Thanks for the feedback! The speed of the beeping sound should be the main tell for whether you're about to strike gold or a land mine, but maybe I'll make the differences between beeping speeds a bit clearer and more pronounced in a future build. Also, gold can sometimes spawn right on top of where a land mine is, which can admittedly create a good deal of uncertainty in some cases.
A general rule is that the longer you stay out, the more gold you'll earn. I experimented with different durations of battery life for the metal detector to find the right level of tension while also making players more comfortable in trying to find as much gold as reasonably possible. Basically I wanted players to keep going, but I also didn't want them to stay out there forever. I am definitely thinking of taking this further with an expanded version at some point so that players can have more things to spend gold on in the long run though...