360 ORIGIN AND DEVELOPMENT OF ORE-DEPOSITS. 



Origin of metallic deposits apart from metallic silicate roch 

 crumllings. 

 Still another argument for the efficacy of thermal waters in 

 bringing up lead and silver from the depths, in regions where 

 there are no eruptive rocks, is thus stated by Prof. Smyth. 

 "Finally, how are we to cope with those districts in which we 

 find little or no mica, no augites or hornblendes, the large areas 

 for instance of clay slates in central Wales, where we have no 

 granite contacts and no intrusions of igneous dykes, and yet 

 scores of well-developed lodes, many of them exceedingly 

 productive of lead ores and often rich in silver ? .... It seems to 

 me that no leaching out of metallic mineral from the country 

 walls will elucidate the problem, but that we are nearer its 

 solution by invoking the aid of thermal waters."* 



The absolute necessity of such chemically charged thermal 

 waters seems to be admitted by all who have made a special 

 study of the lodes in the West of England, and by most of 

 those who have recently studied lodes in other countries.! 



We thus reach the conclusion that in most cases sulphur, 

 part at least of the metallic bases of such sulphides as pyrites, 

 chalcopyrite, galena, and blende, oxide of tin, and the various 

 fluo-silicates and fluo-boro-silicates have a "deep-seated" origin, 

 and that they have for the most part been brought into their 

 present positions either directly by the agency of ascending 

 thermals, or indirectly by the elevation and intrusion of eruptive 



* Smyth, Pres. Address, op cit. p. 195. 



f Lindgren, in referring to the silver deposits of the Carlico district in 

 California, says : "on the whole it seems to me most probable that ascending 

 thermals have extracted ore and gangue from the eruptive rocks at a certain 

 although not exceedingly great depth, and that for chemical and physical reasons 



the principal precipitation took place (in complex fissures) near the surface... 



Most of the ore-deposits occur in liparite or in its tufas, as veins along fractures 

 and dislocations of a more or less regular character ; as simple, once open and 

 subsequently filled fissure-veins ; as impregnations along complex fissure-systems 

 (gangziige) or filling and cementing more or less extensively fractured zones 

 (Trummerziige). The gangue is predominantly barite with jasper ; the present 

 ores are haloid salts of sUver, hydrosiUcate and carbonate of copper resulting 

 from primary rich silver sulphides and copper pyrites." Trans. Am. Inst. M. 

 Eng. Except for small differences in the character of the ores and rocks this 

 description would apply well to the Torreon Mine in Chihuahua. See Journ. 

 R.I.C. 



