Geological and Geochemical Investigation of Plutonic Suites in the Sisson Brook Area York County, New Brunswick

Abstract

A sequence of plutonic rocks in the Sisson Brook claims group owned by Kidd Creek Mines Ltd., range in composition from gabbro at the margin through diorite and quartz diorite to the Nashwaak Granite at the core. Field relations show the gabbros to be oldest, granites the youngest. A regional foliation developed in the gabbro, diorite and to a lesser extent quartz diorite is evidence they have undergone a regional metamorphic event. The contortion into tight ptygmatic folds of small granitic dykes in quartz diorite outcrops near the Nashwaak Granite attests to a compressional metamorphic event. Mineralogically however, there is no evidence that suggest the rocks have undergone more than a low grade of metamorphism. With the exception of location C1, the granites are not foliated, indicating their emplacement post dated metamorphism. The rocks are calc-alkaline and metaluminous with the exception of the granites which are peraluminous. This is consistent with trends seen in chemical variation diagrams which suggest that, excluding the granites, the rocks are co-magmatic. It is proposed here that the latent heat of crystallization from cooling gabbro, diorite, and quartz diorite magmas melted enclosing country rock producing a melt of granite composition. All rock types have been effected to various degrees, by a late stage K, Rb-metasomatism.