The above posts are 100% correct, The V3i is an awesome gold machine! You haven't told us what state(s) your friend plans to prospect in. Most of the Western states where nuggets are found will have pretty severe minerals and I mean really bad. Relax! Your V3i will handle them. Work on your ground balance skills until you really understand the procedure. Rob has given the procedure many times on this forum, do a search and follow his advice. 20 pumps will not be enough in bad minerals, but the V will win the battle :0)) You will probably want to have multiple search coils, like the 6x10 or 4x6 shooter. The stock 10"DD will work, but a smaller coil is much better. Your V is going to be very noisy, so go slow, very slow. Don't forget to play with your various sensitivity settings, If you run a bit too hot, you might have trouble with GB. Just lower the RX gain and AM sens until the V settles down and go have some fun.
Learn to trust your V! Most of the negative VDI #'s will be iron, but some need to be investigated. I have found some really neat mine relics in the - 0 to 15 VDI range. Most gold will be from 0 to 15 or so, but a really large specimen can register much higher.
If you go to a local detector shop, be prepared for brand/area loyalty. They will say all sorts of things that are pure BS. Whites MXT & V3i's are for amateurs, or they can't handle our minerals. Don't buy into that kind of propaganda! Your V3i will hunt with any detector built and excel where most others won't!.
John London