The 
Ruby Mine
The ruby mine is one of the new features that was recently added.
You have to purchase rubies to acquire the Ruby Mine. Once you’ve purchased the rubies, you get the mine.
The mine provides different amount of total rubies, depending on various (currently unknown) factors.
You will receive a small portion of rubies per day, until the mine is empty. The above screenshot shows 250 rubies a day, until you’ve earned 90,000 rubies. That means it will take you 360 days of playing to empty the mine.
At this point, I don’t know what happens if you miss a day collecting the rubies. Do they stay in the mine until you collect them, or do they “disappear” since you missed a day?