Another solution, which requires no external scripts :
create a trigger covering your mined area, and activated by anybody present (or whichever side you want, of course).
In the activation field, write :
"trig setpos getpos _x" foreach thislist
Now create another trigger, as big as you want it to be, also activated by whatever you need, and call it "trig".
In the activation field, write :
mymine="_myammo" camcreate getpos trig
This should do the trick, as you said you only needed ONE mine.