Granduc mine: Historical mineral inventory: 5,000,000 tons 1.84% Cu. -
Past production - +/- 34 mil tons grading 1.9% Cu???
Granduc Mine Area - Stacked VMS lenses, structurally complex (fold repititions?), thickened in fold hinges.
Said to be a Windy Craggy analogue.
Hypothetical new south extension zone, 770m length, 200 m vertical, 4.5 m thickness, 70 deg. dip. indicated by widely spaced drilling.
2% Cu, 20 g/t Ag, .25 g/t Au. Open to South and down-dip.
Another 300 m south possibly indicated by outcropping of the zone to the south of southernmost drill intercepts.
Challenging logistics including elevation, topography, snowfall. Assumed that 10 mile ore haulage tunnel needs to be refurbished.
Surface infrastructure, except for housing in Stewart B.C., completely dismantled.
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This area gets some of the heaviest snowfalls on earth, averaging about 800 inches each year, with the record at over 1,100 inches. To the men working at the camp, the 16 feet of snow that fell in the second week of February 1965 merely meant some extra work to keep their work areas usable. But high above the camp, incredible pressures were building as the snow deepened."
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"Virtually the entire camp was wiped out by the avalanche. Some of the survivors were missed when the slide split into two forks, and many were able to dig themselves out when they were buried. Bertram Owen-Jones, a 20-year-old cook, was holding a knife when the cookhouse was blown apart - caught under a portion of wall, he was able to use the knife to cut himself free after 3 hours. The tunnel had only been driven 28 feet when the avalanche struck, and several men were protected inside it.
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Portal Camp was never reopened. No technology available could protect men working in that location against another avalanche. The options for extracting the ore were few - an open-pit mine would be impossible due to the snowfall, so engineers had to find a way to cut the tunnel using only the camp at Tide Lake, 10.3 miles from the main ore body. The huge extra expense involved nearly forced the mine into receivership, but on the basis of reserves of 32,500,000 tons of 1.93% copper ore, refinancing was arranged.
work restarted, progress was amazing -
several world records were set by the tunnelling crews:
Best single-day advance - 155 feet
Best six-day advance - 601 feet
Best month's advance - 2,320 feet
Fastest one-mile advance - 73 working days
While the tunnel crews were at work, a permanent camp and a massive concentrator were also being constructed at Tide Lake. To get supplies in and concentrate out, a 32-mile all-weather road was built to reach Stewart, where a large dock was built to berth ore freighters as large as 50,000 tons. The town of Stewart quadrupled in size, with the modern "Granduc Subdivision" extending to the north of town. By November 1970, everything was completed - the final bill came to $115,000,000, over twice the original budget. Only 3 months later, however, the first shipload of copper concentrates were on their way to Japan.
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explorenorth.com
"Traditional mining methods could not have solved Granduc's problems. Low-cost highly-productive methods had to be developed for, or adapted to, Granduc's special situation. The Granduc mine employed three mining methods: sublevel caving, sub- level open stoping, and mechanized cut-and- fill. Each method, that was used at Granduc, was a model of modern, efficient, and safe mining practice. The miners used mechanized, multi- drill jumbos to drill the ore and rubber- tired load-and-haul equipment to remove the ore after it is blasted. These load-and- haul units can move freely within the mine from level to level, by means of an internal ramp system connecting mine levels on a 15 per cent slope. Ore passes connect the different levels, and the ore dumped into them at each level is collected by a gathering system and delivered to the underground crusher .
Granduc's ore was crushed once at the mine, stored, and then loaded into these 50-ton side-dump ore cars to be hauled in 15 or 20-car trains to the concentrator at Tide Lake.From the crusher, ore traveled by conveyor belt to two bins, from either of which it was loaded into 50-ton railroad cars for the ten- mile trip to Tide Lake. Speed and volume with safety, were essential elements here therefore the ore trains include 15 to 20 cars and the electric locomotives are capable of pulling the trains at 40 miles per hour. A round trip would take slightly more than one hour The same locomotives haul mining crews to and from the mine in specially-designed passenger cars.
On reaching the concentrator end of the tunnel at Tide Lake, the ore trains dump their loads into a storage bin. Conveyors then raise the ore to the fine crushing plant where it was crushed and then conveyed to fine ore storage bins located ahead of the grinding circuit. The high cost of steel grinding media at Granduc made some form of autogenous grinding attractive. Ore pebbles were screened out of the feed to the fine crushing plant and replace most of the steel balls that would otherwise be used as grinding media in the grinding circuit. There were two grinding lines, each consisting of one rod mill and two pebble mills. The pebble addition and the grinding circuits were completely instrument-controlled and operate with a minimum of supervision. The ore, after grinding, follows the conventional practice of flotation, thickening, filtration and drying.
The dried concentrate was then hauled by trucks over the 32-mile road to the marine terminal in Stewart. A special design, using cylindrical tanks, enables these trucks to carry fuel oil on the return trip to the mine. Snow crews work continuously during the winter to keep this road open because the six concentrate trucks made a total of 24 round trips each day to keep ahead of mine production, and men traveled in and out every day.
The marine terminal in Stewart was located at the head of a fjord, the Portland Canal, 120 miles from the open Pacific Ocean. The terminal could handle ships as large as 50,000 tons displacement. The first shipload of Granduc concentrate left Stewart for Japan in January, 1971."
stewartbc.com
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So, very hypothetically:
+/- 5,000,000 tons remaining at Granduc Mine grading 1.8% Cu, 20 g/t Ag(?), 0.3 g/t Au.
Theoretical new south zone, 1100m x 5 m width x 250m vert., assumed same grade. |
