Odds ‘n’ Sods — Newmont breaks the ice at the Granduc mine

Among the more dramatic adventures in the history of the Granduc copper mine in British Columbia were the flooding of the mine workings and consequent abandonment of the project. Only by drilling diamond drill holes through the massive South Leduc glacier were operators able to tap and seal off underground water flows.

The Granduc mineral showings were discovered in 1931, but it was not until 1953 that Newmont Mining joined with Granby Consolidated Mining, Smelting and Power Co. to explore the copper zones for Granduc Mines Ltd. Exploration continued unabated up to March, 1958. Over this period camps were set up on glaciers, over which cat trains moved freight; aircraft were employed extensively to service the site; tunnels were driven into Granduc Mountain; and a shaft was sunk to 700 ft. In the meantime, tens of thousands of feet of drill holes were bored through the mineral deposits. Finally, a preliminary estimate of 32.5 million tons grading 1.9% copper was established.

Then the unexpected happened.

A raise was driven from the 2475 level directly below the glacier to explore the depth of bedrock over the zone and confirm seismic data. At 69 ft. of advance, the raise broke into the bed of the South Leduc glacier, and the resulting inflow of water flooded the underground workings. As a result, the work program was halted on March 15, 1958.

A study of the ore zone indicated that access to the lower elevations of the structure was required in order for the mine’s potential to be developed. Hence, it would be necessary to dewater the lower workings of the shaft so that operators could investigate and outline the ore configuration. This meant that the 2475 level raise entry into the bed of the glacier would have to be sealed off to prevent further inflow of the glacial river.

A 4-year study examined possible methods where the mine could be protected from water discharged from the ice sheet. After a great expenditure of time and money on test-drilling and seismic work, it was deemed feasible to drill a hole, or holes, from the surface of the glacier to intersect the raise at 2475 level and then pour a cement grout mixture through this hole into the opening to seal off the mine from water inflow. However, precise survey control would be required to direct the hole, since the entire glacier was moving relative to the fixed raise target (albeit at a slow rate).

Finally, it was decided that drill holes would be driven from the surface of the South Leduc glacier.

A hole was aimed at the raise intersection, and a large stockpile of cement grout was accumulated for use when the hole entered the raise. The drill bit was precisely guided to the opening so that all that remained was the pass sufficient grout down the hole to seal off the workings.

Len White, a former mine manager at the project, explained that more than 15,000 bags of cement were poured down the drill hole before movement of the ice prevented further action. Subsequent testing indicated that the grout had done the trick.

The situation now called for the mine workings to be dewatered, and the path was open to explore and confirm the Granduc ore zone. In 1962, after a bulk-head was constructed to seal off the 2475 level permanently (immediately under the South Leduc glacier), this work was resumed.

Two years later, Newmont put the Granduc mine into production. The entire undertaking is a classic example of how technical ingenuity and expertise, combined with a great deal of intestinal fortitude, can succeed in developing a major mineral resource in Canada’s rugged frontier.

— S.J. Hunter, a retired mining engineer and regular contributor, resides in Vancouver, B.C.