From the record
“Mountain Iron Mine is a former mine in Mountain Iron, Minnesota, United States. Opened in 1892, it was the first mine on the Mesabi Range, which has proved to be the largest iron ore deposit ever discovered in the United States.”
Wikipedia article Mountain Iron Mine, CC BY-SA 4.0.
One of 126 National Register listings published here for St. Louis County · listed in 1968 · category: Site · built in 1892 · a National Historic Landmark.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service