Robert Hallowell Richards

“ When the miner hoists his ore [1] to the surface, the contained metal may be either in the native uncombined state, as, for example, native gold, native silver, native copper, or combined with other substances forming minerals of more or less complex composition, as, for example, telluride of gold, sulphide of silver, sulphide of copper. In both cases the valuable mineral is always associated with minerals of no value. ”

“ The concentration of ores always proceeds by steps or stages. Thus the ore must be crushed before the minerals can be separated, and certain preliminary steps, such as sizing and classifying, must precede the final operations which produce the finished concentrates. ”

“ Magnetism is a most direct and simple method of separating minerals where it is available. The discovery that by the use of electro-magnets of great power minerals formerly regarded as non-magnetic are attracted, has made it possible to separate several classes of minerals present in an ore ”