bmmonb.] LEADVILLE MINING DISTRICT. 411) 



From the city a fine view is had of the Arkansas valley and of the 

 Sawatch mountains beyond it. That of the Mosquito range is much less 

 satisfactory, owing to foreshortening. To the east of the city the ground 

 slopes upward in a succession of benches or gently-rounded hills, known 

 successively as Fryer Hill and Carbonate Hill, Yankee Hill and Iron 

 Hill, etc., in which, as will be readily perceived from the unsightly 

 dumps of waste that disfigure their surfaces, mining has been most 

 extensively carried on. Although the greatest amount of underground 

 work has been done within a mile or two of the town, within which 

 distance there is an almost continuous network of subterranean pas- 

 sages reaching down several hundred feet from the surface, rich mines 

 are by no means confined to this area, but are found up to the very 

 crest of the range, at altitudes of 12,000 to 13,000 feet, and also beyond 

 the crest on its eastern slopes. 



The various smelting works, in which a portion of the ores produced 

 here are smelted, are situated along the streams issuing from the moun- 

 tains at either extremity of the city. 



The greater part of the ores come from ore bodies in the Lower Car- 

 boniferous limestone, generally known as the Blue or ore-bearing lime- 

 stone. During the lirst few years the productive minerals were car- 

 bonates of lead, and chlorides and bromides of silver, in a gangue of 

 iron and manganese oxides mixed with clay and silica. These ochreous- 

 looking ores are generally known among miners as "Carbonates,'' irre- 

 spective of whether the lead occurs, as here, mainly in the form of 

 carbonate, or, as at Red Clitf in similar deposits, largely as sulphate. 

 All these ores, being the result of secondary alteration by surface waters 

 — a natural process of concentration that has removed a larger propor- 

 tion of worthless materials, such as sulphur and zinc, than of the 

 precious metals— were not only richer but better adapted for smelting 

 than those which are obtained at the present day from the unaltered 

 ore bodies below the zone of oxidation. While, therefore, theaggregate* 

 annual product of the district in tons of ore has regularly increased, 

 its intrinsic value has fallen somewhat below that of early days. 



As at present mined, the ore bodies, which are of enormous size, 

 consist mainly of galena, iron pyrite. and zinc blende. Copper has, as 

 a rule, been conspicuously absent, but of late years a deep seated ore 

 body, at a lower geological horizon than those generally worked, has 

 been found to carry a considerable proportion of its value in this metal 

 in an admixture of copper pyrite. In some of the large pyrite bodies 

 small but appreciable quantities of tellurium occur. In others, bis- 

 muth has been found with the lead carbonates, and these also carry an 

 unusually large proportion of free gold. Gold is found generally in 

 deposits occurring exclusively in the porphyry bodies and quartzites; 

 in them it is not infrequently associated with galena. The limestone 



