Mines are World Buildings that you can occupy permanently. They provide resources (Lumber, Ore, Sulfur, Crystal, or Gold) to the Castle they are attached to.
The number of mines you can control at any given time is based on your Rank. Each mine that you control will increase the total amount of resources produced hourly by 20-40 units respectively. The castle that will receive the bonus will be determined by which castle the hero sent to occupy the mine was sent from. Please note that there is no bonus given to production or your hero’s load for keeping a hero at a standard mine.
Taking a mine is done by dispatching a hero(requires 30 actions) and after that by perfoming a mine action(requires 75 actions) which will increase the % bonus:
Currently the best mine control strategy is to control one type of mine if you are active enough to use market to redistribute it at regular intervals. Some items give % of a resource, even if the item doesn't mention it. You just have to try the item to find out if it gives a set amount of that resource or a %.
There is no benefit to keeping a hero at any mine other than to protect it. You are allowed 5 mines & 25 Heroes at 1,000,000 fame. So to keep a hero at each mine is a waste of Heroes. Any hero that you consider extra should be used as a castellan equipped with your race specific castellan spells.
Your hero will not collect any extra resources from any standard mine, the only “mine” that will give your hero resources for occupying it is a Resource and Experience Building.
Farming high level treasures can bring in much gold so after you are able to do hit level 9-11 treasures Gold Mines become virtually useless.