CH- Don't know where "Up North" you're located but the UP of Michigan was the country's first Cu mining region. My boss is a geologist and showed me some cool copper-silver rocks that people sell on ebay. I'll finsd out the name of them tomorrow. Glaciers may have moved Cu rocks down to your location or somehow gravel got brought to your location, although generally gravel isn't hauled long distances for road work.
Here's some info on MI's copper mining
Copper I
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