Gold reward is determined by threat tables in fates. Remember: you have to damage 1 mob at least 1 time to get credit.

As a healer, you should get gold every time.

Quick Guide
1. Arrive at fate
2. tab to first mob and apply your instant dot (both healers have one)
3. spam a few heals for 10 seconds
4. tab to mob apply dot
5. repeat steps 3 and 4
6. get gold

You should also be able to get gold without healing. tab target mobs and apply dot.