Oh! A gold coin you say? Well, thats a bit different than hunting generic inland dirt gold jewelry...You can try to pattern others success, or just hit it and dig it all hoping Luck will prevail, we see that sometimes by complete noobs pulling a nice gold coin........
But, for most gold coins, location seems to be the primary reasoning, letting the trash tell you if you are in the proper paydirt...hunt old dirt where native gold coins may be lurking etc......do a lot of research, or hunt the water...we see most gold coins found by the beach and water guys, usually in a necklace sconce...
If you have the means, go and buy one from your LCS, sweep it with your rig and commit that specific tone to memory...I am fairly confident theres a dozen gold coins lost within 5 miles of my house...some may be buried under the roadway or sidewalks, some are lost in 30' of water...never the less, they are out there....the big trouble is, if a gold coin is sitting underneath a nail, pocketknife, or V nickle, you are right back to digging it all!..
Mud