I've got a site where they may be a cache of gold coins. It would be 2-4 feet deep in a clay jug. It's buried in red clay, which is very mineralized soil. I'm trying to figure out which type of equipment to use, such as a large PI loop, GPR, magnetometer or maybe a Electromagnetic (EM) antenna, like OKM makes. I've been told that a cache of gold coins will not show any bigger (surface-area-wise) than a single coin, even though they are touching each other, but a solid a gold bar would show a bigger surface area, because it's solid. I was wondering if this is true, and if anyone could recommend what equipment would work best in these conditions. Per the Lorenz site, (a German company that makes very good PI units) their 1 meter loop is too big to pick up on a single coins and their double-d coil (the one the can differentiate between ferrous and non-ferrous) doesn't go much past 15 inches on a coin. I was also told by a GPR manufacturer that GPR does not work well in mineralized soil. Not sure what to do.