Technically Speaking….

The Orca Quarry on Vancouver Island is somewhat of a geological anomaly in that it is located on a glacial outwash deposit that was not deposited directly by the glaciers as they retreated at the end of the last ice age approximately 13,000 years ago. Rather, the deposits that were deposited directly were breached or washed up by huge amounts of water which were probably damned up behind things like thermal moraines as the glaciers melted and receded. When these large volumes of water rushed down slope from roughly west to east (in this case), they basically turned the usual deposition on its ear as they lost energy fairly rapidly when they hit relatively level topography allowing the finer silts and sands to drop out quickly and the coarser cobbles and boulders to end up closer to the top of the succession than one would normally expect in a typical sedimentary deposit.

…and legally

Orca Sand and Gravel Ltd. owns 100% of the Orca Quarry, and is in turn owned 88% by Polaris Minerals and 12% by the Namgis First Nation. The Kwakiutl First Nation participates in the project through an Impact and Benefits Agreement. The Board of Orca Sand and Gravel Ltd. has two representatives from the local community, including George Speck Sr., of the Namgis First Nation, who is Chair of the Board. Fifty per cent of the 45-member team at the Orca Quarry are members of these First Nations communities, and 25% of the team are women.

this material ever reaches the Orca shipping dock, the work that goes on just a few hundred metres inland in the quarry itself is quite impressive and deserves a closer look.

As mentioned in the geological description of the site in the adjacent box, the quarry is quite unusual in its mineral formation and because of this, mining the aggregates has been quite easy by comparison to in conventional quarries.

First and foremost from a cost and production perspective, all materials are gathered by scrapers (there’s no blasting required) and to ensure a consistent run-of-pit balance of fine and coarse materials, the deposit is mined in a single bench by three CAT 637G, tandem-powered machines with a rated capacity of 26 m3. The scrapers develop a down-gradient loading face with a slope of approximately 3:1, horizontal to vertical. This configuration provides the process plant with the highest probability of a universe blend of coarse and fine aggregates from the stratified deposit.

Each machine weighs 52047 kg, can haul up to 40 tonnes, and comes with a $1.3-million price tag. Polaris has three of them, plus a CAT D8T tracked dozer that is used to support the scraper operation by surface clearing, cleaning up the active extraction area, assisting the scrapers with loading, and building and maintaining access roads. There’s also a 980H Loader on site.

The pit floor elevation is controlled by the water table and/or the quality of the aggregate. The pit floor has a mean elevation of 20 m to 25 m, and the top of the operating face has a maximum elevation of 110 m. Therefore, the maximum operating face of the quarry has an elevation in the order of 90 m.

As required by one of the environmental concerns mentioned earlier, pit operating boundaries are controlled by setbacks established around the quarry, including Highway 19 to the west where the only indication that a quarry exists is in the form of a tree-lined and manicured roadway leading to a sign at the entrance. The illuminated sign itself is now somewhat of an attraction to passing motorists because of its attractive design and electronic display showing “Accident-Free Days” in large numbers.

In any event, great measures have been taken by Polaris Minerals to ensure that its Orca Quarry is a good neighbour.

Like all quarries, however, there is a certain amount of noise and that can’t be avoided, especially in the hopper area where a steady stream of scrapers deliver material every six minutes from the face to portable dump hoppers that are fitted with grizzly screens to reject oversized material. The quantity of oversized rock (>152 mm) in the deposit is limited and is stockpiled.

Material that passes through the grizzly is collected on a ‘field’ conveyor system for transport to the process plant. The dump hoppers will operate from their current location for about another year or so before being moved closer to the operating face to help keep the aver- age scraper distances relatively constant over the mine life.

The deposit has 118.7 Mt of remaining reserves at an estimated in-situ specifi c gravity of 2.01 t/m3. Based on the updated NI 43-101 Technical Report, the extraction could build to 8.7 Mtpy by 2015. Remaining mine life is estimated to be 17 years and the Company is actively looking to expand its resource in the land surrounding the Orca deposit.

To further describe the overall operation, the processing plant is designed to handle 1,500 tonnes per hour and uses 1,514 liters of fresh and 22,713 liters of recycled water per minute. Located beneath the raw pile are three vibrating feed gates opening into a tunnel through which the primary (CV01) conveyor runs.

When the plant is running, gates open and conveyor (CV02) feeds raw material into the plant where it is sorted by the (SC01-02) screen decks, and any gravel larger than 25.4 mm is sent by conveyor (CV03) to a primary cone crusher that is also backed up by a second crusher for proportioning the materials.

Materials that pass through the first screens are deposited on conveyors (CV05-06) and carried to washing screens where large and small gravel is again separated and stockpiled. Sand passes through the screens and is transferred by pumps to de-watering screens where all materials over two microns go into piles. Finer residue is sent to a thickener tank where it is mixed with a benign flocculant that sticks it together, causing it to sink.

The residue is then drained from the bottom of the thickener tank and sent to the belt presses which extract water and extrude the fine sand as a heavy, silty material. Again, in keeping with Polaris Minerals’ concern and agreements for the environment, the by-product is used for reclamation work at the quarry.

With the sand and gravel processed and ready to go, Polaris has installed four stacker conveyors, each about 27.5 m high, to place the finished products into four stockpiles, two for sand and one each for 25 mm x 12.5 mm gravel and 12.5 mm x 4.75 mm gravel. Each pile can store more than 100,000 tonnes and underneath each pile are three vibratory gates which open onto a high-speed conveyor for blending the materials as per the customer’s specifications.

Located under the stockpiles is a 275-m-long reclaim tunnel containing the high-speed conveyor that moves the sand or gravel at speeds of up to 215 m per minute. The aggregate then drops onto a loadout conveyor that travels under neighbouring Highway 19 then overland to the shiploader.

Special consideration for the environment was further made by Polaris during the overland and outside of the quarry proper portion of moving the materials. First of all, a large tunnel was built under the conveyor to allow wildlife to cross the area. Secondly, all drive mechanisms are enclosed for safety and finally, thousands of wooden timbers were placed on the ground to support the conveyor system instead of digging and pouring concrete foundations for the conveyor system.

All in all, the Polaris Minerals’ Orca Sand & Gravel Quarry on B. C.’s Vancouver Island is a perfect example of how mining can work in harmony with the environment and how questions can be answered without too much trouble.