A preliminary survey of a province or favorable metallogenic environment, by such various means as geological mapping, geochemistry or geophysics, will usually result in the location of a certain number of prospects. If one of these prospects locates a mineralized zone, the next step is to determine its value and extent by a more detailed survey involving, for example, drilling, trenches or even, sometimes, drives. The locations of these samples are generally not regular, but are based on geological considerations such as the need to verify the existence of the mineralization and to provide a qualitative description of it (e.g., mineralogy, tectonics, metallogenic type). The results of such sampling may be a proper basis on which to plan further reconnaissance, but they are not entirely suited for quantitative estimations of tonnage and yardage. The first estimations will tend to be more qualitative than quantitative, as will be the geologist's image of the deposit.