226 ORE-DEPOSITION IN TRUNK-CHANNELS 
ORE-DEPOSITION IN TRUNK-CHANNELS OF CIR¬ 
CULATORY GROUNDWATERS 
By Charles Keyes 
Although ore deposits so often occur along the restricted lines of 
free-flowing groundwaters it does not follow, as we have been 
so commonly led to believe, that the presence of ore-bodies in 
such situations is solely due to the long continuance of unusually 
great volumes of waters passing by. Ore-localization is almost 
invariably determined by other and entirely unrelated factors. As 
recently and conclusively shown it is only under especial geologic 
conditions that any parts of underground trunk-channels become 
commercial ore-repositories. As loci of ore-deposition altogether 
too much importance appears to have been attached to these sub¬ 
terranean streams. The conception is very largely a purely 
theoretical one; and has its foundation in certain analogies drawn 
from the field of general rock-metamorphism. 
In contradistinction to slow and general groundwater circula¬ 
tion trunk-channel movement of course refers to relative rapid 
flowage through more or less open passages such as are occasion¬ 
ed by faulting, shearing or solution enlargement along joint-planes. 
The broader signification sometimes attached to the term that re¬ 
gards trunk-channels as equivalent to any section of a terrane 
through which groundwater moves seems directly to contradict 
the more generally accepted definition. 
Practical consideration of the relations existing between ore- 
deposition and groundwater circulation indicates that ascending 
and descending movements are not the features to be particularly 
contrasted. Only in a very limited sense are these two dis¬ 
tinctions of practical service. The fundamental comparison to 
be made is between the trunk-channels of the vadose zone and 
those of the profound region. Soon after passing below ground- 
