Mining historically played an important role in the economies of Great Lakes states and provinces, and it continues to be an economically important industry today.1,2 Some of the most important commodities mined in the Great Lakes region include:
- Iron ore – Iron ore is the principle material used to manufacture steel. In 2011, mines in Minnesota and Michigan shipped 99% of the usable iron ore produced in the U.S.3
- Limestone – Limestone is often crushed and used for road construction projects, to manufacture cement, and as a component in the steel-making process. Limestone blocks may also be used as building materials.
- Sand, gravel, and crushed stone – These materials are used in the construction industry. Pure sand is also used in foundries to create casts and molds, and to make glass.
Mapping coastal mines as a Great Lakes stressor
The final GLEAM stressor layer for mines considers all metal mines (historic and active) and active limestone/dolomite mines within 2 km of the shoreline of the Great Lakes to be potential sources of contaminants.4,5 Though these two types of mines impact the Lakes in slightly different ways, we did not differentiate between them in our analysis.
Metal mines (active and historic)
Metal mines play a role in leaching pollutants into lake waters and sediments. Metals accumulate in sediment, where they impact benthic invertebrates and the organisms that feed on them.6 The majority of metal mines in our dataset are historic. Due to the potentially long legacy effects associated with metal mines, they may still be having an impact on Great Lakes habitats and food webs.
Limestone/dolomite mines (active)
Unlike metal mines, chemical leaching is not expected to be a serious impact associated with limestone/dolomite mines. We include these mines because of the associated land disturbance and large footprint that some mines occupy adjacent to the Lakes. For example, Calcite Quarry located near Rogers City, MI, on the shore of Lake Huron is the world’s largest limestone mine.
Locations of metal and limestone mining operations within 2 km of the Great Lakes shoreline
- Historic copper mines concentrated around the Keweenaw Peninsula in Michigan’s Upper Peninsula. Large quantities of mine tailings were dumped into Lake Superior along the western shore of the Keweenaw between 1895 and 1968.6
- Historic silver, gold, iron and zinc mines are located along the north shore of Lake Superior
- Limestone/dolomite mines occur primarily along the northern shore of Lake Ontario, around Georgian Bay and the northern ends of Laker Huron and Lake Michigan, largely following the Niagara Escarpment of dolomitic limestone that shapes in part the basins and landforms of Lakes Ontario, Huron and Michigan
- The northeastern region of Lake Ontario in the vicinity of Kingston, ON (locally known as “Limestone City”) is another active area of limestone mining
Mines are not differentiated by size or likely impact due to lack of necessary data. The influence of mines was propagated into the Lakes assuming that the influence of a mine declined to 10% of its initial value within 5 km and 1% within 10 km.
Spatial distribution of coastal mines as a stressor in the Laurentian Great Lakes (Inset: Keweenaw Peninsula, Lake Superior)