Ore and Fuel miners are the basic income of each colony, in addition to the Fuel Refinery and the Ore Refinery. You need to research "Mobile Resource Collectors" and complete the "Mobile Extraction" facility to unlock both miners. Each miner requires a trained miner colonists to build and become increasingly expensive the more you own.
The income from each miner can be improved by completing the "Refining Equipment's" facility and later on even more by completing "Submolecular Extraction".
The cost of a ore miner is calculated with the following formula:
1 Ore Miner = (numminers*(numminers/6)/6)+1
While the cost of fuel miners are calculated with the following formula:
1 Fuel Miner = (numminers*(numminers/8)/8)+1