Gt.blockores.0/en

ore blocks are not normal blocks. Because of the enormous range of ores GregTech can generate, all GregTech ore blocks are non-ticking TileEntities. However, for bandwidth reasons, only GregTech ore blocks that are visible to players have their TileEntity data sent to them. The result is that, in cases of server lag or network bugs, GregTech ore blocks can temporarily appear as featureless gt.blockores.0 blocks.

gt.blockores.0 blocks do not drop anything when broken, and as such users should not attempt to break them.

Under most circumstances, these blocks should revert to actual ore blocks almost immediately. If they do not, log out then log in to the server again (forcing the identifying packets to be re-sent). If problems persist, consider filing a bug report.