Red Chris – Exploring it’s Roots
CIM Edmonton 2008
Chris Taylor, Lee Ferreria,
The Red Chris copper-gold deposit (ore reserves of 276 million tonnes grading 0.35% copper and 0.27 g/t gold – 2004 feasibility study), acquired by Imperial Metals in 2007, is hosted by the Red Stock, a Late Triassic hornblende monzonite to quartz monzodiorite that is emplaced in island arc volcanics of the Stikine terrane. In 2007, Imperial Metals completed one of the best drill holes ever reported from a British Columbia porphyry deposit, with vertical drill hole 07-335 returning 1024.1 metres of continuous mineralization grading 1.01% copper, 1.26 g/t gold and 3.92 g/t silver.
The Red Chris deposit has characteristics of both alkalic and calc-alkalic porphyry deposit types. Alkalic features include a monzodioritic host intrusive, alkalic volcanic host stratigraphy and low levels of molybdenum. Calc-alkalic features include quartz-sulfide vein stockworks, phyllic and argillic alteration assemblages, and low magnetic signature. The large tonnage of the Red Chris deposit is also more typical of calc-alkalic porphyries.
Mineralization at Red Chris is strongly associated with quartz stockworks within the East and Main Zones. There is a marked gradation in copper:gold ratios from east to west across the deposit. The East Zone displays a high average copper:gold ratio of 1.25, as well as the high overall grades seen in hole 07-335. To the west, the Main Zone has an average copper:gold ratio of 0.71, and more moderate overall grades, as seen in drill hole 07-336, also drilled by Imperial Metals in 2007. This vertical drill hole intersected 996.4 metres grading 0.40% copper, 0.38 g/t gold and 3.12 g/t silver. Immediately west of the Red Chris deposit within the Red Stock, the Gully and Far West Zones have copper:gold ratios of 0.50 and 0.33, respectively, as well as a decrease in the overall consistency of quartz stockwork formation and mineralization grades.
The recent drilling has shown copper-gold mineralization is both vertically consistent and deep-seated. While the geological resources have been significantly expanded, the mineralized system remains open at depth and further expansion seems probable.
The original size and shape of the Red Stock has been modified by significant high-angle extensional faulting. Exploring for displaced mineralization across these structures and expansion of the high-grade mineralization beneath the known deposit will be the primary goals of upcoming work. Near-surface delineation within the planned pit design will also be addressed.
Imperial Metals is working toward development of an open pit mine at Red Chris and expects to update the feasibility study in 2008, followed by a production decision. The recent announcement of the power grid extension into northwest British Columbia with the Northwwest Transmission Line providing power at Bob Quinn has been an important step towards the development of Red Chris.