When I return to starport in order to sell my minerals, the Trade Depot states that no artifacts are present and does not list the minerals that I mined. I can't "get rich" if it won't buy anything but artifacts. Did my download not load something?

In SF2, the starport literally only buys artifacts. You can dump redundant trade maps there. They sell the minerals needed for repairs. Alien trade centers will buy your minerals. Demand changes randomly every 24h.