ores,
and the usual gradual transition from unreplaced schists to those
completely replaced by massive sulphides. The localization of the most
important mineralization in an inverted trough is good evidence that the
solutions came from below, and the nature of the mineral associations
suggests an origin through the work of hot waters associated with
igneous intrusives. The diorite, being most closely related in time and
space with the ore bodies, seems the most logical source of the ore
materials.

Secondary concentration of the Jerome ores has proceeded along the
general lines previously outlined (pp. 46-50, 202). Here again the
evidence is clear that the ores were concentrated in an earlier period,
in this case in pre-Cambrian times, probably during the long interval
required for the base-leveling of the pre-Cambrian mountains. Since
Cambrian times the deposits have been for the most part buried by later
sediments. Some of the deposits are still protected by this overlying
blanket and mining has not yet reached the zone of altogether primary
sulphides. Others have been faulted up and again exposed by erosion; but
since being uncovered, steep slopes and rapid erosion have apparently
favored the scattering of the copper rather than its concentration and
enrichment. In the United Verde Mine, oxidizing conditions at present
prevail to the bottom of the chalcocite zone.

The very large reserves of the Katanga copper belt of the Belgian Congo
are in the form of tabular masses in schistose and highly metamorphosed
Paleozoic sediments. The ore bodies are roughly parallel to the bedding,
but in instances follow the schistosity which cuts across the bedding.
They consist dominantly of the oxide minerals, though in several ore
bodies sulphides have been shown by diamond-drilling. The ores have a
high content of cobalt and also carry precious metals. The origin of the
deposits is not known, but has been ascribed to granitic masses
intrusive into the schists.

=Sedimentary copper deposits.= In the later phases of the metamorphic
cycle, the agencies of transportation (in solution) and sedimentary
deposition have resulted in some low-grade deposits of copper sulphides
in sedimentary rocks. Deposits of this type are found in the Rocky
Mountain region, where they are referred to as the "Red Beds" coppers,
but are of no commercial importance. Similar deposits in Germany, the
Mansfield copper-bearing shales, have been worked for som