To make the rustroot extract, you must have the Prospecting skill. With the prospecting skill also comes a Prospecting Action, under the Adventure menu. You must have rustroot extract in your inventory to use this action, and it will scan a 1000x1000-tile area around you for possible mine locations (giving results such as Mineral, 15% accessible, which means that it is 850 tiles away from you or something to that effect), upon which you need to build a mine hole. You should also get Yeomanry or Lawspeaking, or whatever you want so that you can claim the mine immediately. It's not a good idea to leave a mine in unclaimed territory. Good luck!
P.S. You should use "affects" instead of "effects" in the title. Affect is a verb, effect is a noun.
