Northeast Haliburton – Bancroft Area

Northeastwards the Haliburton-Bancroft nepheline syenite and syenite gneiss belt continues to the Ottawa River but with only small, isolated occurrences of nepheline syenite in Denbigh, South Algoma, Sebastopol, Brougham and Admaston Townships (Hewitt, 1961, p. 102). These occurrences are usually associated with nepheline- free syenites, paragneisses and limestones and are generally similar to the more extensive belt to the southwest. Lumbers (1982) has recently published an account of the geology of Renfrew County which includes the northeastwards continuation of the Haliburton-Bancroft area and takes the mapping beyond the area covered by Hewitt (1961). The approximate area in Renfrew County designated as alkaline syenites by Lumbers (1982, Maps 2459-62) is indicated on Fig. 55 and is seen to be very extensive indeed, but there is an almost equal area of peralkaline granites together with small areas of mafic alkaline rocks which are not shown on the map. The relative paucity of nepheline syenites in this area, but great abundance of peralkaline syenites and granites, distinguishes it from the better known areas further south. The commonest lithology of the syenites comprises perthite, albite, sodic pyroxene, amphibole, biotite and accessories; locally quartz is present and such rocks grade into the peralkaline granites. The granites are similar to the syenites with sodic pyroxene the dominant mafic mineral, and both rock types commonly contain patches and reticulating networks of veinlets of sodic pyroxene which are similar in appearance to those found in fenites (Lumbers, 1982, Photo 9). No detailed petrological work has yet been done on the most northeasterly parts of the Haliburton- Bancroft area, notably in the townships of Westmeath, Ross, Wilberforce and Bromley (Fig. 55).