Rhodochrosite with Manganite

specimen number:
2062228

location:
Montreal Mine, Iron Co., Wisconsin, USA

description:

The Montreal mine, situated just west of the city of Montreal in Hurley, Iron County, Wisconsin, was a legendary underground iron ore operation that ranked as one of the deepest and most productive mines on the historic Gogebic Iron Range. Geologically, the deposit is a Paleoproterozoic sedimentary iron-formation localized within the heavily folded and faulted Ironwood Iron-Formation, which consists of interbedded chert, cherty carbonate, and hematite-rich layers dipping steeply to the north at approximately 60 degrees. High-grade, soft hematite and goethite ore bodies were formed through extensive secondary supergene enrichment, where deep-circulating meteoric waters dissolved silica along structural traps formed by the intersection of impervious Keweenawan diabase dikes and the sedimentary bedding planes. Historically, iron ore was first discovered at the site in 1882, and formal underground extraction commenced in 1886 under the management of the Montreal Mining Company, which later became a subsidiary of Oglebay Norton Company. The mine operated continuously for nearly eight decades, utilizing the massive, four-compartment Number 5 shaft to reach vertical depths exceeding 4300 feet, making it the deepest underground iron mine in the United States before the depletion of economically viable reserves led to its permanent closure in August 1962.

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