Airborne magnetics is probably the fastest and most cost effective way to get a good 'first look' at an exploration area. For this reason it has long been a standard exploration tool, particularly in the early stages of an exploration program.
Airborne radiometrics (or spectrometry) is the practice of measuring the natural radiation emitted from the surface rocks. In contrast to magnetics it only represents the top few inches of cover and so represents the surficial geology.
Airborne VLF data is a passive electromagnetic method that depends on high power marine communication transmitters as the energy source. It is generally collected along with magnetic and or radiometric data on a 'best effort' basis and the results are more qualitative than quantitative, but may still yield useful information at a very low cost.