Gold Box - This is a bonus that is dropped during a battle. It awards the player 1000 crystals. There are drop zones for Gold Boxes on every map. Most maps have several drop zones.
Originally the Gold Box was dropped when battle the fund reached a multiple of 700 crystals. Since Update 1.78.0 it can now appear in a battle with any fund size. The probability is 1 in 10,000.
On February 19th 2016, an option to disable Gold Boxes dropping in PRO battles was added.
FAQ: Gold box
Q: Can Helpers or Admins drop Gold Boxes?
A: No, Gold boxes are completely random. They have a 1 in 10,000 chance of dropping.
Q: How long after the notification does the Gold box starts dropping?
A: Since Update 354, You will have 30 seconds after the notification before the Gold box starts dropping
Q: Where do Gold boxes usually drop?
A: The best place to start looking would be the middle. After you have scanned that area try looking in your or your enemies bases, the edges of the map or other obvious places.
Tankers from the community have put together a list of every place a goldbox drops on every map. This list can be found here
Q: How can I find out where a Gold box is dropping?
A: You are looking for a white square with a golden crystal in the middle. Move your camera to its highest point so you can see as much ground around you as possible. After about 15 seconds since the notification has appeared, bring your camera down to the lowest it can go and start looking in the sky for the gold
Q: What is the best/easiest way to catch a Gold Box?
A: Have a read through this guide to Gold Box Hunting
Q: Can Gold Boxes be disabled?
A: Yes. There is now an option to disable gold boxes dropping in pro battles