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A company that plans to dig a sprawling iron mine near Lake Superior is asking for permission to drill 15 new test holes, the Wisconsin Department of Natural Resources said Friday.

Long cylinders of rock pulled from the small holes will allow Gogebic Taconite to learn more about iron deposits and waste rock — including any problematic material such as sulphide and asbestiform grunerite.

Sulphide leaches environmentally devastating acid runoff, and asbestos can be deadly if inhaled.

The company has said it likely will be able to engineer solutions if large amounts of the substances are found. The DNR found a rock containing asbestiform grunerite on the site last year, but company officials have been saying they don’t expect large quantities.

Core sampling began last year, when Gogebic Taconite drilled eight test holes. Each sample was 13/8-inch in diameter. Samples collected total 5,870 feet. The deepest hole drilled went 1,100 feet into the mine site, company officials said.

In October, Gogebic Taconite spokesman Bob Seitz said five more core samples would be drilled this winter. It’s unclear why the number increased to 15. Seitz didn’t immediately return phone calls Friday seeking comment.