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

Abstract

The Cheverie Zn-Pb occurrence, within the Windsor Basin of southern Nova Scotia, is associated with intense carbonate alteration of a mafic dyke and surrounding deformed dark grey siltstone and shale of the Carboniferous Horton Bluff Formation. The mafic dyke, consisting of euhedral plagioclase (An45-60), augitic pyroxene, and ilmenite with late-stage mesostasis and granophyre, is subalkaline, has within-plate affinities and is similar to E-MORB; clinopyroxene chemistry indicates a transitional subalkaline-alkaline chemistry. Dating (40Ar/39Ar whole rock) of the mafic dyke indicates emplacement 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 Walton barite-base metal deposit and suggests a metallogenic affinity. Two phase (LH20-V) fluid inclusions in vein carbonate homogenize at 156° to 265°C and have salinities of 0-22 wt. % equiv. NaCl. Stable isotopes analyses indicate: (1) δ34S values of -4.5 and +2.2 ‰ for galena and -4.4 ‰ for sphalerite; and (2) δ13C values of -8.8 and -1.4 ‰ and δ18O values of +22.5 and +21.2‰ for carbonate, with the latter equating to +11.7 to +13.0 ‰ for formation temperatures of ca. 200°C. The fluid chemistry is consistent with basinal-type fluids originating within the Windsor Basin and interacting with liquid petroleum and other lower-temperature and lower-salinity fluids. A similar fluid history has been inferred for the Carboniferous Walton and Gays River deposits of southern Nova Scotia. The timing of mineralization is consistent with the previous estimates of ca. 300 Ma for other mineralization hosted by the Horton and Windsor groups in the Carboniferous of Nova Scotia.