Thats gotta be the toughest target of value out there...even a thin silver chain is hard enough to find, let alone locate down in the grass roots...Now medium sized gold link chains in the 15gr realm give off a good enough signal for a guy to ponder...and at least 15 gr is worth some money, a thin gold chain I would think would be almost impossible to find in a modern park, on account of all a guy may likely hear is that tiny clasp..and if the grass is deep, probably wont even hear that beyond 3-4" from the coil I would guess..let alone it would probably be in the sub 5gr weight realm...I dont know, that sure would be a trophy target to hunt for and actually find not on an accident...but by a dedicated search for one...
I do go out every day hunting thinking 'chains' and focusing on those strange soft low signals..smallest one I've found is the aforementioned 15gr...then I got two other monsters, so theres gold chains out there that dont get heard or explored if they do...its not a signal that stops you dead in your tracks, but one signal you just get curious enough to check out...Good Luck!
Mud