U, FE, AND LI ISOTOPE RATIOS IN THE MINERALIZED AND BARREN AREAS OF THE KOMBOLGIE BASIN

The Paleo- to Meso-Proterozoic Jabiluka unconformity related uranium mine is located within the Alligator River Uranium Field, found in the Northern Territories, Australia. The uranium ore is hosted in the late middle Paleoproterozoic Cahill Formation, which is unconformably overlain by a group of unmetamorphosed conglomerates known as the Kombolgie subgroup. The Kombolgie subgroup provided the source for oxidized basinal brines, carrying U as the mobile form U(VI), which interacted with reducing lithologies in the Cahill formation, thus reducing U(VI) to the solid U(IV), and leading to the precipitation of uraninite (UO2). In order to characterize fluid interaction with the ore body and compare that to areas without mineralization, several isotopic tracers were studied on a series of clay samples from drill core at Jabiluka as well as in barren areas throughout the ARUF. Among the potential tracers, three were selected: U (redox sensitive and recent fluid mobilization), Fe (redox sensitive), and Li (fractionated by hydrothermal fluids and adsorption reactions). δ238U values were found to be closely linked to the mineralogy, with samples with higher K/Al ratios (indicating high illite and low chlorite concentrations) having higher δ238U values. This demonstrates that 235U preferentially absorbs onto the surface of chlorite during hydrothermal circulation. In addition, δ234U values lie far from secular equilibrium (δ234U of 30‰), indicating there was addition or removal of 234U from the surface of the samples from recent (<2.5Ma) interactions of mobile fluids. δ57Fe values were found to be related to lithology and spatially to known uranium deposits. Decreasing δ57Fe values were found with increasing depth to the unconformity in a drill hole directly above the ore zone, but not in drill holes in the barren area. Similarly to δ238U, δ7Li is found to correlate with mineralogy, with higher δ7Li values associated with samples with more chlorite. In addition, higher δ7Li values are found at greater depth throughout the basin, indicating that the direction of the mineralizing fluid circulation was upwards from the Cahill formation to the Kombolgie subgroup.

Background Measurement Techniques and Sensitivity Studies for the SNO+ Neutrinoless Double Beta Decay Search

The control of radioactive backgrounds will be key in the search for neutrinoless double beta decay at the SNO+ experiment. Several aspects of the SNO+ back- grounds have been studied. The SNO+ tellurium purification process may require ultra low background ethanol as a reagent. A low background assay technique for ethanol was developed and used to identify a source of ethanol with measured 238U and 232Th concentrations below 2.8 10^-13 g/g and 10^-14 g/g respectively. It was also determined that at least 99:997% of the ethanol can be removed from the purified tellurium using forced air ow in order to reduce 14C contamination. In addition, a quality-control technique using an oxygen sensor was studied to monitor 222Rn contamination due to air leaking into the SNO+ scintillator during transport. The expected sensitivity of the technique is 0.1mBq/L or better depending on the oxygen sensor used. Finally, the dependence of SNO+ neutrinoless double beta decay sensitivity on internal background levels was studied using Monte Carlo simulation. The half-life limit to neutrinoless double beta decay of 130Te after 3 years of operation was found to be 4.8 1025 years under default conditions.