Chapter 27 



THE FIELD OF ECONOMIC GEOLOGY OF SEDIMENTARY 

 MINERAL DEPOSITS * 



V. E. McKelvey 



Geologist, U. S. Geological Survey 

 Spokane, Washington 



Minerals and rocks mined from syngenetic sedimentary deposits 

 make up about 36 percent of the value of the total annual domestic 

 mineral production (Table 1). About 3 percent of the annual out- 

 put comes from altered sedimentary rocks, such as the Lake Superior 

 iron ores, which, though their value arises from secondary enrichment, 

 resemble sedimentary rocks more than they do rocks of any other 

 kind. Only about 13 percent of the production comes from igneous, 

 metamorphic, vein, and replacement deposits. The remaining 48 per- 

 cent of the production consists of fluids, such as petroleum and brines, 

 most of which are recovered from sedimentary rocks. 



Notwithstanding the economic importance of sedimentary mineral 

 deposits, it is safe to say that the principles of sedimentation, or of 

 geological science in general, are rarely applied to their exploration and 

 exploitation.f Most sedimentary materials have a low unit value 

 compared to those of other origin, and many of them are relatively 

 easy to find, appraise, and follow in mining (McKinstry, 1948, p. xv). 

 Most companies that mine only unaltered sedimentary deposits do not 

 employ geologists, and, if a geologist is consulted at all, usually it is 

 to pass judgment on a property that the company is considering buy- 

 ing, or to solve specific problems connected with appraising the reserves 

 or following the ore in an active mine. The principles of structural 

 geology and stratigraphy are generally more useful in the solution of 

 these problems than are those of sedimentation, and the mining geol- 

 ogist with a good background in general geology is apt to be better 

 qualified to solve them than one who, though he has specialized in 

 sedimentation, is not familiar with the methods of field and economic 



* Published by permission of the Director, U. S. Geological Survey. 

 t If petroleum were considered a sedimentary mineral deposit, it would be a 

 notable exception. 



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