134 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 188. 
presence of fluorite and hubnerite in some of the lodes of the Silver- 
ton region, and the occurrence of alnnite and diaspore, in connection 
with metasomatic alteration of the country rock apparently brought 
about by acid waters and locally very pronounced in character, are 
all to some extent indicative of pneumatolytic processes. But, as 
Lindgren 1 remarks, fluorine and boron compounds are found in some 
deposits which are certainly not of pneumatolytic origin, nor even 
formed at high temperature. The Silverton lodes, as a whole, possess 
neither the distribution nor the mineralogical characters of those 
deposits to which in the light of present knowledge an essentially 
pneumatolytic origin can be most safely assigned. The known igne- 
ous masses had certainly solidified and probably had lost much of 
their heat before the lode fissures were formed. It is most probable 
that the transportation and concentration of the Silverton ores was 
effected chiefly by meteoric waters, which derived their chemical and 
mechanical energy mainly from the heat connected with volcanism 
and from pressure, but possibly in some minor part, also, to g-ises and 
vapors given off at high temperature by solidifying igneous rocks and 
taken into the deeper meteoric circulation. 
It is difficult to determine the exact character of the solutions which 
deposited the ore of the Silverton quadrangle. Many natural solvents 
are known for the common gangue minerals, for sulphide minerals, 
and for gold. According to Doelter's 2 experiments, pyrite, sphalerite, 
galena, stibnite, chalcopyrite, arsenopyrite, and bournonite are all 
appreciabty soluble iri pure water under the influence of moderate 
heat (80° C.) and pressure. Galena and pyrite are soluble in water 
containing carbon dioxide, and gold and copper are soluble in solutions 
of sodium carbonate. 3 
Solutions of sulphydric acid or sodium sulphide are relatively active 
solvents of gold, as well as of pyrite, chalcopyrite, bournonite, arsen^ 
opyrite, galena, and sphalerite, according to the investigations of 
Becker 4 and Doelter. 5 The experiments of Doelter in particular 
indicate that heat and probably pressure increase the solvent action, 
although the law of this increase of the different minerals is unknown. 
Solution is also favored by a great preponderance in the mass of the 
solvent and by the long contact of solvent and solid under favorable 
conditions of heat and pressure. Obviously these latter conditions 
are those common in nature, but which can be only very imperfectlj 
realized in the laboratory. It appears, therefore, that nearly a] 
aqueous solutions that occur in nature may, under suitable condi 
tions of heat and pressure, act as solvents and carriers of the heavy 
1 Metasomatic processes in fissure veins: Trans. Am. Inst. Min. Eng., Vol. XXX, 1900, p. 644. 
2 Chemische Mineralogie, Leipzig. 1890, p. 188. 
3 Doelter, loc. cit., pp. 190-191. 
4 Natural solutions of cinnabar, gold, and associated sulphides: Am. Jour. Sci., Vol. XXX, 188' 
pp. 199-210. Also Mon. U. S. Geol. Survey, Vol. XIII, 1888, pp. 432-433. 
5 Loc. cit., p. 192. 
