ISOTOPE GEOCHEMISTRY OF SIDERITIZED HOST ROCKS, WALTON BA DEPOSIT, KENNETCOOK SUBBASIN, NOVA-SCOTIA, CANADA

Although sideritized limestone of the Macumber Formation hosts the Ba (Cu, Pb, Zn, Ag) Walton deposit of Nova Scotia, siderite is an uncommo n gangue mineral of carbonate-hosted base metal deposits. This paper e valuates whether the abundant siderite at Walton represents a diagenet ic stage of burial or whether it represents the first stage of hydroth ermal mineralization. The Walton deposit was the largest mine of groun d barite in Canada, producing approximately 4.5 million metric tons (M t) of >90 percent BaSO4 between 1941 and 1978. It is located at the so uthern margin of the Maritimes basin and is hosted by Visean, entirely sideritized, fine-grained limestone of the lower Windsor Group. Walto n 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 -2.8 1 parts per thousand) and delta 18O(VPDB) (-6.0 to -3.21 parts per tho usand), and high Sr-87/Sr-86 (0.71035B0.72124). These attributes make the Walton siderite very distinct isotopically from the marine precurs ors and from any known hydrothermal or fresh-water siderite. Calculate d delta(18)O values for theoretical hydrothermal siderite, based on es timated salinity and temperature of the Walton hydrothermal fluids, ar e lower than those measured. Therefore, as no petrographic or isotopic evidence was found to suggest a genetic link with mineralization, sid erite at Walton is not considered to be an alteration product of the b arite-forming process. Rather, the geology, petrography, and isotope g eochemistry support a sideritization model of diagenesis under shallow burial conditions.