Old B&W movie where the conmen get conned

A while back I saw an old black & white movie (probably from the 1930's or 1940's) where a woman got connected bu some people. I think it was set either in South Asia or South America and the woman who got conned into buying some land that was supposed to have a treasure (gems or gold). Another guy (a well known actor, like Humphrey Bogart or James Cagney) helped her out by making the conmen think that the land did actually contain the gems or gold that they had told her about.