Tiberium is C&C 1. Red Alert does not have Tiberium, but ores and gems. And ores can be found on the superficial layer of the earth, so it is not that much of a stretch. Although from a game design perspective, it is greatly simplified.
Using harvesters to scoop up gold and gems is kind of dumb, but I think it's acceptable as a game design convention.
I feel like Generals had the best economic design out of any C&C game. Your helicopters / trucks / bare-footed workers simulate modern logistics by collecting crates of resources from a "warehouse". Once they are collected, you can switch to your secondary economy of pumping oil, getting supplies delivered by the UN, stealing money from the internet, or selling goods on the black market.
