Vf. Hodge et al., RHENIUM, MOLYBDENUM, AND URANIUM IN GROUNDWATER FROM THE SOUTHERN GREAT-BASIN, USA - EVIDENCE FOR CONSERVATIVE BEHAVIOR, Geochimica et cosmochimica acta, 60(17), 1996, pp. 3197-3214
Dissolved Re, Mo, and U concentrations, and the concentrations of the
major cations and anions, were measured in groundwaters from twenty-th
ree springs in the southern Great Basin, USA, from June 1992 through M
arch 1994. Rhenium concentrations ranged from 5 +/- 1 pmol/kg to 190 /- 20 pmol/kg. The highest Re values were observed in the saline groun
dwater of Saratoga Spring in Death Valley and Cold Spring in Ash Meado
ws, whereas the lowest Re concentrations were found in Nevares Spring
in Death Valley. The mean Re concentration for all of the spring water
s sampled is 44 +/- 33 pmol/kg. The concentrations of Re differs drama
tically for groundwaters that discharge from the regional Paleozoic ca
rbonate aquifer and for local groundwaters from felsic volcanic rocks.
The mean Re concentration for groundwaters issuing from the carbonate
aquifer is 37 +/- 14 pmol/kg (which is similar to the average Re valu
e reported for seawater, i.e., 39.8 +/- 0.2 pmol/kg), whereas for the
spring waters that discharge from the felsic volcanic aquifers, the me
an Re concentration is 18 +/- 3.5 pmol/kg. The overall mean concentrat
ions of U and Mo in these groundwaters are 18 +/- 12 nmol/kg and 120 /- 60 nmol/kg, respectively. Differences in the U and Mo concentration
s for groundwaters from the carbonate aquifer and those from the volca
nic aquifer are also observed such that the mean U and Mo concentratio
ns in the carbonate groundwaters are 13 +/- 5 nmol/kg and 106 +/- 40 n
mol/kg, respectively, and the mean U and Mo concentrations in the volc
anic spring waters are 31.5 +/- 4 nmol/kg and 94 +/- 12 nmol/kg, respe
ctively. By comparison, U and Mo concentrations reported for seawater
are 13.9 nmol/kg and 107 nmol/kg, respectively. In the oxygenated grou
ndwaters of the Great Basin, Re, Mo, and U appear to be acting conserv
atively, as in seawater, as evidenced by the covariance observed betwe
en Re, Mo, and U with chloride, sodium, and sulfate. Groundwaters disc
harging from the regional carbonate aquifer in Ash Meadows typically e
xhibit a U/Re ratio of about 300 while groundwaters that discharge in
Death Valley from local felsic volcanic sources have ratios of about 1
700. Waters in the remainder of the Death Valley springs are intermedi
ate and may result from the mixing of the carbonate and volcanic deriv
ed waters. The Re, Mo, and U concentrations in addition to the major s
olute chemistry, indicates that dissolution of carbonate rocks is of p
rimary importance in the groundwaters from Ash Meadows, whereas the we
athering of felsic volcanic rocks contributes substantially to the che
mical signatures of the Death Valley groundwaters. The differences bet
ween U/Re ratios and different aquifer materials suggest that there is
a relationship between the dissolved U/Re ratios and the aquifer mate
rials. Similar Re/Mo/U ratios for the groundwaters from the carbonate
aquifer and seawater are strongly suggestive of quantitative uptake of
these trace elements from seawater by carbonate mineral precipitation
and subsequent quantitative release of these trace elements during di
ssolution of the carbonate rocks by groundwater. The substantially lar
ger salinity normalized Re, Mo, and U concentrations in the groundwate
rs compared to seawater, rule out the possibility that these groundwat
ers represent simple mixing of dilute terrestrial waters and seawaters
or reconstitution of evaporite deposits by groundwater dissolution.