Frank Balint HBSc thesis abstract

Thesis Title: 
The Neys Diatreme, Coldwell Alkaline Complex, Northwestern Ontario

The Neys Diatreme is a sharply defined structure consisting of large, subround fragments set in a finely comminuted matrix of the same material.  It is located on the west side of the Coldwell Peninsula where it is seen to cut rocks of the Coldwell Alkaline Complex.  The diatreme itself is cut by later dykes.

Detailed mapping and sampling of the diatreme and the immediate host rock have been undertaken to determine the shape, extent and lithologic relationships of the structure.  Studies of the petrography, mineralogy and geochemistry of the clasts and dyke rocks have also been made.

The Neys Diatreme contains clasts of alkali feldspar syenite, layered olivine monzo-gabbro and nepheline syenites, all of which belong to the Coldwell alkaline complex.  Minor exotic clasts of undeformed porphyritic felsite and basic volcanics are also present.  In addition basic hornfels clasts are found which are believed to originate from the contact aureole of the Coldwell intrusion.

The shape of the diatreme suggests structural control of its emplacement.  Turbulent flow, the result of high velocities achieved by a gas-solid phase of a volatile-rich magma, is postulated as generating the diatreme breccia.  Block faulting is interpreted to have occurred in the Coldwell Complex.  This may be assumed to have initiated the intrusion of this type of structure.