40 lEON PYEITES. 



cost of extraction amounted to £2 2b. 4d. per ton, without esti- 

 mating wear and interest on capital. The above charge is rather 

 high, as fuel during that period was unusually dear, and the fur- 

 nace being but 4 feet wide instead of 5 feet, increased the 

 labour cost, as less work is done at the same cost than would be 

 incurred in working a larger furnace. Another element in the 

 cost is the mercury which is lost, amounting to lib. 13 oz. per 

 ton — a large proportion of which, I think, might be saved by 

 improved appliances for that purpose, together with the gold 

 contained in it. The immediate cause of this loss of mercury 

 is the severe trituration to which it is subjected with the sand. 

 This was found indispensable, for whenever, through oversight or 

 experiment, a less degree of trituration was applied than that now 

 used, or the sand ground too wet, the return of gold was in- 

 variably diminished by several per cent. 



In carrying out these operations, I found that a la7ye pro- 

 portion of galena in the mineral seriously interfered with the 

 extraction of the gold, but a small proportion of the sulphides of 

 copper, zinc, or lead, produced no appreciable eifect. 



Taking the process as it stands, we have been unable to find 

 one that would at less cost extract the same proportion of gold, 

 or could be safely trusted in unskilled hands with only occasional 

 supervision. 



Me. Thompson also read the following return : — 



Retitens of Pyrites treated at the Port Phillip Company's Works, Olunes, 

 since October, 1866 : — 



Minerals treated : 1S67, 215 tons 17 cwt. ; 1868, 366 tons 9 cvrt. ; 1869, 

 401 tons 11 cwt. ; 1870, 431 tons 9 cwt.; 1871, 561 tons 2 civt. ; 1872, 368 

 tons 6 cwt. ; 1873, 294 tons. 



Gold, contents per ton, per assay : 1867, 4 oz. 16 dwts. 6'93 grs. ; 1868, 



3 oz. 18 dwts. 6-56 grs. ; 1869, 4 oz. 1 dwt. 19-15 grs. ; 1870, 3 oz. 11 dwts. 



4 34 grs. ; 1871, 4 oz. 7 dwts. 1099 grs. ; 1872, 5 oz. 18 dwts. 1936 grs. ; 

 1873, 4 oz. 10 dwts. 16-30 grs. 



Total Gold obt ained : 1867, 960 oz. 13 dwts. ; 1868, 1,322 oz. 13 dwts. ; 

 1869, 1,515 oz. 11 dwts. ; 1870, 1,370 oz. 4 dwts. ; 1871, 2,290 oz. 1 dwt. ; 

 1872, 2,061 oz. 9 dwts. ; 1873, 1,268 oz. 17 dwts. 12 grs. 



Gold extracted, per ton : 1867, 4 oz. 9 dwts. ; 1868, 3 oz. 12 dwts. 4 grs. : 



1869, 3 oz. 15 dwts. 1160 grs. ; 1870, 3 oz. 3 dwts. 12-60 grs. ; 1871, 4 oz. 

 1 dwt. 15-20 grs. ; 1872, 5 oz. 11 dwts. 22-56 grs. ; 1873, 4 oz. 6 dwts. 

 7-63 grs. 



Percentage of Gold extracted : 1867, 92-43 ; 1868, 91-71 5 1869, 9228 ; 



1870, 89 24 ; 1871, 93-34 ; 1872, 94-22 5 1873, 9519. 



