SOLUTION OF THE METALS. 1073 



While the subclass is named "Ores precipitated by ascending aqueous 

 solutions," possibly a more exact heading would be either "Ores precipi- 

 tated from solutions deficient in oxygen," or "Ores precipitated from deep 

 solutions." From the chemical point of view the fundamental fact is that 

 the solutions are deficient in oxygen. It follows from this that the solu- 

 tions must be sufficiently deep or sufficiently protected from the surface 

 to be free from oxidizing effects. Thus the subclass corresponds rather 

 closely to Posepny's "Ores of the deep circulation."" But since the great 

 majority of ores belonging to the subclass under discussion are deposited 

 from -solutions, the vertical element of which at the time of precipitation 

 is ascending rather than descending, the heading chosen is given as the 

 name of the subclass. 



SOLUTION OF THE METALS. 



In the first stage of the concentration of many deposits the waters are 

 descending. They move slowly downward, are widely dispersed in small 

 passages, have an exceedingly large surface of contact with rocks, and are 

 subject to increasing- temperature and increasing pressure. All of these con- 

 ditions favor solution to the point of saturation. The various metalliferous 

 elements present in exceedingly small quantities in the rocks, as well as 

 many other compounds, are picked up. This follows from the law of phys- 

 ical chemistry, that a solution holds some part of all the elements with which 

 it is in contact. 



In the work of solution of the material for the ores, and in the deposi- 

 tion of it by the water, the two physical factors, temperature and pressure, 

 are of great consequence. It is shown (Chapter III) that increase of 

 temperature increases the activity of the water in two ways — first, the speed 

 of the solution is very greatly increased by rise of temperature, and at 

 temperatures of 100° C, and especially at a temperature of 185° C. and 

 above, the activity of water is no less than amazing (p. 79). The effect of 

 increase in temperature upon the activity of underground solutions can 

 not be too strongly emphasized. It is also shown that as the temperature 

 rises in general a larger quantity of material may be held in solution, at 

 least for moderate increases of temperature, probably as high as 100° C. 

 (pp. 79-81). 



«Posepny, F., The genesis of ore deposits: Am. Inst. Min. Eng., 2d ed., 1902, pp. 1-72. 

 MON XLVII — 04 68 



