Unburied Treasure

A large group of spectators waited for the U.S. Army Corps of Engineers’ tug and barge at the Lilly Pond dock inside the breakwall of the Portage Canal North Entry in Michigan’s Upper Peninsula. 

A flatbed semitrailer truck waited, too, to carry to its new home the spectacular curiosity that the crowd anxiously wanted to see. 

No wonder the interest. How often is an almost 20-ton boulder of nearly pure natural copper pulled from the bottom of Lake Superior? Almost never, I can tell you from personal experience. I’m the one who found this copper chunk ... and it took 10 years, a mountain of forms, part of a federal grant and a U.S. Army Corps crew to raise it.

But first I had to find it....

For well over a century, the Keweenaw Peninsula served as home to a multi-billion dollar copper industry. The roots of mining here, though, go back even further, thousands of years. Native people first discovered the nearly pure copper and silver deposited in fissure veins within the local basalt matrix. The malleable copper was easily shaped into valued tools. Along the sparsely vegetated shores of Lake Superior and the inland lakes of the post-glacial period, the ancients mined the red metal - some believe for about 10,000 years - and it was traded in a huge area of North America and perhaps beyond.

As both a diver and an amateur geologist, I always knew I’d have an excellent chance of discovering copper, silver and associated minerals if I could just spend a summer diving on exposed basalt reefs in Lake Superior offshore along the Keweenaw Peninsula. In 1991, I got the chance to test my theory.

Usually, Lake Superior warms enough for wet-suit diving by mid-July, when I had time off. The area that I wanted to cover would be too large to simply swim through. What I needed was a reliable crew member to tow me around the Eagle River Shoals of Great Sand Bay on a 60-foot ski rope behind my little 14-foot open boat. Don Kauppi of Copper Harbor, always interested in trying something new, agreed to team up for the summer.

In theory, we should discover all decent-sized fissure veins of copper as long as we paralleled the shore and the basalt reef. The theory held and within a few hours of “trolling,” I had crossed several veins of copper littered with pieces of native metal. Here was a discovery for which those early native and European prospectors might search their entire lives. I was awed by the knowledge that human hands had never touched these copper specimens.

Each time we went out, we found new copper veins - some with minute attachments of silver. Then one day, Don towed me over a nicely sculpted piece of copper about 6 feet long and 3 feet high. What a beauty! As per my standard procedure, I let go of the tow line and trailed the vein. Loose copper ran richly along its length. As I followed the vein toward open water, I scanned for more metal. There remained only about 50 yards of exposed basalt before the vein would dip into the deeper sands and sediments of the lake bottom and disappear from sight.

Suddenly, I lost sight of the vein under some boulders. Well, that’s the end of that, I thought. Then I noticed the edge of something flat and large, not a normal boulder. It was copper! An enormous hunk of pure metal - well camouflaged by a layer of the brownish organic material covering the lake bottom.

As I hovered over it, I tried to estimate its length. Any diver will tell you that your mask magnifies underwater objects. So this must be smaller than I’d first thought. But a few minutes of examination had me shooting to the surface faster than normal (looking back, I’m glad I was in only 30 feet of water). I shouted excitedly to Don. When he came close enough to decipher my clamoring, Don knew it was something big. But as we headed home for the day, he doubted that my descriptions could be accurate.

The next day we went back, tape measure in hand, and I carefully measured the copper - 19 feet long, more than 8 feet wide and averaging 18 inches thick.

Wow! A copper “nugget” weighing about 20 tons and apparently detached from the vein. Now, could we get it out?

First we needed salvage permits from the Michigan Department of Natural Resources and the U.S. Army Corps of Engineers. Don and I set to work filling out forms. Several weeks and many phone calls later the disappointing decision came through: leave the copper on the bottom as part of a newly enacted underwater preserve meant to protect the few remaining shipwrecks that dot the Keweenaw Peninsula. This great blow killed my hopes to raise my copper treasure.

Five years later, in 1996, I started a new job designing exhibits for the A.E. Seaman Mineral Museum on the campus of Michigan Tech University (MTU) in Houghton. One day I mentioned our copper discovery to Stan Dyl, director of the museum. I asked if I could use the museum as leverage to re-apply for salvage permits.

Stan thought it was an excellent idea. The copper boulder could become part of the museum’s collection, where it would be properly curated and put on display.