DENVER & RIO GRANDE WESTERN ROUTE. 



109 



tion of supplies while he has been driving tunnels in search of ore; 

 which has carried lumber and other material for building mine 

 works and even heavy machinery up the steep mountain trails. 



MAIN LINE OF RAILROAD FROM MALTA TO GRAND 



JUNCTION. 



Soda Springs and Evergreen Lake, two resorts of local interest, 

 are 2| miles west of Malta. Evergreen Lake is said to be very attrac- 

 tive, and Soda Springs is much visited by those who hope to be bene- 

 fited by the use of the waters. 



A little north of Malta, at the crossing of a strong stream from the 

 east known as the East Fork of the Arkansas, the north end of the 

 Leadville loop connects with the main line. The East Fork heads in 

 the Mosquito Range, on the Continental Divide, northeast of Lead- 

 ville. The pass between the head of this stream and Tenmile Creek, 

 the head stream of Blue River, has been named Fremont Pass, on the 

 supposition that Fremont crossed the range at this place in his ex- 

 pedition of 1845, but the " Pathfinder " probably crossed at Tennes- 

 see Pass. 



in the rocks from the surface has not 

 hscending from great depth or by 

 Svaters sinkmg down through cracks in 

 the rocks from the surface has not 

 been satisfactorily determined, but 

 since the ores were originally de- 

 posited they have certainly been con- 

 centrated by what is called " enrich- 

 ment " — tliat is, by the solution by 

 surface waters of the disseminated ore 

 and its redeposition at a lower level. 

 The ores are generally most abundant 

 beneath the layers or " sills "of por- 

 phyry, but they are found also in some 

 places below the quartzite. 



The ores originally consisted of sul- 

 phides of the principal metals — lead, 

 zinc, copper, iron, and probably sil- 

 ver — but the silver was so much dis- 

 seminated that it has been difficult to 

 detect. Geologic work in the district 

 has shown that the ores were deposited 

 after the intrusion of the gray por- 

 phyry into the limestone and before 

 the rocks were broken by the faults 

 shown in figure 26. After they were 

 deposited in fissures and solution 

 cavities in the limestone much of the 

 overlying mantle of rock was remov'ed, 

 and the ores were brought within the 

 zone of weathering by surface waters. 



When the sulphides ^^•ere thus ex- 

 posed to weathering they were dis- 

 solved, changed to carbonates and 

 oxides, and redeposited by the de- 

 scending surface waters in a rather 

 narrow zone, which has yielded most 

 of the ores mined up to the present 

 time. The extreme richness of the sil- 

 ver ore mined when the cami> was at 

 the zenith of its fame was due to the 

 fact that the silver was redeposited 

 near the surface and was the first valu- 

 able mineral to be reached in most of 

 the mines. Many of the mines are 

 now working sulphide ores, which are 

 much leaner than the carbonate and 

 oxide ores of the early days. The 

 great increase in the value of the zinc 

 in 1915 was due both to an increase in 

 the production of ore and to a great 

 increase in the price of the metal. 

 This increase in price led to the re- 

 working of dump heaps for the zinc 

 ore that had been thrown away in the 

 earlier and more prodigal exploration 

 of the ore bodies. It is perhaps for- 

 tunate that zinc was so nearly worth- 

 less in the early days, for that led to 

 its conservation imtil the World War, 

 when the demand for it was unprece- 

 dented. 



