The Coldwell Complex, of Neo-Helikian age intrudes Archean metasedimentary and metavolcanic rocks during three intrusive episodes. The major rock units of two episodes, Center I and Center III, were studied in petrographic detail. In addition, exotic and cognote xenoliths were examined. An overview of mafic and felsic dikes and structural features completed the study.
Field mapping and microscopic examination were used to detail changes in lithologies. Several x-ray diffraction determinations were made on opaque minerals.
The study defined textural changes across both the Center I border gabbro and ferro-augite syenite. This will aid in the formulation of an evolutionary model for the western contact and perhaps the intrusion in general.
Three textural and mineralogical variations were noted in Center III quartz-syenite and a porphyritic and contaminated porphyritic-porphyroblastic quartz-syenite were defined.
Structural relationships indicated a correlation between joint forming episodes and dike forming episodes.
Studies of mafic and felsic dikes and correlation with structural data indicated some dike forming episodes were closely related to some joint forming episodes.