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This is a subject thatthe owners of mining properties would do well to study. Thefact that the surface offers a complete section of the ore-deposits and of their surroundings is often lost sight of; before attemptingdeeper work it is well to explore the surface thoroughly withtrenches and test pits. If no ore is found by this work, and noindication found of residual conditions suggesting that oreonce existed at this level, then deeper exploration is notwarranted.

That an ore is refractory is often apparenton simple inspection, as, for instance, a lead-silver ore thatcarries much zinc, or copper in an ore for which cyanidation wouldbe natural treatment. A general knowledge of metallurgy isnecessary to the examining engineer, and while a discussion of thedetails and costs of treatment are out of place in a report on a prospect, the amenability of the ore to metallurgical treatmentshould be borne in mind.

The regularity of a deposit togetherwith its size determines the cost of development. Of two depositsthat contain a like quantity of payable ore, the regular depositis by far the more valuable.

In the exploration of prospectsit should be expected that many ventures will prove failures, asthe exceptional success will more than repay a number of unsuccessfulventures.

The final object of a mining examinationbeing a profit for the client for whom the work is done,the price and terms asked are considerations second to none; inthe United States they are too often but slightly considered, andsales of undeveloped properties are made at prices that largelydiscount even a decidedly favorable outcome for the proposeddevelopment.

The presence of ancient workingsshould not be assumed to indicate a valuable property.Those that have had much to do with antiguas in Mexico haverespect for the ability of the pioneers to follow, to extract, and totreat ores. These properties were worked with slave labor; acertain proportion of the force being detailed to grow food forthe miners, the labor cost of mining was practically nil; very lowgrade material, therefore, could be mined, as almost any recoveryfrom the ores was profit.

The examination of a prospectis a very different undertaking from the examination of a mine;prospects are not expected to show ore reserves as a basis forpurchase, and in the last analysis the recommendation of aprospect rests on an opinion rather than demonstrable facts.The examination of a prospect requires that all significantsamples shall be taken and a thorough geological investigation bemade, which need not, however, be put in formal shape unless ityields a favorable result. The question to be answered inexamining a prospect is: "What chance has it to make a mine?"

Preliminary examinations areprecisely what the term implies, and are undertaken to determinethe advisability of making a formal examination. There isalways a reason why a mine is offered for sale, which may or maynot be known from the start; frequently the chief object of thepreliminary examination is to determine this reason for selling.

In the opening of any property two distinct objects should be kept in mind—the development of known ore-bodies, and the exploration for further deposits.

The surface affords a complete section of the geological features of any district, and in all but the simplest occurrences a geological map of the surface and a few vertical sections are invaluable guides in the examination or exploration of any district. All significant outcrops of rocks, dikes, beds, veins, faults, shear zones and so forth should be determined and their strikes, dips, and elevations recorded on a large scale map, from which the data may be referred for study to a horizontal plane.