VADOSE ORE DEPOSITION 
389 
the geologic structures are exceptionally clearly shown is in the 
Magdalena lead and zinc district in central New Mexico 
Copper deposits north of Paradise, in the Chiricahua Range, in 
southeastern Arizona, appear to be similarly formed. The type 
is a common one throughout southwestern United States. 
Under conditions of a normally moist climate numerous cases 
are found in the Ozark region. I have recently called attention 
to the Sugar Orchard zinc mines, south of Lead Hill, in Boone 
county, Arkansas; and Branner has also noted other well- 
marked instances. On the whole, this type of deposits is not 
nearly so frequent in occurence as is generally supposed. 
In a single stratum, or geological formation, gash-veins are 
formed along joint-planes by the contraction of the rock-mass 
through dolomitization, or through the removal of part of the 
walls by solution. The Dubuque (Iowa) lead and zinc-crevices 
are the best known’examples, early described by Whitney 
and more recently by Leonard Grant’s still later investiga¬ 
tions are especially instructive. Many of the Ozark lead and 
zinc-deposits are of similar origin, although the features are often 
largely obscured by other phenomena. 
In the arid regions the same type of ore-formation is quite 
prevalent. Among zinc deposits those of Potosi, in the Spring 
Mountains of southwestern Nevada, are especially noteworthy; 
they are described by Bain , 
So far as vadose deposition is concerned all fissure-vein 
phenomena may be considered together in this connection. As 
now generally understood, secondary sulphide-enrichment really 
applies only to mineral veins originating from the depths. The 
inference is that the ore-materials from the upper weathered 
parts of a vein are carried down the vein and precipitated within 
it at groundwater-level. 
At the present time the subject of secondary sulphidic enrich¬ 
ment of ore deposits is probably receiving much more attention 
than it really deserves. Much more is claimed for the process 
by its enthusiastic advocates than is warranted. In only a re- 
27 Mining Magazine, Vol. XII, p. 109, 1905. 
28 Trans. American Inst, Mining Eng., Vol. XE, p. 202, 1910. 
29 Arkansas Geol. Surv., Ann, Rept. 1892, Vol. V, p. 33, 1900. 
30 Iowa Geo*!. Surv., Vol. I, p. 451, 1858. 
31 Iowa Geol. Surv., Vol. VI, p. 36, 1897. 
32 Economic Geology, Vol. I, p. 240, 1906. 
33 Bull. U. S. G. S., No. 285, p. 116, 1906. 
