108 



GUIDEBOOK OF THE WESTEEX UNITED STATES. 



been the prospector's constant companion in his lonely wanderings 

 over these bleak ranges and his main dependence for the transporta- 



priee of the metals. One of the most 

 striking features shown by the dia- 

 gram is the remarkable increase in the 

 value of the output of this district 

 since 1902, with the exception of 1908, 

 1909, and 1910. This great increase in 

 the total has been due largely to the 

 marketing of great quantities of ziuc. 

 In 1915 the zinc amounted to $8,989,154 

 out of a total of $13,839,401. 



Figure 26 shows the gradual de- 

 cline in the production of silver from 

 a maximum in 1880 and of lead from 

 a maximum in 18S1-S2. It also shows 

 that at first gold formed only a small 



SVI 



years it was small. After 1901, how- 

 ever, it increased rapidly until in 

 1915 it was more than two-thirds of 

 the total output of the district. 



Thus Leadville, which began in 1860 

 as a gold camp, became in 1879 the 

 greatest silver-lead district this coun- 

 try has ever produced and in 1915 be- 

 came predominantly a zinc district. 



The nature and occurrence of the 

 ores of Leadville bear little resem- 

 blance to those of the Cripple Creek 

 district, described on pages 47-51. At 

 Cripple Creek the ores were probably 

 deposited from waters that ascended 



500 



1,000 



1300 Feet 



FiGuEE 27. — Section through some of the workings at Leadville, showing the relation of 

 the ore to the limestone, porphyry, aud quartzite. wp, White porphyry; gp, gray por- 

 phyry; Ivl, Leadville limestone; pq, parting quartzite; wl, white limestone; qtz. 

 lower quartzite ; gr, granite. The ore bodies are indicated by cross hatching. The 

 straight heavy lines represent faults, and the axrows show the direction of movement. 



percentage of the whole but that in 

 1893 it began to increase and that in 

 1900 it ■ attained a maximum of 

 $2,500,000. Since that time it has 

 run fairly regularly at somewhat over 

 $1,000,000 a year. Copper began to 

 form a notable percentage of the total 

 in 1889. but since that year the out- 

 put has been veiy regular, its value 

 amounting to about $500,000 a year. 

 The production of zinc has become one 

 of the spectacular features of the 

 Leadville district. The production of 

 this metal first bec-ame noticeable in 

 the returns for 1896, and for a few 



from deep in the interior of the earth 

 through fissures in the breccia that 

 fiUed the throat of an old volcano. At 

 LeadviUe the ores replace limestone, 

 but they are closely associated with 

 sheets of porphyry that were forced 

 while molten in between the layers of 

 limestone or between the limestone 

 and adjacent quartzite. This re- 

 lation is shown in figure 27, which 

 represents a section through some of 

 the workings. Whether or not the ores 

 were brought to this place by waters 

 ascending from great depth or by 

 waters sinking down through cracks 



