I think Relichunter97 may be right - I think i'm seeing a hallmark on the lower end of that oval backplate too - Great finds - I would be very
psyched to find that one . I do think it can be safely repaired with a ring mandrell - very likely without having to remove the stone . Bring it
to a local silversmith , he (or she ) can likely round the shank with gentle pressure of a small mallot and mandrell . You had a great day !
test it if you want to , but I'm all in-- this thing is sterling ! I'll bet the farm on it , nice piece of turquoise too !! I do hope you'll
have the shank corrected.