Matthew Melchiorre HBSc thesis abstract

Thesis Title: 
Petrology and Geochemistry of the Copper Bar Cu-Ni-PGE Prospect, Northern Ontario

The Copper Bar Prospect, located southwest of Thunder Bay, Ontario is of interest for Ni-Cu-PGE exploration. Five historic trenches are found along the dike though there are no records of any results from them. The Copper Bar dike is a tholeiitic diabase intrusion, dominated by a sub-ophitic texture of plagioclase and pyroxene (primarily orthopyroxene). Sulphide mineralization is fairly consistent along the dike forming blebby fine- to medium-grained blebs. Fine-grained disseminations of chalcopyrite, pyrite and sphalerite are found throughout the dike. Secondary chalcopyrite mineralization is found in fractures in the more heavily altered samples. Three groupings can be distinguished petrographically and geochemically, Group one corresponding to more altered portions of the dike where complex mineralization is observed with galena, pyrrhotite, pyrite, magnetite, sphalerite, bornite, chalcopyrite, covellite, chalcocite and pentlandite with other trace sulphide mineralization. Group two represents relatively unaltered samples dominated by sub-ophitic texture. Mineralization in these samples is minimal, usually occurring as fine-grained disseminations of chalcopyrite, sphalerite and pyrite. Group three occurs as a more coarse-grained sample with overprinting blebby magnetite, pyrolusite and ilmenite phases. Generally, group three is similar to group one. Secondary pulses of magma seem to have effected the more altered samples with chalcopyrite rimming some sulphide grains and filling fractures. Overprinting sulphides and coarse- grained zones also indicate possible secondary magma pulses during emplacement of the dike. Though the dike presents favorable mineralization, low grade values were seen for Cu, Ni, Pt, Pd, Rh, Ir and Co. Partial melting and fractionation as well as failure to reach sulphide saturation sufficient to assimilate crustal sulfur are considered probable causes for the low grades observed. Positive Th and negative Nb anomalies typical of MCR-related intrusions indicate deep crustal contamination. Geochemical results also showed a strong vanadium depletion and slight titanium depletion. Group one samples showed more crustal contamination then group two, and group three had a distinct enrichment of heavy rare earth element not seen in group one or two.