The role of structure and tectonics in the formation of hydrothermal ore deposits and the localization of high-grade mineralization associated with fractures is well documented. In this study we have characterized the structural setting associated with uranium mineralization in the Coles Hill uranium deposit by relating the observed metamorphic and structural features (mylonitic foliation and fractures) to regional tectonic activity. Drill cores and outcrops observed in this study show that NE/SW oriented fractures appear to be related to Mesozoic movement along the Chatham Fault. NW/SE oriented fractures cross cut and offset the NE/SW oriented fractures by1 to 2 cm and therefore post-date the NE/SW oriented fractures. NW/SE fracture orientations and parallel to the NW/SE regional cross faults and are suggested to relate to the formation of the cross faults during post Triassic basin inversion. Uranium mineralization is located within horizontal to shallowly dipping fractures suggesting uplift and erosion to form possible tension veins. The cross faults with NW/SE orientations created pathways in which uranium bearing hydrothermal fluids could migrate from the Triassic basin shales westward into the adjacent highly fractured crystalline rocks, precipitating uranium due to oxidation-reduction reactions. / Master of Science

Development of a scientific basis for management of uranium bearing wastes and contaminants requires information from natural geologic systems. The following study of the Coles Hill uranium deposit and associated weathered zone constrains processes leading to the natural attenuation of uranium within an oxidizing, fluid rich environment typical of the eastern US. At the Coles Hill deposit fracture hosted, primary U(IV) bearing mineral assemblages formed during hydrothermal activity associated with Mesozoic faulting. The most abundant ore assemblage consists of coffinite and apatite, but uraninite-zeolite and uraninite-calcite assemblages are also present. Within the shallow bedrock there is a uranium redox transition where alteration of U(IV) minerals has produced secondary uranium minerals. Geochemical data suggests that the volume of rock containing this U(IV)/U(VI) transition is acting as a closed system with respect to uranium mass transport during oxidation. The dominant mechanism of uranium fixation within the oxidizing zone is the precipitation of Ba-U(VI) phosphates (meta-autunite group). Speciation and mineral stability calculations indicate that ground waters from the Coles Hill weathered zone are saturated with respect to Ba-meta-autunite and that this mineral is capable of buffering dissolved uranium concentrations to values lower than 20 parts per billion. U(VI) phosphates of the meta-autunite group are not stable in the vadose zone (soil pH ~ 4.5) at the Coles Hill site. In this zone uranium is associated with (Ba, Ca, Sr) aluminum phosphate of the crandallite group as well as with phosphate sorbed to iron oxy-hydroxide mineral coatings. Uranium leached from the vadose zone is reprecipitated as new meta-autunite minerals below the water table due to higher pH conditions of ~6.0 and relatively high activity ratios of dissolved phosphate to carbonate (e.g. log [H2PO4-/HCO3-] > -3). It is estimated that the U(VI) phosphates responsible for the natural attenuation of uranium at this site persist within the weathering zone for hundreds of thousands of years. Thus, the Coles Hill deposit represents an excellent natural laboratory for the study of uranium attenuation with potential applications for the design and implementation of cost effective remediation and containment strategies, such as soil amendments techniques and in-situ reactive barriers technologies. / Ph. D.

The Coles Hill uranium deposit in Pittsylvania County, Virginia represents the largest unmined uranium resource in the United States, with an estimated resource of 110 million pounds of U3O8 in place with a cutoff grade of 0.025 wt% U3O8. The deposit is localized along a geologic unit that parallels the Chatham Fault, which separates the Triassic Danville Basin to the east from the older crystalline rocks to the west. The location of the Chatham Fault is important to understanding distribution of ore and for developing an effective mine plan. In this study the Chatham Fault location has been inferred from ground conductivity and ground penetrating radar (GPR) surveys. Anomalies in the data are consistent with previously mapped fault locations based on drillhole and geophysical data, such as gravity and magnetic surveys, collected in the 1980s. These results confirm that the strike of the Chatham Fault is approximately N40ºE and dips to the southeast with dip values ranging from 70º, in the northeast, to 50º, in the southwest. / Master of Science

The Coles Hill uranium deposit in Pittsylvania County, VA, is the largest un-mined uranium deposit in the United States. The deposit is located in the Virginia Piedmont in a geologic unit located immediately west of the Chatham Fault, which separates the granitic rocks of the Virginia Piedmont to the west from the metasediments of the Danville Triassic basin to the east. Groundwater at the site flows through a complex interconnected network of fractures controlled by the geology and structural history of the site. In this study groundwater is characterized in a small study area just south of the main deposit. Methods used in this investigation include electrical resistivity profiling, bore hole logging, a pumping test, and age dating and water chemistry. In this thesis groundwater flow is confirmed to occur from the Piedmont crystalline rocks across the Chatham Fault and into the Triassic basin at the study area as evidenced by pumping test data and static water-level data from observation wells. Well logs have identified fractures capable of transmitting water in the granitic rocks of the Piedmont, the Triassic basin metasediments and the Chatham Fault but the largest quantities of flow appear to occur in the Triassic basin. A definable recharge area for the groundwater present at Coles Hill can not yet be determined due to the complexity of the fracture system, but age dating confirms that groundwater is composed of both young and old (>60 years) components, indicating that at least a portion of groundwater at Coles Hill originates from a more distant area. / Master of Science

A study of the Millennium and Eagle Point basement-hosted deposits was conducted to obtain a comprehensive understanding of the alteration in these two atypical uraniferous systems and to apply these findings in formulating effective exploration strategies. In addition, an investigation of the Wheeler River “apparently barren” sandstone-hosted alteration system was conducted to provide insights into the critical events needed in order to form sandstone-hosted unconformity-related deposits. At Millennium, the atypical alteration halo, wherein the inner chlorite halo is much smaller than other basement-hosted deposits, is the result of pervasive muscovite alteration of the basement rocks by Na-K-Fe basinal brines during the pre-ore stage at ca. 250°C. As alteration of the basement rocks progressed, the basinal brines acquired Ca, Fe and Mg while creating up to 20% voids in the basement rocks. Prior to the mineralizing event, the chemically modified basinal fluids formed a minor Fe-rich chamoisite halo that demarcates a redox front during the ca. 1590 Ma syn-ore stage, where uranium ore was precipitated. At Eagle Point, the atypical alteration halo, wherein dolomite and calcite alteration is more significant than other basement-hosted deposits, is the result of more intense pre-Athabasca Basin alteration. The Eagle Point deposit is also distinct by significant late remobilization of primary uraninite into secondary structures that occurred at ca. 535 Ma. At the Wheeler River “apparently barren” alteration system, the critical factor for the lack of uranium mineralization in the sandstone is the temporal relationship between the different fluids with the uranium-bearing oxidized basinal fluids present prior to the reduced chemically modified basinal fluids and reduced basement fluids. However, the possibility of a small basement-hosted uranium deposit at Wheeler River cannot be excluded because the sudoite-producing basement fluids may represent basinal brines that reacted with basement lithologies to become reducing and Mg-rich, and therefore may have precipitated uraninite during this process. The results of this study support the genetic model in which basinal fluids were likely the source of uranium deposits and that the basement fluids were unlikely significant sources of uranium in sandstone-hosted deposits. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2009-09-30 14:49:03.688