Groundwater geochemistry at the Koongarra uranium ore deposit was investigated in order to gain a detailed understanding of the migration of uranium in a highly weathered water-rock system. Koongarra groundwaters are quite dilute with the total dissolved solids usually below 200 mg/l. The pH is slightly acidic or neutral, and the major chemical characteristics are dominated by magnesium and bicarbonate. Partial pressures of CO2 in the deeper groundwaters are substantially elevated relative to those of surface waters. Groundwater in the mineralized zones exhibits elevated levels of uranium up to three orders of magnitude above background levels. Total organic carbon levels are generally low, suggesting that uranium complexation by organic species plays a minor role. Due to the high bicarbonate concentration, uranium appears to be mobile in the weathered zone as uranyl carbonate complexes. Other inorganic uranium complexants are not present at levels sufficient to influence uranium speciation, with the possible exception of phosphate. On the basis of chemical and isotopic evidence, there are two major inputs of groundwater to the system. The first of these is flows from the vicinity of the Koongarra fault into the Cahill formation, which hosts the uranium mineralization. A second major source is infiltrating waters which permeate downward from the surface, and cause a gradual mixing and dilution of the characteristics of groundwaters from the mineralized zone. The migration of uranium in groundwater is not only perpendicular to the fault, but includes a component at an angle to it. In the vicinity of borehole C1 (due south of the ore zone), uranium concentrations are comparatively high, given the distance from the orebody. Moving away from the ore zone to the south-east, there is a gradual decrease of groundwater uranium concentrations to background levels over approximately 200 meters, which coincides with the uranium distribution in the solid phase. Therefore, at Koongarra, uranium seems to have migrated over distances of approximately 200 m toward the south-east over a time period estimated to be 1 to 1.5 million years.
The concentrations of uranium series radionuclides in groundwater were determined to investigate the migration behavior of radionuclides in the Koongarra ore deposit. Particular attention was given to 238U and alpha-emitting radionuclides in its decay chain, including 234U, 230Th, 226Ra, and 222Rn, and beta-emitting 210Pb. Disequilibrium between various members of the 238U decay chain in the Koongarra system arises from a combination of factors, including differences in solubility, surface affinity, the degree of weathering, diffusion of gaseous 222Rn, alpha-recoil effects and redox processes. Measured groundwater 234U/238U activity ratios were below unity in the surficial weathered zone (shallower than about 20 m depth), and greater than unity in the deeper unweathered zone (>30 m depth). These were attributed to various mechanisms related to the alpha-recoil process. Groundwater concentrations of 230Th, and also 230Th/238U ratios were extremely low, indicating that thorium is immobile in this system. Radium-226 was relatively immobile in groundwaters of the weathered zone, with lower 226Ra/238U ratios than deeper groundwaters. This was attributed to co-precipitation of radium together with manganese and ferric hydroxides at the base of the weathered zone, and also to the greater abundance of radium-sorbing minerals in the weathered zone. Large excess concentrations of 222Rn were found in most Koongarra groundwaters, indicating substantial loss of 222Rn from the solid phase despite its short half-life. The 210Pb/222Rn ratios were relatively constant and it was possible to compute an average scavenging residence time for 210Pb in the groundwater of about 6 days using a simple box model. The patterns of dispersion of uranium series radionuclides in Koongarra groundwaters also suggest that present-day migration is toward the south of the orebody. This conclusion is in agreement with the outcome of the geochemistry study.
Radiochemical NAA method has been studied for natural yttrium along with co-existing rare earth elements (REE). After neutron irradiation to the samples in the JRR4 reactor for a few hours with 6-8×1013 n/cm2sec, yttrium and REE mixture was separated as a group. Yttrium-90 was determined without further separation by a beta counting method using two appropriate absorbers. The interference due to other activities was reduced further by an anti-coincidence method in a well type NaI(Tl) scintillator as a guard counter. The pure hard beta ray, Emax = 2.3 MeV, emitted from 90Y has a long range and was useful to discriminate other softer beta and gamma activities of REE nuclides. For terrestrial rocks and chondritic materials, the interference from REE did not exceed 10% of the overall signal recorded by an ordinary GM counter. The usefulness of this method was illustrated by applying milligram quantities of standard rock samples and a bulk chondritic sample of Maralinga, CK4. An extreme example was the 0.5-1 milligram sized Group II CAI inclusion samples hand-picked from the Allende chondrite. They have higher La/Y ratios, 30 to 250 times higher than the solar abundances. The sizes were sub-nanogram of Y and Ho. The lower abundance ratios of Y/Ho could be determined in these samples.
Laboratory experiments on leaching of lanthanoids (Ln's) from andesitic rocks by acidic aqueous solutions were carried out in order to find some clue to better elucidation of Ln patterns of acidic hot spring waters in nature. Ln's are different from major elements but phosphorus (P) in behavior upon leaching: While leaching of the major elements continued even at the reaction time (tR) of 64 h, that of Ln's seemingly finished by tR=2 or 4 h. The behavior of P upon leaching was dissimilar to that of other major elements but rather resembled that of Ln's. This indicates that a part of each Ln may exist as phosphates in rocks. Light Ln's were found to be leached out by acidic waters more easily than heavy Ln's. This could be due to the difference in ionic radii of Ln's and/or be attributed to the difference in resistance to dissolution by acidic waters among various Ln-containing minerals in the rocks used in the present experiments. The results obtained are successfully applied to the elucidation of the Ln patterns of the waters from the Kusatsu-Yubatake hot spring, the Kusatsu spa, Gunma and from the Obuki hot spring, the Tamagawa spa, Akita.
A simple ion chromatographic technique is described for the routine determination of the Fe2O3/FeO ratio in geological samples. The iron species were eluted using pyridine-2, 6-dicarboxylic acid (PDCA), and photometrically detected at 520 nm as mono- and divalent complexes using a wavelength detector. An analysis is completed in approximately 10 minutes and, unlike commonly applied titrimetric methods, does not require an independent measurement of the total iron content of the sample. The technique is applicable to sample sizes of 25-50 mg, enabling the analysis of fragments of quench glass and individual large mineral grains. Results from the analysis of 7 international standard reference materials of widely differing Fe2O3/FeO ratios show a high degree of reproducibility (2σ=±0.02 in Fe2O3/FeO ratio) and are, with one exception, in close agreement with recommended published values.
New compilation data for major, minor and trace elements in 17 GSJ (Geological Survey of Japan) reference samples, “Igneous rock series” is presented as 1994 values. The compilation is based on reported data in publications and personal communications received by April 1994, which we have evaluated statistically in consideration of analytical methods and analytical procedures. In this 1994 compilation recommended or preferable values for 79 elements are proposed.