Chap. XXVII.] 
METHODS USED ABEOAD. 
577 
exceeds 0-10 per cent., but silica is rather high, ranging from 2 or 3 up to 15 per 
cent. The jig concentrates range in silica 2 or 3 per cent, higher than the lump ore 
produced at the same time.' 
As a further example of the trouble that is thought worth while 
Methods of mining, wash- '^^ ^ther parts of the world in working manga- 
ing, etc., employed in nese-ore deposits, SO as to make use of all pos- 
Panama. ^jj^l^ j ^1^,^ following abstract from a 
paper by Mr. E. G. Williams, entitled ' The Manganese Industry of 
the Department of Panama, RepubHc of Columbia '. Trans. Amer. 
Inst. Min. Emj., XXXIII, pp. 214, 215 (1902). 
' The discovery outcrop is about 100 ft. below the summit of the hiU. An 
open cut was begun about 20 ft. below the outcrop and carried in until the walls 
were 100 ft. high. The mountain, rising faster than the ore-body, gave a con- 
stantly increasing over-burden to remove ; and this, ■« ith the difficulty of holding 
the side-waUs, led to the abandonment of open-cut work and the beginning of under- 
ground mining in 1898. A tunnel was driven into the ore-body from the open-cut 
level, and from the same level a shaft was stmi; 110 ft. and two levels were opened. 
The mine is drained by a timnel on the bottom level connecting with the shaft. 
" The ore is usually stoped for the entire width of the deposit, both heavy tim- 
bering and supplementary fiUing being required. At some points it is necessary 
to leave piUars of ore in place, to be extracted when the stope is about to be finally 
abandoned. The ground is difficult to hold, because of the decomposed rocks 
surrounding the ore and the large masses of clay associated with it. Occasionally 
a pocket of clay is opened which is under heavy pressme from the surrounding 
rock or ore. As soon as an outlet is furnished, the clay begins to flow into the 
stope in a plastic mass ; and great difficulty is often experienced in checking 
this flow. The most satisfactory method of working — indeed, the only one by which 
the soft clay walls can be held — is to keep the slopes filled to within about 7 ft. of the 
roof. The ore-shoots and man-ways are built up from the level below, as the filling 
is carried up. The material for filling, apart from what is furnished from waste 
in the mine, is obtained outside, on the open-cut level. 
' Square-set timbering has been used in large stopes, but it has been found better 
and cheaper, where the filHng system was employed, to support the roof with cribs 
of round logs, which accommodate themselves, without damage, to the shrinkage 
of the newly-filled material and the pressure from the ore. 
' The ore from the lower levels is hoisted to the open-cut level by a gasoline hoist, 
which was installed on account of the difficulty of obtaining a supply of water 
through the dry season. 
' The ore is hand-picked on the open-cut level, the large pieces going direct to 
the tramway which connects the mine with the railroad, while the small pieces 
and finely-powdered ore are transported separately, taken to the log-washer, and 
screened after washing. 
' The size above 0"5-in. mesh is hand-picked and shipped ; the finer portion 
being reserved until a suitable concentrating-plant shall have been erected. This 
care in sorting the ore is rendered necessary by the presence of particles of jasper 
in the ore, which, if not removed, subject the ore to a penalty for silica. 
' The ore is stored on the upper level of a 50-ton bin at the loading terminal 
of a Bleichert tramway. This tramway, about one-third of a mile in length, has 
