More on Glacial Gold
(NEVER underestimate the immense power of glaciers.)
Canadian miner "PL" contacted me with a few questions about glacial gold. His queries were astute and I thought they, along with my overall response, would provide grist for the mill in terms of an entire post. So here goes.
An Extremely Powerful Force
Right off the get-go many of you should be aware of the fact that nearly all the placer gold found in the Midwestern United States and the upper Midwest (Ohio, Indiana, Minnesota, etc.) was glacially deposited. At various points in the distant geological past large glaciers moved slowly southward from Canada into the U.S. As this glacial movement occurred it swept with it gold "ground out" from host veins or, at times, placers in the Land of The Maple Leaf. The term "ground out" is quite appropriate here since glacial erosion is an extremely powerful force. Image a gigantic rock crusher or grinder moving slowly across Canadian terrain on its way south, downing forests and leveling hillsides, gathering up and rolling huge boulders forward, and grinding large rocks into sand. Geologists believe that some of these ancient Canadian glaciers stretched and widened as far as millions of square kilometers (1,000,000 kilometers = 621,371 miles) as they ground their way from Canada into the U.S. as far south as the midsection of our nation. Then, as the climate warmed, Canadian glaciers retreated slowly northward again only to renew their southward movement into the U.S. during the next glacial epoch. Throughout this entire series of "ebb and flow" movements these ancient glaciers carried gold with them that they had scoured out in Canada.
(You can't beat a Canuck when it comes to gold mining.)
One of PL's questions concerned the size of glacial gold. He asked if I thought larger or coarser gold such as nuggets could be found if one were to prospect the bedrock of current streams that had once been in the path of glacial activity. This is a good question and it begs answering so let me give it my best shot. Anything is possible, right? That said, I do know that here in the U.S. where glacial gold deposits have been worked in the Midwest and Upper Midwest some small nuggets have been recovered over the years but most of the gold in American glacial till (i.e., glacially deposited gravels) is usually restricted to small grains and flakes, with occasional larger flakes turning up. In Canada, you're closer to the original sources of that gold so any gold that "escaped" the grinding clutches and mechanical forces of glacial movement could (and probably would be larger) but you always have to bear in mind the extreme reduction of materials that any glacier exerts, anytime and anywhere. If a glacier has passed over bedrock it will have scoured that bedrock pretty well, whether in Canada or anywhere else. However, eons of time have passed since the glacial epochs I already mentioned. Current gold-bearing streams and rivers that exist in known glacial areas of the past might indeed produce lots of large gold but that gold might not (note I say "might not") have been deposited as glacial till but by the erosion and breakdown of veins, stringers, or placers that are part and parcel of a given area's original gold mineralization and deposition. Granted, all of this is supposition and I've never been a big fan of working glacial till. Nor am I highly experienced working glacial gold deposits. But once again, Ma Nature can do some pretty weird things when it comes to depositing gold.
(Glacial gold from Ohio...it probably came from Canada eons ago.)
Good to Go
The overriding factor to understanding glacial gold and working glacial till is to understand completely the forces at work that were responsible for breaking that gold away from its sources, carrying it along over hundreds or thousands of years, and all the while reducing that entrained gold through pressure, movement (however slow), and friction. Gold is very soft and it wouldn't take much time (geologically speaking, that is) for larger pieces of gold to get ground down to flakes or microdots. All of this is a moot point, however, if you run into patches of glacial till carrying LOTS of gold. Then you're good to go. I've always said I'd rather have an ounce of fine gold in my poke than a quarter ounce nugget and I still stand by that statement. Nuggets are great and fun to recover and look at but gold is gold and quantity is always better than...well...quality unless you have nice specimen to sell to a collector for big bucks.
(These small pieces were recovered in Pennsylvania!)
Hang tough out there.
(c) Jim Rocha 2017
Questions? E-mail me at firstname.lastname@example.org