As an Aminer, you have 3 pathways of income to choose from, Industry, Tax, and Mining. Industry will give you goods per turn that you sell on the market, Tax is housing and population that will give you credits per turn, and Mining will give you a mineral production per turn. Which one you are researching infra in to be most effective in is the one you want to put your land into. As Mineral miner, you don`t need land, you need planets. As tax , you put your land into housing and build your population up. As Industry you put your land into industrial and make your goods per turn.