The Zn-Pb carbonate-hosted deposit of Jubilee, Cape Breton, Nova Scotia, shows organic matter and clay mineral alteration assemblages that are attributed to hydrothermal processes. The metal-rich brines had a high iron activity that slightly increased the iron content in chlorite within and immediately around the Zn-Pb deposit. The illite crystallinity index and the proportion of interstratified illite-smectite day minerals decrease whereas the reflectance (R o ) increases (0.67-0.95%) in the mineralized areas indicating higher temperatures in these areas relative to that in the nonmineralized background. These R o values indicate a maximum burial temperature near 100 degrees C in the latter and temperatures ranging from a minimum of 150 degrees C to a maximum of 230 degrees C in the former. The day mineral indicators are in agreement with these conclusions.Based on temperature and kinetics of organic matter alteration, the hydrothermal activity that produced the Jubilee deposit was active for a relatively short period of time. Only a few tens or a few hundreds of thousand years would have been necessary to increase the R o from its background (0.67%) value to a maximum value of 0.95 percent observed near the Jubilee fault and in the main Zn-Pb sulfide zone. The duration of this heating is assumed to correspond to that of the mineralizing process.