Prospector's Field book and Guide - by H.S Osborn and M.W. Von Bernewitz - This book originally written by Osborn and later revised by Von Bernewitz is one of the classics when it comes to prospecting. It covers how to do field analysis via blowpipe, then covers geology and mineralogy of each element and tells you how to prospect for them and what to look for when in the field, how to do field analysis via simple chemicals, and gives examples of other deposits to use as a reference.