Gregory R. Laws HBSc thesis abstract

The Coldwell Complex, a group of Neohelikian alkaline rocks cutting the Archean Schreiber-White River Greenstone Belt, is the result of three westward migrating centres of intrusion.  The Little Pic River Breccia Zone is located two to three kilometers from the western margin.  Centre III syenites, xenolith compositions and dike structures are the major topics of discussion in this thesis.

Field mapping and detailed petrographic studies allowed an intrusional history to be derived for the local area.

The Little Pick River Breccia Zone is determined to be an intrusive breccia with post-intrusive block faulting altering the structure to the west.  Different structural levels are interpreted to be present in the Coldwell Complex (Mitchell and Platt, 1982).  Considering the high volume of country-roick metavolcanic xenoliths, it is surmised that the Little Pic River Breccia Zone is a "near to roof" assemblage which was downfaulted.

Textural variants of the early Centre III syenites described as coarse-grained, contaminated-porphyroblastic and fine-grained, are present.  Several colour variations of later Centre III quartz syenites also show widely variable textural relationships, grading from medium-grained to pegmatitic. 

Metavolcanics and Centre II xenoliths show varying degrees of metasomatism, resulting in porphyroblast growth and/or complete alteration to secondary mineral assemblages.

Microsyenite dikes are an important structural feature, locally defining a regional stress pattern.  Compositons vary widely in this group, hence no particular dike phase can be correlated to a specific joint set.