VADOSE ORE DEPOSITION 
285 
port of the suggestion seems to be entirely lacking. When the 
subject shall have been especially investigated tangible proofs may 
be forthcoming. 
In the arid regions of the Western Hemisphere, Latin-Ameri- 
can miners recognize several distinct horizons or sub-divisions 
which are designated by appropriate names. These sub-zones 
have in fact some scientific foundation. They are distinguishable 
chemically, mineralogically and metallurgically. In mining oper¬ 
ations their differences are taken into account. The recognition 
of these sub-zones seems destined to play an important part in the 
consideration of ore-genesis, as well as in practical mining explora¬ 
tions. 
Many of the descriptions of mines in western United States 
indicate a certain sequence of ore-materials between the surface 
of the ground and the deep-lying water-table. The real signifi¬ 
cance of these observations is scarcely yet realized. The only 
writers inclined to lay especial stress upon this phenomenon are 
Fuchs and DeLaunay,^^ who make out, in northern Mexico, no less 
than six distinct zones. These zones are based chiefly upon the 
mineralogic characters. The sub-zones are distinguishable upon 
other grounds. I have referred to them in another place; and 
they are made the subject of special consideration elsewhere. In 
the present connection attention only need be called to their verity 
and importance. 
Notwithstanding the fact that the process of ore-deposition and 
ore-reduction goes on mainly under the conditions characterizing 
the profound zone, the horizon of so-called secondary sulphide 
enrichment lying at and just below groundwater-level belongs 
properly to the vadose field. The ore-material there converted 
into the sulphide form comes chiefly, if not entirely, from above. 
Little if any is derived immediately from below. 
Since the bonanza zone, or the zone of secondary sulphide en¬ 
richment, has become industrially so important, the question of 
the specific sources of its ore-supplies assumes new aspects of 
great interest to mining. Being generally regarded as mainly 
the result of downward percolating meteoric waters on low-grade 
veins, it gives strong support to certain facies of ore-genesis which 
22 Traite des Cites Minereaux et Metaliferes, T. II, p. 816, 1893. 
23 Trans. American Inst. Mining Eng., (Bimon. Bull. No. 55), p. 547, 1911. 
