Refilling mines

[Red_Hummingbird]

On the tip of the day, it says, 'Refill your mines before they run out, so you don't have to rebuild them'.
Please can someone tell me how to do this?
Thank you

[Ias87]

You can buy refills for gems in the trader.
But this is a very expensive way to do it, and in most cases (gold mines not included) it is cheaper to send out your geologist again, and rebuild the mines.

[Drusek]

'Pay us money to refill your mines before they run out, or rebuild them again and again and again...'.

fixed

[Red_Hummingbird]

Thanks guys. Now I know.
I was hoping to avoid using blue gems. :-(