Whereas the Aurizon South Zone is a near vertical vein-like structure, with grades high enough to consider as a high-grade, underground mining target, the Berkey “Porphyry Style” prospect represents potential for a large-scale, low grade, bulk tonnage, open pit copper deposit.
Educational Note: Geologists describe an intrusive igneous rock such as a granite or a diorite as “ porphyritic”, when one or more the constituent crystals within the rock are larger than the other crystals. Most commonly, intrusive rocks which may host a “porphyry-copper deposit” display these porphyritic textures, hence the name “porphyry deposit” is used. The related copper-bearing sulphides (commonly as chalcopyrite or bornite) may occur within fractures or veinlets (a stockwork), or, as disseminations within the altered porphyritic host rock (latter as crystals or “grains” inside the host rock’s mass instead of occurring along fractures or “cracks” in the rock). This disseminated type of mineralization can provide more homogenous, consistent quantities of metal across large bodies of granitic rock. Some of the world’s largest mines occur as such porphyries.
Discovered August 2015 while prospecting within recent logging clear-cut blocks, this new showing features disseminated chalcopyrite within a pink, potassium-feldpar-rich syenite dike which intrudes a large stock of grey monzonite. The unique occurrence supports EnGold’s Conceptual Exploration Model, derived from the integration of geological, geophysical and geochemical results, which predicts the presence of a previously undiscovered, copper (+ gold, silver) mineralizing porphyry intrusion.
Preliminary surface work shows the overburden-covered dike varies in width from 2.4 to more than 5 m wide along 25m strike (open). Chalcopyrite is uniformly disseminated as very fine to coarse (0.1-2.0 mm) specks.
Chip and grab samples assay 0.3 to 0.5 percent copper. Although the surface exposure is currently limited this new, well mineralized “Berkey Phase” represents an important discovery. EnGold plans to drill test this new prospect to determine size and establish possible genetic relationships with surrounding known mineralization. Petrographic analyses of four bedrock grab samples from the Berkey prospect confirm strong and pervasive potassic alteration that may be late-magmatic rather than truly hydrothermal. The dominant sulphide is chalcopyrite, and pyrite is replaced by supergene copper sulphides, chalcocite/covellite. Dr. Craig H.B. Leitch performed the petrographic examinations and reported that the Berkey Phase “textures and alteration/mineralization are strongly reminiscent of alkaline Cu-Au porphyry style typical of the Kamloops/Afton area of B.C. (e.g. Sugarloaf diorite).”