The second stop of the day is at the Hill Annex Mine, an iron mine that has been turned into a MN State Park.  It is only a short drive from the last stop at the Holman Esker.  According to the sign at the entrance to the park:
The Hill Annex Mine produced iron ore so rich it could be shipped to eastern steel mills with almost no processing.  In 1912, Arthur Iron Mining Company, a subsidiary of the Great Northern Railroad, owned by James J. Hill, began developing the mine.  By 1914, it had produced over 5,000 tons of high-grade ore.  The Interstate Iron Company, an affiliate of the Jones and Laughlin Steel Corporation, leased the property in 1917 and retained an interest in the mine until it closed in 1978.

The World Wars depleted Minnesota's richest ore bodies.  In 1941, during World War II, the Hill Annex shipped 3,500,000 tons of ore, the largest annual shipment it ever produced.  By 1950, most of the mine's high-grade ore was gone.  Jones and Laughlin installed equipment capable of producing a shipping ore from the lower-grade formations, but production continued to decline until adverse economic conditions forced the property to close in 1978.

The 1848 Northwest Territorial Act required sections 16 and 36 of each township to be reserved for educational use.  The Hill Annex Mine, located within section 16 boundaries, paid over $27 million in royalties to the Minnesota School Trust Fund during its 66 year history.

     The Mesabi Iron Range follows much of Highway 169 from Grand Rapids to Virginia where it makes a hook south and then continues northeast to Babbitt.  Along the road it is easy to see the waste piles of the iron mining operations as well as some remnants of mining equipment. 

     It is likely that the iron formations formed on the north shore of what is called the Animikie Basin.  The Animikie Basin was formed from the Penokean orogeny, a mountain building process in central Minnesota that left a bedrock formation of granite. When iron rich waters would come near the shore the iron would be oxidized by the production of oxygen from the primitive plants in the shallow waters.  Over time some of the low grade ore was enriched by a natural leaching process.  The enriched ore was the first to be mined and as the easily accessible high-grade ore was depleted many of the mines turned to taconite mining to stay productive.

     History  The history of Hill Annex dates back more than a century. The land was originally leased for mineral exploration in 1892. It was leased again in 1900 for a period of more than 50 years. Mining began in 1913 and continued until 1978. Hill Annex Mine produced 63 million tons of iron ore, and was the sixth largest producer in the state. Over its 60 years of operation, mining technology changed drastically. In the early days, horses provided the power. Eventually steam and then electrical power replaced the horse-drawn equipment. When the high-grade ore finally played out, the mine was sold to the Iron Range Resources and Rehabilitation Board (IRRRB) for $1. The IRRRB developed the tour route, converted the clubhouse into a museum/visitor center, and gave tours of the mine for 10 years. In 1988, the Minnesota Legislature made Hill Annex Mine a state park. 
     Geology  The origins of the underlying bedrock formations in the park date back over 2.7 billion years. The two bedrock formations are an iron-bearing metamorphic formation and a metamorphosed sedimentary rock formation. Although the area was mined extensively, it is probable that deposits of other minerals still remain.
     Landscape  The open pit mine has become a lake frequented by osprey, gulls and loons. When the mine shut down in 1978, the pumps that kept it dry over the decades were stopped, and the water seeped back in. The tour offers visitors panoramic views of the mine pit lakes and the rock walls in their various hues of red. (1)
     The boulder (left) is a conglomerate known as cretaceous ore.  It has a high iron content as well as the remains of plants and animals from the Cretaceous period.  It was this high quality ore that could be shipped to steel mills with very little processing.  During the tour one of the most interesting things to me was the size of the reject pile that contained high quality ore but was not processed because the pieces were too large (more than 6") to fit into the crusher.  This ore is already mined and could be used but probably not any time soon as the steel mills prefer the uniformity of the taconite pellets.
     The photo at the right shows an early ore truck before the use of hydraulics.  Notice the unusual arrangement of the body of the truck compared to the driver.  The driver would look over the body of the truck stopping quickly when he wanted to dump the load.  Inertia of the load would tip the box forward causing it to empty.

     The photos below show the east side of the pit from the observation stand. The waste piles are at the top with two exposed layers of the light colored overburden (basically glacial drift that contains no ore) and reddish colored ore.  Notice that the layers of the ore slope downward (from north to south) at a slight angle.  This angular bedding is typical of all the mines in the Mesabi Range and supports the idea that the ores were formed in shallow marine environments as the shore depth slowly increased to the south.

     The Biwabik Iron Formation, the rock formation of the Mesabi Range, has a cap of Virginia Slate (in areas where erosion has not exposed the ore) followed by the iron containing ore with a Pokegama Quartzite and Lower Precambrian rock basement.


 

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1.  http://www.dnr.state.mn.us/parks_and_recreation/state_parks/hill_annex_mine/narrative.html