VADOSE ORE DEPOSITION 
387 
harbor ore-materials, derived from vadose circulations, as often, 
perhaps, as they do deposits derived directly from the depths 
through magmatic emanations. 
Volcanic breccias, or pyroclastic layers, are exceptionally fav¬ 
orable beds for the accumulation of ores of vadose nature. They 
form porous beds long after they are laid down and are often 
also the abode of metallic sublimates. Typical deposits are dis¬ 
played in the silver mines of Socorro Mountain, New Mexico. 
Whatever the origin of the irregular chambers and passages in 
the soluble rocks it is certain that they are often filled with 
detrital materials and ores. Some of these filled caverns are 
manifestly old channel-ways of subterranean waters which have 
become dammed; others are enlarged in a vertical direction only; 
and their fillings long remain because of local impondment-con- 
ditions. Even in the moist climate of the Ozarks, in Arkansas 
and Missouri, are presented many phases of the phenomenon, 
as is lately noted In the arid regions the lead and zinc 
deposits of Santa Eulalia, in Chihuahua, Mexico, the copper ores 
of Jimulco, Mexico, the lead ore-bodies of Sierra Mojada, in 
Coahuila, Mexico, and the gold, silver and lead deposits of the 
Cave mine, near Mitford, Utah, are good examples. At Santa 
Eulalia the chambers assume large proportions; for the vadose 
zone extends to depths of 1000 to 1500 feet. 
Inequalities of unconformity-planes produce basins carrying 
ores much oftener than might be gathered from perusal of the 
descriptions of mines. Unconformities are geologic structures 
which in most mining districts commonly escape notice. They 
frequently are marked by the juncture-line of two diverse kinds 
of rock. The horizon is usually a porous one and hence is a 
favorable situation for ore-materials to gather. Not uncommonly 
a clastic and an eruptive rock are brought together; and the 
inference is that the ore-body is a contact-deposit. 
One of the most instructive deposits of this kind, noted by 
Winslow is in the Doe Run lead-mine in southeastern Missouri. 
In the Diomea mines, in the Sierra Mojada, lead and copper 
carbonates and copper sulphides occur under these conditions, 
according to *Malcolmson Blake’s descriptions of the mala- 
22 Missouri Geol. Surv., Vol. VII, p. 673, 1894. 
21 Trans. American Inst. Mining Eng., Vol. X, p. 203, 1910. 
23 Trans. American Inst. Mining Eng., Vol. XXXII, p. 117, 1902. 
24. Ibid., Vol. XVII, p. 479, 1889. 
