From what I have read on various websites, everyone generally agrees with Thebluefish' comment.

At level 50, every 75k exp. gets you an [Elder Gem][1].
Once you've reached the Elder Gem cap for the day, all experience points you get will be converted into silver.

From what I've read it seems you can farm 1 platinum to 1,5 platinum per hour, given that you've found a good spot to farm.

Note: This information was gathered from players who reached level 50, meaning that it's speculation, but backed up pretty well.
  [1]: http://wildstar.gamepedia.com/Elder_Gem