REPORT OF DEPARTMENT OF METALLURGY. 249 



taining some of the first gold-duel taken out by Captain Marshall on the 

 19th of January, 1848. The fact that these specimens were collected so 



long ago, and that the date of collection is known in almost every ease, 

 adds very greatly to their value. Indeed, it would be absolutely impos- 

 sible to duplicate many of the specimens. 



A very interesting series of specimens was obtained from the Brewei 



Mine, South Carolina, in which the principles of hydraulic mining U 



carried on in California are applied. 



In the extraction Of gold only a few processes have been illustrated. 

 A very line collection was obtained from the North Bloomfield Mine, 



Nevada County, California, representing the average of the rock as it 



is washed down by the little giant, the mercury used to catch the gold 

 in the riffles, the amalgam as it is collected in the riffle-boxes, the puri- 

 fied amalgam, the gold produced from retorting the amalgam, tine 

 gold, and coarse nnggets of gold that are picked np off the floor of 

 the mine at the clean-up. To this series is added a collection showing 

 the heavy minerals associated with the gold which are taken out from 

 the riffle-boxes with the amalgam. This is an exceedingly interesting 

 and valuable collection, illustrating as it does not only the extraction of 

 gold, but also as illustrating a process which is without doubt the most 

 economical of any mining process carried on anywhere, the actual 

 cost of moving a ton of material from the mine, collecting and saving 

 the gold, and discharging the waste material being but a few cents. 



The next collection illustrates the extraction of free gold from aurif- 

 erous pyrite by stamping the material and collecting the gold, as an 

 amalgam on copper plates, as carried on at the Bobtail Mill, Black 

 Hawk, Gilpin County, Colorado. This collection shows the ore as re- 

 ceived at the mill, which consists of a mixture of iron and copper pyrite 

 disseminated through quartz and clay (the gold occurs in the pyrite) ; 

 the crushed material as it is passed through the sieves of the stamps: 

 the battery pulp; the gold amalgam as scraped from the copper plates; 

 the gold resulting from the retorting of the amalgam ; the concentrations 

 obtained by allowing the heavy portion of the material to settle out in 

 running water, consisting of pyrite and calcopyrite and. containing a 

 very considerable amount of gold ; and the sand or waste material. It 

 is the only illustration of extracting gold by stamping and amalgamat- 

 ing that we have, and in the future development of the plan it would 

 be desirable to add two or more series, illustrating the treatment of 

 different characters of ore. 



In the smelting of auriferous material a collection was made at the 

 Colorado Smelter, at Butte, Mont., by the curator. This represents the 

 various ores available to this smelter, the fuel and iluxes used, the 

 matte produced, ami the slag. The work at this smelter is only the first 

 step in the process. The matte, which contains about 60 percent, of 

 copper, together with the gold and silver of the ores, is shipped to the 

 Argo Works, near Denver, for further treatment. 



