- Eagle River Geology
- Eagle River Exploration
Purchased in 1994, preproduction development at the Eagle River Underground Mine commenced in 1995 and the first gold bar was poured on October 17, 1995. The preproduction capital cost, net of gold produced during the preproduction period, amounted to $15.5 million. Commercial production was declared January 1, 1996, and to date, it has produced 1,050,000 ounces of gold from 3.6 million tonnes at an average recovered grade of 9.1 gAu/tonne, mainly from the main producing structure, the 6 and 8 Zones. Its deepest development to date is at 900 metres below surface. The recent discovery of at least two new significant parallel zones in the west portion of the mine (the 300 and 7 Zones) have helped increase Mineral Reserves and Mineral Resources and have stimulated an increased pace of exploration drilling. The mine is currently operating approximately 500 tonnes per day.
Gold bearing quartz veins at Eagle River are hosted primarily by subvertical to steeply north dipping east-west striking shear zones within an elliptical quartz diorite stock with dimensions of 2.0 kilometres east-west and 0.5 kilometres north-south.
The quartz diorite stock intrudes a steeply dipping north-facing sequence of thin mafic to intermediate volcanic flows, flow breccias and interflow volcaniclastic rocks.
A number of different ore zones have been distinguished that constitute different segments of the overall shear zone corridor and each has its own gold grade characteristic. Mineable portions of the individual zones form ore shoots that plunge steeply to the east. The bulk of the historic production has come from the 6 and 8 Zones, which are entirely within the intrusive quartz diorite, while the 2 Zone mineralization is hosted in sheared mafic volcanic rocks just east of the stock.
The 8 Zone is characterized by a series of thick, white laminated quartz vein lenses. The veins vary in thickness from one metre to 15 metres, averaging about 2.5 metres. Commonly portions of the vein system can be selectively mined with mining widths varying between 1.2 and 7.5 metres. Gold is concentrated in highly strained quartz of grey colour and in sericite-chlorite lamellae with accessory sulphide minerals including pyrite, pyrrhotite, galena, sphalerite, and chalcopyrite. The gold grade in Zone 8 has averaged about 8.0 grams of gold per tonne with individual stoping blocks ranging from 5.0 to 12.0 grams of gold per tonne. The 6 Zone is a distinct and discrete shear zone that forms a splay off the shear hosting Zone 8 mineralization. The vein varies in thickness from 0.5 metres to 2.0 metres. Locally the vein is folded back on itself forming tight S-folds or “ballrooms” which form plunging, pipe-like bodies 12 to 15 metres in diameter. Zone 6 is high-grade averaging 12 to 18 grams of gold per tonne and has very competent wall rocks. Because of its high-grade character, Zone 6 traditionally provided economic backbone of the mine until 2008. At a depth of 650 metres the vein structure exits the quartz diorite stock and ceases to carry economic grades.
In general, the ore shoots mined to date occur at a spacing of 400 metres along a 2.4 kilometre strikelength. They appear to be spatially related to an array of oblique 110º striking mafic dykes, which pre-date mineralization and deflect into and out of the shear zones.
Gold mineralization is structurally concentrated within highly strained portions of the various quartz veins. Ore microscopy indicates that 60% of the gold occurs along quartz-sericite grain contacts, 32% along sulphide-gangue contacts and 1.4% within sulphide grains. The grains are generally less than 500 microns, free milling and 40 % recoverable by gravity methods. Gold grains less than 5 microns account for a negligible percent of the total gold. Free gold generally occurs as a multitude of fine grains which result in a relatively low sub sampling variance generating very good assay precision for a vein type gold deposit.
Since 2008, the bulk of production has come from the 808 and 811 Zones in the western portion of the mine. In 2013, two new parallel zones, the 7 Zone and the 300 Zone were discovered 200 metres and 400 metres north, respectively, of the main 8 Zone shear. Detailed drilling in 2014 defined good grades and initial development and production commenced in 2015. The northern portion of the quartz diorite stock has not been systematically explored. The recent recognition of the potential of these parallel structures across the length of the mine workings forms the basis of the geological model on which the current exploration program is planned.
Eagle River Mine: 1.1 M oz of Production
Eagle River Parallel Gold Zones Remain Open
Eagle River Parallel Gold Zones Remain Open
2016 Drill Results Extend 7 Zone Towards Surface, Production Commencing Q4 2016
300 Zone Drift Results, September 2016
The Eagle River Complex is a mature mining operation that demonstrates considerable promise. A modest increase in drilling in recent years has led to new discoveries and has doubled mineral reserves, net of depletion.
The recent recognition of parallel structures at Eagle River has opened our eyes to potential on the doorstep of existing infrastructure. The newly recognized No. 7 and 300 Zones currently comprise 49% of Mineral Reserves and 55% of Mineral Resources at Eagle River. To date, they have only been identified in the west end of the mine, at depth. Surface and underground drilling currently underway will provide a first pass evaluation of 1.8 kilometres of previously untested potential adjacent existing mine workings.
2016 Eagle River Exploration Program