This is small gold production, where you can claim and develop more gold beyond just your home claim.
To build out your abandoned mines and their infrastructure (groundworks spots) you'll need to use a construction kit (the red box with gears). As soon as you claim an abandoned mine, additional spots appear. To settle this spots with mining machinery and increase the amount of delivered gold from the abandoned mine in the abandoned mine building in your Home Claim, you'll have to apply construction kits to these spots. Keep in mind that different groundworks spots will need different amount of construction kits to start work.
To get construction kits, head to the construction depot and order delivery (to do so, you'll need materials).