How do you get the benefit of natural wonders that are mountains?

I started a game of Civilization 5 (BNW + G&K) and early on in the game I discovered a natural wonder called Cirro de Potosi, which is a mountain. When I discovered it, the advisor popped up and said that I gain happiness and get a benefit if the tile is worked (in this case +10 gold). I settled my second city right next to the wonder and I don't appear to be getting any benefit from this tile.

How do you get the benefit of natural wonders that are mountains? I can't assign citizens to the tiles and I am right next to the thing, which means it is within my borders, but looking at the city screen this new city still has 0 gold output, when I was expecting 10 gold per turn. I even advanced a few turns to see if it wasn't immediate but I still noticed no change.

Solution 1:

To work a tile means you have a citizen on it, not a worker unit. To see which tiles are being worked, click on the city and enable manual citizen management. each tile within your borders will have a circle that is either gray (not being worked) or green (is being worked).

Solution 2:

In addition to what was said by VanBuzzKill, there are natural wonders that don't produce yield (food/production/gold/culture/faith/science) but give happiness - in case of these, you don't need to allocate citizen to work these tiles. Its enough to have the natural wonder within your civilization borders and you'll get the happiness boost.