474 



METALLUKGY. (GOLD.) 



enabling it to resist wear and tear, or adapting 

 it to cutting purposes, need to be backed by a 

 tougher material competent to resist strains 

 and great vibration. 



Gold. Improvements in the extraction of 

 gold by amalgamation have been applied by 

 Mr. Rowland Jordan, by means of which the 

 percentage of the precious metal that is lost 

 during the process is very largely reduced. 

 Under the ordinary methods of extracting gold 

 with mercury, in case such substances as iron, 

 sulphur, arsenic, lead, tin, zinc, or copper, are 

 associated with the gold, they have the effect 

 through their own chemical action of so " sick- 

 ening" or subdividing the mercury as to pre- 

 vent its exerting its full power on the precious 

 metal. Some of the gold, moreover, being 

 coated with complex substances, passes away 

 with the water and sand, instead of being ar- 

 rested by the mercury. In Mr. Jordan's method 

 the ore is ground up and thoroughly commi- 

 nuted in a "Jordan fine crusher," while a cur- 

 rent of air takes up the pulverized material 

 and conveys it to a settling or collecting cham- 

 ber, whence it passes by its own gravity to an 

 apparatus which automatically regulates the 

 feeding of the powder into the amalgamator. 

 The amalgamator contains a body of mercury 

 from thirty to fifty inches in depth, and the 

 powdered ore is delivered at the bottom, 

 whence, being lighter than the mercury, it 

 rises through the bulk of this substance to 

 the surface as fast as the controlling mechan- 

 ism will allow, yielding up the gold in its pas- 

 sage. The refuse sand here encounters another 

 air-current, which conveys it to the waste-pits, 

 or to another machine for the separation of any 

 sickened mercury, which may have been car- 

 ried away by the amalgamator air-blast. The 

 last machine effectually separates every par- 

 ticle of mercury, and thus obviates the ordi- 

 nary waste of this valuable metal. Mr. Jor- 

 dan's process embodies four novel principles 

 or conditions of treatment : First, the ore is 

 reduced and the gold is amalgamated while it 

 is in a perfectly dry condition ; second, the ore 

 is reduced entirely by impact and not by abra- 

 sion, so that the particles are not rubbed or 

 ground together, and their complete separa- 

 tion and individuality are maintained; third, 

 tne ore, finely divided, clean, and dry, is sub- 

 jected to the action of mercury under pressure 

 and under the operation of mechanism which 

 continually separates the particles, and is kept 

 beneath the mercury long enough for every 

 particle of the gold-bearing powder to be ef- 

 fectually acted upon by it; fourth, the whole 

 process is automatic. 



The gold-ore of the Providence mine in 

 Nevada City, California a heavily sulphu- 

 reted quartz is treated by a chlorination pro- 

 cess. The dried sulphurets are roasted in a 

 three-storied furnace of elliptic plan, where 

 the ore is passed in succession from the third 

 or topmost hearth, to the second or middle, 

 and first or lowest hearth, one per cent, of salt 



being spread evenly over the ore while it is on 

 the last hearth. By this process the follow- 

 ing effects are produced in the charge : Any 

 arsenic or antimony present is oxidized and 

 volatilized; the sulphides of iron, copper, zinc, 

 and silver pass through stages of oxidation; 

 and by the addition of salt most of the silver 

 is converted into a chloride, and some chloride 

 of copper is formed, while the rest of the base 

 metals are completely oxidized. The gold is 

 left in a metallic state. The roasted ore, hav- 

 ing been partly cooled in a pile under the 

 furnace, is spread out till quite cool, and is 

 then sprinkled with water and thoroughly in- 

 termixed, after which it is passed through a 

 sieve. The sieved ore is transferred to the 

 chlorination-tubs, where chlorine gas is passed 

 through it for twelve hours, after which it 

 is left to digest for two or three days, or till 

 the chlorination is found to be complete. In 

 this condition, that of terchloride, the gold is 

 soluble in water, and can be leached out of the 

 mass. The gold is then precipitated in a fine 

 metallic state by a dilute solution of sulphate 

 of iron. When a sufficient amount of it has 

 collected in the precipitating-tanks, it is dipped 

 out, drained and dried, melted, and run into 

 bars. The process for the extraction of the 

 silver, which remains in the ore-pulp as a 

 chloride, is based on the reaction of calcium 

 hyposulphite and silver chloride. This results 

 in the formation of a soluble double hyposul- 

 phite of calcium and silver, from the solution 

 of which the silver can be precipitated as a 

 sulphide by soluble polysulphide of iron. 



Gold in veins is supposed to have come 

 from the adjoining rocks, but hitherto no 

 case of its occurrence in workable quantities 

 throughout the mass of such rocks seems to 

 have been recorded. Museum specimens of 

 country rock charged with gold are not un- 

 common, but in such cases the deposition of 

 the precious metal in the rock is clearly con- 

 nected with the filling of the adjacent vein. 

 According to Prof. Derby, the district of Cam- 

 panha and Sao Goncalo, in southern Minas- 

 Geraes, Brazil, affords an example of extensive 

 mining operations in decomposed gneiss, in 

 which the almost complete absence of veins 

 and of the other usual concomitants of gold is 

 remarkable. The terrain is largely composed 

 of decomposed gneiss, the rock itself being 

 seen only in the streams, and in a few cases 

 in the bottoms of the old mines, and it is in 

 the decomposed material that the workings 

 are chiefly carried on. The quartz-veins are 

 comparatively rare and insignificant. Some of 

 the hills have been worked in ledges or ter- 

 races, and successive coatings a few yards thick 

 have been more or less completely stripped off, 

 as one would peel an onion ; a mode of work- 

 ing which is of itself sufficient to prove that 

 the gold was found in workable quantities very 

 generally distributed throughout the mass of 

 decomposed gneiss. The same conclusion is 

 presented in an unpublished report to the Bra- 



