Silver with Copper

specimen number:
2102252

location:
Keweenaw Peninsula, Michigan, USA

description:
A branching crystallized grouping of native silver, very little attached matrix. Minor native copper is present.

The Keweenaw Peninsula of Michigan is home to the world's largest deposit of native copper, situated within the Mesoproterozoic Keweenawan Supergroup. Geologically, these deposits formed approximately 1.1 billion years ago when copper-bearing hydrothermal fluids filled the gas bubbles (amygdules) of basaltic lava flows and the voids between pebbles in conglomerate beds. This unique setting produced massive amounts of pure native copper and remarkable "half-breed" specimens, which are rare natural intergrowths of native copper and native silver. Historically, the region saw some of the earliest mining in North America by indigenous peoples, followed by a massive industrial boom that began in the 1840s. Major operations like the Calumet and Hecla Mining Company dominated the landscape for decades, with large-scale industrial mining continuing until the closure of the White Pine mine in 1995. Today, the district remains a legendary site for mineral collectors who search the historic poor rock piles for world-class specimens of native copper, silver, and associated minerals like datolite and prehnite.

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