ic oxide, as in the Clifton-Morenci
district of Arizona. It is clear that the ore-bearing solutions in
these cavities, before the crystallization of the heavy mineral
inclusions, held dissolved not only much larger quantities of mineral
substances than can be taken up by water at ordinary temperatures, but
also a substance like ferric oxide which is entirely insoluble under
ordinary cool conditions.

(5) The association of the ores with minerals carrying fluorine and
boron, with many silicate minerals, such as garnet, amphiboles,
pyroxenes, mica (sericite) and others, and with other minerals which are
known to be characteristic developments within or near igneous masses
and which are not known to form under weathering agencies at the
surface. Various characteristic groupings of these associated minerals
are noted. In limestone much of the mass may be replaced by garnet and
other silicates in a matrix of quartz. In igneous rock the ore-bearing
solutions may have altered the wall rock to a dense mixture of quartz,
sericite, and chlorite. Where sericite is dominant, the alteration is
called sericitic alteration. Where chlorite is important, it is
sometimes called chloritic or "propylitic" alteration. The chloritic
phases are usually farther from the ore deposit than the sericitic
phases, indicating less intense and probably cooler conditions of
deposition. Locally other minerals are associated with the ores, as, for
instance, in the Goldfield district of Nevada (p. 230), where alunite
replaces the igneous rock. Alunite is a potassium-aluminum sulphate,
which differs from sericite in that sulphur takes the place of silicon.
In the quartzites of the lead-silver mines of the Coeur d'Alene district
of Idaho (p. 212), siderite or iron carbonate is a characteristic gangue
material replacing the wall rock.

Quartz in some cases, as noted above, gives evidence of high temperature
origin and therefore of igneous association. Jasperoid quartz, as well
illustrated in the Tintic district of Utah (p. 235), may show texture
and crystallization suggestive of deposition from colloidal solution,--a
process which can occur under both cold and hot conditions, but which is
believed to be accelerated by heat.

Certain minerals, such as magnetite, ilmenite, spinel, corundum, etc.,
are often found as primary segregations within the mass of igneous rock.
These and other minerals, including minerals of tin and tungsten,
monazite, tourmaline, ru