Ore Deposits
65
Atmospheric oxygen might have also influenced the distribution and
isotopic composition ofthe sulfur compounds.
PUCHELT et al. (1971a) concluded that a given volcanic area appears to
have a typical sulfur isotope ratio. The data of PUCHELT et al. (1971a) do
not favor equilibrium conditions between the different sulfur species in
the geothermal areas investigated. For instance in some pairs of sulfate
and elemental sulfur the sulfate is isotopically lighter than the elemental
sulfur. Kinetic effects appear to be responsible for the observed values,
H2 32 S should be oxidized faster than H2 34 S. The data of SCHOEN and RYE
(1970) imply that, at least in Yellowstone Park, most of the hydrogen
sulfide oxidizes to sulfur inorganically, whereas elemental sulfur oxidizes
to sulfuric acid biologically.
IV. Ore Deposits
The generation of an ore deposit that involves a hydrous fluid has
various aspects, some of which are: 1) A source of the ore, 2) the dissolving of the ore and other components in the fluid phase, 3) the migration
of the ore-bearing fluid, and 4) the selective precipitation of the ore
constituents in favorable environments.
Many geologists have tried to explain ore deposits by means of relatively simple models. However, the processes by which minor constituents of the crust become concentrated into bodies of economically
valuable ore are very complex. The water, dissolved salts, metals, sulfide,
and other critical constituents of each deposit may be derived from two
or even more sources.
A major geological problem is to explain the formation of the relatively large accumulations of nearly insoluble sulfides. The low solubilities of many metal sulfides has raised the important question as to how
they can be transported in large quantities in aqueous solutions without
the need for gigantic volumes of water.
One approach to the classification of ore deposits is based mainly on
bD and 15 18 0 determinations of the ore fluid. Five typical ore-generating
systems have been reviewed by WHITE (1968) with respect to the origin of
the water:
"1) Providencia, Mexico: close magmatic affiliations and a probable
magmatic source for its ore fluid, metals, and sulfide.
2) Mississippi Valley type: connate water dominant in the ore fluid
during sulfide and fluorite stages, and likely sedimentary rock sources
for most critical constituents.
3) Salton Sea geothermal system, California: meteoric water dominant in the ore fluid; probably most of the dissolved metals and salts are
65
Atmospheric oxygen might have also influenced the distribution and
isotopic composition ofthe sulfur compounds.
PUCHELT et al. (1971a) concluded that a given volcanic area appears to
have a typical sulfur isotope ratio. The data of PUCHELT et al. (1971a) do
not favor equilibrium conditions between the different sulfur species in
the geothermal areas investigated. For instance in some pairs of sulfate
and elemental sulfur the sulfate is isotopically lighter than the elemental
sulfur. Kinetic effects appear to be responsible for the observed values,
H2 32 S should be oxidized faster than H2 34 S. The data of SCHOEN and RYE
(1970) imply that, at least in Yellowstone Park, most of the hydrogen
sulfide oxidizes to sulfur inorganically, whereas elemental sulfur oxidizes
to sulfuric acid biologically.
IV. Ore Deposits
The generation of an ore deposit that involves a hydrous fluid has
various aspects, some of which are: 1) A source of the ore, 2) the dissolving of the ore and other components in the fluid phase, 3) the migration
of the ore-bearing fluid, and 4) the selective precipitation of the ore
constituents in favorable environments.
Many geologists have tried to explain ore deposits by means of relatively simple models. However, the processes by which minor constituents of the crust become concentrated into bodies of economically
valuable ore are very complex. The water, dissolved salts, metals, sulfide,
and other critical constituents of each deposit may be derived from two
or even more sources.
A major geological problem is to explain the formation of the relatively large accumulations of nearly insoluble sulfides. The low solubilities of many metal sulfides has raised the important question as to how
they can be transported in large quantities in aqueous solutions without
the need for gigantic volumes of water.
One approach to the classification of ore deposits is based mainly on
bD and 15 18 0 determinations of the ore fluid. Five typical ore-generating
systems have been reviewed by WHITE (1968) with respect to the origin of
the water:
"1) Providencia, Mexico: close magmatic affiliations and a probable
magmatic source for its ore fluid, metals, and sulfide.
2) Mississippi Valley type: connate water dominant in the ore fluid
during sulfide and fluorite stages, and likely sedimentary rock sources
for most critical constituents.
3) Salton Sea geothermal system, California: meteoric water dominant in the ore fluid; probably most of the dissolved metals and salts are