A comparison of magnetic character and alteration in three granite drill cores from eastern Canada

Bulk magnetic susceptibility (BMS) measurements have been made on granite drill cores from the St. George batholith (New Brunswick), the South Mountain batholith (Nova Scotia), and the Wedgeport pluton (Nova Scotia). The primary magnetite concentrations of the two Nova Scotia cores are statistically indistinguishable, thus lending support to the hypothesis that the Wedgeport pluton, despite being 50 Ma younger, is a satellite of the South Mountain batholith.The St. George core has a primary magnetite concentration over 30 times greater than the Nova Scotia cores, but low-temperature alteration (attributable to subsurface weathering) has greatly reduced its magnetite content. The two Nova Scotia S-type granites are shown to fall into the ilmenite-series category, whereas the St. George granite, which is either S- or A-type, is transitional between the magnetite and ilmenite series.The general observation of intergranular hematite and reduced BMS in the outcrops of some granites is suggested to have important consequences for primary oxidation studies and aeromagnetic interpretation.