Zn-Pb mineralization associated with a mafic dyke at Cheverie, Hants County, Nova Scotia: implications for carboniferous metallogeny

The Cheverie Zn-Pb occurrence. within the Windsor Basin of southern Nova Sc otia. is associated with intense carbonate alteration of a mafic dyke and s urrounding deformed dark grey siltstone and shale of the Carboniferous Hort on Bluff Formation. The mafic dyke, consisting of euhedral plagioclase (An( 45-60)). augitic pyroxene, and ilmenite with late-stage mesostasis and gran ophyre, is subalkaline, has within-plate affinities and is similar to E-MOR B; clinopyroxene chemistry indicates a transitional subalkaline-alkaline ch emistry. Dating (Ar-40/Ar-39 whole rock) of the mafic dyke indicates emplac ement at 315 Ma thus providing a minimum age for ductile deformation of the sedimentary rocks and a maximum age for the mineralization. The occurrence of pyrite, marcasite, sphalerite (Fe-poor and Fe-rich), and galena with bitumen is similar to the metal association at the nearby Walto n barite-base metal deposit and suggests a metallogenic affinity, Two phase (L-H2O-V) fluid inclusions in vein carbonate homogenize at 156 degrees to 265 degreesC and have salinities of 0-22 wt. % equiv. NaCl. Stable isotopes analyses indicate: (1) delta S-34 values of -4.5 and +2.2 parts per thousa nd for galena and -4.4 parts per thousand for sphalerite; and (2) delta C-1 3 values of -8.8 and -1.4 parts per thousand and delta O-18 values of +22.5 and +21.2 parts per thousand for carbonate, with the latter equating to +1 1.7 to +13.0 parts per thousand for formation temperatures of ca. 200 degre esC. The fluid chemistry is consistent with basinal-type fluids originating with in the Windsor Basin and interacting with liquid petroleum and other lower- temperature and lower-salinity fluids. A similar fluid history has been inf erred for the Carboniferous Walton and Gays River deposits of southern Nova Scotia. The timing of mineralization is consistent with the previous estim ates of ca. 300 Ma for other mineralization hosted by the Horton and Windso r groups in the Carboniferous of Nova Scotia.