue mineral of carbonate-hosted base metal deposits. This paper evaluates whether the abundant siderite at Walton represents a diagenetic stage of burial or whether it represents the first stage of hydrothermal mineralization.The Walton deposit was the largest mine of ground barite in Canada, producing approximately 4.5 million metric tons (Mt) of >90 percent BaSO 4 between 1941 and 1978. It is located at the southern margin of the Maritimes basin and is hosted by Visean, entirely sideritized, fine-grained limestone of the lower Windsor Group.Walton siderite is finely crystalline and replaces the precursor limestone without textural disruption; it generally predates barite and sulfides. The siderite is characterized by low delta 13 C values (-5.1 to -2.81ppm) and delta 18 O VPDB (-6.0 to -3.21ppm), and high 87 Sr/ 86 Sr (0.71035B0.72124). These attributes make the Walton siderite very distinct isotopically from the marine precursors and from any known hydrothermal or fresh-water siderite. Calculated delta 18 O values for theoretical hydrothermal siderite, based on estimated salinity and temperature of the Walton hydrothermal fluids, are lower than those measured. Therefore, as no petrographic or isotopic evidence was found to suggest a genetic link with mineralization, siderite at Walton is not considered to be an alteration product of the barite-forming process. Rather, the geology, petrography, and isotope geochemistry support a sideritization model of diagenesis under shallow burial conditions.