Estimates grow of underground ore's amount, value

In a small clearing in a pine forest south of Ely, three workers man a 40-foot-tall rig, lowering a cable into a small hole that descends nearly half a mile.

For about three weeks, a hollow drill bit tipped with diamonds has been grinding through the rock that starts just below the surface headed to a depth of 2,300 feet. Every 10 feet, workers pull up a section of the drill core — a pole of rock about three inches thick. It takes these workers about 15 minutes to reel all the cable back up and bring the core to the surface.

Workers take the 10-foot-long core, which weighs about 120 pounds, to the Ely Warehouse of Twin Metals, the company planning an enormous mine just south of the Boundary Waters Canoe Area. A team of geologists will analyze every inch of it to help estimate the amount of mineral deposits beneath the ground.

This summer, Twin Metals estimated the land contained nearly $100 billion worth of copper, nickel and precious metals. But that could change later this month when the company is expected to release another estimate.

Twin Metals trails only Polymet among the several companies pursuing efforts to mine the region's rich mineral resources. Both companies have been reporting growing estimates of the amount and value of the ore underground.

At first glance, the drill core retrieved by Twin Metals workers appears to be just a dull gray section of a rock. But an inspection by Kevin Boerst, the company's chief geologist, notes valuable minerals.

"Here's some bits right in here," Boerst said, after spraying water on a section of core to highlight tiny flecks of minerals. "You see some paler cream color, some nice gold color. There's different sulfide minerals that are the ore minerals in this deposit."

"They have enough material already defined for over 60 years of operation at a very high processing rate,"

Those flecks are tiny bits of copper and nickel, and the company keeps careful track of where and how far underground they appear.

Workers use diamond saws to cut the pole into sections. Then a variety of chemical and other tests determine how much of the rock is comprised of valuable minerals.

The results come back in fractions of a percent. Copper might represent just two-thirds of 1 percent of the rock. Gold might comprise only 75 parts per billion. In other words, the company would have to mine more than 13 million pounds of rock to produce one pound of gold.

Over the past six years, Twin Metals has pulled cores from more than 400 holes under the forest in northeast Minnesota.

Workers started with a grid pattern, but are now filling in the grid. Each new sample adds detail to a three-dimensional visualization of the ore body underground, and where the richest concentrations of metals are. As they drill more holes, explained Boerst, the picture grows clearer.

"You get a higher density, a higher statistical confidence," he said. "This is what you need to be able to prove to ourselves, to the community, to the government, and to our investors. Is this stuff mineable? Is this something worth pursuing, or is this a pipe dream?"

At this point the company and outside experts are convinced that the mining operation is much more than a pipe dream.

Independent mining industry analyst John Tumazos expects Twin Metals' assessment of deposits to keep growing as more drilling is completed.

But Tumazos said much of the company's drilling now doesn't aim to determine out how large the deposit is. Instead, he said, the company hopes to find the best location to start mining.

"They have enough material already defined for over 60 years of operation at a very high processing rate," he said.

But any actual mining is still years away. Twin Metals must first complete an early feasibility study, develop a mine plan, and then go through what could be several years of environmental permitting.

Many conservation groups remain highly skeptical that copper-nickel mines like Twin Metals can prevent acid mine runoff from damaging Minnesota lakes and rivers. Until Twin Metals can convince state and federal regulators they can do that, the minerals the company has discovered will remain deep underground.

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• Follow Dan Kraker on Twitter: http://twitter.com/dankraker

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