THE SOURCES AND USES OF IRON PYRITES. 
119 
the whole, would be worth say Is. 8 d . ; a sum far too small to 
cover the cost of any known method of treatment. 
At the present time all the principal pyrites deposits are 
worked as large quarries or open cuttings from which a certain 
amount of overburden has to be removed, while the mineral is 
transported by locomotive power over railways connecting the 
mines with their respective shipping ports. The very extensive 
scale upon which they are now conducted will be gathered from 
the following figures. 
At Tharsis, during the year 1877, no less than 371,230 cubic 
yards of overburden were removed and 435,876 tons of pyrites 
extracted ; of this amount 249,299 tons were shipped for the use 
of alkali manufacturers, manure makers, &c., while 186,577 
tons were retained for local treatment for copper. In addition 
to this 45,41 5 tons of ore were extracted and treated at Calanas, 
while the amount of copper precipitate exported amounted to 
7,199 tons. 
The total quantity of pyrites raised during 1877 from the 
Tharsis and Calanas mines was 481,920 tons, and the average 
number of work-people employed throughout the year 3,181, 
embracing a population of about 6,500 either resident on or 
dependent upon the mines. 
The Eio Tinto mines, like the Tharsis, are worked a del 
ouvert , and during the year 1877, 773,366 cubic yards of over- 
burden were removed as well as 771,751 tons of pyrites 
extracted; of this amount 251,360 tons were exported, and 
520,391 tons retained for local treatment. During the same 
period copper precipitate representing 2,735 tons of metallic 
copper was exported, and at the close of the present year the 
annual production of metallic copper will probably not have 
fallen short of 6,500 tons. 
At the San Domingos mines the total production of pyrites 
in 1877 was 341,000 tons, of which 163,000 tons were exported, 
while the copper precipitate shipped amounted to 3,050 tons ; 
as in the case of the Rio Tinto works, the local production of 
copper during the current twelve months will be much larger 
than in 1877. 
The largest deposits of pyrites are those of Rio Tinto, where 
three very wide and nearly parallel lodes are known to exist ; 
of these, however, the more southerly only is at present 
worked. Hundreds of Roman shafts are scattered over the out- 
crop of the central and northern deposits, and it is believed 
that a very large proportion of the ores which have furnished 
the vast heaps of ancient slags accumulated in this vicinity were 
obtained from these lodes. 
At San Domingos and Tharsis the mines were found by the 
present proprietors in the exact state in which they were left 
