long range electronic locator

Dear friends of the Tech Forum,

I am a experimenter. Now, my interest consist in electronic long range precious metal locator. I need only the stage, can be filter, for a classifier circuit system por gold. I have some results to detect coins and other objects in long distance (near 150 feet)with different apparatus of my invention, but the problem is the great sensibility toward copper and brass.

Your friend of Paraguay, South America

Esteban

Thank you!

congratulation you have success to make long range locator electronic, for gold is depend on your frequency you use, for gold I suggest 5 Khz
until 7,5 Khz square wave, but I don't know a circuit you make it's use frekuensi or magnetic respon.