210 GEOLOGICAL SURVEY OF THE TERRITORIES. 



The roasting requires from twelve to fifteen hours and the smelting 

 twelve hours more in th« reverberatory furnace. The matt, after being 

 separated from the argentiferous lead, is stored away to be worked over 

 at the end of every run ; or if the furnace clogs uj) some of it is added, to 

 clean it out by its fusibility. 



A run occupies usually twenty days, more or less. In regard to the 

 amount of work done by this company the following statement may be 

 of interest, as giving the total from January to August of 18G9. 



Total number tons of ore treated in furnace, 188. 



Average assay value of ore per ton, 200 ounces. 



Percentage of assay ¥«:ilue saved, 90 per cent. 



The Terrible shaft is opened four hundred feet below the Brown. In 

 April last the workmen were shut out from their shaft by the rapid 

 invasion of water, but since then there has been no trouble. The Ter- 

 rible ores have already attained a widespread reputation for richness. 

 The main differenice between them and the Brown ores is that they are 

 richer in brittle, and the Brown in ruby, silver.* 



The Baker mine.—The mill belonging to this company is situated some 

 four miles up the canon known as West Argentine, and on the opposite 

 side of the creek from the Brown lode. It is one of the very finest 

 structures of the kind ever erected in this Territory, but was not quite 

 completed at the time of my visit. On the floor of the mill under the 

 apertures through w^hichthe ore is to be delivered, is a drying hearth for 

 drying the wet ores. After the moisture has been driven off the ore is 

 crushed in Dubois's breaker and ball-crusher. The former of these 

 machines resembles the breaker known generally in Europe under the 

 name of " the American nut-cracker.'- The ball-crusher is a cylinder 

 formed of strong iron staves, which are attached at their extremities to 

 two stout iron disks in such a way as to leave a very small crack between 

 each two of them. Three to four hundred pounds of iron balls are then 

 put in with the ore and the cylinder revolved on its axis. The finely 

 powdered rock falls through the cracks into a hopper built to receive it, 

 and through this hopper into an iron cylinder twelve feet long and eight 

 feet in diameter, with a helix attached to its inner surface for the pur- 

 pose of continually turning the ore, and thus presenting a fresh surface 

 for oxidation. Fire is at first applied, and this cylinder is made to rotate 

 slowly, and in a short time the sulphur of the ore is ignited, whereupon 

 the extraneous fire is withdrawn and the oxidation continues w4th the 

 assistance of the heat from the burning sulphur. The sujDply of atmos- 

 pheric air to the interior is regulated by means of a door to an opening 

 at one extremity of the cylinder's axis, while the volatilized oxides of lead 

 and zinc and silver are led through a -pipe connecting with the other 

 extremity of the axis to condensing chambers and thus saved. 



After a thorough roasting the ore is let out upon cooling floors, and 

 from that transferred to the amalgamating barrels. 



The Baker ores contain much ziucblende and will average perhaps sixty 

 -ounces silverper ton, though occasionally rich pockets are met with in the 

 mine, the ores from which have given remarkably high results. Eed and 

 "White varieties of fluorspar occur largely as gangue rock of the lode. 



The Burleigh tunnel. — This is about half a mile distant from the Brown 

 lode toward Georgetown. The object had in view by the i^roprietors of 

 this tunnel is to intersect all the lodes whose strike is with the trend of 

 the mountain in which it is being driven. The rock is quite hard, and 

 souly one hundred feet had been bored when it was inspected. The boring 



* The average assay value of brittle silver is five thousand ounces per ton. 



