An aeromagnetic anomaly, similar to the ones associated with known Monteregian plutons, occurs over a low hill at Grand Bois, about 4 km west of Mount Johnson. In the area of this anomaly, a gravity high of over 1.60 mgals and also two outcrop localities with igneous rocks of Monteregian types, were detected. Therefore, it is concluded that the aeromagnetic anomaly is caused by a blind Monteregian pluton, for which the name "Grand Bois Intrusion" is proposed.

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