Copper

specimen number:
8311552

location:
Baltic Mine, Houghton Co., Michigan, USA

description:

Superb grouping of crystallized native copper. In great condition all around.

The Baltic mine, situated near South Range in Houghton County within the historic Keweenaw Peninsula copper district of Michigan, United States, was a highly successful and long-lived underground native copper operation. Geologically, this deposit is hosted within the Mesoproterozoic-age Portage Lake Volcanics of the Midcontinent Rift System, where hot, metal-bearing hydrothermal fluids mineralized the exceptionally wide, steeply dipping Baltic Amygdaloid Lode, a porous and brecciated top of a basaltic lava flow that precipitated pure native copper and minor native silver alongside unique copper-arsenic minerals like domeykite and algodonite within a matrix of calcite, quartz, and epidote. Historically, the rich lode was discovered in 1897 by John Ryan, and the Baltic Mining Company was formally organized that same year to develop a multi-shaft underground complex. The mine quickly became a major producer, pioneering the use of a specialized waste-rock backfilling method to safely support its wide underground chambers and coming under the management of the prominent Copper Range Consolidated Company in 1901. Production continued steadily through the early twentieth century, providing critical copper supplies during World War I, but declining ore grades at extreme depths combined with the harsh economic realities of the Great Depression forced the permanent cessation of all underground mining operations in 1932.

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