Why copper-bearing rocks here, but not there?

I recently did a backpacking trip in the Grand Canyon that included Horseshoe Mesa. There are old copper mines there, and beautiful green and blue copper-bearing rocks visible. I asked (in a facebook forum), why just in that one place and not other places in the Grand Canyon, given how the rock layers in the Grand Canyon tend to repeat themselves for miles and miles. The url is what somebody posted as the answer. It was so satifying to have a question and have it be so thoroughly answered.

The top pic appears to show a steel barrier around the mineshaft opening, although it also looks roughly like a multi-level &quot;Chinese gold washing machine.&quot;<p>The latter is a low-cast static set of table(s) that water can wash metal flakes with no moving parts, and is popular for its low cost or use in areas with no mechanicl parts supply. So gravity is used to separate materials, similar to how river bends make alluvial gold deposits. Early ones were made of wood, but steel would also work.<p>You can see YT videos of a similar design in the defunct Cornwall tin mine.<p>(In ancient&#x2F;olden times, the main industrial metal was bronze, alloyed from copper and tin. Tin is very rare since it has an odd atomic number, with the historical mines being in Afghanistan and Cornwall. Before the Iron Age, Cornwall could have been the &quot;El Dorado&quot; of its time. Iron&#x2F;steel is found everywhere on earth except Japan, so steel democratized industry across Europe and Asia, but Japan had to start WW2 for it.)<p>(Most gold mining is collecting flakes, not nuggets. 1 gram per ton is usually considered commercially viable, and more makes it dramatically moreso.)