Hello,
Go to tab "General Settings", button advanced..., in new window go to tab "Looting and farming options" and add id of veins at ignore in textbox "Don’t harvest object (one id by line)".
You can get id of object in wowhead URL, in this URL (Copper Vein):
http://www.wowhead.com/object=1731/copper-vein
you can find "object=1731", the Id is 1731 and it is an object (you need to put objects in this list, if url contain "item=1234" it is item id and this not works on "don't harvest object").
If you need help to get objects id tell me name of veins.