Mineralogy and Geology. 137 
Ist. Free gold capable of concentration by washing. 
2nd. Free gold in a lamellar form liable to be carried off by 
suspension in water. 
. 3d. Mechanically combined, gold enclosed in particles of pyrites, 
but capable of being liberated by further gri . 
The ai of concentration adopted at Morro Velho mines, is 
extremely simple, cheap and economical, consisting of a series of 
inclined tables or boards 18 inches in width, falling about one inch 
in a foot, and covered with bullock skins tanned with the hair on, 
for about 30 feet and followed by other inclines covered by baize 
nkets. These inclined sluices are called strakes. The follow- 
ing table gives many important details relating to this system as 
employed at Morro Velho mines :— 
Name of | No.of | No.of iene’ Mado Apes of boty paw eee hy aed is soe 
ee strakes) strakes. squ're ft.) ff Ore Seam stenten calcein nie. 
ft wm | in cub. ft. 
Lyon, ....| 30]. 36/31 10/1 6 | 1,719 | 46:83 | 36-73] 288 | 210 | 20-00 
Cotesw'tth} 12] 13/30 6/1 4 545 | 32°21 | 16°92] 104 | 65] 5-50 
9| 8/27 011 6| 324/ 29-61] 10°94| 48| 48] 2°76 
erring,..| 24/ 29/35 0| 1° 6 | 1,232| 35-64] 34:56] 228 | 174 | 18-00 
Powles, ..| 36} 42|33 7|1 34) 1,821 | 27-B5| 66-10) 336 | 252 | 28-47 
Addison, | 24/ 30/31 10| 1 5 | 1,352 | 38-04| 35°54| 240 | 170 | 17-00 
136 | 158 6,993 mac tl ae D218 
Portion to its weight to be saved by any known method and fioats 
off With the slimes, Its quantity is believed to be about 10 a 
cent of the original amount of gold in the ore. The second is 
and by a subsequent system of strakes. 
wae System of amalgamation of the concentrated ores at Morro 
elho is described in detail with careful drawings. It depends es- 
aa on the use of revolving barrels containing 16 cubic feet, or 
a half tons of wet sand, with 60 Ibs. mercury and a sufficient 
og es clean water to give the necessary degree of fluidity to 
®. per ton of ore stam The average cost of extracting the 
oe from the mine ed its reduction, including every expense 
Seneral management, etc., for the last ten years has been 25s. pet 
