Prospect for gold is essentially the basic examination of a mineable prospect. Prospects are not expected to show gold ore reserves as a basis for purchase, and in the last analysis the recommendation of a prospect rests on an opinion rather than demonstrable facts. The examination of a gold prospect requires that all significant samples shall be taken and a thorough geological investigation be made, which need not, however, be put in formal shape unless it yields a favorable result. The question to be answered in examining a prospect is: what chance has it to become a gold mine? The same hesitation should not be felt in recommending that a prospect be acquired under option as is justifiable before advising the purchase of a developed mine. It should be remembered that the majority of gold prospects have been examined many times, and that no brilliant showing of payable ore will be encountered; any fairly consistent showing of geological promise is worth considering, and merits the expenditure of a few hundreds or a few thousands of dollars in preliminary work, which, if it yields a favorable result, may be followed by more serious development.
It is important to mention that gold mining booms, even if founded on mistaken estimates, frequently lead to the discovery of valuable properties; this is due to the fact that the excitement of a boom leads to much shallow prospecting, which often exposes conditions not evident from an inspection of the immediate surface. Test pits and trenches may be considered as halfway between examination work and exploration, and while inexpensive, they not infrequently yield important results. For example the study of gold deposits should not be assumed to indicate a valuable property. Those that have had much to do with old gold deposits in Peru have respect for the ability of the pioneers to follow, to extract, and to treat ores. These properties were worked with slave labor; a certain proportion of the force being detailed to grow food for the miners, the labor cost of mining was practically nil; very low gold grade material, therefore, could be mined, as almost any recovery from the ores was profit.
Similar conditions probably obtained wherever mines were operated by the Spanish, or by the ancients. In this way, it is difficult to find high-grade gold ores. The first step in the examination of an old gold operation is to make a survey and to map all the workings, placing on the map all the geological data obtainable. The pioneers did not understand faults, and never drove exploratory cross-cuts; not infrequently a detailed geological study of an old gold operation results in finding important ore-bodies. By means of samples, the grade of gold ore left in the mine by the pioneers can be ascertained, and this will often determine whether or not the property may be expected to yield a profit with the application of modern metallurgical processes; all ore above this minimum gold grade may be assumed to have been extracted.
Old prospectors did not follow the ore very far below water level, and the ore in which is primary, offers an attractive opportunity; in most cases, however, the gold ores mined were secondary, and probably do not continue far below the old workings before changing to low-grade primary material. In the prospection the mode of extracting the gold ore to the surface should be carefully considered. The old gold prospectors employed small bags without much care and several times the samples got contaminated and the assays were not realistic.