Porcupine Joint Venture
Porcupine joint venture partners Goldcorp (51% and operator) and Kinross Gold (49%) own three mines–the Dome, Pamour and Hoyle Pond–and a central processing plant at the Dome mine near Timmins, northeast Ontario. This valuable partnership produced 340,000 oz of gold in 2006, and is looking at a promising future in the historic gold camp.
One particularly interesting exploration target is the former Hollinger mine, which has been on care and maintenance for 20 years. The mine opened in 1910. When the Porcupine JV teams first looked at the Hollinger site, they were going to prepare a closure plan. But the more they looked, the more they thought the old mine still had potential. Existing information from over 80,000 diamond drill holes was entered into digital format, and another 80,000 m of diamond drilling has been completed since 2004.
At the end of 2006, the Hollinger resource was estimated to be 40.3 million t grading 1.65 g/t Au in the indicated category and 44.2 million t grading 1.57 g/t Au in the inferred category. And it lies only 5.0 km from the Dome mill. A further $7.0 million will be spent in 2007 for additional drilling at Hollinger before a decision is made whether to mine the resource or close the site.
Drilling continues to define and discover high-grade resources in the vicinity of the Hoyle Pond mine. The focus of the work is the new South Sediment contact. The discovery hole returned an 8.1-m intersection that graded 10.25 g/t Au from the 1170 level. Other holes have cut 22.5 m of 5.32 g/t Au, 13.5 m of 19.58 g/t Au, 14.3 m at 9.87 g/t Au and 2.2 m at 34.48 g/t Au. The Hoyle Pond mine is the target of a $4.36-million program that will drill over 72,255 m of core in 2007.
The joint venture partners have also uncovered hints of excellent exploration potential at the Pamour North Contact and the Broiling Porcupine targets. Core has returned assays as high as 10.03 g/t Au over 10.0 m.
“The Porcupine Joint Venture built its reputation on a long history of mining in the Timmins camp,” said mine general manager Chris Cormier, “and we are going to continue building mines so we can be around for another hundred years.” In the pipeline are two potential open pit projects at former producers and a handful of potential underground projects.
The venerable Dome mine began production in 1910 as an underground operation. Mining of a low-grade open pit resource began in 1988 and continued until 2005. Underground operations, which had been on care and maintenance since 2004, were restarted last year. Access to the Dome mine is via the 1,670-m-deep No.8 shaft, which was commissioned in 1981. The primary mining method is longholing with variations practised for pillar recovery and bulk mining in active stopes from the 11 to the 25 level.
Mining of the Hoyle Pond deposit began in 1985, and the mine produced its two-millionth ounce of gold in 2005. This underground mine boasts both a shaft that services a tracked haulage level at 720 m and two ramps. An automated winze was commissioned in October 2005 on the 655 level. Mining methods include conventional cut and fill, shrinkage and panel mining in narrow veins. Longhole with paste fill is practised in wider stoping areas.
The earliest mining of the Pamour deposit occurred from 1911 to 1914. it was restarted in 1936, and a number of owners worked it until 1999. The Porcupine JV reopened the property as a truck-and-shovel pit in 2005, and closure is planned in 2012. Ore from the Pamour pit is hauled to the mill by a fleet of Caterpillar trucks.
Three ore sources–the Dome (10%), Hoyle Pond (10%) and Pamour pit and stockpile (80%)–yield average head grades of 2.87 g/t Au. Run of mine ore is crushed and screened in three stages until 80% passes –12 mm. Fine ore is then fed to either of two parallel rod-and-ball mill grinding circuits. Nameplate capacity is now 12,000 t/d.
Slurry is cycloned and the underflow portion feeds a bank of five Knelson concentrators. The gravity concentrate is leached in a ConSep Acacia reactor, and the high grade solution feeds a dedicated electrowinning circuit. Depending on the ore source, as much as 45% of the gold is recovered in the gravity/EW circuit.
Thickener underflow (55-60% solids) provides the feed for the leach circuit. After leaching, slurry is passed through a conventional CIP circuit, and the pregnant solution feeds a second EW circuit. Gold dor bars are poured on site. Total gold recovery is 92.6%.
The CIP tails are screened, sampled and impounded. Between May and October each year, they undergo Inco SO2 and air treatment to eliminate residual cyanide, and are treated with ferric sulphate and lime to precipitate heavy metals before any water is discharged.
A century of gold output is a remarkable accomplishment at the Dome, but Canada’s longest-producing gold mine may be nearing the end of its reserves. Rather than look back, the Porcupine JV is looking toward the future, outlining new reserves in all the most promising areas of the Timmins camp.