Summary:
The Shakespeare copper-nickel deposit is hosted within gabbroic rocks (Shakespeare Intrusion) of the Nipissing Intrusive Suites situated along the north contact between the mafic intrusive body which crosses the Property and quartzites of the Mississagi Formation.
The Shakespeare intrusion hosts semi-massive to disseminated sulfides (Sproule et al. 2007). Sulfides, including pyrrhotite, chalcopyrite, and lesser pyrite, are present throughout the intrusion in varying proportions, mostly in trace amounts. Significant accumulations are present as:
- disseminated pyrrhotite and chalcopyrite blebs at the melagabbro/gabbro contact, usually ~1 mm in size, typically comprising <1% of the rock;
- heavily disseminated to patchy net-textured (10-15%) pyrrhotite, chalcopyrite, pentlandite, and gersdorfite in rounded blebsthat reach up to 2-5 cm in size, in the upperzone of the melagabbro;
- blebby pyrrhotite and chalcopyrite in the lowersections of the melagabbro and the base of the quartz gabbro.
The sulfides have experienced variable degrees of recrystallization during metamorphism. They vary from pristine magmatic blebs, to recrystallized blebs, to stringers, the latter of which tend to be richer in chalcopyrite.
Where the mineralization is proximal to shear zones that cross-cut the deposit, the sulphides can be sheared and attenuated. These sheared sulphides, together with the patchy-network textured mineralization, create an interconnectivity in the sulphidesthat allows portions of the deposit to be identified by remote electromagnetic (EM) geophysics surveys, a valuable tool in exploring for extensions to the deposit. The mineralized zones also contain abundant inclusions of quartzite, blue quartz eyes, and rare diorite. The ores have compositions consistent with having been derived from the Shakespeare magma and to have equilibrated at moderate magma: sulphide ratios (500-1000).
The total strike length of Shakespeare mineralization is approximately 1,700 m and extends to a depth of ~550m. The deposit is subdivided into a West and East resource zone.
The west zone appears to plunge to the west at ~15° and is of a slightly lower grade than the Eastzone. It is currently defined to a depth of ~120m and abruptly terminates at its western-most edge, possibly due to offsetting by faults. Deeper exploratory holes by URSA Major identified two lenses of mineralization down to ~210m depth. Although more work is required to better define these lenses, they may represent a fault-displaced down-dip extension of the east zone mineralization.
The east zone plunges ~30° to ~40° east from surface and generally has higher grade mineralization, particularly nearer surface. The mineralized zones currently extends over ~1km and plunges from surface to a depth of ~ 550m. It remains open to the west and the up-dip and down-dip extensions have not been tested by drilling, leaving considerable opportunity to expand the resource.
The Shakespeare deposit has recently been interpreted to represent a new style of mineralization for the Nipissing Gabbro with Ni-Cu-PGE mineralization hosted inside the intrusion (Sproule et al. 2007).
The intrusion is a complex differentiated sill approximately 14 km in strike length and approximately ~300 to ~430 in thickness. It comprises two distinct magmatic packages: 1) a Lower Group composed of unmineralized pyroxenite and gabbro, and 2) an Upper Group composed of mineralized melagabbro, quartz gabbro, and biotite quartz gabbro-diorite.
The Shakespeare intrusion formed from a tholeiitic parental magma (Sproule, et al., 2007). All of the rocks in the intrusion are enriched in LREE relative to MREE and HREE, enriched in highly incompatible lithophile elements (HILE: Cs, Rb, U, Th, Nb, Ta, LREE) relative to moderately incompatible lithophile elements (MILE: Zr, Ti, HREE) and are strongly depleted in Nb and Ti relative to elements of similar incompatibility. These geochemical characteristics suggest that the Shakespeare magma underwent extensive degrees of crustal contamination prior to emplacement. Although other parts of the Nipissing Gabbro suite exhibit similar geochemical characteristics, the Shakespeare intrusion is more enriched in HILE and more strongly depleted in Nb-Ti, and therefore appears to have undergone greater degrees of crustal contamination.
Heavily disseminated to patchy net-textured (10-15%) Fe-Cu-Ni sulfides (pyrrhotite–chalcopyrite–pentlandite) occur in the upper zone of the melagabbro near and at the contact with the overlying quartz gabbro and in the melagabbro dykes. The mineralized zone contains abundant inclusions of quartzite, blue quartz eyes, and rare diorite. The ores have compositions consistent with having been derived from the Shakespeare magma and to have equilibrated at moderate magma: sulfide ratios (500-1000).
The Ni-Cu-PGE mineralization in the Shakespeare deposit appears to have resulted from the following
processes:
- generation of Nipissing magmasin the mantle;
- contamination of Nipissing magmas by continental crust enroute through the crust;
- introduction and crystallization of contaminated butsulfide-undersaturated magmas into the
Shakespeare intrusion, forming the Lower Group;
- further, and apparently relatively local crustal contamination and sulfide saturation, of Nipissing magmas, resulting in the incorporation of abundant xenoliths of country rocks and the generation of moderate amounts of Ni-Cu-(PGE)sulfide melt;
- introduction of the xenoliths and sulfide-bearing magma into the Shakespeare intrusion, forming the Upper Group, with heaviersulfidessettling at the base of the new crystallization floor resulting in low-moderate R factor values. (Sproule et al. 2007; Dastil 2014)
The elevated U-Th content of the gabbroic rocks hosting the Shakespeare deposit suggests sulphide saturation was reached by assimilation of U-Th-rich crustal material. The proximal pyritic-quartz- pebble-conglomerates of the Matineda Formation are rich in uranium, thorium and are proposed as the source for the crustily-derived sulphur (Dastil 2014).