I've had a "diamond mine" since last September. My primary city is on "R". I was working it for right at a year before I started my diamond mining city on "B". For me, WWs and Fountains of Youth are my primary diamond producers. I do the GE every week, and I do hit quite a few diamonds there, but the real workhorses are the Wells and Fountains. Wells and Fountains produce diamonds 1-2% of the time. Each time one produces, it will give you 50 diamonds. I have a combined total of 48 Wells and Fountains in my mining city (collected from the GE and Special Events. Watch the special events for the "daily prize"...when it's a WW, grab 'em!!). I will hit at least one 50 diamond haul out of my crop almost every 24 hour cycle (which is right about 2% of the time). I've also started adding Fountains and Wells to my main city as I get them. I'm not as focused on those in my main city, but what I have are also kicking out diamonds now and then. I'm producing right at 300 diamonds a week from just my Wells and Fountains. I will normally hit between 50 and a 100 in the GE each week on my diamond city as well. I've gone from never having any diamonds to buying all of the diamond expansions available to me in both cities. I also regularly spend diamonds on extra negotiating turns in the GE. Even with those expenditures, I STILL have over 3000 diamonds in my account...and that balance grows each week.