PROCESSES OF ALTERATION-OXIDATION. 
203 
rock, but the quantity is not greatly changed. Manganese is greatly concentrated, 
locally, on the seams of the rock. As to alkalies, the accumulation of potassium 
begun during the vein-forming process is continued or at least maintained during 
oxidation. Pyrite is converted into sulphuric acid and sulphates, and the per¬ 
centage of sulphur is greatly decreased in the oxidized ore. Part of it remains as 
sulphate, but as there appears to have been no corresponding decrease of the bases 
it would seem likely that a considerable part of it was carried away as free acid. 
Little change is noted in the titanium, while phosphoric acid and zinc appear to 
have increased. The small quantities of other metals do not seem to differ notably 
from those observed in fresh vein material (p. 172). An increase of water to 3 or 5 
per cent is a natural consequence of the formation of kaolin and other hydrated 
salts; locally it may increase up to 14 per cent, which is the amount contained in 
pure kaolin. 
INFLUENCE OF OXIDATION ON GOLD, SILVER, AND TELLURIUM. 
In gold-quartz veins of the ordinary t} r pe it is common to find a very decided 
enrichment in the oxidized part of the deposit, due chiefly to a considerable reduc¬ 
tion of volume of the ore by solution and removal of many of the constituents, 
mainly of the sulphides. In some cases a solution and reprecipitation of gold may 
have taken place, but this is assuredly not the rule. It is also common to find that 
a very decided leaching of silver has taken place in the upper part of oxidized veins 
containing this metal, and this leaching is often accompanied by deposition of 
chloride or native silver at moderate depth, and by argentite and other secondary 
silver-bearing minerals in a zone a short distance underneath the water level. 
There is little indication of any decided enrichment of the oxidized ores in the 
Cripple Creek district. Owing to the structure of the veins and the small quantity 
of sulphides present, the reduction of volume of the oxidized veins is very slight; 
in fact, under certain circumstances an increase of volume may take place. The 
fresh telluride ore is apt to be extremely rich in places and high-grade pockets occur 
impartially in oxidized and fresh portions of the veins. The richest ore ever shipped 
from the district came from a depth of about 500 feet in the El Paso mine, where 
almost no oxidation occurs, even at the surface. 
Whether a slight enrichment has taken place or not is not easy to decide. We 
incline to the belief that the oxidized ores as a whole are somewhat richer than the 
corresponding telluride ore. The results obtained by Pearce on the specimen from 
the Moose mine mentioned above (p. 201), one-half of which was oxidized, tend in 
the same direction. The fresh portion contained 12.24 ounces gold per ton, while 
the oxidized portion yielded 14.58 ounces. This difference may, however, simply 
depend upon unequal distribution of the gold. 
Regarding the silver there is more decided evidence of leaching. Much silver 
occurred in the oxidized portions of the Moose and the Blue Bird veins* but there 
are no data from the production of the mines to show whether any leacliing has taken 
place. Pearce’s results would seem to indicate that a removal of silver had taken 
place during oxidation, for in the fresh ore he found 6.7 ounces silver per ton, while 
none was contained in the oxidized portion. The analyses of the oxidized ores of 
Stratton’s Independence tend also to show a removal of silver, as does the fact that 
