According to the above method, the ores coming
from the mine are classified into the four following divisions:
1. Very rich ore, averaging about six per cent. of silver, or containing
say 2,000 ounces of silver to the ton (of 2,000 lb.).
2. Rich ore, averaging about one per cent. of silver, or say from 300 to
400 ounces of silver to the ton.
3. Ordinary ore, averaging about 1/2 per cent. of silver, or say from 150
oz. to 200 oz. of silver to the ton.
4. Gangue, or waste rock, thrown on the dump heaps.
The first of these qualities--the very rich ore--is so valuable as to
render advantageous its direct export in the raw state to the coast for
shipment to Europe. The cost of fuel in Bolivia forms so considerable a
charge in smelting operations, that the cost of freight to Europe on very
rich silver ores works out at a relatively insignificant figure, when
compared with the cost of smelting operations in that country. This rich
ore is consequently selected very carefully, and packed up in tough
rawhide bags, so as to make small compact parcels some 18 in. to 2 ft.
long, and 8 in. to 12 in. thick, each containing about 1 cwt. Two of such
bags form a mule load, slung across the animal's back.
Pages:
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47