Postwar years 1865-1880
Calumet Mining Company Stamp Mill, 1870, near Calumet pond

The period following the Civil War was one of great difficulty for the majority of the mines, and yet in these years came the discovery and development of one of the richest mines in the world, the Calumet & Hecla.
The demand and price for copper decreased following the war, closing most of the smaller and newer mines.  Most of the fissure mines (those relying solely on mass and barrel copper for their production) were also unable to sustain themselves, and investors were slowly realizing the importance of the amygdaloid and conglomerate veins (and also the large amount of capital required to open these).  But due to a nationwide depression following the stock market crash of 1873, financing became more difficult.  The great C&H mine almost did not make it through its early years of 1866-1870.
Here are some companies that you may find interesting...

Amygdaloid M. Co.
Central M. Co.
Girard M. Co.
St.Clair M. Co.
Other companies
Calumet & Hecla