At a given depth, the acceleration due to gravity increases over denser rock units, gravity mapping is quite useful for mapping geological trends and structure; generally speaking ore is always denser than the surrounding country rock it lies in. While in itself it's usually not used to spot...
I've got two older Trimble handhelds; an older Juno ST, and a Pathfinder XB (Bluetooth GPS), and the quality/durability is just not there. The Juno I have is based on an HP Ipaq base, which is anything but bush-worthy, and the Pathfinder I've had to coat it in silicone to make it somewhat water...
... and you can import your shp files easy enough using custom maps, but you need to convert to raster format first. The easiest way to do this I've found is with GlobalMapper, it has an excellent tool that converts and uploads the kmz files directly to the GPS.
www.globalmapper.com
It's been...
Newbie here. Geophysicist. I have a Trimble 5700 system and a R7/R8 system for work. I'd recommend the Garmin 62 series, very durable, loaded with features, best of which is the custom maps feature, it's nice not to be reliant on Garmin's mapsource products. You can upload your own customs maps...