Ch. 27] APPRAISAL 497 



second factor includes reserves and quality of the material. The third 

 factor concerns minability of the deposit — thickness of the bed, sim- 

 plicity of the structure, nature of the walls, thickness and nature of the 

 overburden, and similar factors that control the ease and cost of min- 

 ing. The fourth factor involves the metallurgical characteristics of 

 the material, its amenability to low-cost methods of concentration or 

 processing, or its suitability for the purpose intended. The fifth is the 

 availability of water, timber, fuel, power, or other raw materials that 

 may be vital to the operation planned. The relative importance of 

 these factors differs with respect to various materials or situations, 

 and an unfavorable report on any one of them may be enough to elimi- 

 nate the deposit from further consideration. 



Many of these factors are plainly not geologic, and, actually, many 

 examinations or appraisals are made by mining engineers or even 

 metallurgists. Though the geologist, engineer, or metallurgist may be 

 called on to make the complete appraisal, none is qualified to do so 

 alone unless the property is an extremely simple one whose merits and 

 suitability are obvious, or unless the individual chosen is a man of 

 exceptionally broad experience and sound judgment. As a matter of 

 fact, specialists from all these fields often share the responsibility 

 for the appraisal of properties calling for a large capital investment. 



The geologist is best qualified to determine the tonnages of various 

 classes of materials, the position and structure of the bed, and the 

 depth of overburden. Decisions as to what portions of the deposit 

 are of suitable structure to be mined or milled require a thorough 

 knowledge of mining and metallurgical methods. These decisions 

 must be made before the tonnage of material which can be extracted 

 at a profit can be calculated; if the geologist calculates minable re- 

 serves singlehandedly (this practice is undesirable), he at least in- 

 forms himself about the requirements imposed by the mining and 

 metallurgical methods to be employed. The discussion here deals only 

 with calculation of tonnages of various classes of materials, not min- 

 able reserves. 



The first step in estimating tonnages and in working out the position 

 and structure of the deposit is to make a geologic map of the area. 

 Techniques employed in mapping, choice of scale to be used, etc., 

 are discussed elsewhere and need not be repeated here. Suffice it to 

 say that the map must show both facts and inferences. The geologist 

 not only needs to keep the facts separate from his conclusions for his 

 own benefit, but others are also entitled to know the basis for his con- 

 clusions; on the other hand, the facts are seldom complete enough 

 to show the structure and extent of the deposit, yet assumptions re- 



