Basically IP surveys can detect sulfides in the subsurface. End of story. I am not a geophysics expert but have run surveys and my understanding is that they do not detect layers or determine the thickness of anything. They provide exploration programs with subsurface targets.

Simply stated, the ground is juiced up with current. Sulfide minerals take on a charge. Once the current is turned off the charged sulfides slowly give up their charge and this is what is measured. This is why when sulfides are present they create a "chargeability" anomaly. Precious metal content has nothing to do with the results, the sulfides either have precious metal content or they don’t. The only way to find out is to go taste them with a drill bit.

Even in epithermal systems there are sulfides that may be close to the precious metal bearing zone that can be totally barren of precious metal values. Typically there is zonation to the halo of alteration within epithermal precious metal systems, one of these zones is called the propyllitic alteration zone, it can be heavily enriched in sulfides but totally barren of precious metals. They will give a nice IP anomaly; generate some excitement for a while until they are drilled. But like "Been There" has noted, it is nearly as important for a "mine" to define barren ground as well as ore bearing ground. Facilities need to be sited and waste dumps located in order to minimize mining costs, especially in low-grade bulk mineable deposits. The profit in each ton is small, so this kind of deposit needs millions of tons of ore.

Once again, I am not an expert in geophysics, but this is what I understand. Be cautious, sulfides doesn't always mean gold.