Past Cobb-L-Stones Articles

White Pine Copper
by Tom Toothman

August 2021

If you go to the CCGMS clubhouse and walk to the far end of the main meeting room, you will see a large sheet of copper metal on the mantle above the small fireplace. The copper sheet is 28” × 26”, but is only about 1/4” thick. It weights around 25 pounds. We recently cleaned it with a weak acid in water so that you can see the native copper metal free of a thin layer of oxidation that had colored it green and black.

Copper from White Pine Mine at the CCGMS clubhouse

We know some of the history of this large specimen due to good labeling when we bought it in 1995. The copper was originally from the White Pine Mine in Ontonagon County in the Up-per Peninsula (UP) of Michigan. The massive native metal copper deposits in the Keweenaw Peninsula of the UP were formed by volcanic activity that started just over 1 billion years ago.

This specimen is from a secondary deposit located just south of the
volcanic region and was created in sedimentary layers in a shallow sea a
few hundred million years later. This ore body, the economically
recoverable portion, was 5 miles long by 2.5 miles wide. The mine
eventually reached a final depth of 2500 feet.

Like many mines, activity started and stopped over its history. The first mining period only lasted from 1880 to 1882 and then a longer second period of 1907 to 1921. Although this was a large lode of copper, much of it was not native metal, but in the form of a sulfide mineral called chalcocite. To eventually become a viable deposit the ore needed to be crushed to the size of fine sand, the metals concentrated by a process called flotation separation and then smelted to remove the sulfide/sulfur elements.

The mine reopened in 1953 and work continued until it was closed in 1995. During peak production in the mid-1970’s, as many as 3000 people worked there with 25,000 tons of ore being processed each day. When the mine closed it ended 150 years of modern copper mining in the UP area. This recent history does not include prehistoric mining by Native Americans that spanned back an estimated 8000 years. You can still collect cop-per and related minerals in the UP area- at least in the summer months. Total metal recovered from the White Pine Mine was 4 billion pounds of copper and 45 million ounces of silver.

We have seen similar, but larger specimens of copper from this mine at museums in the US. The largest we have seen is at the Smithsonian Natural History in Washington, D.C. This piece is mounted by itself on a large wall and is about 15 feet long by 5 feet high.

Photo by Tom Toothman

Cobb County Gem & Mineral Society