For the second one, you might need a spell which targets only goldmine. In order to do so, you can use let's say Chain Lightning which targets even invulnerable units, does no damage and has only 1 target. Now, let's go to the triggers.
Trigger
Event - an unit begins casting an ability
Conditions - Ability being Cast equal to (Yourability)
Actions - If (Unit Type of (Target Unit of Ability being Cast) not equal to Goldmine) then do actions
-> Order (Casting Unit) to Stop
-> Play (Casting Unit)'s Stand Animation
-> Game - AutoTimed text to (Player Matching Condition (Matching Player) is equal to (Owner of (Casting Unit))): Must target Goldmine
Trigger2
Event - an unit starts the effect of an ability
Conditions - Ability being Cast equal to (YourAbility)
Actions - Neutral Building - Add Gold to Gold Mine (Add x gold to (Target Unit of Ability being Cast))
That should do it.
For the first one, I don't actually get what you want? Create a tree from nothing? If so, try Darky's.