DULUTH, Minn. (AP) -- Northshore Mining Co. has agreed to pay a penalty of over $240,000 for air-quality violations at its taconite plant in Silver Bay.

The Minnesota Pollution Control Agency said Thursday that the plant was emitting excessive amounts of very fine dust that is unhealthy to breathe. Excessive dust was measured both at the plant and at the nearby Silver Bay Marina.

But the agency says Northshore is also taking steps to prevent future violations, including dust-control improvements at its large taconite pellet storage yard at the plant on Lake Superior.

In addition to paying the penalty and improving its dust-control capabilities, the agency says Northshore offered to spend nearly $80,000 to upgrade the MPCA's aging air-quality-monitoring network across the state.