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Mineralogy and Geology. 135 
adopted, the carefulness of the management being such that the 
whole data needed to present a complete exhibit of all the operations 
The ore treated at Morro Velho mines is chiefly a mixture of 
magnetic, arsenical and common iron pyrites, freely disseminated 
rarely, copper pyrites are present in the vein. e composition of 
what is called “pure ore” may be taken at about 43 per cent silica, 
T yritous matter. Of these minerals, arsenical 
€ quantities. Pure specimens of this substance afford, by 
assay, from four to six ounces of gold per ton, and wherever crystals 
his mineral make their appearance the yield of the precious 
metal is large. Cubical pytites is of more frequent occurrence, but 
is far less rich in gold, yielding at best but about an ounce and a 
uf of gold perton by assay. Magnetic pyrites, the most abundant 
sulphid, is very slightly auriferous, pure specimens yielding but 
about four dwt. per ton, Branches of clay slate are often found in 
€ principal veins, and this rock, under such circumstances, com- 
parts the vein is cavernous, and less close in its texture than in 
others ; but where drusy cavities are frequent, the yield of gold 
es; the most productive matrix for gold is a compact mix- 
ture of quartz an pyrites with varying quantities of slate. The 
~~ metalliferous deposit called the Cachoeira, Bahu, and Quebra 
anella, is one continuous, very irregular vein, varying In width 
from seven to seventy feet, and at one point reaching one hundred 
feet. The average thickness at the present depth 176 fathoms 
pos 6 feet) perpendicular on the Cachoeira and 165 fathoms on the 
m 
r grates, passes 
ver bullock skins and then lower down over woolen cloths (blan- 
*The last : : ; almost 
accounts which have reached us are information of the c 
i destruction of these remarkable mines by a disastrous fire, rendering active 
°Perations impossible for a long time to come. 
