Choose one of the following Rocks for more details:
Native Copper-bearing Conglomerate
As North America's rift failed, sulfur-poor solutions percolated through its rocks, taking copper from basalt and depositing it in overlying sediments.
This rock contains tiny sedimentary particles of gold, uraninite, and pyrite. Such ores can no longer form. Higher levels of oxygen in today's atmosphere would alter the uraninite and pyrite particles before they could be deposited.