Thanks Hengli. I'll continue checking it.
Thanks for the feedback guys but I know it's random. I've been mining for more than 6 months. I wouldn't start a topic for only one poor mining. I'm speaking of an average.
It's not random, it depends on how many times your mine gets attacked. If you have noticed doing a 10 hour mine during the day will usually net you 10 diamonds. However if I do a 10 hour mine at night I will usually get at least 1 or 2 mines that will give 30+ diamonds. I have got as much as 47 diamonds on my mines, think more then that but I can't remember the specific values. I'll do a few mines a record my data. The one I just looted that was done during the day resulted with about 10, 10, 16, 13 diamonds. I expect this run to give at least double diamonds in total for all 4 mines.
Also being a higher lvl will overall most likely net you less diamonds since often there are a lot more players at higher lvls and are more active in using all their resources plundering enemy mines. This will greatly depend on how old your server is and if it has had any merges. I imagine server 1-50 have 80%+ of all the active players at max lvl or as of the recent patch 90+.