NEW GEOLOGICAL MAPS OF THE GOLDENVILLE AND HALIFAX GROUPS, SOUTHWESTERN NOVA SCOTIA: AN INVESTMENT IN UNDERSTANDING THE MEGUMA TERRANE AND ITS RESOURCES

Twenty-five, 1:50 000-scale geological maps of the Meguma terrane in southwestern Nova Scotia were released in the Fall of 2012 by the government of Nova Scotia. These maps are the culmination of 14 years of field mapping, combined with collaborative petrological, geochemical, and geochronological studies. They resolve some long-standing controversies about stratigraphic relations and age, and will encourage mineral exploration that could have long-term benefits for the province. Meguma terrane is the most outboard northern Appalachian terrane and is characterized by a 13 km-thick, Lower Cambrian to Lower Ordovician turbiditic sequence. The traditional two-fold division into the metasandstone–dominated Goldenville Group and the overlying slate-dominated Halifax Group has been retained, but the Chebogue Point shear zone divides these groups into western and southern stratigraphic packages containing different formations. The lower part of the Goldenville Group contains the trace fossil Oldhamia, which suggests an age of late Early Cambrian, whereas the coticule-bearing uppermost formation yielded an acritarch species consistent with Middle Cambrian (Epoch 3) age. The conformably overlying Halifax Group includes basal pyritiferous units that yielded a Late Cambrian (Furongian) assemblage of acritarch species. Overlying formations contain Early Ordovician graptolites and acritarchs of similar age. Samples collected up section from the graptolite occurrence yielded acritarch species that are indicative of the later Tremadocian and Floian. In both packages, psammitic rocks are dominantly feldspathic wacke, and have mineralogical and geochemical compositions indicative of a similar source area dominated by quartz and plagioclase with a likely deposition in a rift along the Gondwanan margin. Up section fine material increases in relative abundance and sediments are derived from more ancient cratonic areas indicated by detrital zircon ages and ε_Nd values. The Meguma terrane has long been known for its gold deposits. The new geological map has changed the traditional understanding of this resource by showing that some gold mineralization is stratigraphically controlled and disseminated throughout the host formations and is not entirely related to quartz veining as assumed in earlier models.