382 
VADOSE ORE DEPOSITION 
This function has much greater significance in the vadose than 
in the profound zone; and in the arid regions, where the vadose 
zone is developed to such large proportions, it acquires an im¬ 
portance wholly unknown outside of excessively dry countries. 
Broadly considered, all the various original and acquired geo¬ 
logic structures which determine the main conditions of ore- 
localization may be reduced to the single geometric type of a 
thin band or belt sufficiently porous in character to permit the 
ready movement of groundwater currents through it. Whether 
the band be of the nature of stratification-plane, fault-line, 
crushed-belt, or cavernous solution-zone, an essential element 
is its more or less marked permeability. A necessary attendant 
condition for ore-deposition seems to be that the porous band 
shall have been recently formed, tilted, folded, displaced or other¬ 
wise orogenically disturbed. New relations and new channels of 
groundwater circulation thus established become the chief factors 
in new ore-localizing possibilities. 
In the vadose zone especially do the new conditions there 
imposed often give rise to extensive impondment conditions, 
where ore-materials in solution may be readily precipitated. 
These relations of impondment and ore-accumulation are so 
closely dependent upon one another and so fundamentally genetic 
in character that the attendant geologic structures constitute 
definite and distinctive factors by which vadose ore-bodies may 
be with advantage, scientifically and practically grouped. The 
criteria of such classification are particularly useful in the con¬ 
sideration of ore deposits formed under conditions of arid climate; 
but they are also applicable to ore phenomena displayed in moist 
lands. 
Among ore-bodies mined today it frequently occurs that their 
origin, often ascribed directly to the action of igneous intrusions 
because they are in contact, or are near by, is only remotely or 
not at all connected with such eruptive masses. Were the 
effects of the latter alone depended upon there would be more 
frequently no ores mined. That many of these deposits are 
developed into operating mines is largely due to the fact that in 
the vadose zone peculiar geologic structures have produced locally 
favorable conditions for ore-improvement or concentration. It 
is in the arid regions, because of the deep vadose zone, that the 
