Denison Mines (Canada)

Abstract The unconformity-related uranium (URU) deposits in the Proterozoic Athabasca Basin (Canada) represent the richest, and one of the most important, uranium endowments in the world. Most of the URU deposits are associated with pre-existing graphitic basement faults that were reactivated after the formation of the basin. These graphite-rich structures have been widely used as a vector for exploration, but the nature of the association of the URU deposits with graphitic basement faults has been debated for over four decades. Proposed roles of graphite include: (1) as a direct reducing agent to reduce U6+ to U4+ and precipitate uraninite; (2) as a precursor of hydrocarbons (mainly CH4) produced in situ or nearby and then used as a reducing agent for uraninite precipitation; (3) as a precursor of hydrocarbons produced at depth that were remobilized to the site of mineralization and acted as a reducing agent for uraninite precipitation; and (4) as a lubricant facilitating faulting and fluid flow that led to uranium mineralization. This paper uses the Phoenix uranium deposit in the southeastern Athabasca Basin as a case study to address these uncertainties. Petrographic studies indicate that there is no direct contact between graphite and uraninite at microscopic scales, and the content of graphite in the graphitic metapelite along the ore-controlling WS Shear Zone does not show a systematic change with the distance from the unconformity surface. Raman spectroscopic studies of graphite suggest that the degree of structural disorder of graphite, expressed by various parameters related to the D bands and G band ratios, does not change systematically with the distance from the unconformity surface either. The minor irregularities in these parameters near the unconformity are better explained by paleo-weathering related to the unconformity and/or diagenetic processes than by hydrothermal activity related to uranium mineralization. Based on these observations and interpretations, the role of graphite as an in situ reducing agent, either directly or as a provider of hydrocarbons, is discounted. It is proposed that hydrocarbons derived from graphite at depth, tapped by episodic reactivation or seismicity of the basement faults that was facilitated by graphite as a lubricant, were responsible for URU mineralization.

To evaluate if HB vaccination can yield a booster effect on the anti-HBs level of those naturally acquired HBV positive markers. Sera were collected from 1399 newly enrolled university students aged between 18-20 years at the entrance medical examination in 2001. Forty-four students (28 males and 16 females) with positive serum anti-HBs and anti-HBc markers served as an observation group and another 44 students (24 males and 20 females) without any HBV markers as the control. HB vaccination was given to all the students without positive serum HBsAg according to 0, 1, 6 month regimen and the peripheral venous blood was sampled from those of both observation and control groups for anti-HBs detection one month after the second and third doses. Anti-HBs levels were measured by ELISA. The seroconversion rate of anti-HBs in the control group was 100% after the second dose, but the geometric mean titers (GMTs) were low. The tendency of serum anti-HBs changes after the 3rd dose was completely different between the two groups. Although more than half of those with positive anti-HBs and anti-HBc showed a mild increase of anti-HBs levels after the 2nd boosting dose (mean anti-HBs level was 320:198 mIU), but the increase of serum anti-HBs titer was much smaller than that in the control group. The averages of their initial serum anti-HBs levels and the levels after the 2nd and 3rd doses were 198, 320 and 275 mIU respectively. All the subjects from the control group had an obvious increase in their serum anti-HBs levels which was nearly 4 times the baseline level (302:78 mIU). HB vaccination can not enhance anti-HBs levels in those with positive serum anti-HBs and anti-HBc markers.

Canada, for 20 yr, has had the popular image of being the fortunate possessor of large reserves of a strategic mineral fuel and possessor of a producing industry born in a boom atmosphere, impatiently awaiting and preparing for the nuclear future to be realized. Shortly after the peak production year of 1959, the uranium industry experienced a rapid decline, one that only three companies survived as continuing producers. But by 1967 the industry was rebuilding, with producers emphasizing security and stability of supply to consumers through long-term contracts; by 1969 the international market had weakened because of oversupply, and many consumers adopted a wait-and-see attitude. The Canadian scene was transformed in 1970 when an alarmed Canadian government announced its intention to restrict foreign equity in new producer companies to 33%. A stalemate resulted, exploration was seriously dampened, and legislation to formalize the policy statements has not yet emerged. The world market passed through a depressed phase until the energy crisis, precipitated by the politics of oil, created sudden changes in fuel priorities and national policies. In Canada a uranium policy, announced in September 1974, established priority for domestic requirements, required annual review of uranium reserves, restricted export sales contracts to ten years, and required stringent nuclear safeguards agreements with importing countries. The practical application of the policy still is in its early stages, and progress has been slow. Canada will remain a major exporter for some years, since export commitments of 120 000 tons U3O8 to 1993 have been made; however, most producers are reluctant to consider new commitments until additional production capacity plans and domestic commitments are met.