I used to have mining since launch, and competition was so intense even when the server had 2 or 3 layers that I only ever managed to get 1 blue gem from nodes while I had mining for a couple of months and I only managed to mine 2 or 3 Rich Thorium Veins.
I GOT. 1 BLUE. GEM. IN. 2. MONTHS. OF. DAILY. ROUNDS. OF. MINING. FOR. THORIUM. IN. 4. DIFFERENT. ZONES.