Gogebic iron range, Gogebic County, Michigan, USAi

Regional Level Types
Gogebic iron range	Mineral Province
Gogebic County	County
Michigan	State
USA	Country

LOCATION: The Gogebic Range is an elongated area of iron ore deposits located within a range of hills in Gogebic County, northern Michigan, and partially within Iron County, Wisconsin, just south of Lake Superior. It extends from Lake Namakagon in Wisconsin eastward to Lake Gogebic in Michigan, or almost 80 miles. Though long, it is only about a half mile wide and forms a crescent concave to the southeast. The Gogebic Range includes the communities of Ironwood in Michigan, plus Mellen and Hurley in Wisconsin.

HISTORY: First produced in 1884. Iron ore was shipped via rail from the Gogebic Range to the Lake Superior port in Ashland, Wisconsin where it was loaded onto vessels and shipped to various Great Lakes ports throughout the region for further transport or smelting into Steel.

For decades in the late 19th century and into the 1920s, the Gogebic was one of the nation's chief sources of iron. Iron from the Gogebic helped to fuel the industrial boom in the Upper Midwest during these years. By 1930 mining was winding down in the area. The mines began closing as the national economy suffered from the Great Depression. The result was widespread economic devastation in the communities of the Gogebic Range.

In 1960, the cost of producing a long ton of ore from an underground mine in the Gogebic range was $11.80, as compared to $10.88 for the Marquette Range, and $9.87 for the Menominee Range. Decline in costs from 1959 was due to closing higher-cost mines as demand fell off.

Some mines continued to operate into the 1960s, but the volume never reached the same levels as in the earlier boom years. A defining event was the last shipment of iron ore in August 1967 to Granite City Steel in Illinois.

Ore was mined from around 40 individual mines between 1877 and 1967. Iron mines of the era exploited the "natural" (soft) iron-rich ores in a 15 kilometer-long stretch in the central portion of the range straddling the Michigan-Wisconsin state line. These mines were mainly of the underground shaft type, which were among the deepest iron mines in the country. Due to these characteristics, and the greater associated costs involved with extracting the ore, these mines were unable to compete economically with the larger open pit iron mines in northern Minnesota and elsewhere.

MINERALOGY: Mineralization is a range of Fe deposit (Mineral occurrence model information: Model code: 241; USGS model code: 34a; BC deposit profile: F10; Deposit model name: Superior Fe [BC name is Lake Superior & Rapitan types iron-formation]), hosted in the Paleoproterozoic Ironwood Iron-Formation.

GEOLOGY: Local/area rocks include rocks of the Early Proterozoic Baraga Group; Tyler Formation (Light- to dark-gray, feldspathic, fine-grained sandstone, argillaceous siltstone, and argillite. Near base, ferruginous argillite contains beds of cherty sideritic and pyritic iron-formation). Regional geologic features include N-dipping sediments. Region trends E-W.

The Ironwood Iron Formation lies in stratigraphic sequence with the other Paleoproterozoic rocks. All rocks dip 50-55N. The structure is thought to be a monocline or the N limb of an E-W anticline. The N-dipping Paleoproterozoic rocks are cut by Paleoproterozoic diabase dikes and Fe mineralization seems to be associated with the dikes. The dikes are almost perpendicular to the dip of the rocks. During Paleoproterozoic time the entire area of Michigan's Upper Peninsula was regionally thermally metamorphosed, creating zones of metamorphism from chlorite to sillimanite, exclusive of kyanite only. The Gogebic Iron Range is in the chlorite zone of metamorphism, but it should be noted that this area is the least metamorphosed of all the Upper Peninsula-Wisconsin iron ranges.

PRODUCTION: Ore mined: 259,307,689 metric tons (1884-1967).

Other Databases

Wikipedia:	https://en.wikipedia.org/wiki/Gogebic_Range
Wikidata ID:	Q5577341
Link to USGS MRDS:	60001574

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