Gold is the currency used in Minethings to purchase Items and Mines from other players. Gold is a universal item which means that it is not city specific - the money from a sale in Harmond can be used to purchase something in Daigard, for instance. Gold can be mined from any mine. Gold findings range from 1-5g for a "yellow" find, 6-25 for a "green" find, 26-105 for a "blue" find, 106-300 for a "red" find, and up to 625g for a "purple" find. Nothing is known about orange gold finds, because they (in theory) do not exist and apparently the maximum find is 625. This remains untested because gold is usually only mined in a starter mine, and the starter mine does not have orange items.
There are currently no ways to remove gold from the game; there are no money sinks.