GT can only disable vanilla ores. All other ores must be disabled in the config of the mod spawning them. So in case of forestry ores in the forestry config. Even IC2 with default configs keeps generating its own ores, so it must be disabled in it's config.
Alright, i got it all working now! Thank you sir for your fast replys, and a huge thank you for developing this, i enjoy playing this version of gregtech so much and your work on this is very much appreciated!