70
C. Variations of Stable Isotope Ratios in Nature
matic" H20 in the hydrothermal fluids; and 3) the temperatures of formation of the alteration mineral assemblages.
SHEPPARD et al. (1969, 1971) determined the D/H and 180j160 ratios
in alteration assemblages from porphyry copper deposits and other hydrothermal mineral deposits.
The following conclusions can be drawn from these studies: The D/H
and 180j160 ratios of hypogene clays show a clear-cut geographic correlation with the isotopic variations displayed by present-day meteoric
waters. In many situations where the D/H values of meteoric and primary magmatic waters are significantly different, the isotopic data require that the hypogene hydrothermal solutions responsible for intermediate and advanced argillic alteration contain a large amount of meteoric water. Qualitative temperatures, depending on assumptions, have
been calculated in the range of 360 to 280
0
C for sericitization and 460 to
390
0
C for potassic alteration. ESLINGER and SAVIN (1971) empirically
calibrated a quartz-illite geothermometer on hydrothermally altered
rocks. They obtained temperatures between about 200 and 300
0
C.
v. Water Cycle
One of the most interesting topics of modern geochemistry is the
water cycle in nature. The importance of the role of water in nearly all
geological processes cannot be overestimated.
Types of water can be classified in a number of ways. Most commonly they are grouped according to 1) origin, in terms of meteoric,
connate, or juvenile water; 2) chemistry, e.g. bicarbonate, sulfate, or
chloride water; and 3) total salinity, e.g., freshwater and brine.
The term "meteoric" applies to water that has gone through the
meteorological cycle, which is evaporation, condensation, and finally
precipitation. All continental surface waters - such as rivers, lakes, and
glaciers - fall into this general category. Because meteoric water may
seep into the underlying rock strata, it will also be found at various
depths of the lithosphere.
The ocean, although it continuously receives the continental run-off
of meteoric waters as well as rain, is by general agreement not regarded
as being of meteoric nature.
The terms "freshwater" and "brine" are frequently employed. The
upper boundary for freshwater is 1 % salinity, which is about the maximum salt concentration tolerated by the natural freshwater fauna and
flora. Waters beyond the concentration of ocean water are known as
brines.
The total concentration of dissolved solids in seawaters has a mean
value close to 3.5%, but concentration reaches as much as 4% in par-
C. Variations of Stable Isotope Ratios in Nature
matic" H20 in the hydrothermal fluids; and 3) the temperatures of formation of the alteration mineral assemblages.
SHEPPARD et al. (1969, 1971) determined the D/H and 180j160 ratios
in alteration assemblages from porphyry copper deposits and other hydrothermal mineral deposits.
The following conclusions can be drawn from these studies: The D/H
and 180j160 ratios of hypogene clays show a clear-cut geographic correlation with the isotopic variations displayed by present-day meteoric
waters. In many situations where the D/H values of meteoric and primary magmatic waters are significantly different, the isotopic data require that the hypogene hydrothermal solutions responsible for intermediate and advanced argillic alteration contain a large amount of meteoric water. Qualitative temperatures, depending on assumptions, have
been calculated in the range of 360 to 280
0
C for sericitization and 460 to
390
0
C for potassic alteration. ESLINGER and SAVIN (1971) empirically
calibrated a quartz-illite geothermometer on hydrothermally altered
rocks. They obtained temperatures between about 200 and 300
0
C.
v. Water Cycle
One of the most interesting topics of modern geochemistry is the
water cycle in nature. The importance of the role of water in nearly all
geological processes cannot be overestimated.
Types of water can be classified in a number of ways. Most commonly they are grouped according to 1) origin, in terms of meteoric,
connate, or juvenile water; 2) chemistry, e.g. bicarbonate, sulfate, or
chloride water; and 3) total salinity, e.g., freshwater and brine.
The term "meteoric" applies to water that has gone through the
meteorological cycle, which is evaporation, condensation, and finally
precipitation. All continental surface waters - such as rivers, lakes, and
glaciers - fall into this general category. Because meteoric water may
seep into the underlying rock strata, it will also be found at various
depths of the lithosphere.
The ocean, although it continuously receives the continental run-off
of meteoric waters as well as rain, is by general agreement not regarded
as being of meteoric nature.
The terms "freshwater" and "brine" are frequently employed. The
upper boundary for freshwater is 1 % salinity, which is about the maximum salt concentration tolerated by the natural freshwater fauna and
flora. Waters beyond the concentration of ocean water are known as
brines.
The total concentration of dissolved solids in seawaters has a mean
value close to 3.5%, but concentration reaches as much as 4% in par-