As for man formed gold items, probably thousands.
Years ago I discovered that many gold items detect like U.S. nickel coins and some like trash metal. Most fine gold chain just doesn't detect...period (unless it's within a couple inches of the surface).
Quality gold finds are extremely scarce. I used to hunt underwater at large swinging beaches back in the 60's to about mid 80's and I sometimes dug a foot or more deep for a junk ring or piece of low grade gold jewelry. Quality gold just wasn't lost all that often. It happened, yes, but was one in 10,000. One has at least a 10,000 times better chance of finding quality gold today in one of those unpaid storage auctions than with a metal detector (but it sometimes does happen).
The top places for lost buried REAL gold coins and REAL gold jewelry today would be certain places off limits for hunting. Places in large cities where once stood brothels, hotels, gambling joints, etc., but now are paved or just plain unsafe to hunt.
Anytime one walks through a large modernized city with hundreds of years of very active history, one is walking over more gold than one would believe.
People a 1000 years from now will be digging gold we missed.