A few yrs ago I was hunting an old house built in 1840. The nails were so abundant by the front porch I decided to just sit there in the shade and 'take a break' using just my pin pointer. I pulled up a huge pile of nails and siding snips like yours. Whoa & behold -imagine my surprise when I found a 1877cc dime beneath all that junk!
So my suggestion is "Dig it all"... if at a good old house site and have the energy :thumbsup02: Fyi I don't do this at trashy 'newly established' city parks unless I find an old house site using map overlay.