Efficient Mine

The Efficient Mine is a special metal-production building that can only be constructed on top of Underground Ruins. It refines raw inputs into Scrap Metal and is categorized under Metal production. The building is intended to provide a higher-throughput source of Scrap Metal for smelting and supports two production recipes that trade treated wood and optional extracted material for large batches of metal scrap.

The Efficient Mine has two recipes:

• 1 Treated Plank → 5 Scrap Metal. With a fully staffed Efficient Mine (10 workers) and a steady supply of Treated Planks, a single mine can supply approximately 2.77 Smelters.
• 1 Treated Plank + 2 Extract → 10 Scrap Metal. When supplied with both Treated Planks and Extract and staffed with 10 workers, a single mine can supply approximately 5.55 Smelters.

Construction and placement rules require building the Efficient Mine directly above Underground Ruins; entrances were adjusted in Update 6 so that mine entrances sit at ground level. Worker capacity was increased in Update 7 so Efficient Mines have 10 workers by default (up from 5). Update 7 also changed the basic recipe to the current Treated Plank → 5 Scrap Metal and added or adjusted the second recipe (used by Iron Teeth’s Efficient Mine variant) to use 1 Treated Plank + 2 Extract → 10 Scrap Metal.

Practical usage notes:

• Prioritize a steady flow of Treated Planks to the mine to keep it operating continuously; output scales with worker availability and input supply.
• Supplying Extract in addition to Treated Planks doubles scrap output per cycle and significantly increases how many smelters one mine can feed, making the second recipe ideal when Extract is abundant.
• Because the building must be placed on Underground Ruins, choose ruin locations that allow efficient logistics (roads or conveyors) to smelters and storage.
• Staffing matters: maintain population and job assignments to keep the mine at its full 10-worker capacity for maximum throughput.