Abstract

Carbonate-hosted zinc and lead deposits occur in two settings in the Humber Terrane of western Newfoundland: (i) associated with dolomitized units and breccias in Cambrian and Ordovician shelf-facies carbonate rocks; and (ii) as open-space, vein, and breccia fillings associated with calcite within or near the margins of Carboniferous basins. We report 11 new lead-isotope analyses from deposits of the former type on the Great Northern Peninsula (the GNP suite) and 8 new analyses from deposits of the latter type on the Port au Port Peninsula and the northern part of the Bay St. George subbasin (BSG suite).The isotopic composition of lead in galena from the GNP suite defines linear trends in which the lead-isotope ratios increase with stratigraphic height in the Cambro-Ordovician sequence. These trends are interpreted as mixing lines; samples at the non-radiogenic end have very low 207Pb/204Pb but high 208Pb/204Pb ratios relative to 206Pb/204Pb and are interpreted as representing substantial evolution in high-grade metamorphic rocks of the Grenville Structural Province that underlie the sedimentary succession. The more radiogenic source(s?) is probably located within the sedimentary pile and contributed metals to the fluids during their migration to the deposition sites.Lead isotopes in deposits in the Bay St. George area cluster near average crustal model growth curves. Metal sources for these deposits, considered by previous workers as diagenetic in origin, are interpreted as being clastic sediments within the sedimentary basin.

You do not currently have access to this article.