This fully updated textbook is intended for the economic geologist who deals with the evaluation of deposits at an early stage of development. It offers rules for quick and easy calculations based on the application of approximate data. It provides both the student and the geologist in the field with a complete set of rules and methods enabling them to perform a quick initial evaluation of the deposit without the support of specialists or computers ¿ even if he is left to his own resources. All rules for calculations are illustrated with examples, and mistakes and pitfalls the authors encountered during their careers are pointed out.