GEOSPATIAL ANALYSIS OF LAKE WATER CHEMISTRY AND ADJACENT MINING ACTIVITIES ON THE IRON RANGE AND DULUTH COMPLEX

Proposed copper-nickel mining of the Duluth Complex in northern Minnesota will have effects on both the environment and humans in the region. This impact will come from a by-product of mining, which is dissolved sulfate discharge. In addition to the future by-product production, there are already around a hundred years of previous mining on Minnesota’s Iron Range that has already produced sulfate discharge. Sulfate concentrations over 10 mg/l have been found to negatively affect populations of wild rice (Zizania palustris), the Minnesota state grain and an important resource for Native American tribes. In 1974, Minnesota established a state standard that waters used for the production of wild rice must be under 10 mg/l. Many water bodies on the Iron Range are significantly higher than this standard (some over 1000 mg/l). It is not known definitively whether these high levels are the result of the natural abundance of pyrite and other sulfide minerals in Iron Range bedrock, or of the increased sulfide weathering rates due to mining activities. We present a spatial analysis of Iron Range water bodies and their hydrologic connection to mining pits, and tailings basins. Using ArcGIS, several water bodies were identified that appear to have no influence from the mines, and have not previously been sampled for sulfate. These sites may be visited in the next few weeks to be sampled, and analyzed to show a standard level of sulfate for the region. If iron mining has caused high sulfate levels, copper-nickel mining east of the Iron Range has the potential to do the same to the water bodies surrounding the Duluth Complex.