Best long range detector I ever used is the computer, has access to - maps geological and other, aerial and satellite photos, historical records, personal accounts, heaps of good advise here on T-Net. So far it is unaffected by time of day, phase of the moon, solar flares or bad moods, though lightning wiped it out pretty thoroughly once.
I don't rule out the use of physic mediums, dowsing rods, spirit guides, mushroom circles and the like, just don't buy them off any non billionaires. If it worked, the first one would make it's owner filthy rich.
If I had one that worked, I wouldn't sell any others, the last thing I'd want would be other guys walking around picking up all the easy stuff. Nuggy