RE: Problems with IPthanks, Russ. I think those are good desriptions/explanations for us non-geophysicists.
I keep envisaging a massive sulphide target. Being familiar with the concept of inducing a charge on discrete sulphide particles (the way it was explained to me the concept of parallel plates in a condenser was used)my impression was that a continuous (or partly continuous) conductive body would not allow the build-up of charges on the individual platelets. Thus, IMO, an EM method would be more useful than IP.
I must admit that I did not think as much about resistivity, and surely a conductive body would be much less resistive than barren rock, so I reckon a smart fella could still pick out the conductor using IP. I note, though, that your write-up says that the method is best suited for porphory copper deposits where there is usually very low quantities of sulphides.
In my limited experience, which is a bit dated, we paid a couple of hundred dollars per line mile of VLF and Magnetometer survey (done simultaneously by one operator) and thousands of dollars per line mile for IP which had a crew of at least 3 people and lots of set-up and moving time.
If the target is indeed a massive sulphide deposit I would still think that an EM method would be as effective (IMO more effective) than an IP survey, and at much less dollars. I think you (or maybe it was someone else)mentioned the difficulties of finding a narrow, near-vertical "sheet" of ore with IP. I would think that "sheet" would be an ideal target for EM.