380 
VADOSE ORE DEPOSITION 
law of groundwater movement, that mine-waters are always in 
motion down a slightly inclined plane, that ores are not deposited 
everywhere evenly in the vadose zone, and that where the move¬ 
ment is interrupted, or stagnation prevails, ore-materials are 
precipitated or tend to settle down. 
Notwithstanding the fact that mine-waters tend to drop their 
loads into the rock-cavities through which they pass the mineral 
matter in solution may replace other components in the wall-rock. 
This chemical interchange may take place along the walls of the 
channel, or along the lines of stratification-planes, or of joint 
and fault-planes. Whether mural or stratal in character there 
are good grounds for assuming that in the vadose zone cavity¬ 
filling and wall-replacement are, partly at least, functions of the 
rate of groundwater motion. 
In the light of the most recent tests regarding the locus of 
maximum ore-deposition the theory of trunk-channel localization 
of ores, as advanced by Van Rise ^ needs to undergo considerable 
modification before it can be made acceptable. For the greater 
part of their courses trunk-channels of the groundwater circula¬ 
tion are as already stated, lines of ore-depletion rather than of 
ore-enrichment. Localization of ores is not due to the fact alone 
that the deposits are along lines of trunk-channels but mainly 
to entirely dififerent causes, as is elsewhere pointed out. 
One of the most practical results accomplished by the Missouri 
Geological Survey, during the period when it was in my charge, 
was the determination of the direct dependence of ore-localiza¬ 
tion upon certain geologic structures. In the great pitching 
syncline of Joplin, reaching from the center of the Ozark dome 
westward out into Kansas and Oklahoma, cross-bars or low 
arches, trending transversely to the axis of the main trough, 
were found to mark the locations of all the large mining camps. 
The ore-bodies were found to be mainly on the up-hill sides of 
the cross-bars which were high enough to retard, or impond, the 
mineral-laden waters flowing freely down the open stratification 
planes of the master syncline. ^ When carefully investigated, 
many of the smaller mining camps were discovered to be similarly 
situated with reference to cross-arches. 
3 Treatise on Metamorphism, p. 1202, 1904. 
4 Trans. American Inst. Mining Eng., Vol. XE, p. 213, 1910. 
