This is the likely outcome from digging a massive open pit iron mine near the Bad River in Northern Wisconsin, scientists conclude. Read the entire report, and remember that the hundreds of millions of cubic yards of acid runoff-producing blasted waste rock (formerly the Penokee Hills) will be allowed to be dumped under rewritten environmental rules - - a/k/a Walker's 'environmentally safe' mining bill - - in or at the edge of waterways that drain to Lake Superior.
Unlike the Precambrian iron formations mined in Minnesota and Michigan, the Ironwood Iron Formation in the Gogebic Range is steeply tilted (ca. 60° to NNW) and has limited natural exposure at the surface.
A stably benched 200-300 m deep open pit mine in the Ironwood would therefore have a very large surface area and would require the removal of an immense volume (on the order of 330 million m3) of waste rock. Responsible monitoring and managing such a volume of waste rock, and a pit of such depth, over the long term would pose significant engineering challenges.
Although the economic target mineral in the Ironwood Formation is an iron oxide (magnetite), the overburden rock that would be stockpiled as waste (the Tyler Formation) contains significant amounts of reduced iron as sulfide (pyrite, pyrrhotite and related minerals), which could react with oxygen to generate acid mine drainage. The iron carbonate (siderite) present in small quantities in the Tyler Formation would not help to mitigate acid production, and the fine grain size of the rock would accelerate the generation of acidic solutions.
A 3-meter thick pyrite-bearing layer within the Ironwood Formation itself also has the potential to generate acid drainage, given the fine grain size to which the Ironwood would be crushed onsite for the magnetic separation process. The Tyler and Ironwood Formations also have surprisingly high phosphate concentrations, and mobilization of this material could lead to eutrophication of water bodies...
The scale of a modern open pit mine in the Gogebic Range would be completely different from historic mines in the region, which were localized, primarily underground mines that targeted high grade ore and did not involve excavation of the Tyler Formation.