ECONOMIC GEOLOGY 



CHAPTER I 

 ORE DEPOSITS 

 INTRODUCTION 



What constitutes an ore deposit? An ore deposit may be de- 

 fined as a body of rock which contains metals or metallic com- 

 pounds in sufficient quantity to allow the profitable extraction 

 of some metallic content. A few of the metals occur in the native 

 state. This is especially true of the precious metals: gold, silver 

 and platinum. The most common occurrence of the commercial 

 metals is that of the sulphides, oxides, hydrous oxides, carbonates, 

 etc. Some mineral deposits which to-day do not fall within the 

 definition of an ore deposit, may by subsequent concentration 

 become sufficiently enriched to be of economic importance. 



Associated with the metallic minerals are certain non-metallic 

 minerals. The commonest of these is quartz, SiO 2 ; next in the 

 order of importance is calcite, CaC0 3 , then fluorite, CaF 2 , barite, 

 BaSO 4 , and siderite, FeC0 3 . Of less importance than the five 

 minerals mentioned there appears as gangue minerals dolomite, 

 rhodochrosite, feldspars, amphiboles, pyroxenes, etc. It often 

 occurs that a large part of the vein consists of gangue and the eco- 

 nomic product occupies the position of a thin seam within the 

 vein-filling. 



These gangue minerals are of lower specific gravity than the ores 

 and may often be mechanically separated from them. Again they 

 are so barren of metallic minerals as to permit separation through 

 the hand sorting of the ore. The gangue is then transported to 

 the dump, while the material containing the valuable metal is 

 carried to the mill for treatment. 



Primary Source of Ores. The question naturally arises, what is 

 the primary origin of the ores? Four principles are cited by 

 C. R. Keyes, in his " Ultimate Source of Ores :" (1) Deposition from 

 sea water. (2) Inclusions of metallic minerals as accessories in 



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