There is no single device which can indentify, map and measure gold ore. Simply can't be done and I wouldn't even try to looking for a device like that. There are a lot of websites that claim they have such a device but they are all frauds. Just don't believe everything you read. A lot of people will gladly take your money selling worthless electronic junk.
It'll take lots of painstaking work and money to find, map and measure a potential gold deposit.
If you want to find gold, buy a metal detector and look for gold nuggets. That's going be your cheapest option.