Algodonite, Domeykite

specimen number:
2262260

location:
Mohawk Mine, Keweenaw Co., Michigan, USA

description:
Rich heavy masses of algodonite and domeykite, known sometimes as mohawkite, with quartz.

The Mohawk mine, situated near Mohawk in Keweenaw County, Michigan, is a world-famous mineral locality celebrated for producing exceptionally fine specimens of rare copper arsenide minerals, most notably algodonite and domeykite. Geologically, this historic deposit is situated within the Neoproterozoic-age Portage Lake Volcanics, a thick sequence of native copper-bearing basaltic lava flows and interbedded conglomerates. Unlike the typical native copper mineralization found throughout the Keweenaw Peninsula, the Mohawk deposit is unique because hydrothermal fluids rich in arsenic ascended through localized, steeply dipping cross-fissure faults, reacting with the native copper to precipitate a complex suite of gray, metallic copper arsenides including domeykite, algodonite, and the localized mixture known as mohawkite within a calcite gangue matrix. Historically, the Mohawk Mining Company began formal underground development and surface quarrying operations at the site in 1898 after the arsenic-rich veins were discovered during regional exploration. The mine operated with high intensity across six deep shafts, producing massive amounts of copper ore until declining metal prices, escalating underground production costs, and the depletion of the highest-grade arsenide chutes forced the permanent closure of all underground mining operations in 1932.

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