ORIGIN OF TIIK VEINS. 2o7 



carbon-dioxide, as well as dissolved calcic carbonate. It certainly con- 

 tained sodium as carbonate taken up from the feldspars of the adjoining 

 rocks, probably also as silicate and chloride. It further contained sul- 

 phur, in what form is not certain, but most i)robably as sulphuretted 

 hydrogen or as sulpho-salts. The presence of large quantities of sul- 

 phates does not appear probable. 



Waters of this composition, containing abundant carbon-dioxide, are 

 only known in nature as ascending, usually hot springs. The process 

 of deposition took place as follows: 



At fii*st the car])onated waters began to act with great energy on the 

 soluble minerals in the wall-rocks of tlie fissures, converting them more 

 or less completely into a mixture of carbonates, potassium-micas and 

 pyrites, adding calcium-carl)onate and sulphur, probably also potassium, 

 to them, and abstracting sodium. Finally, this process being completed, 

 and the walls usually coated with crystals of carbonates, the formation 

 of the latter ceased, and in this surrounding of carbonates the silica now 

 began to be dei)osited, and with it the gold and the rest of the metallic 

 sulphides. 



A most interesting question in connection with this subject is, why the 

 walls should, to such a large extent, act as a separating barrier for the gold 

 and most of the sulphides. Mr G. F. Becker, in discussing the quick- 

 silver deposits of the Pacific coast,* has suggested that this may be due 

 to an osmotic action, transmitting through the septum only the chem- 

 ically active solutions. 



Admitting that the gold-quartz veins were deposited by such mineral 

 waters, the next question is, in what form the gold and other metals were 

 in solution. While not intending to enter into a detailed discussion of 

 the ditticult problems associated with the question,*!" I would like to call 

 attention to a few general facts connected with them. Gold is soluble 

 at 200° centigrade in a 10 per cent solution of carbonate of sodium to 

 the extent of 1.23 per cent (Doelter), while silver is hardly attacked. 

 Silicates of alcalies dissolve gold at 250° centigrade to the smaller ex- 

 tent of 0.101 (Doelter and Liversidge). ]k\sides, gold is more or less solu- 

 ble in a great many other salts (T. Egleston). G. F. Becker has shown 

 the solubility of gold in alkaline sulphides, and the solubility of the sul- 

 phides of Hg, Fe, Cu and Zn in either sodic sulphide, sodic sulph-hydrate 

 or sodic carl^onate, i)artly saturated witli sulpliuretted hydrogen. Sili- 

 cate of gold, the existence of which was first suggested by G. Bischof, 

 has been frequently mentioned as })rol)ably contained in mineral waters; 



• MinernI Resources of the United States, 1892, p. 21. 



t Mr A. Liversidge hiis recently given iin interesting liistoric r<S8um6 of the experiments regard- 

 ing tlie solubility of gold, as well as many original experiments, in tlie Proc. Roy. Soc, New South 

 Wales, vol. xxvii, 1893, p. vn. 



XXXIII-BuLL. Geol. Soc. Am., Vol. G. 1894. 



