CARBON AND OXYGEN-ISOTOPE GEOCHEMISTRY OF CALCITE FROM THE JUBILEE ZN-PB DEPOSIT, CAPE-BRETON ISLAND

The Jubilee Zn-Pb deposit, Nova Scotia, is one of many similar prospec ts hosted within Early Carboniferous limestones in the Maritime region of eastern Canada. At Jubilee, laminated limestone is overlain by tra nsitional, interstratified limestone and anhydrite, with massive anhyd rite capping the sequence. Mineralization is stratabound and hosted wi thin the Pembroke breccia, which probably formed as a result of dissol ution of anhydrite interbeds within carbonate host-rock. Mineralized-m atrix breccia is the main host of the ore, and contains pyrite, marcas ite, sphalerite, galena and barite, in addition to calcite. Liquid hyd rocarbons and solid bitumen are abundant, particularly within sulfide- rich domains, and also occur as inclusions within sphalerite and barit e. Carbon and oxygen isotope values have been obtained for five variet ies of calcite from the Jubilee deposit: (1) finely laminated, unminer alized host limestone (pelsparite), delta(18)O between +26.3 and +27.1 parts per thousand SMOW, delta(13)C between +0.4 and +2.2 parts per t housand PDB, (2) early diagenetic calcite, delta(18)O = +29.1 parts pe r thousand, delta(13)C = +1.4 parts per thousand, (3) micritic to spar ry calcite (replacement of anhydrite?), locally associated with minor, disseminated sulfides, delta(18)O between +24.3 and +25.5 parts per t housand, delta(13)C between -24.0 and -22.8 parts per thousand, (4) ma in ore-stage, breccia-cementing calcite, delta(18)O between +23.9 and +24.7 parts per thousand, delta(13)C between -27.1 and -24.9 parts per thousand, and (5) post-mineralization, drusy calcite, delta(18)O betw een +21.6 and +22.5 parts per thousand, delta(13)C between -23.4 and - 23.2 parts per thousand. Using the isotopic data for calcite from Grou ps 3 and 4, and previously reported results on fluid inclusions (90-15 0 degrees C), an average delta(18)O value of +9 +/- 3 parts per thousa nd was calculated for the mineralizing fluid. This value is typical of an evolved basinal brine, as has been suggested for other deposits in the area. However, the delta(13)C values (-27.1 to -22.8 parts per th ousand) of calcite from Groups 3, 4 and 5 are much lower than ore-stag e calcite from the other deposits in the region (-10 to +3 parts per t housand). Anhydrite dissolution, association of hydrocarbons with sulf ides, and very low delta(13)C values for most secondary calcite at Jub ilee together suggest coupled oxidation of hydrocarbons, reduction of sulfate and precipitation of calcite at the site of mineralization. Co ntribution of inorganic carbon (e.g., from dissolution of host limesto ne) was very limited during calcite precipitation associated with mine ralization.