kansomk] METHODS OF MINING AND TREATMENT OF ORES. 41 
capacity of the tramway, it being restricted in this instance by the 
limitations of a small Huson tramway which was bringing ore down 
from upper workings to what is now the main adit. The expense of 
running these well-constructed gravity tramways is comparatively 
small, and they are remarkably smooth and efficient in operation. 
The ores of the Silverton quadrangle arc commercially divisible 
into shipping ores and milling ores. The former are shipped direcl 
to the smelter as crude ore They include such high-grade ores as 
can not be treated economically by simple milling processes and such 
ores as contain but a small proportion of worthless gangne. The 
milling ores include such gold ores as can be readily amalgamated or 
concentrated and those silver-lead ores in which the valuable min- 
erals are associated with considerable quartz or other gangne mate- 
rial. .Most large mines produce both grades of ore, while the output 
of the smaller mines, without mills, is uecessarily usually restricted to 
shipping (»!•<'. Exclusive of the ore from the Revenue tunnel, which 
really comes from the Telluride quadrangle, the bulk of the crude 
ore at present shipped from the Silverton quadrangle goes to the 
American Smelting and Refining Company's smelter at Durango. 
Heavy lead ores preponderate. The treatment charge varies from $2 
bo $11, the higher rale being for siliceous or " dry " ores. An extra 
chare of 50 cents per anil (1 per cent of 1 ton) is made for ores run- 
ning over L0 per cent of /inc. 
The treatment of milling ores varies considerably with their char- 
acter. Formerly many lixiviation plants, usually employing some 
modification of the original August in process, were installed in the 
region for the treatment of argentiferous ores. This process, involv- 
ing a chloridizing roasting of the ore and subsequent leaching out of 
the chloride of silver by the use of strong brine, proved successful in 
treating the ore of the Polar Star mine, about 95 percent of the silver 
being saved, in many cases, however, it was a failure, the ores not 
being adapted to its employment. At the present time it is no longer 
used. Mechanical concentration, coupled in some cases with amalga- 
mation, has entirely replaced the various chemical processes, and the 
concentrates thus obtained are shipped to the smelters. 
The silver-lead ores, carrying usually some gold and copper, are 
crushed by rolls or stamps and, after proper sizing in revolving 
■screens, are concentrated by means of jigs and shaking tables. For 
his purpose the Wilfley table is most in use, although Woodbury, 
Bartlett, and Cammett tables and Frue vanners are also emplo} 7 ed, 
tnd a special form of "end-shake" table is in use in the Silver Lake 
nill for saving the slimes. Where the ore to be treated is rich in 
jalena the tendency in most of the newer mills is to substitute 
oils for stamps. Huntington mills are frequently employed for 
©grinding tailings. 
The richer ores, carrying i'we gold, require different treatment. In 
