If that's the same as "Wasn't That a Mighty Day," which I learned from a Bob Gibson record, it's a three-chord minor: on the banjo I play it solo in Cmin with Fmin and G7 (or capo up for Dmin with Gmin and A7 if I'm playing ensemble).

On "Doc Watson on Stage" with Merle Watson, Doc sings a version of "Nine Pound Hammer" which he attributes to John Lee Hooker--Merle plays the accompaniment with only two chords: C and C7. An interesting arrangement.

--seed