Preliminary Evaluation of Establishing an Underground Taconite Mine, to be Used Later as a Lower Reservoir in a Pumped Hydro Energy Storage Facility, on the Mesabi Iron Range, Minnesota

Abstract

Ten sites, with some deep drill hole information, were crudely evaluated for their potential to establish a deep-seated underground taconite mine that would be located to the immediate south of the Mesabi Iron Range. Such a mine would produce a cavern that could be used as a lower reservoir in a Pumped Hydro Energy Storage (PHES) facility that would be connected to a surface reservoir (abandoned water-filled mine or tailings basin) via a mine shaft. The lower reservoir would be excavated from ore that would help to reduce the costs of producing the cavern. Out of the ten evaluated sites, there are four candidates that appear to be the most enticing with regards to establishing an underground mine in areas that would not be mined using conventional open pit methods. These higher priority candidates are: 1. Taconite area – mining of a taconite ore body on the west end of the Mesabi Iron Range could produce a cavern up to up 140 feet high, with a holding capacity of 14 billion gallons (43,200 acre-feet), and a maximum head of 700 feet below the surface; 2. Cliffs-Erie area – mining of metamorphosed high-grade taconite from the eastern Mesabi Iron Range could produce one or two caverns, each up to 90 feet or more high, with a maximum head of 1,235 feet below the surface; 3. Northshore area – mining of metamorphosed high-grade taconite from the eastern Mesabi Iron Range could produce a cavern up to 150 feet high (based on crude data), with holding capacity of 7.8 billion gallons/24,045 acre-feet (based on 150 foot high cavern), and a maximum head of 600 feet below the surface; and 4. Dunka Pit area – mining of metamorphosed high-grade taconite from the eastern Mesabi Iron Range could produce one or two caverns, separated by a fault zone as follows: a) an upper underground cavern/reservoir 􀂃 up to 110 feet high, 􀂃 with a holding capacity of 1.5 billion gallons/4,635 acre-feet (with potential to expand to the south), 􀂃 with a maximum head of 450 feet below the water-filled and abandoned Dunka Pit taconite mine; b) a lower underground reservoir 􀂃 up to 90 feet high, 􀂃 with a holding capacity of 365 million gallons/1,120 acre-feet, 􀂃 with a maximum head of 800 feet below the Dunka Pit taconite mine. While these four sites have sufficient drilling to make preliminary estimates on water holding capacities, more drilling would be needed to fully assess their ore potential. In the event that any of the above four sites are eliminated due to conflicting land uses, any of the other six sites discussed in this report could be chosen for underground mining. These sites are classified as “lower priority” only because detailed drilling to define the full potential of an underground mine is lacking. Out of this lower priority group, the Eveleth area would be the next best candidate. The lowest priority candidates would be the Two River Reservoir area and McKinley area.