GRAPHICS OF ORE-ORIGIN. 



BY CHARLES R. KEYE^. 



In the main ore deposits are precipitated in aqueous solutions. Solu- 

 tion, transportation and deposition of ore-materials are distinctly pro- 

 cesses operating through the medium of subterranean waters. The 

 sources of the ore-minerals, the courses they follow through the geo- 

 logic formations, and the immediate causes of their localization, are 

 factors of prime importance in the consideration of ore-genesis. Ob- 

 scure as is the migration and changes of ore-materials it is possible, 

 as will be seen presently, to represent graphically the general courses. 



As recently pointed out the various phases of primary ore-genesis 

 may be all reduced to four principal groups: (1) extraction from sea- 

 water; (2) inclusion of metallic minerals as accessories in the igneous 

 rocks themselves and the subsequent liberation and segregation of the 

 ore-materials through weathering-processes; (3) production of metal- 

 liferous bodies in connection with rock-masses in a molten state, either 

 through magmatic secretion or liy expulsion of the A^olatile compounds 

 of the metals during the progress of magma-cooling; and (4) deriva- 

 tion of metallic particles from extra-terrestrial sources, and their later 

 segregation through the action of percolating surface-waters. Of these 

 several groups contention regarding the first mentioned is now obsolete ; 

 the conceptions concerning the second and third enter into nearly all 

 of the recent discussions of the subject; the idea of the last receives yet 

 only incidental attention, but is likely to prove the most important 

 of all. 



On the theory of meteoritic agglomeration, the original and often 

 the immediate source of ore-materials cannot be in nature so largely 

 magmatic as it is vadose. Qualified in some ways and strenghtened in 

 others, the general arguments of Forchhammer, Sandberger, AVinslow, 

 Van Hise and Bain assume a new interest and an added value. The 

 main shortcoming, if such it really be, is merely in ascribing a sole 

 or principal origin of the ore-materials to rock-weathering, when a 

 somewhat broader interpretation of the facts seems necessary. 



