The Midwest Test

He told The Northern Miner Magazine on a site visit that shaft-sinking went “very, very well.” Water inflows topped out at 9 gal per min and, even with installation of a concrete lining every inch of the way, the rate of advance was 7.5 ft (2.3 m) per day.

A station has been cut at the 170-m level and an Eimco 24 track mucker has been lowered in preparation for drifting towards the orebody. So far, ground conditions have required only rockbolting. However, the nearer drifting advances toward the ore zone, some 185 m from the shaft, shotcreting will provide stability. “There is an alteration halo around the orebodies. It’s not only a faulted environment, but the ground has been altered to clay,” said Larry Richardson, site supervisor and senior mine geologist. Project Engineer Glenn Blackford said “the material here is supposed to be very badly broken above the orebody.”

Actual test mining will incorporate an Ingersoll-Rand RBM7 raise borer with a 1.2-m head to blind bore more than 30 m down into the orebody. The raiseborer’s rods and head should be heavy enough to sink toward the ore. Barite mud will hold the walls of the opening and the cuttings will be discharged into a lead-lined and completely enclosed ore car, which will then be transported to surface. As much as 200 cu m of ore will mined. The project timetable calls for a production decision by late 1990.

“We’re breaking new ground, if you’ll pardon the pun, using a machine that’s meant to pull rather than push,” said Blackford. Test mining should be completed by early September.

The entire Midwest orebody has reserves of 56 million lb grading 1.25% U3O8. Within that reserve, a richer portion of 37 to 39 million lb grades 2.78%. This pod of richer ore is roughly 40 m wide and 100 m long. The orebody as a whole strikes for 900 m and sits 200 m below Mink Arm, an extension of South McMahon Lake. Richardson has been going over the drill data from more than 650 holes punched into the deposit to reinterpret and recalculate the reserves for a firmer fix on the deposit’s configuration.

At the time of our visit (Westwind Aviation of Saskatoon serves the area), surface facilities included a water treatment plant and ponds, a headframe, offices for Thyssen and Midwest personnel and buildings for the compressors, garage and so on. Living quarters and cafeteria are a few miles to the south at a permanent camp established by Points North Freight Forwarding. Thr ee 70-kw Detroit Diesel generator sets provide the power and four Atlas Copco compressors provide mine air. The water treatment plant is currently treating mine water to remove radium and other contaminants. The 12-m-diameter test mining shaft will become the production shaft should the test prove successful. Whether Midwest builds its own mill or decides to have ore custom-milled has yet to be decided. Initial metallurgical work has been conducted by Melis Engineering of Saskatoon.

The Midwest Joint Venture is owned 45% by Denison Mines. The other partners are Bow Valley Resources (20%), Uranerz Exploration and Mining (20%) and PNC Exploration (15%).

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