Monday, March 12, 2012

Gold in the Midwest: Placer Gold in the Saint Croix River (Part 1)

(The Saint Croix River is highlighted in yellow in this map.)

 "The Dalles"

You would-be Minnesota and Wisconsin placer gold miners take note: there is placer gold to be found in the Saint Croix River that forms part of your state's boundaries. This area, known to locals as "The Dalles," even got a write up in the Minnesota Engineering and Mining Journal back in 1902.


Back in those days, clued-in locals would scramble to recover placer gold from bedrock cracks and crevices during extreme low-water conditions caused by the closure of a logging dam upstream. In "The Dalles," the Saint Croix cuts a narrow channel through ancient basalt lava flows and gold-bearing gravels are subsequently deposited into bedrock cracks and crevices as well as packed behind large obstructions in the rocky river bed itself.

Nuggets and Fine Gold

According to the historical record, gold recovered from "The Dalles" area included nuggets and coarse pieces, as well as large amounts of very fine gold. The largest nugget recovered in the old days in the Saint Croix River weighed in at a little over 10 grams, or about 1/3 troy ounce. 

 (Basalt boulders and bedrock of "The Dalles.")

Geologists believe "The Dalles" gorge acted as a large, natural sluice box where gold and heavy black sands concentrated in large amounts in and behind "irregularities" in the Saint Croix's bed. Although the experts are not entirely sure of the source of this placer gold, one theory postulates that it may have been gold that was "re-worked" by the river itself from a large gravel bed just north of "The Dalles."

Just upstream of "The Dalles" gorge, the Saint Croix River flows through a wide valley where the existing bedrock is composed of Cambrian Period shales and sandstones. Millenia ago, both river and glacial sediments containing gold were deposited close to the boundary created by these shales and sandstones and the basalt bedrock exposed at "The Dalles." This contact zone is believed to be the major source of placer gold in the Saint Croix River.

There's more to come on gold in the Saint Croix, so stay tuned. Good luck until next time.
If you liked this post, you may want to read: "Where to Find Placer Gold (List B)"

(c)  Jim Rocha (J.R.)  2012

Questions? E-mail me at jr872vt90@yahoo.com


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