Abstract

Mineralizing fluids for Pb-Zn-Ba deposits located on the platform of the Fundy/Magdalen Basin, were hot (150°-250°C) saline brines that were very similar isotopically and chemically to oil-field and basinal brines. The brines probably originated from under the Windsor Group evaporites in the southern part of the deep Magdalen Basin. Horton Group clastic rocks and the Pembroke Breccia were likely aquifers for the brines. A Rb-Sr isochron indicates a homogenizing event at 300 ± 6 Ma in the Horton strata directly below the Pembroke Breccia; an event that coincides with a pulse of regional tectonism recorded in the stratigraphic succession.

Mathematical modelling of excess pore fluid pressure buildup under the evaporite seal was carried out using the TWODEPEP finite element program. Results indicate that during periods of rapid sediment or tectonic loading, fluid pressures could have approached the lithostatic load. At least one sudden massive hydrofracturing, fluid expulsion event occurred by 300 Ma and possibly as early as late Windsor time (336 Ma).