Simple Triggering Question

Im kind of new to game triggering (Iv been doing mostly cinematic triggers), and Im having very newbie problem.. How can I order group of slaves (wisps, peons) to gather gold and wood?

Pick all units in region X (or within X distance of point) matching (unit-type == peon) or (unit-type == wisp) and do
Order picked unit to do order picked unit to harvest [whatever]. This is a unit - order targeting a unit.

Or even better, you could do what ThyFlame said except instead of picking one place to harvest, you could pick a random gold mine in a reigion about 800 around the unit (in other words the only gold mine). Thyflame's idea works better if you want to order them once at the beginning of the game, however.

Thanks to both of you, that helps lot :D .