The Arrowhead region of Northern Minnesota is a wilderness covered with trees, lakes and open pit mines. One lake, less than a mile from the Birch Lake Exploration Project, once was an open pit iron ore mine. To execute the drill plan, roads will be cut into the woods and some drilling will take place from barges on lakes.
More than 2,300 feet below the ground, deep in the heart of Minnesota’s Arrowhead region, IDEA International Drilling of Virginia, Minn., is taking core samples. This area someday will be a mine producing copper, nickel and precious metals, all of which were among the elements found in the ore body that also included platinum and palladium.
Ernest Lehmann, chairman of Franconia Minerals Corp. of Minneapolis, knew there were resources in Northern Minnesota, and after more than 20 years of exploration, Lehmann (along with his original partners and business venture) and Franconia are closer than ever to developing a new mine.
Since 1985, the venture and its predecessors have drilled 37 holes (with wedged offsets, this adds up to 91 intercepts in this region) looking for minerals. In the late 1990s, the venture began working with IDEA to fulfill its exploration drilling needs.
Exploration drilling is more than getting the permits, telling the contractor where to drill and letting him go to work. This has been a real partnership between the venture and IDEA. Exploring for minerals is the goal, but sometimes it’s necessary to reinvent ways to get to the minerals, so IDEA often is investigating new ways to drill.
Wedge drilling is a perfect example of that. In 2000, they moved to maximize drilling efforts by beginning a strategy of wedge drilling. Dick Backstrom, owner of IDEA, says, “This was a proven drilling method, but we knew of no one doing it with PQ-size pipe.”
“Wedge drilling maximizes the confidence in the mineralized zone, and, at these depths, gives us a way of obtaining economically larger amounts of sample for metallurgical testing,” explains Lehmann. Wedges are installed to expand the recovery from each hole. This hole will have four wedges installed, but that number can go up or down, depending on the desired ore sampling.
The Wedge and the Hole
This process of wedge drilling was learned through the venture’s former partner, Impala Platinum of South Africa. Once one hole is drilled through the mineralized zone, additional holes can be drilled off the original by plugging the hole just above the mineral zone. Inserting a wedge will deflect the bit in different directions, so a much wider sweep of the zone can be explored without additional drilling from the surface.The wedge is a solid-steel rod tapered from one end to just past the middle. It has a stopper screwed in the base that can be expanded once it is lowered to its desired depth. It doesn’t matter which direction the wedge sends the drill string when it passes it, the holes will be electronically surveyed before the next wedge is placed above it.
The core samples are 3.345 inches in diameter and core runs are 10 feet long. The process of retrieving the core sample is done using cable to lower an overshot through the drill pipe. It then connects to a spear at the end of the head assembly on the core barrel. When the overshot attaches to the head assembly, it releases pressure-sensitive latches, allowing the inner barrel to be retracted through the center of the drill string.
To save time, as soon as the full core barrel reaches the surface, the crew immediately sends a second inner barrel down the hole so drilling can resume. They then will extract the core from the core barrel and log the depth of the samples. The core samples are delivered to the geologist each day.
Exploration drill pipe comes in multiple sizes, and because the owner wants to maximize the samples from the ore body, IDEA drills with 4 -inch HWT-size pipe. IDEA likes the HWT-size pipe because it is lighter in weight and threads well. The core barrel is sized much the same way. Because IDEA uses PQ-size core barrel with an inner diameter of 3.345 inches, the CS3001 drill rig can pull back HWT-size pipe approximately 4,000 feet.
Bits used for this type of drilling are impregnated with diamonds. For this application, they would use a PQ Hobic #7 impregnated bit. IDEA will spend about three weeks drilling the initial hole to total depth, and then an additional couple of weeks wedging and drilling off that pilot hole. The mineralized zone is between 1,600 feet and 2,600 feet below the surface. This pilot hole was drilled at an 83-degree angle, and the next hole will angle even greater.
The metallurgy plan includes drilling holes 660 feet to 13,200 feet apart, ultimately removing 45 tons of core samples over the next year. They have completed about 10 percent of the drilling at this time.
Bulletproof Drilling
The CS3001 isn’t the first exploration drill IDEA has purchased from Atlas Copco. They also have a CS1000, but wanted the greater pullback for the HWT-size pipe.Brian McCabe oversees drilling operations for IDEA. He is most impressed with the rig’s power saying, “The drill has so much power, we can keep the engine turned down and still get the performance needed.”
He also said the guys who run the CS3001 really are proud of what the rig will do. Learning to run the new rig wasn’t an issue, either. They say it was really easy to get the feel from the first start-up. One of the drillers never had operated an exploration drill, and had it down in just a couple weeks.
McCabe has been very happy with the drills, “The CS1000 has been a great drill for us and has proven to be indestructible, and the 3001 is looking to be just as bulletproof.”
Long-range Planning
Exploration is a long process. When Ernie Lehmann began this adventure 21 years ago, he knew it would take time and money. The drilling phase of this project will continue for another year, and then the mining and environmental planning phase will continue for a year after that.
Lehmann expects the venture to begin sinking its first shaft in 2009, with ore coming out beginning in 2010. The 25 years to reach that point, and the roughly $26 million dollars invested may look like a huge number, but the hundreds of millions in U.S. dollars worth of metals the venture expects to mine out of Minnesota’s Arrowhead should cover that bill.
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Lehmann expects the venture to begin sinking its first shaft in 2009, with ore coming out beginning in 2010. The 25 years to reach that point, and the roughly $26 million dollars invested may look like a huge number, but the hundreds of millions in U.S. dollars worth of metals the venture expects to mine out of Minnesota’s Arrowhead should cover that bill.
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