ORES DEPOSITED BY GASEOUS SOLUTIONS. 1053 



has been a favoiite hypothesis ever since ores were a serious subject for 

 investigation. The idea goes back as far as Elie de Beaumont," who sup- 

 posed that the majority of ore deposits were thus produced. This theory 

 has been especially applied to ores of mercury and tin. During the last 

 ten years the idea has again been taken up and emphasized by a consider- 

 able number of vigorous advocates, of whom V~ogt, Beck, Lindgren, Weed, 

 and Kemp are well known. 



Recently Weed* gave a classification of ores in which he separates 

 pneumatolytic deposits, fumarolic deposits, and gas-aqueous deposits, giving* 

 each as one of the major classes. The deposits here placed by Weed 

 together comprise a very large proportion of ore deposits. Spurr 6 also has 

 given a classification of ore deposits in which contact metamorphic deposits, 

 deep-seated g*aseous deposits, fumarolic deposits, and solfataric deposits are 

 recognized as classes. Weed divides his pneumatolytic, fumarolic, and 

 gas-aqueous deposits into subclasses and groups. Moreover, the ores of 

 gold, sih*er, and copper of man}' well-known districts are assigned to each 

 of these classes and to the various subdivisions of the classes. However, 

 neither Weed nor Spurr gives the criteria by which he distributes the 

 various ores among the pneumatolytic, fumarolic, solfataric, and gas- 

 aqueous deposits. Nor are the criteria even given by which deposits are 

 known to be formed by gaseous solutions. It has been shown that the 

 heavy anhydrous minerals of the zone of anamorphism probably develop 

 at temperatures above that of the critical temperature of water. (See pp. 

 182-185, 685.) This has led me to hold that where such minerals have 

 developed with ores formed from solutions, such solutions are gaseous. 

 But I am unable to formulate any criteria,, except purely theoretical ones, 

 which subdivide the deposits of gaseous solutions into pneumatolytic, 

 fumarolic, and solfataric. Indeed, I hold that the entire class of ore 

 deposits produced by gaseous solutions, while important, is small as 

 compared with ores deposited from aqueous solutions. 



Ores deposited from gaseous solutions above the critical temperature 

 of water may conceivably be produced in the zone of anamorphism in Cou- 

 rt Bull. Soc. geol. de France, 2d ser., vol. 4, 1846-47, p. 1249. 



*The genetic classification of ore bodies, a proposal and a discussion (including papers by W. H. 

 Weed and J. E. Spurr): Eng. and Min. Jour., vol. 75, 1903, pp. 256-258. 



