Best to concentrate on certain parts of old mining areas that really suit VLF's, like the shaft spoil piles, surface quartz, and areas where bedrock is close to surface (gullies, creeks, hill tops etc.)
Look for Argyle's tips on running the Eureka, as some of his methods for setting up the Eureka fly in the face of what is suggested in the owners manual. VLF's can have a bit of a learning curve when used in goldfields with plenty of hot rocks and ground mineralisation to keep you on your toes, and may take quite a few hours of use before understanding how the detector responds to targets. Many small gold targets can be nothing more than a wobble in the threshold, and not a screaming signal like a lot of people expect, hence why Argyle recommends to set the threshold higher than what the manual suggests.
Argyle was adamant that the threshold be set up so it is stable (Whites reccommend the same with their detectors), and to do this, you will have to reduce the sensitivity to suit the ground you are working on. Sometimes you can get better results from running a lower sensitivity vs trying to run it flat out to try and get max depth. If the sensitivity is too high, resulting in a wavering threshold, you won't be able to hear the faint threshold rises and dropouts of good targets.
No different with PI detectors, they also require a stable background threshold, as most of their targets start off as only a slight wobble in the threshold, with the signal becoming more pronounced as the overburden is removed from the target.
Gold will have a more mellow response vs the sharp pronounced response of junk iron target. By far the best way to get used to this, is to purchase a small nugget, and test it out in the ground in your local area at various depths, or use a small lead sinker, as this will give off a similar response to gold. If you start to find small lead buckshot in the field, then chances are you have the detector set up properly.
I don't know whether you have read this, but here's a field test of the Eureka, and some good info on how to use the discrimination to weed out unwanted iron targets (takes you straight to a pdf download)
http://files.sotmarket.ru/instr/spo...etalloiskateli/manual-minelab-eureka-gold.pdf